• 专利附录
  • 专利说明
  • 权利要求
  • 类似技术
  • 同族专利
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    • 专利摘要:
    An iterative screening method (100) of a sample of electrolytic capacitors having a predetermined nominal voltage is provided. The method may include measuring (108) a first leakage current of a first set of capacitors, computing a first average therefrom, and removing capacitors from the first set having a first current. leakage equal to or greater than a first predetermined value, thereby forming a second set of capacitors. The second set can be subjected to a burn-in process (114) where a test voltage can be applied, then a second leakage current of the second set of capacitors can be measured and a second average can be calculated. Capacitors having a second leakage current equal to or greater than a second predetermined value may be removed from the second set, forming a third set of capacitors.
    公开号:FR3069328A1
    申请号:FR1856818
    申请日:2018-07-23
    公开日:2019-01-25
    发明作者:William A Millman；Marc V. Beaulieu；Michael I. Miller；Mark Leinonen
    申请人:AVX Corp；
    IPC主号:
    专利说明:

    SCREENING METHOD FOR ELECTROLYTIC CAPACITORS
    The present application claims the benefit of the provisional application of the United States Serial No. 61/695,657 having the filing date of August 31, 2012 and the provisional application of the United States Serial No. 61,768,623 having the filing date filed on February 25, 2013.
    Electrolytic capacitors are used in various medical, military, aerospace and commercial applications where it is essential that the capacitors be reliable and have extremely low failure rates. As such, various screening methods such as accelerated aging tests, reflow tests, overvoltage current tests and breakdown voltage tests have been developed to screen electrolytic capacitors in order to eliminate parts defective. However, many of these tests have failure criteria which are concerned only with catastrophic failures (i.e. fuse failures), and which are likely to release defective parts among the population of good parts, and these screening methods are not capable of detecting latent defects. For example, although a fuse may not have failed under highly stressed conditions such as high voltage and high temperature, the capacitor under test may still be damaged during screening, which can lead to long-term instability. Traditional methods of screening and delivering high reliability electrolytic capacitors have involved Weibull calculations based on lot-by-lot sampling where a small number of capacitors are subjected to highly accelerated voltage conditions (e.g. 1.5 times the nominal voltage (VR)), temperature (e.g. 85 ° C) and time (e.g. 40 hours or more) during debugging. However, traditional Weibull debugging allows parts that are statistically different pre-scavenging to feed the normal post-scavenging population because there is no pre-scavenging screening to eliminate the parts showing early failures. Although a large portion of these parts appear stable during long-term reliability testing (i.e. duration testing), possibly due to self-healing during debugging, a portion of the parts reaching normal population is unstable and may have long term reliability concerns in the field. Weibull statistical computation promotes the practice of leaving these parts unstable in the population so that a Weibull distribution can be created for classification purposes, as described in MIL-PRF-55365H. As a result, screening using a Weibull test cannot ensure the removal of unstable or defective capacitors from the population, which can lead to a batch of capacitors that exhibit an unacceptable level of reliability. Thus, despite the benefits achieved, there is a need for an improved screening method for electrolytic capacitors which can detect and eliminate capacitors with latent faults as well as a method for determining the predicted failure rate of screened capacitors which does not take not taking into account the eliminated capacitors, contrary to the Weibull process.
    According to an embodiment of the present invention, there is disclosed a method of iterative screening of electrolytic capacitors having a predetermined nominal voltage. The method includes measuring a first leakage current from a first set of capacitors and calculating a first average leakage current therefrom, and removing capacitors from the first set that have a first current measured leakage equal to or greater than a first predetermined value, thereby forming a second set of capacitors. The first predetermined value is equal to one or more standard deviations above the first average leakage current. The method further includes subjecting the second set of capacitors to a burn-in treatment. The burn-in treatment includes applying a predetermined test voltage to the capacitors which is about 0.8 to about 1.2 times the nominal voltage. After the burn-in treatment, a second leakage current from the second set of capacitors is measured and a second average leakage current is calculated from it. Then, the capacitors of the second set which have a second measured leakage current equal to or greater than a second predetermined value are removed from the second set, thereby forming a third set of capacitors. The second predetermined value is equal to one or more standard deviations above the second average leakage current.
    In another embodiment, a method of providing a batch of capacitors to a customer is disclosed. The method includes determining a nominal voltage for the capacitors, and iterative screening of the capacitors to remove the capacitors from the batch having a leakage current above a predetermined value at each iteration. The predetermined value is equal to one or more standard deviations above the average leakage current measured at each iteration. After screening, the batch of capacitors can be supplied to the customer without derating the nominal voltage.
    In yet another embodiment, there is disclosed a method of calculating a predicted failure rate for electrolytic capacitors. The method includes subjecting the capacitors to a burn-in treatment at a first temperature and a first voltage for a first duration; subjecting the capacitors to a duration test at a second temperature and a second voltage for a second duration; and determining the number of capacitors that fail after the duration test based on the number of capacitors having a leakage current above a predetermined level, wherein the calculation for determining the predicted failure rate excludes capacitors that failed before the burn-in treatment.
    Other features and aspects of the present invention are set out in more detail below.
    A full and enabling disclosure of the present invention, including its best mode for those skilled in the art, is set out more particularly in the rest of the description, including a reference to the appended figures, in which:
    Figure 1 is a block diagram illustrating an embodiment of the method of the present invention;
    Figure 2 is a sectional view of an embodiment of a solid electrolyte capacitor which can be screened by the method of the present invention;
    the figure is a sectional view of another embodiment of a solid electrolyte capacitor which can be screened by the method of the present invention;
    the figure is a sectional view of an embodiment of a liquid electrolyte capacitor which can be screened by the method of the present invention;
    FIG. 5 is a graph plotting the first leakage currents for a sample of capacitors and the separation of the leakage currents into three zones;
    FIG. 6 is a graph showing the post-assembly leakage current of the parts of "Zone 1" in FIG. 5;
    FIG. 7 is a graph showing the leakage current of the parts of “Zone 1” in FIG. 5 after having undergone a test of duration of 1000 hours at 125 ° C at 2/3 of the nominal voltage;
    FIG. 8 is a graph comparing the leakage current for each of the “Zone 1” capacitors subjected to a test of duration of 1000 hours at 125 ° C. at 2/3 of the nominal voltage at various stages of the test of duration;
    Figure 9 is a graph showing the change in leakage current for each of the capacitors from Figure 6 to Figure 7;
    FIG. 10 is a graph showing the leakage current of 3 different batches of “Zone 1” capacitors subjected to a burn-in of 125 ° C and then a test of duration of 2000 hours at 85 ° C at nominal voltage at various stages of the duration test;
    FIG. 11 is a graph showing the leakage current of 3 different batches of “Zone 1” capacitors subjected to a burn-in of 125 ° C and then a test of duration of 2000 hours at 85 ° C at nominal voltage at various stages of the duration test;
    FIG. 12 is a graph showing the leakage current of 2 different batches of “Zone 1” capacitors subjected to a burn-in of 125 ° C and then a test of duration of 2000 hours at 85 ° C at nominal voltage at various stages of the duration test;
    FIG. 13 is a graph showing the leakage current of 2 different batches of “Zone 1” capacitors subjected to a burn-in of 125 ° C and then a test of duration of 2000 hours at 85 ° C at nominal voltage at various stages of the duration test;
    FIG. 14 is a graph tracking the leakage currents of the capacitors with the ten highest leakage currents post-debugging but still within the cut-off limit of three standard deviations at the measurement of the first leakage current when the capacitors are subjected to a duration test of
    000 hours at 85 ° C at nominal voltage;
    Fig. 15 is a graph showing the leakage current behavior of capacitors which failed the first leakage pre-scavenging screening and were initially categorized as "Zone 2" parts but exhibited self healing and would have become "Zone 1" parts during subsequent testing;
    Fig. 16 is a graph showing the leakage current behavior of capacitors which failed to screen for the first leakage current but were within 0.01 * CV * 12;
    Fig. 17 is a graph comparing the pre-scavenging leakage current of a group of capacitors to the post-scavenging leakage current of capacitors after submission to the debugging process of the present invention and to the Weibull debugging process;
    FIG. 18 is a graph comparing the leakage current of capacitors passing the pre-scavenging screening process of the present invention with the drift of leakage current of capacitors failing the pre-scavenging screening process after submission 85 ° C duration test capacitors;
    Figure 19 is a graph comparing the leakage current for capacitors when tested at 25 ° C and 125 ° C;
    Fig. 20 is a graph comparing the pre-burn-in leakage current of a batch of capacitors with the post-burn-in leakage current of the capacitors after submission to the burn-in process of the present invention and the Weibull burn-in process;
    Fig. 21 is a graph comparing the pre-scavenging leakage current of multiple batches of capacitors with the post-scavenging leakage current of the capacitors after submission to the debugging process of the present invention and the Weibull debugging process;
    FIG. 22 is a graph comparing the duration test of capacitors subjected to pre-scavenging screening and the subsequent debugging process of the present invention to the Weibull debugging process;
    FIG. 23 is a graph showing the drift in the leakage current after a duration test at 85 ° C. of capacitors subjected to the screening process and to the debugging process of the present application;
    Fig. 24 is a graph comparing the pre-test capacitor duration leakage currents in a batch with the post-test capacitor duration leakage current, where the capacitors are grouped in zone 1 units, zone units 1 to the boundary, and area units 2 as shown in Figure 5;
    Figure 25 is the graph of Figure 24 which is scaled to show the leakage current of up to about 0.25 microamps (μΑ);
    Fig. 26 is a graph showing a method for determining whether a batch of capacitors is an outlier / outlier compared to other batches of capacitors; and Figure 27 is a sectional view of an embodiment of a hermetically sealed capacitor which can be screened using the method of the present invention.
    Repeated use of reference characters in this specification and the drawings is intended to represent identical or analogous features or elements of the present invention.
    Those skilled in the art should understand that the present discussion is a description of exemplary embodiments only, and is not intended to limit the broader aspects of the present invention.
    Generally speaking, the present invention relates to a method for iterative screening of electrolytic capacitors. The method for screening a batch or sample of electrolytic capacitors (i.e. 2 or more capacitors) described in the present application includes measuring the leakage current of the capacitors at multiple iterations in the process test then removal of the capacitors from the sample or batch which have a leakage current as determined above a predetermined value by statistical analysis at each iteration. For example, the leakage current of a first set of capacitors, which can include all the capacitors in the batch, can be measured, and the capacitors in the first set having a leakage current above a predetermined value after the first leakage current measurement can be removed from the batch or sample, and the remaining capacitors form a second set of capacitors which can be subjected to additional testing. The additional test may include a heat treatment to conduct the capacitors at a predetermined voltage, such as the nominal voltage of the capacitors, which is a predetermined nominal value which refers to the nominal nominal voltage for continuous operation up to 85 ° C.
    The nominal voltage is based on the thickness of the dielectric layer.
    Debugging processing can be used to apply stress to the capacitors to detect any unstable parts when measuring the leakage current from the second set of capacitors.
    After the debugging process is complete, additional processing such as reflow can occur, which can apply additional stress to the capacitors. Either before reflow or after reflow, a second iteration of screening can take place, where the leakage current for each of the capacitors in the second set is measured, and the capacitors in the second set having a leakage current beyond a new and second predetermined value are removed from the second set, forming a third set of capacitors which can then be subjected to an additional test. Furthermore, a third screening iteration may take place at the end of the screening process, where the leakage current for each of the capacitors in the third set is measured, and the capacitors in the third set having a leakage current beyond of a third predetermined value are removed from the third set, forming a fourth set of capacitors. The first, second and third predetermined values are determined by statistical analysis. In addition to screening the capacitors based on the leakage current, other parameters such as capacitance, equivalent series resistance (RSE) and dissipation factor (FD) can be measured and the capacitors can be additional screening based on a statistical analysis of the results of medium capacity, CSR and FD. Without being limited by theory, it is believed that subjecting the capacitors to be screened to a burn-in treatment at a predetermined test voltage which is close to their nominal voltage, as opposed to a test voltage which is 1.5 times their nominal voltage, which can permanently damage the capacitors, in combination with subjecting the capacitors to multiple iterations of leakage current testing to screen any capacitor above a predetermined value in each iteration can effectively screen unstable capacitors by screening to produce a batch of capacitors with extremely high reliability and extremely reliable failure rates and
    Such low failure capacitors are essential in certain applications, including medical, military and aerospace applications.
    An embodiment of the method of the present invention is shown in the block diagram of Figure 1, although it should be understood that the steps may be performed in a different order, and additional testing or iterative screening may be conducted to further eliminate faulty or unstable capacitors. The iterative screening method 100 of Figure 1, for example, shows various process steps 102 and screening steps 104 which are implemented to arrive at the specific outputs 106.
    Process steps 102 include a first iteration current measurement (pre108, debugging 114, remelting 120, second iteration leakage current measurement (DCL) (post-debugging) 126 and a leakage current measurement ( DCL) of third iteration 132.
    The leakage currents in steps 108, 126 and 132 are measured using a leakage test set which measures the leakage current (DCL) at a predetermined temperature and at nominal voltage after a minimum of 10 seconds . For example, the leakage current can be measured after 3 minutes at a temperature between approximately 20 ° C and approximately 85 ° C, through a load resistor having a minimum resistance of 1 kQ which is connected in series with the capacitor, with a nominal voltage applied. Leakage current can also be measured at higher temperatures (i.e. hot DCL), although the applied voltage can be about 2/3 of the rated voltage at temperatures higher than about 85 ° C, up to about 140 ° C, such as about 125 ° C, to normalize the stress applied on the capacitor to that undergone, for example, at about 85 ° C. Leakage current, or DCL, refers to the amount of current flowing through a capacitor when a DC voltage is applied after charging the capacitor. Generally, leakage current can be used to determine if a capacitor has faults or could be faulty, and a capacitor may require to have leakage current below a minimum level if it must be qualified for use in a given application. The leakage current depends on a multitude of factors, such as the voltage applied to the capacitor, temperature conditions, and the type of electrolyte used in the capacitor. As will be discussed below, results from leakage current measurements taken at various iterations of the screening process can be used to determine whether a capacitor is acceptable or whether it should be removed from a given lot or sample.
    Turning now to the process steps, screening steps, and specific outputs, the iterative screening method of the present invention is discussed. In a first iteration of the screening process, a first leakage current can be measured for the batch or sample of capacitors to be tested (i.e. a first set of capacitors), as shown process step 108 of Figure 1. The first leakage current can be determined at a temperature which varies from about 20 ° C to about 150 ° C in some embodiments. For example, DCL can be measured at a temperature ranging from about 20 ° C to about 30 ° C in some embodiments, such as about 25 ° C, from about 75 ° C to about 95 ° C in some embodiments, such as about 85 ° C, and about 100 ° C to about 150 ° C in yet other embodiments. For example, the temperature can vary from about 110 ° C to about 140 ° C, such as from about 120 ° C to about 130 ° C, such as about
    125 ° C. However, when the leakage current is measured at a temperature higher than about 85 ° C, as mentioned above, the voltage applied during the leakage current measurement can be around 2/3 of the nominal voltage, as mentioned above. Regardless of the temperature at which the first leakage current is determined, a first average leakage current can be calculated from the data collected relating to the first leakage current measurements for the first set of capacitors. After the first average leakage current is determined, a first predetermined value can be calculated for the first set of capacitors, which can be equal to one or more standard deviations above the first average leakage current. In some embodiments, however, the first predetermined value may be equal to three or more standard deviations above the first average leakage current. This is demonstrated by process step 110 where the first limit (i.e., predetermined value) is determined. Then, all capacitors having a first leakage current above the first predetermined value can be removed from the sample or from the batch because they represent potentially unstable capacitors or outliers, as shown in the output step 112. At the same time, all capacitors having a first leakage current below the first predetermined value pass the first screening iteration and can remain in the batch or sample for further screening beyond the first iteration screening, thereby forming the second set of capacitors.
    After removal of the capacitors above the first predetermined value, the second set of capacitors (i.e. the capacitors in the batch or sample which have passed the screening of first iteration 112) is subjected to a burn-in treatment as shown in process step 114. Generally, debugging is the process by which capacitors can be subjected to harsh conditions to determine if they tend to fail early in their life. The burn-in treatment 114 may involve the selective control and application of a predetermined test voltage to the capacitors, as shown in step 116. The burn-in treatment may be carried out at a temperature which may vary from about 100 ° C to about 150 ° C in some embodiments, from about 110 ° C to about 140 ° C in other embodiments, and from about 115 ° C to about 130 ° C in yet other embodiments of achievement
    For example, the second temperature can be 125 ° C.
    Regardless of the temperature at which the heating or burn-in treatment 114 is carried out, the burn-in treatment can occur for a period ranging from about 25 hours to 75 hours in one embodiment. At the same time, the time of the burn-in process can vary from about 35 hours to about 50 hours in other embodiments, such as from about 40 hours to about hours.
    For example, the time of the debugging process can be 42 hours.
    In addition, regardless of the temperature or time window of the burn-in process, the burn-in process includes the selective control and application of a predetermined voltage to the second set of capacitors. The applied voltage is generally a ratio of the nominal voltage of the capacitors to be tested. For example, the voltage to be applied may vary from about 0.7 to about 1.3 times the rated voltage in some embodiments, from about 0.8 to about 1.2 times the rated voltage in other modes embodiments, and from about 0.9 to about 1.1 times the nominal voltage in yet other embodiments. For example, the voltage applied during the burn-in process may be approximately 1.0 times the nominal voltage of the capacitors remaining in the sample or lot to be tested. It has been discovered that subjecting the capacitors in the second set to a burn-in treatment performed at about 1.0 times the nominal voltage of the capacitors allows sufficient screening of unstable or defective capacitors in subsequent screening iterations without damaging the capacitors, which were observed at higher voltages, such as those used during the Weibull test. Generally, the debugging processing step 116 leads to a reduction in the leakage current of the base population of capacitors and can be used to further expose unstable units, as shown in output 118. It should be noted that the reduction leakage current at this stage may be due to self-healing, so that a second iteration leakage current screening step 130 may be conducted for the second set of capacitors which have passed the screening step. first iteration leakage current 112 to remove any outliers or defective parts after the debugging process has been completed. The second iteration leakage current screening step 130 can be performed after debugging, or after the reflow process step 120, as discussed in more detail below.
    If desired, soldering via the reflow process step 120 can be performed on the second set of capacitors before measuring a second iteration leakage current 126 for the second set of capacitors. The reflow process step 120 may subject the capacitors to additional stresses in order to discover additional unstable capacitors during the second iteration leakage current screening 130. However, as noted above, this specific order of process does not is not required, and it should be understood that in some cases, the second iteration leakage current screening 130 may be completed after the debugging treatment 114 but before the reflow 120. In some cases, it may even be possible to perform the 'reflow step on the first set of capacitors.
    If the reflow process step 120 is completed before subjecting the second set of capacitors to the second iteration leakage current screening step 130, as shown in Figure 1, it can be completed after the burn-in processing . Generally, reflow is the process by which capacitors can be soldered to a board. Brazing by reflow after burn-in can isolate capacitors that have become unstable due to the additional thermomechanical stress that the reflow process exerts on the capacitors, as shown in output 124 of Figure 1, when the second set of capacitors is subjected to second iteration leakage current screening 130. For this reason, reflow can be performed prior to second iteration leakage current measurement 126 to further screen and remove any unstable parts. The basic reflow soldering process includes the steps of applying a soft solder paste to the desired tabs on a printed circuit board (PCB)
    such as menu FR-4, placement of the capacitors in the dough, and 1 ' application of heat on the whole, what bring the soft solder in dough to melt ( refusal ion). The soft solder himself then wet on the PCB and terminations of capacitor, drive to the cord connection of solder
    desired. The reflow process can take place in a linear convection oven as shown in step 122 in Figure 1. The linear convection oven can have a peak temperature profile of around 200 ° C to around 280 ° C in some embodiments, such as from about 205 ° C to about 270 ° C in other embodiments, and from about 210 ° C to about 260 ° C in yet other embodiments. For example, in medical, military and aerospace applications where SnPb (lead-based) soft solders that can melt at a lower temperature are used, reflow can take place at a temperature ranging from about 210 ° C to about 225 ° C. At the same time, for commercial applications using lead-free solder which melts at a higher temperature, reflow can occur at a temperature ranging from about 245 ° C to about 260 ° C. Note that although the reflow process discussed above uses a convection oven, the reflow process can also use an infrared convection oven or a vapor phase oven, and can be conducted by wave soldering or using a hotplate.
    After the reflow process is complete, a second iteration leakage current can be measured for the second set of capacitors, as shown in Figure 1 as process step 126, although in some embodiments, the second leakage current can also be measured before reflow. The second leakage current can be measured for capacitors successfully screening the first iteration leakage current 112 (i.e. the second set of capacitors) which have also been subjected to the burn-in treatment 114 and reflow 120, as shown in Figure 1. The second leakage current can be determined at a temperature between about 20 ° C and about 150 ° C in some embodiments. For example, DCL can be measured at a temperature ranging from about 20 ° C to about 30 ° C in some embodiments, such as about 25 ° C, from about 75 ° C to about 95 ° C in some embodiments, such as about 85 ° C, and about 100 ° C to about 150 ° C in yet other embodiments. For example, the temperature can vary from about 120 ° C to about 130 ° C, such as about
    125 ° C. However, when the leakage current is measured at a temperature higher than about as mentioned above, the voltage applied during the leakage current measurement can be about 2/3 of the nominal voltage, as mentioned above. above. Regardless of the second current of the temperature at which the leakage is determined, a second average leakage current can be calculated from the data collected relating to the measurement of the second leakage current for the second set of capacitors. After the second average leakage current is determined, a second predetermined value can be calculated for the second set of capacitors, which can be equal to one or more standard deviations above the second average leakage current. In some embodiments, however, the second predetermined value may be equal to three or more standard deviations above the second average leakage current. This is demonstrated by process step 128 where the second limit (i.e. the predetermined value) is determined. Then, all capacitors having a second leakage current above the second predetermined value can be removed from the sample or from the batch because they represent potentially unstable capacitors or with outliers, as shown in the output step 130. At the same time, all capacitors having a second leakage current below the second predetermined value pass the second screening iteration and can remain in the batch or sample for further screening beyond the second iteration screening, thereby forming the third set of capacitors. Note that if the reflow process 120 was not carried out before measuring the second leakage current for the second set of capacitors, after the second iteration of the leakage current screening, the third resulting set of capacitors can be subjected to the process of reflow 120 as mentioned above.
    As an additional process step, a functionality test 132 may be undertaken to determine standard capacitor characteristics for the capacitors passing both the first iteration leakage current screening 112 and the second iteration leakage current screening 130 discussed above (i.e. the third set of capacitors). At this point, additional unstable or defective capacitors can be screened and removed from the batch or sample based on additional statistical analysis. The functionality test can be performed at a temperature ranging from approximately 15 ° C to approximately 35 ° C. in some embodiments, or from about 20 ° C to about 30 ° C in other embodiments. For example, testing can be done at 25 ° C.
    Regardless of the temperature at which functionality 132 testing is conducted, a third iteration leakage current can be measured for the capacitors remaining in the sample (i.e., the third set of capacitors ), as shown in Figure 1. Regardless of the temperature at which the third leakage current is determined, a third average leakage current can be calculated from the data collected for the third leakage current measurements for the third set. of capacitors. After the third average leakage current is determined, a third predetermined value can be calculated for the third set of capacitors, which can be equal to one or more standard deviations above the third average leakage current. In some embodiments, however, the third predetermined value can be equal to three or more standard deviations above the third average leakage current. This is demonstrated by process step 134 where the third limit (i.e. the predetermined value) is determined. Then, all capacitors having a third leakage current above the third predetermined value can be removed from the sample or from the batch because they represent potentially unstable capacitors or with outliers, as shown in the output step 136. At the same time, all capacitors having a third leakage current below the third predetermined value pass the third screening iteration and may remain in the batch or sample for release or for further screening beyond the third iteration screening, forming thus the fourth set of capacitors. Thus, these capacitors will have undergone at least three iterations of leakage current screening based on a statistical analysis to ensure that the capacitors remaining in the batch are highly reliable with an extremely low risk of failure.
    Additional tests (not shown in Figure 1) may be performed on the capacitors screened in the third iteration 132. In addition to screening based on leakage current, the capacitors passing the first two iterations of screening for leakage current (i.e. the third set of capacitors) can be tested for their measurement of equivalent series resistance (ESR), dissipation factor (FD) and capacitance. These capacitors can then be further screened to remove any unstable parts based on a statistical analysis collected as to CSR, FD and capacity. For example, if the capacitance is measured, the capacitors can be screened based on meeting a guard band tolerance limit, while if the RSE and / or FD are measured, any outliers present at- more than 1 or more standard deviations above the average cut-off limit will be rejected from the lot or sample to be made available for
    use. The process of screening such as described in the present invention can be done at both on of the capacitors at solid electrolyte and on of the
    liquid electrolyte capacitors. The solid or liquid electrolyte capacitor screened by the method of the present invention can be used in a variety of applications including, but not limited to, medical devices, such as implantable defibrillators, pacemakers (pacemakers), cardioversion machines , neural stimulators, drug delivery devices, etc. ; automotive applications; military applications, such as RADAR systems; consumer electronics, such as radios, televisions, etc. ; And so on. In one embodiment, for example, the capacitor can be used in an implantable medical device configured to provide a high therapeutic voltage (for example between approximately
    500 volts and approximately 850 volts or, desirably, between approximately 600 volts and approximately 800 volts) of treatment for a patient. The device may contain a container or housing which is hermetically sealed and biologically inert. One or more conductive wires are electrically coupled between the device and the patient's heart via a vein.
    Cardiac cardiac electrodes are arranged to detect activity and / or provide blood pressure to the heart. At least a portion of the lead wires (for example an end portion of the lead wires) may be disposed adjacent to or in contact with one or more of a ventricle and an atrium of the heart. The device also contains a capacitor bank which typically contains two or more capacitors connected in series and coupled to a battery which is internal or external to the device and supplies energy to the capacitor bank. Due in part to the high conductivity, the capacitor screened by the method of the present invention can achieve excellent electrical properties and thus be suitable for use in the capacitor bank of the implantable medical device. For example, the equivalent series resistance ("RSE") - the magnitude at which the capacitor acts as a resistor during a charge and a discharge in an electronic circuit - can be less than approximately 1500 milliohms, in some embodiments of less than about 1000 milliohms, and in some embodiments, of less than about 500 milliohms, measured with a polarization of 2 volts and a signal of 1 volt at a frequency of 1000 Hz.
    After a sample or batch of capacitors has been screened by the method of the present invention, the sample or batch of capacitors can be provided to a customer without the need to first derate the voltage at which the capacitors can be used at a level which is lower than the predetermined nominal voltage. In other words, the screening process can filter unstable capacitors so that the capacitors supplied to the customer can be used at their nominal voltage as opposed to a lower voltage (i.e., derated).
    To further minimize the risk of the presence of latent faults in a batch of capacitors which have been screened according to the iterative screening process mentioned above, an additional screening step based on a comparison of the screened lot with other screened lots of capacitors can be performed as a safeguard to filter a screened batch having an average leakage current which is an outlier / outlier in comparison to the average leakage current of all screened batches considered as a whole. The average leakage current of all the screened lots considered as a whole is designated by the general average leakage current. As shown in Figure 26, the general average leakage current of multiple batches of capacitors after they have been screened can be determined. The average leakage current for each of the screened batches can be determined using
    capacitors in the lot screening of current of capacitors who have sustained burn or all of it tra
    who have successfully passed the first leak, such as on additional iteration heat treatment and / or additional screening. Then, all batches of capacitors having an average leakage current above a predetermined value, such as a leakage current value which is one or more standard deviations above the leakage current of general average for all batches, may be rejected as a batch to be supplied to the customer. For example, a lot with an average leakage current that is more than three standard deviations above the overall average leakage current may be rejected. This additional screening step may limit the variation from batch to batch of the capacitors that are supplied to the customer.
    At the same time, since the screening method of the present application involves the removal of a batch of capacitors from all capacitors having an initial leakage current above a predetermined level before the burn-in process, where such capacitors can be qualified as early failures or youthful defect, it is not possible to calculate a predicted failure rate with the traditional Weibull model as described in MIL-PRF-55365H. In addition, we note that the Weibull process fails to take into account the effects of multi-side reflow of surface mount parts on substrates in its calculation of predicted failure rate. As such, when using the screening method of the present application, it should be understood that the predicted failure rate can be calculated via a new method as explained below.
    First, it should be understood that to determine the predicted failure rate of a batch of capacitors supplied to a customer, before any calculation is made, a simulated production routine is completed on a sample from the population, where the production routine includes two-side reflow. Then, a calculation is made based on the behavior of the sample through a simulated production routine. Generally, the predicted failure rate calculation is based on two main steps where the duration test results of a number of parts at an accelerated temperature (e.g. 125 ° C) and a voltage (e.g. 2/3 of the nominal voltage) for a specific duration, are translated into an equivalent number of component / device hours at 25 ° C. Next, the number of failures and equivalent component / device hours are used to calculate a predicted failure rate and the average time between failures. Determination of equivalent device / component hours is based on MIL-HDBK-217 reliability prediction using the Arrhenius model as applied to solid tantalum capacitors, where the Arrhenius model is used to predict acceleration failure due to increases
    MIL-HDBK-217 temperature, and in which the manual is referenced for all purposes. The calculation of equivalent device / component hours also takes into account
    The activation energy of the tantalum capacitors, which can range from approximately 1.08 eV to approximately
    1.15 eV.
    At the same time, the failure rate calculation is based on a chi-square calculation for a time bound sample test, where the degrees of freedom are equal to the sum of the number of failures and
    1, multiplied by 2. The parameters to be entered in the calculation of the failure rate include the nominal voltage of the capacitors, the number of capacitors tested, the number of hours during which the capacitor parts have been tested. test, test temperature, test voltage, number of failures, desired confidence level, desired application temperature and desired application voltage. The resulting calculated outputs include component / device hours equivalent to 25 ° C as demonstrated by the duration test of a specific number of samples at one voltage and
    a specific temperature during a duration trial specific, which take in account a postman acceleration of temperature test, a postman
    test voltage acceleration and a predictive failure rate calculation for the total population of capacitors from which samples were selected based on the number of failures that occurred during the duration test and the total number equivalent component / device hours, which also takes into account an application voltage acceleration factor. Finally, from the predicted failure rate calculation, the average time between failures (TMED) in hours can be determined.
    First, to determine the component hours equivalent to the end-use application temperature of the capacitors being screened, a test temperature / screen temperature acceleration factor and a voltage acceleration factor d assay / screening can be determined. Formula 1 below shows how the Test Temperature Acceleration / Screening Factor (FATE) can be determined, and includes the conversion of application and test temperatures to Kelvin degrees:
    (Formula 1)
    At the same time, how the test / screening factor (FATEC) formula 2 below shows voltage acceleration can be determined:
    FATEC =
    Voltage d trial
    Nominal voltage (Formula 2)
    In addition, formula 3 below shows how the component hours equivalent to the application temperature of the capacitors are determined:
    Component hours equivalent to application temperature = (number of capacitors tested) (Test hours) (FATE) (FATEC) (Formula 3)
    Then, the equivalent component hours can be converted to equivalent component years if desired. Then an application voltage acceleration factor (FATA) can be determined, as shown in formula 4 below:
    (Formula 4)
    Now, using the calculations from the previous formulas, we can calculate the failure rate, where the failure rate is shown to be failure in percent per 1,000 hours. The failure rate is based on a chi-square distribution and includes the determination of the inverse of the unilateral probability of the chi-square distribution. Formula 5 shows the equation for determining the failure rate:
    Failure rate per 1000 hours)
    (Formula 5)
    The "CHIINV" function calculates the chi-square value of two factors - the confidence level factor and the degrees of freedom factor. The confidence factor is 1 minus the input confidence level expressed as a decimal number. The degree of freedom factor is twice the sum of the number of failures observed during the capacitor life test and one. This factor represents the test of the sample which is for a specific duration, independent of the number of failures. The chi-square value is then divided by twice the equivalent component hours determined in formula 3. The result is then multiplied by the application voltage acceleration factor (FATA) as determined in formula 4, after split FATA in advance by two. Then, this result is multiplied by a factor of 1,000 times 100, or 100,000, to express the final predicted failure rate as “failures in percent per 1,000 hours. "
    After the predicted failure rate in percent failure per 1,000 hours has been determined as shown above in Formula 5, the failure rate can be converted to mean time between failures (MTED) in hours as shown below in formula 6:
    Failure rate in% for 1000 hours
    100
    100
    (Formula 6)
    When the formula 5 shown above is used after the duration test to determine the predictive failure rate of screened capacitors according to the method of the present application, the predicted failure rate of the capacitors can range from about 0.000005% failures per 1,000 hours to approximately 0.01% failures per 1,000 hours, such as from approximately 0.000008% failures per 1,000 hours to approximately 0.009% failures per 1,000 hours, such as approximately 0.00001% failures per 1000 hours to approximately 0.008% failures per 1000 hours when determined at a confidence level of approximately 50% to approximately 99.9%, such as approximately 55 % to about 95%, such as from about 60% to about 90%. In a particular embodiment, the predicted failure rate of the capacitors can range from about 0.00001% of failures per 1000 hours to about 0.008% of failures per 1000 hours at a confidence level of about 90%.
    As mentioned above, the capacitors screened by the method of the present invention can be solid or liquid electrolyte capacitors. A solid electrolyte capacitor generally contains a capacitor element which includes an anode body, a dielectric layer and a solid electrolyte. The capacitor may also contain an anode electrical conductor (eg ribbon, wire, foil, etc.) which is electrically connected to the anode body for connection to an anode termination. The tube metal composition (“metal valve” containing a metal which is capable of oxidation) of a compound based on tube metal, such as tantalum, niobium,
    Aluminum, hafnium, titanium, their alloys, their oxides, their nitrides, and so on. For example, the tube metal composition may contain an electrically conductive oxide of niobium, such as
    Niobium oxide having an atomic ratio between niobium and oxygen of 1: 1.0 ±
    1.0, in some embodiments 1: 1.0 ± 0.3, in some embodiments
    1: 1.0 ± 0.1 and in some embodiments
    1: 1.0 ± 0.05. For example,
    Niobium oxide can be NbOo, 7, NbOi, o,
    NbOi, i and
    NbÛ2. In one embodiment, a tube metal powder is used, which is compacted using a conventional powder mold to form a porous anode body. After that, the porous anode body is sintered to form a porous integral body.
    Once constructed, a dielectric layer can be formed by anodically oxidizing ("anodizing") the sintered anode body. This leads to the formation of a dielectric layer which is formed over and / or within the pores of the anode body. For example, a tantalum anode (Ta) can be anodized into tantalum pentoxide (Ta2Os).
    Typically,
    1 anodization is carried out by initially applying an electrolyte to the anode, such as by immersing the anode in
    1 electrolyte.
    The capacitor element also contains a solid electrolyte which functions like the cathode for the capacitor.
    In one embodiment, the cathode of a solid electrolyte capacitor can be made primarily from manganese dioxide and is formed by a process generically called manganization. In this process, a conductive counter electrode coating is formed over the dielectric formed by anodization. The manganization step is typically carried out by immersing the anodized device in a solution of manganese nitrate and by heating the impregnated device in a moist atmosphere to convert the nitrate into a solid conductive manganese dioxide. In other words, a solid manganese dioxide electrolyte can be formed by the pyrolytic decomposition of manganese nitrate (Mn (NC> 3) 2) · Such capacitors having a cathode formed from manganese dioxide can operate at high temperatures, such as up to about 250 ° C, such as up to about 230 ° C, when the capacitor is a hermetically sealed capacitor, discussed in more detail below
    In another embodiment, the solid electrolyte can also be formed from one or more layers of conductive polymer. The conductive polymer can include poly (pyrroles); poly (thiophenes), poly (3,4ethylenedioxythiophenes) (PEDT); poly (anilines); poly (acetylenes); poly (p-phenylenes); poly (phenolates); etc. ; and their derivatives. The anode portion can also optionally be applied with a layer of carbon (eg graphite) and a layer of silver, respectively. The silver coating can, for example, act as a conductor that can be soldered, a contact layer and / or a charge collector for the capacitor and the carbon coating can limit the contact of the coating. with solid electrolyte. Such coatings can cover all or part of the solid electrolyte.
    Regardless of the particular manner in which the capacitor is formed, it can be connected to terminations as is well known in the art. For example, the anode and cathode terminations can be electrically connected to the anode conductor (for example a foil or a conductive wire) and to the cathode, respectively. Generally speaking, it is desirable to electrically isolate the anode termination from the cathode termination so that the capacitor operates as desired. To achieve such isolation, a variety of techniques can be used. In one embodiment, for example, any oxide and / or cathode layer (s) formed on the conductor can (can) simply be removed by an etching process (for example chemical, laser, etc.).
    As indicated above, the solid electrolyte capacitor which can be screened by the method of the present invention contains an anode termination to which the anode lead wire of the capacitor element is electrically connected and a cathode termination to which the cathode of the capacitor element is electrically connected.
    Any conductive material can be used to form the terminations, such as a conductive metal. The terminations can be connected using any technique known in the art, such as welding, adhesive bonding, refractory metal paste, etc. Once the capacitor element is attached, the connection support / the terminations can be enclosed within a housing, which can then be filled with silica or any other known encapsulation material. The width and length of the housing can vary depending on the desired application. Suitable enclosures may include, but are not limited to, for example, "A", "B", "C", "D",
    "E", "F", "G", "H", "J", "K", "L", "M", " NOT ", " P ", "R", "S", "T", "V", "W", "Y" or "X " (AVX corporation). Whatever cut
    of a housing employed, the capacitor element is encapsulated so that at least a portion of the anode and cathode terminations is exposed. After encapsulation, the exposed portions of the anode and cathode terminations can be aged, screened and cut to the desired size.
    As discussed above, the anode conductor can be in the form of a sheet or wire, etc., and can be formed from a tube metal compound such as tantalum, niobium , niobium oxide, etc. For example, the screening method of the present invention can be used to screen many embodiments of electrolyte capacitors, such as the solid electrolyte capacitors shown in Figures 2 and 3. As shown in Figure 2, the capacitor with solid electrolyte can use an anode conductor which is in the form of a sheet. In addition, as shown in Figure 3, the solid electrolyte capacitor can employ an anode conductor which is in the form of an electric wire.
    For example, in one embodiment, the capacitor to be screened can employ a sheet (eg plate, sheet, etc.) which is bonded to the anode body, as shown in Figure 2. Various examples of such capacitors are described , for example, in US Patent Nos. 5,357,399 to Salisbury; 6,751,085 to Huntington; 6,643,121 to Huntington; 6,849,292 to Huntington; 6,673,389 to Huntington; 6,813,140 from Huntington and 6,699,767 from Huntington, which are given for reference only. In Figure 2, an embodiment of a solid electrolyte capacitor 200 which can be screened by the method of the present invention is shown, which includes an anode conductor 210 in the form of a sheet. The anode conductor 210 is bonded to a compressed anode body 213 made of a tube metal composition (for example, tantalum). Although other bonding means can be used, in a particular embodiment, the anode conductor 210 is bonded to the anode body 213 using an adhesive 212. The adhesive 212 can initially be applied to a surface of the anode conductor 210. After that, the compressed anode body 213 can be disposed on the adhesive 212. The anode body 213 and the anode conductor 210 can then be sintered to provide a bond to form between the adhesive and the metal of both the anode body and the anode conductor. Once attached, the anode body 213 can then be anodized and coated with a solid electrolyte as described above. If desired, additional layers may be employed, such as a layer of carbon 227 and / or one or more layers of silver 221 or 222, as also discussed above. The capacitor 200 may also include an encapsulating resin at the side walls 224 which sheath the anode body 213. End caps 228 and 229 are provided as cathode and anode terminations, respectively, of the capacitor 200.
    Another embodiment of a solid electrolyte capacitor which can be screened by the method of the present invention is shown in Figure 3. The solid electrolyte capacitor 300 can employ an anode conductor 360 which is in the form an electric wire embedded in the porous anode body. In such an embodiment, after forming the capacitor element, 330, anode and cathode terminations can be electrically connected to the anode electrical wire 360 and to the solid electrolyte layer 354. The specific configuration terminations may vary as is well known in the art. Referring to Figure 3, for example, there is shown an embodiment which includes an anode termination 370 and a cathode termination 380. In this particular embodiment, the cathode termination 380 contains a portion 382 in electrical contact with the bottom surface 339 of the capacitor element 330. To attach the capacitor element 330 to the cathode termination 380, a conductive adhesive can be employed as is known in the art.
    The anode termination 370 contains a first portion 376 positioned substantially perpendicular to a second portion 374. The second portion 374 contains a region 351 which carries the anode wire 360. If desired, region 351 may have a " U-shape "to further accentuate the surface contact and mechanical stability of the electrical wire 360. The anode electrical wire 360 can then be welded to the region 351 with a laser or by any other suitable method. Once the capacitor element is attached to the terminations, it is enclosed within a resin casing, which can then be filled with silica or any other known encapsulation material. Referring again to FIG. 3, for example, a particular embodiment of such an encapsulation box for a capacitor 300 is shown as element 388. The encapsulation box 388 provides structural protection and additional thermal to capacitor 300. After encapsulation, exposed portions of the respective anode and cathode terminations can be aged, screened and cut. If desired, the exposed portions can optionally be bent twice along the outside of the housing 388 (for example at an angle of approximately 90 °).
    Another embodiment of a solid electrolyte capacitor which can be screened by the method of the present invention is a hermetically sealed capacitor, such as the capacitor shown in Figure 27. As shown in Figure 27, a capacitor element with solid electrolyte 520 is hermetically sealed within a housing 522 to form the capacitor 500. Any of a variety of different materials can be used to form the housing, such as metals, plastics, ceramics and and so on. In one embodiment, for example, the housing includes one or more layers of a metal, such as tantalum, niobium, aluminum, nickel, hafnium, titanium, copper, silver, l steel (for example stainless), their alloys (for example electrically conductive oxides), their composites (for example a metal coated with an electrically conductive oxide) and so on. In another embodiment, the housing can include one or more layers of a ceramic material, such as aluminum nitride, aluminum oxide, silicon oxide, magnesium oxide, calcium oxide, glass, etc. as well as their combinations.
    The housing can have any desired shape, such as cylindrical, D-shape, rectangular, triangular, prismatic, etc. Referring to Figure 27, for example, an embodiment of a capacitor assembly 500 is shown, which contains a housing 522 and a capacitor element 520. To increase the volumetric efficiency, the capacitor element 520 may have a length (excluding the length of the anode conductor 560) which is relatively similar to the length of an interior cavity 526 defined by the housing 522. Furthermore, it should be understood that although only one element of capacitor 520 is shown in Figure 27, housing 522 may include multiple capacitor elements 520. It should also be understood that each of the capacitor elements 520 may be screened by the method of this disclosure separately before being hermetically sealed in housing. Alternatively, it should also be understood that the capacitor elements 520 may be hermetically sealed in the housing 522, after which the capacitor assembly 500 itself may be screened by the method of the present disclosure.
    Although not required in any way, the capacitor element can be attached to the housing such that an anode termination and a cathode termination are formed external to the housing for later integration into a circuit. The particular configuration of the terminations may depend on the desired application. In one embodiment, for example, the capacitor assembly can be formed so that it can be surface mounted, but still remain mechanically robust. For example, the anode conductor can be electrically connected to external and surface-mountable anode and cathode terminations (by tabs, sheets, plates, for example frames, etc.).
    Such terminations may extend through the housing for connection with the capacitor.
    The thickness or height of the terminations is generally selected to minimize the thickness of the capacitor assembly. If desired, the surface of the terminations can be electroplated with nickel, silver, gold, tin, etc. as is known in the art to ensure that the final part can be mounted on the circuit board. In a particular embodiment, the termination (s) is (are) coated with nickel and silver burrs, respectively, and the mounting surface is also plated with a layer of tin solder . In another embodiment, the termination (s) is (are) coated with thin external metal layers (for example gold) on a base metal layer (for example copper alloy) to further increase the conductivity.
    In some embodiments, connection members may be employed in the interior housing cavity to facilitate connection to the terminations in a mechanically stable manner. For example, referring again to Figure 27, the capacitor assembly 500 may include a connection member 562 which is formed from a first portion 567 and a second portion 565. The connection member 562 may be formed from conductive materials similar to external terminations. The first portion 567 and the second portion 565 can be integral or separate parts which are connected together, either directly or via an additional conductive element (for example a metal). In the illustrated embodiment, the second portion 565 is provided in a plane which is generally parallel to a lateral direction in which the conductor
    560 extends (for example direction y).
    The first portion 567 is "standing" in the sense that it is arranged in a plane which is generally perpendicular to the lateral direction in which the conductor
    560 extends. In this way, the first portion 567 can limit the movement of the conductor 560 in the horizontal direction to accentuate the surface contact and the mechanical stability during use. If desired, an insulating material
    570 (for example a washer used around the conductor 560.
    The first portion 567 may have a mounting region (not shown) which is connected to the anode conductor 560. The region may have a "U-shape" to further accentuate the surface contact and mechanical stability of the conductor 560. connection of the region to the conductor 560 can be accomplished using any of a variety of known techniques, such as welding, laser welding, conductive adhesives, etc. In a particular embodiment, for example, the region is laser welded to the anode lead wire 560. Whichever technique is chosen, however, the first portion 567 can hold the anode lead wire 560 in substantial horizontal alignment to further enhance the dimensional stability of the capacitor assembly
    500.
    Referring again to Figure 27, an embodiment of the present invention is shown in which the connection member 562 and the capacitor element 520 are connected to the housing 522 by
    Through anode and cathode 527 terminations and
    529, respectively. Anode 527 termination contains a first region
    527a which is positioned within the housing 522 and electrically connected to the connection member
    562 and a second region
    527b which is positioned external to the housing 522 and provides a mounting surface 201.
    Likewise, the cathode termination 529 contains a first region 529a which is positioned within the housing 522 and electrically connected to the solid electrolyte of the capacitor element 520 and a second region 529b which is positioned external to the housing 522 and provides a mounting surface 503. It should be understood that the entire portion of such regions does not need to be positioned within or externally to the housing.
    In the illustrated embodiment, a conductive track 527c extends into a base 523 of the housing to connect the first region 527a and the second region 527b. Similarly, a conductive track 529c extends into the base 523 of the housing to connect the first region 527a and the second region 527b. The conductive tracks and / or regions of the terminations can be separate or integral. In addition to extending through the external wall of the housing, the tracks can also be positioned at other locations, such as external to the external wall. Of course, the present invention is in no way limited to the use of conductive tracks to form the desired terminations.
    Regardless of the particular configuration employed, connection of the terminations 527 and 529 to the capacitor element 520 can be carried out using any known technique, such as welding, laser welding, conductive adhesives, etc. In a particular embodiment, for example, a conductive adhesive 531 is used to connect the second portion 565 of the connection member 562 to the anode termination 527. Likewise, a conductive adhesive 533
    The element is used to connect the capacitor cathode 520 to the cathode termination 529.
    Conductive adhesives can be formed from conductive metal particles contained with a resin composition.
    The metal particles can be silver, copper, gold, platinum, nickel, zinc, bismuth, etc. The resin composition can include a thermosetting resin (e.g. epoxy resin), a vulcanizing agent (e.g. acid anhydride) and a coupling agent (e.g. silane coupling agents). Suitable conductive adhesives are described in the publication of patent application U. S. No. 2006/0038304 of Osako et al., Which is given by reference for all practical purposes.
    Optionally, a polymeric clamp can also be arranged in contact with one or more surfaces of the capacitor element, such as the rear surface, front surface, upper surface, lower surface, lateral surface (s), or any combination of these. Polymeric clamping can reduce the likelihood of delamination of the capacitor element from the housing. In this regard, the polymer clamping may have a certain degree of mechanical strength which allows it to retain the capacitor element in a relatively fixed position even when it is subjected to vibrational forces, but which is not strong enough to let it crack. For example, clamping can have a tensile strength of about 1 to about 150 Megapascals ("
    MPa some embodiments of about about
    100 MPa, in some embodiments from about to about some embodiments, from about 20 to about 70 MPa, measured at a temperature of about 25 ° C. It is normally desired that the clamping is not electrically conductive.
    Although any of a variety of materials can be used, which have the desired mechanical strength properties noted above, vulcanizable thermosetting resins have been found to be particularly suitable for use in the present invention. Examples of such resins include, for example, epoxy resins, polyimides, melamine resins, urea formaldehyde resins, polyurethanes, silicone polymers, phenolic resins, etc. In certain modes of embodiment, for example, the clamping can employ one or more poly (organosiloxanes). Epoxy resins are also particularly suitable for use as a polymeric bridle. Still other suitable conductive adhesive resins can also be described in the publication of patent application
    Osako et al., And the patent
    U. S. No. 7,554,793 of
    Chacko, which are given for reference for all purposes.
    If desired, vulcanizing agents can also be used in the polymeric clamping to aid vulcanization.
    Vulcanizers typically constitute from about 0.1 to about 20% by weight of the clamp. It is also possible to use other additives, such as photoinitiators, viscosity modifiers, suspension aid agents, pigments, stress reduction agents, coupling agents (by non-conductive agents (for example clay, silica, alumina,
    When used, such additives typically constitute from about 0.1 to about 20% by weight of the total composition.
    Referring again to Figure 27, for example, there is shown an embodiment in which a single polymeric clamp 597 is disposed in contact with an upper surface 581 and a rear surface 577 of the capacitor element 520. Then only one clamping is shown in Figure 27, it should be understood that separate clamps can be used to provide the same function. In fact, more generally, any number of polymeric clamps can be used to come into contact with any desired surface of the capacitor element. When multiple restraints are used, they may be in contact with each other or remain physically separate. For example, in one embodiment, a second polymeric clamp (not shown) can be employed, which comes into contact with the upper surface 581 and the front surface 579 of the capacitor element 520. The first polymeric clamp 597 and the second polymeric clamping (not shown) may or may not be in contact with each other. In yet another embodiment, a polymeric clamp can also come into contact with a bottom surface 583 and / or a side surface (s) of the capacitor element 520, either together with or instead of other surfaces.
    Whichever way it is applied, it is typically desired that the polymeric clamping also be in contact with at least one surface of the housing to further encourage mechanical stabilization of the capacitor element against possible delamination. For example, the clamping can be in contact with an interior surface of one or more side wall (s), external wall, cover, etc. In FIG. 27, for example, the polymer flange 597 is in contact with interior surfaces 507 and 509 of the housing 522. While being in contact with the housing, it is nevertheless desired that at least a portion of the cavity defined by the housing remains unoccupied to let the inert gas flow through the cavity and limit the contact of the solid electrolyte with oxygen. For example, at least about 5% of the volume of the cavity typically remains unoccupied by the capacitor element and the polymeric clamping, and in some embodiments, from about 10% to about 50% of the cavity volume.
    Once connected in the desired manner, the resulting package is hermetically sealed. Referring again to Figure 27, for example, the housing 522 includes a base 523 and a cover 525 between which the cavity 526 is formed. The cover 525 and the base 523 can be formed of ceramic, metal (e.g., iron, copper, nickel, cobalt, etc., as well as their alloys), plastic, and so on. In one embodiment, for example, the base 523 is formed of a ceramic material and the cover 525 is formed of a metallic material. The cover 525 includes an outer wall 521 which is integral with at least one side wall 524. In the illustrated embodiment, for example, two opposite side walls 524 are shown in section. The height of the side wall (s) 524 is generally such that the cover 525 does not come into contact with any surface of the capacitor element 520 so that it is not contaminated. The outer wall 521 and the base 523 both extend in a lateral direction (y direction) and are generally parallel to each other and to the lateral direction of the anode conductor 560. The side wall 524 s' extends from the outer wall 521 in a longitudinal direction which is generally perpendicular to the base 523. A distal end 506 of the cover 525 is defined by the outer wall 521 and a proximal end 501 is defined by a lip 553 of the side wall 524.
    More particularly, the lip 553 extends from the side wall 524 in the lateral direction, which can be generally parallel to the lateral direction of the base 523. The lip 553 also defines a peripheral edge 551, which can be generally perpendicular to the lateral direction in which the lip 553 and the base 523 extend. The peripheral edge 551 is located beyond the external periphery of the side wall 524 and can be generally coplanar with an edge 571 of the base 523 The lip 553 can be sealed to the base 523 using any known technique, such as welding (e.g. resistance or laser), soldering, glue, etc. For example, in the illustrated embodiment, a sealing member 587 is used (for example a glass-metal seal, a Kovar® ring, etc.) between the components to facilitate their attachment. However, the use of a lip described above can allow a more stable connection between the components and improve the seal and the mechanical stability of the capacitor assembly.
    Hermetic sealing typically takes place in the presence of a gaseous atmosphere which contains at least one inert gas so as to inhibit the oxidation of the solid electrolyte during use. The inert gas can include, for example, nitrogen, helium, argon, xenon, neon, krypton, radon and so on, as well as their mixtures. Typically, the inert gases constitute most of the atmosphere within the housing, such as from about 50% by weight to 100% by weight, in certain embodiments from about 75% by weight to 100% by weight. weight, and in some embodiments, from about 90% by weight to about 99% by weight of the atmosphere. If desired, a relatively small amount of non-inert gases such as carbon dioxide can also be used,
    Oxygen, water vapor, etc.
    In such cases, however, the non-inert gases typically constitute 15% by weight or less, in some embodiments 10% by weight or less, in some embodiments about 5% by weight or less, in some embodiments about 1% by weight or less, and in some embodiments, from about 0.01% by weight to about 1% by weight of the atmosphere within the housing. For example, the moisture content (expressed in terms of relative humidity) can be about 10% or less, in some embodiments about 5% or less, in some embodiments about 1% or less, and in some embodiments, about
    0.01% to about 5%.
    As mentioned above, the screening method of the present invention can also be used to screen liquid electrolyte capacitors. A liquid electrolyte capacitor generally includes a porous anode body containing a dielectric layer, a cathode containing a metal substrate coated with an electrochemically active coating (eg a conductive polymer) and an aqueous electrolyte. The ionic conductivity of the electrolyte is selectively controlled within a particular range so that the capacitor can be charged at a high voltage. The physical arrangement of the anode, cathode and working electrolyte of a liquid electrolyte capacitor screened by the method of the present invention can generally vary as is known in the art. Referring to Figure 4, for example, an embodiment of a liquid electrolyte capacitor 400 is shown, which includes a working electrolyte 440 disposed between an anode 450 and a cathode 430. The anode 450 contains a film dielectric 460 and is embedded with a conductor 420 (for example an electric wire of tantalum). Cathode 430 can be formed from a cathode substrate 410 and electrochemically active material 490. Although not shown, a separator can be positioned between cathode 430 and anode 450 to prevent direct contact between the anode and the cathode, but by allowing an ion current flow from the working electrolyte 440 to the electrodes. A seal 470 (eg glass-to-metal) can also be used, which connects and seals the anode 450 to the cathode 430. Although not shown, the capacitor 400 can also include a spacer (not shown) which holds the anode 450 stationary within cathode 430. The spacer may, for example, be made of plastic and may be in the form of a washer.
    The present invention can be better understood by reference to the following examples, which refer to Figures 5 to 25 and show the efficiency and reliability of the electrolytic capacitor screening method of the present invention. Examples 1 to 3 and 10 use Figure 5 as a starting point, which traces the first leakage currents for all the capacitors tested in 10 batches and separates them into zones. "Zone 1" includes parts that have a first leakage current which is within three standard deviations of the first average leakage current which, in this case, is measured at a temperature of 125 ° C and a voltage that is equal to 2/3 of the nominal voltage. "Zone 1 at the limit" includes parts that have a first leakage current which is three standard deviations near the first average leakage current but are close to the limit. "Zone 2" includes parts that have a first leakage current above three standard deviations from the first average leakage current. However, the capacitors in "zone 2" have a first leakage current which is less than the upper cut-off limit of 0.001 * C * V R * 12. Note that the upper cutoff limit is calculated from the following equation:
    DCL limit = 0.001 ★ Capacity (C) ★ Voltage
    Nominal (V R ) ★ Temperature factor (FT), where the FT is 12 to 125 ° C. Here, the constant, which is 0.001 in the calculation of the leakage current limit used in Figure 5, is multiplied by the product of the capacitance and the nominal voltage (V R ), which is further multiplied by a factor of 12 to account for a high temperature of 125 ° C. Note that the constant used can be 0.01 for commercial or military applications, while the constant used can be 0.001 in medical or aerospace applications. In Figure 5, the resulting upper cutoff limit based on the variables described above or the product design capacity is 0.225 μΑ. At the same time, "zone 3" includes capacitors having a first leakage current that is both above three standard deviations of the first average leakage current and greater than the upper cutoff limit of 0.001 * C * V R * 12
    Example 1
    Duration test at 125 ° C and 2/3 nominal voltage
    Referring to FIGS. 6 to 9, 100 capacitors per batch from 10 batches entering “zone 1” in FIG. 5 above, were tested at 125 ° C for a period of 42 hours at 1.0 times the nominal voltage of the capacitors. The parts were mounted on FR-4 cards and subjected to a test lasting 1000 hours at 125 ° C and 2/3 of rated voltage. The leakage current (DCL) was then determined at a temperature of 25 ° C and at the nominal voltage for the parts after the completion of the 1000 hour test.
    As seen in figure 6, the capacitors of “zone 1” of figure 5 showed a slightly higher leakage current overall in figure 6 post-assembly compared to figure 5 which, as mentioned above, represents the determination of the first leakage current. However, the capacitors have a leakage current which is still below the severe cutoff / defalliance limit of
    0.225 μΑ predetermined for capacitors.
    Similarly, as seen in the figure
    7, at the end of the test lasting 1,000 hours at 125 ° C at
    2/3 of the nominal voltage, the capacitors in the “zone” in FIG. 5 overall displayed a slightly higher leakage current in FIG. 7 compared to FIGS. 5 and 6. Nevertheless, the capacitors have a leakage current which is still below the 0.225 μΑ failure limit for capacitors.
    At the same time, Figure 8 shows the leakage current measurements for the "zone 1" capacitors as determined at various times during the duration test.
    One capacitor failed by displaying a leakage current above the 0.225 μΑ limit throughout the test, as indicated by the dotted oval, while the other three capacitors displayed leakage currents above the 0.225 μΑ limit at the DCL leakage current measurement for hours, but stabilized during a test of additional duration up to 1000 hours.
    Note that these failed capacitors would have been removed using the screening method of the present invention, but testing continued on the failed capacitors to see how they would behave during a long-term test. As shown, the leakage current for some of the capacitors was above the cutoff limit during the test but then dropped below the cutoff limit at the end of the test. Thus, by not following the screening method of the present invention and being concerned only with end-point life test data, this could lead to accepting capacitors which have unstable characteristics.
    Then, figure 9 shows the change in the leakage current (DCL) for each of the parts of "zone 1" subjected to a test of duration of 1000 hours at 125 ° C at 2/3 of the nominal voltage of the figure 7 in comparison with the post-assembly leakage current in FIG. 6. As shown, the graph of the DCL drift observed during the 1000 hour test at 125 ° C. is represented by a population of good behavior with a drift of Negligible mean DCL.
    Example 2
    Duration test at 85 ° C and at nominal voltage
    Referring to Figures 10 to 13, 10 capacitors per batch from 10 batches entering the "zone 1" in Figure 5 were determined at 125 ° C for a period of 42 hours at 1.0 times the nominal voltage of the capacitors. The parts were then mounted on FR-4 cards and subjected to a 2,000 hour test at 85 ° C and rated voltage. The leakage current (DCL) was then determined for the parts at various stages of the 2,000 hour duration test. As seen in the 10 graphs representative of the 10 batches, all the capacitors were below the cut-off limit of DCL (as shown by the bold line) after 2000 hours of duration test, indicating that the process of iterative screening according to the invention is effective in removing unstable capacitors from the lots tested. Note that the cut-off limit is calculated from the following equation:
    DCL limit - 0.0025 * Capacitance (C) ★ Voltage nominal (V R ) * Temperature factor (FT), where the FT is worth 1 for 25 ° C, 10 for 85 ° C and 12 for 125 ° C. Example 3 Duration test at 85 ° C and nominal voltage, population
    not standard
    Then, individual capacitors with marginal or abnormal performance by burn-in at 125 ° C, were isolated, categorized as part of "zone 1 at the limit" (that is to say figure 14), "travelers from zone 2 to zone 1 "(that is to say figure 15), or" zone 2 "(that is to say figure 16), and subjected to a test of duration at 85 ° C at nominal voltage.
    Referring to Figure 14, a graph is shown which tracks the leakage currents of the capacitors having the ten highest first leakage current measurements which were still within the cutoff limit of three standard deviations (that is, ie "zone 1") at the measurement of the first iteration leakage current in FIG. 5. Although these 10 capacitors have first measurements of leakage current close to the cut-off limit of three standard deviations, the capacitors remained stable during the duration test, indicating the relative efficiency of the leakage current cutoff limit of three standard deviations used in the iterative screening method according to the invention.
    Turning to Figure 15, there is shown a graph which tracks the leakage current behavior of capacitors which failed to debug first leakage current in screening by having leakage currents above the cutoff limit of three standard deviations and were therefore initially categorized as "zone 2" pieces. However, during the debugging, these “zone 2” parts displayed self-healing so that their second iteration leakage current was reduced to enter the second leakage current cutoff limit of three standard deviations (after debugging ). While these capacitors pass the duration test within three standard deviations after 2,000 hours, the iterative screening process of the pending claims rejects these capacitors. Although the capacitors would pass the duration test technically, the instability during the duration test justifies the withdrawal of such capacitors from their respective batches.
    Next, Fig. 16 is a graph showing the leakage current behavior of capacitors which exceeded the cutoff limit of first leakage current by three standard deviations but were within the limit of leakage current of permanent cutoff, which was 0.001 * C * V R * 12. Although most of the capacitors appear stable in the 85 ° C duration test, this population is likely to contain unstable capacitors, as demonstrated by the three faulty units represented by the three dotted lines.
    As shown in Examples 1 to 3, the iterative screening method of the present invention is highly reliable in that a duration test of a sample size of 1000 capacitors screened at 125 ° C at 2/3 of the nominal voltage for 1000 hours and at 85 ° C at full nominal voltage for 2000 hours leads to zero failure up to a qualification leakage current limit of 0.005 * C * V r , which is the half of the current standard military requirement for the duration test, which is 0.01 * C * V R.
    Example 4
    Comparison of pre-burn and post-burn DCL
    In addition, the leakage current of the capacitors was determined at 125 ° C and 2/3 of the working voltage after a 15 second soak before burn-in using the method of the present invention and the comparative Weibull method. In the context of the process of the present invention, the burn-in was carried out at 125 ° C, while the burn-in of the Weibull process was carried out at 85 ° C. As shown in Figure 17, the pre-scavenging leakage current was generally higher than the two post-scavenging leakage currents and varied from approximately 0.7 μΑ to approximately
    1.2 μΑ. At the same time, the post-clearance leakage current of the Weibull process varied from approximately 0.6 μ 0, to approximately 1.3 μΑ, and the post-clearance leakage current of the process of the present application varied from approximately 0.4 μΑ to about 1.0 μΑ. While FIG. 17 shows the parametric drift of the continuous leakage current resulting from the debugging process of the present application, where the overall continuous leakage current is significantly lower, FIG. 17 also shows that the continuous leakage current of parts potentially damaged has been increased, so that the parts have a leakage current of about 0.8 μΑ to about 1.0 μΑ, which can improve the efficiency of the statistical screening method of the present invention.
    Example 5
    85 ° C duration test of capacitors passing or failing screening of first DCL
    Then, the drift in the leakage current after duration test at 85 ° C for 2 sets of capacitors from a batch - 1 set succeeding in screening the first leakage current (pre-debugging) and 1 set failing in screening first leakage current (predetermination) - were compared. The 85 ° C duration test for 2000 hours was performed, after which the leakage current drift for each set of capacitors was determined. The results are shown in FIG. 18, where it is indicated that the capacitors which would have been removed during the screening of first leakage current (pre-burn-in) in the process of the present application exhibit a consequent drift of leakage current after test duration, while the capacitors which successfully screened for the first leakage current (pre-burn-in) and were accepted for subsequent screening exhibited a small leakage current drift after the duration test.
    FIG. 18 therefore demonstrates that the method of the present application can remove inhomogeneous faults in the capacitors tested before the burn-in process via a screening step based on the leakage current where potentially unstable capacitors are removed. Without this screening step, these potentially unstable capacitors can feed the distribution of DCL representing good capacitors after debugging during screening due to the healing process induced during debugging, however, after a duration test, as shown in Figure 18 , these potentially unstable capacitors may exhibit a significant leakage current drift, indicating that these capacitors have faults not characteristic of the rest of the capacitors in the batch. Furthermore, the use of statistical screening before debugging at 125 ° C as described in the present application reduces or eliminates the possibility that this small quantity of potentially parametrically unstable capacitors enters the delivered batch.
    Example 6
    Comparison of leakage current determination at 25 ° C and 125 ° C
    As discussed above, the screening method of the present application determines the leakage current of the capacitors which are screened at elevated temperatures. Figure 19 shows how the determination of the leakage current at high temperatures enhances the possibility of detecting individual capacitor variations in the leakage current within a batch of capacitors which would normally be undetected during a test at 25 ° C (ambient temperature) As shown, the capacitors tested at 25 ° C do not have a parametric drift of leakage current, while a portion of the capacitors tested at 125 ° C does have a parametric drift leakage current, where the leakage current of these capacitors varies from approximately 2 μΑ to approximately 10 μΑ. If the temperature at which the leakage current was measured had not been increased, these outlier capacitors would not have been detected and isolated during batch screening, which means that potentially unstable capacitors would have successfully screened.
    Example 7
    DCL improvement demonstrated with debugging at high temperature
    FIGS. 20 and 21 show the improvement in the overall leakage current when the burn-in temperature is increased in comparison with the conventional burn-in of 85 ° C. associated with the Weibull process. For example, Figure 20 shows the pre-scavenging leakage current for a batch of capacitors, in comparison to the leakage current after the 125 ° C debugging process described in the present application and the 85 ° C debugging process associated with the process. from Weibull. The leakage current for capacitors determined at a high temperature of 125 ° C generally has a lower leakage current than capacitors determined using the Weibull method, however, at the same time, any outliers can be more easily revealed. At the same time, Figure 21 shows that the reduced DCL after the debugging process at 125 ° C described in the present application can be repeated on multiple batches.
    Example 8
    Duration test at 125 ° C and 2/3 of the working voltage for 1000 hours
    Subsequently, FIG. 22 compares the leakage current of capacitors undergoing the initial leakage current screening and the debugging process of 125 ° C. as described in the present application with the leakage current of capacitors undergoing a debugging process of 85 ° C in accordance with the Weibull process after 1000 hours of test duration at 125 ° C and 2/3 of the working voltage where the specified permanent leakage current limit was set at 0.225 μΑ. The leakage current was determined at 25 ° C at the working voltage of the capacitors after a soaking time of 30 seconds. 10 capacitors from 10 batches screened using the process described in this application were tested, together with 170 capacitors tested using the traditional Weibull process at 85 ° C.
    As shown, two capacitors destroyed using the Weibull method were faulted after time testing because their leakage currents were above the predetermined limit of 0.225 μΑ. In particular, the two failing parts had post-clearance leakage currents of approximately 0.4 μΑ and 0.5 μΑ. Furthermore, none of the capacitors screened and tested using the method of the present application was faulty in that none of the capacitors demonstrated a leakage current above the limit of 0.225 μΑ.
    Example 9
    Effect of the screening process on the leakage current
    In addition, the leakage currents of 10 capacitors sampled from 10 batches of capacitors which were subjected to the screening process of the present application after a test of duration at 85 ° C. and nominal voltage for 2000 hours were compared with their currents. duration pre-test leakage. As shown in Figure 23, after 2,000 hours of duration testing, the drift in the pre- and post-duration leakage current was negligible.
    Example 10
    Zone 1 parts duration test, zone 1 at the limit and zone 2 at 85 ° C for 2,000 hours
    In another example, the leakage current for capacitors in 10 batches was determined post-debugging at 125 ° C. The capacitors were then grouped into “zone 1” capacitors, “zone 1 at the limit” capacitors and “zone 2” capacitors as discussed above based on Figure 5. “Zone 1” included the capacitors with a leakage current which was three standard deviations from the average leakage current, which in this case is measured at a temperature of 125 ° C and at a voltage which is 2/3 the nominal voltage. "Zone 1 at the limit" included capacitors having a leakage current at three standard deviations near the average leakage current, but which also had leakage currents close to the limit of three standard deviations (ie say, the capacitors with the 10 highest post-debugging leakage currents which were within the limit of three standard deviations). "Zone 2" included capacitors with a leakage current above three standard deviations from the average leakage current but was also below the upper cutoff limit of 0.225 μΑ. After grouping the capacitors in the appropriate zones, the capacitors were then subjected to 2000 hours of duration test at 85 ° C. Then, the leakage current for each of the capacitors in each zone was measured at 25 ° C.
    As shown in FIG. 24, three capacitors grouped in “zone 2” which were within the limit of severe cut-off leakage current of 0.225 μΑ before duration test were faulty after duration test and had leakage currents of approximately 0 , 75 μΑ,
    1.5 μΑ and 2.75 μΑ. At the same time, all the parts of "zone 1" and parts of "zone 1 at the limit" had leakage currents below the limit of 0.225 μΑ after duration test. This indicates that traditional severe cutoff limits do not effectively eliminate parts that have reliability concerns later, such as capacitors that have leakage currents that were initially within the severe cutoff limit, but had leakage above the severe cut-off limit after duration test.
    Figure 25 is a zoom of the view of Figure 24 and shows that the leakage current of the parts of "zone 2" increased in comparison with the parts of "zone 1" and "zone 1 at the limit" indicating possible concerns. reliability of "zone 2" parts.
    Example 11
    Failure rate calculation for a confidence level of 60%
    In example 11, table 1 below shows the inputs and outputs for a failure rate calculation using the formulas mentioned above. In Example 11, a confidence level of 60% was selected and 30 capacitors with a nominal voltage of 10 were tested for 6 hours at a temperature of 125 ° C at 2/3 of the nominal voltage , which was 6.6 volts. The predicted failure rate was then calculated assuming that the capacitors would be used by the customer at 25 ° C and at a voltage of 5 volts. As shown in Table 1, testing the capacitors at 125 ° C for 6 hours at 6.6 volts was the equivalent of about 2,000,000 hours at 25 ° C and 5 volts, and led to a rate default predicted to be around 0.0029% failures per 1,000 hours.
    EXAMPLE 11: CALCULATION OF FAILURE RATES FOR ITERATIVE SCREENING METHOD
    ENTRIES (10 VGo) EXITS Nominal voltage (V) 10 Component 2 hours (equivalent to Application Temp.) 1,978,593 Number of capacitors mi s under test 30 Component Years (equivalent to Application Temp.) 225.71 Hours tested 6 Test acceleration factor 3 (temperature) 38,234.21 Test temperature (C) 125 Test acceleration factor 4 (voltage) 0.287496 Test voltage (V) 6, 6 Application acceleration factor 5 (voltage) 0.1250 Number of failures 0 Trust level (%) 60 Failure rate 6 (failures in percent per 1,000 hours) 0.002894 Application temperature (C) 25 TMED (Average time between failures) (hours) 34,549,607 Application voltage (V) 5Activation energy 1 of the tantalum tip (eV) 1.08
    Assumptions and factors in the formulas:
    1 Activation energy is adjustable 2 Equivalent component hours are based on model MIL-HDBK-217 for solid tantalum capacitors, and total component hours tested at test temperature are multiplied by the test temperature acceleration factor and the test voltage acceleration factor to obtain the equivalent component hours used in calculating the failure rate.
    3 The test temperature acceleration factor is based on the Arrhenius model; temperatures are in Kelvin, and the constant of
    Boltzmann - 8.63E-5 eV / K 4 The test voltage acceleration factor is the test voltage divided by the nominal voltage, at cube 5 The application voltage acceleration factor is the voltage d application divided by nominal voltage, to cube 6 Predictions of failure rate are based on a distribution of chicory; the degrees of freedom in the use of the chi-square distribution are the number of failures plus 1 multiplied by 2; and the calculated failure rate is multiplied by the application voltage acceleration factor to obtain the final failure rate.
    Table 1
    Example 12
    Failure rate calculation for 90% confidence level
    In Example 12, Table 2 below shows the inputs and outputs for a failure rate calculation using the formulas mentioned above. In Example 12, a 90% confidence level was selected, and 30 capacitors with a nominal voltage of 10 were tested for 6 hours at a temperature of 125 ° C at 2/3 of the voltage rated, which was 6.6 volts. The predicted failure rate was then calculated assuming that the capacitors would be used by the customer at 25 ° C and at a voltage of 5 volts. As shown in Table 1, testing the capacitors at 125 ° C for 6 hours at
    6.6 volts was the equivalent of approximately 2,000,000 hours at 25 ° C and 5 volts and resulted in a predicted failure rate of approximately 0.0072% failures per 1,000 hours.
    EXAMPLE 12: CALCULATION OF FAILURE RATES FOR ITERATIVE SCREENING METHOD
    ENTRIES (10 VGo) EXITS Nominal voltage (V) 10 Component 2 hours (equivalent to Application Temp.) 1,978,593 Number of capacitors mi s under test 30 Component Years (equivalent to Application Temp.) 225.71 Hours tested 6 Test acceleration factor 3 (Temperature) 38,234.21 Test temperature (C) 125 Test acceleration factor 4 (Voltage) 0.287496 Test voltage (V) 6, 6 Application acceleration factor 5 (voltage) 0.1250 Number of failures 0 Trust level (%) 90 Failure rate 6 (failures in percent per 1,000 hours) 0.007273 Application temperature (C) 25 TMED (Average time between failures) (hours) 13,748,671 Application voltage (V) 5Activation energy 1 of the tantalum tip (eV) 1.08
    Assumptions and factors in the formulas:
    1 Activation energy is adjustable 2 Equivalent component hours are based on model MIL-HDBK-217 for solid tantalum capacitors, and total component hours tested at test temperature are multiplied by the test temperature acceleration factor and the test voltage acceleration factor to obtain the equivalent component hours used in calculating the failure rate.
    3 The test temperature acceleration factor is based on the Arrhenius model; temperatures are in Kelvin, and the constant of
    Boltzmann - 8.63E-5 eV / K 4 The test voltage acceleration factor is the test voltage divided by the nominal voltage, at cube 5 The application voltage acceleration factor is the voltage d application divided by nominal voltage, to cube 6 Predictions of failure rate are based on a distribution of chicory; the degrees of freedom in the use of the chi-square distribution are the number of failures plus 1 multiplied by 2; and the calculated failure rate is multiplied by the application voltage acceleration factor to obtain the final failure rate.
    Table 2
    These and other modifications and variations of the present invention can be practiced by those skilled in the art, without departing from the spirit and scope of the present invention. Furthermore, it should be understood that aspects of the various embodiments can be interchanged either wholly or in part. In addition, those skilled in the art will appreciate the foregoing description by way of example only, which is not intended to limit the invention described in the appended claims.
    权利要求:
    Claims (9)
    [1" id="c-fr-0001]
    1. A method of supplying a batch of capacitors to a customer, the method comprising:
    determining a nominal voltage for the capacitors;
    iterative screening (100) of the capacitors to remove the capacitors from the batch having a leakage current above a predetermined value at each iteration, the predetermined value being equal to one or more standard deviations above the leakage current means measured at each iteration; and supplying the batch of capacitors to the customer without derating the nominal voltage.
    [2" id="c-fr-0002]
    2. Method according to claim 1, further comprising the calculation of a general average leakage current for multiple batches of capacitors, in which the batch to be supplied to the customer is included in the calculation of general average leakage current, and verifying that an average leakage current for the lot is within one or more standard deviations of the overall average leakage current.
    [3" id="c-fr-0003]
    The method of claim 2, wherein the average leakage current for the batch is within three standard deviations of the general average leakage current.
    [4" id="c-fr-0004]
    The method of claim 1, further comprising providing the customer with a predicted failure rate for the batch of capacitors, wherein a calculation to determine the predicted failure rate excludes capacitors removed from the batch during a first screening d 'iteration (100) which occurs before a burn-in heat treatment (114).
    [5" id="c-fr-0005]
    5. The method of claim 4, wherein the predicted failure rate calculation uses a
    postman acceleration of voltage (FATEC) based on a voltage applied at lot of capacitors during a trial of duration and a postman acceleration of
    temperature (FATE) based on a temperature at which the duration test occurs.
    [6" id="c-fr-0006]
    6. The method of claim 4, wherein the predicted failure rate is between about 0.00001% failures per 1000 hours and about 0.008% failures per 1000 hours as determined at a confidence level of about 90 %.
    [7" id="c-fr-0007]
    7. Method for calculating a predicted failure rate for electrolytic capacitors, the method comprising:
    subjecting the capacitors to a burn-in treatment (114) at a first temperature and at a first voltage for a first duration;
    subjecting the capacitors to a duration test at a second temperature and a second voltage for a second duration; and determining the number of failed capacitors after the duration test based on the number of capacitors having a leakage current above a predetermined level, wherein the calculation for determining the predicted failure rate excludes failed capacitors before the debugging treatment.
    [8" id="c-fr-0008]
    The method of claim 7, wherein calculating the predicted failure rate further comprises using a voltage acceleration factor (FATEC) based on a voltage applied to the batch of capacitors during the duration test and a temperature acceleration factor (FATE) based on the temperature at which the duration test occurs.
    [9" id="c-fr-0009]
    9. The method of claim 7, wherein the predicted failure rate is between about 0.00001% failures per 1000 hours and about 0.008% failures per 1000 hours as determined at a confidence level of about 90 %.
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    同族专利:
    公开号 | 公开日
    US9541607B2|2017-01-10|
    FR2995084B1|2019-04-12|
    GB201314468D0|2013-09-25|
    US10591527B2|2020-03-17|
    DE102013216963A1|2014-03-06|
    US20170082671A1|2017-03-23|
    FR3069328B1|2021-05-21|
    GB2505566A|2014-03-05|
    CN103675515B|2017-06-13|
    JP6608123B2|2019-11-20|
    US20140067303A1|2014-03-06|
    CN103675515A|2014-03-26|
    FR2995084A1|2014-03-07|
    JP2014049767A|2014-03-17|
    KR102141502B1|2020-08-06|
    JP2018117145A|2018-07-26|
    KR20140029290A|2014-03-10|
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    法律状态:
    2020-07-16| PLFP| Fee payment|Year of fee payment: 8 |
    2021-07-28| PLFP| Fee payment|Year of fee payment: 9 |
    2022-03-04| CD| Change of name or company name|Owner name: KYOCERA AVX COMPONENTS CORPORATION, US Effective date: 20220125 |
    优先权:
    申请号 | 申请日 | 专利标题
    US201261695657P| true| 2012-08-31|2012-08-31|
    US61695657|2012-08-31|
    US201361768623P| true| 2013-02-25|2013-02-25|
    FR1302021A|FR2995084B1|2012-08-31|2013-08-30|SCREENING METHOD FOR ELECTROLYTIC CAPACITORS|
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