• 专利附录
  • 专利说明
  • 权利要求
  • 类似技术
  • 同族专利
  • 引用文献
  • 法律状态
  • 优先权
    • 专利摘要:
    A laser diode assembly is configured with a ceramic mounting member (18) made of a thermally conductive and electrically conductive material. One of the opposite surfaces of the ceramic mounting member supports a laser diode. The other surface of the ceramic mounting member faces and is spaced from a heat sink (10). The ceramic mounting member and the heat sink each have coefficients of thermal expansion that are different from each other. The opposite surfaces of the ceramic mounting member are electroplated with respective metal layers, one of which is bonded to a soft solder layer (16). In an alternative of the invention, the support is further configured with a spacer (14) having the same coefficient of thermal expansion as the ceramic mounting member and bonded to the soft solder layer.
    公开号:CH711148B1
    申请号:CH01304/16
    申请日:2015-03-25
    公开日:2019-10-15
    发明作者:Komissarov C/O Ipg Photonics Corporation Alexey；Miftakhutdinov C/o IPG Photonics Corporation Dmitriy；Trubenko C/o IPG Photonics Corporation Pavel；Berishev C/O Ipg Photonics Corporation Igor；Strugov C/O Ipg Photonics Corporation Nikolai
    申请人:Ipg Photonics Corp；
    IPC主号:
    专利说明:

    Description The present invention relates to semiconductor laser technology and relates to a laser diode assembly; this laser diode assembly is characterized by increased stability.
    Background Art The rapid development of semiconductor laser technology has made the adoption of high power laser diodes more affordable. The constant pursuit of higher laser power requires better thermal management capability in the packaging design to enable controlled operation. Since these laser diodes generate a large amount of heat flows, which can adversely affect their performance and reliability, a thermally effective packaging solution is required in order to be able to quickly dissipate the excess heat generated in the laser diode to their surroundings.
    For high-performance applications, not only the thermal challenges, but also the mechanical integrity of the connections in the laser diode assembly are to be considered. These represent considerable assembly challenges, since the factors discussed below complicate the effort for generating an ideal assembly design.
    1, which shows a typical laser diode assembly, the heat generated in the laser diode is transferred to the surroundings by attaching the diode to a mounting element. In order to ensure efficient heat transfer across the thermal interface, the laser diode must be optimally attached to the laser diode assembly. A thin thermal bond interface, such as soft solder, creates an effective heat dissipation channel through the die attach process. To improve the thermal performance of the laser diode assembly, it is based on the illustration u. a. It is desirable to bring the heat source, such as the laser diode, as close as possible to the heat sink, make the soft solder interface as thin as possible, increase the thermal conductivity of the material, and provide close thermal contact between the laser diode and the heat sink.
    [0005] In each part of a laser diode assembly, thermal bonding interfaces or solders are used because of their electrical wiring, mechanical support and heat dissipation capabilities. These solders can usually be classified into two types: hard solder and soft solder. In general, the solder material must meet the following requirements:
    - It must have the desired processing temperature in order to withstand high temperature operation.
    - It must reduce thermally generated voltages due to the offset due to thermal expansion between the laser diode and the heat sink.
    - It must show little or no deformation during its long-term operation.
    - It must show a low electrical resistivity of a die chip solder to reduce Joule heating with a high injection current.
    Soft solder, which usually contains a high percentage of lead, tin and indium, has a very low yield point and undergoes plastic deformation under tension. Its ability to plastically deform helps to relax a tension developed in the bonded structure. However, this makes the soft solder susceptible to thermal failure and creep rupture, which causes long-term reliability problems.
    As shown in Fig. 1, a soft solder based on indium / Sn / Bi, etc. is conventionally used for bonding a heat sink to a ceramic mounting member. The coefficient of thermal expansion of e.g. Heat sink made of copper is not adapted to that of the ceramic mounting element. The repeated on / off cycle in laser operations, hereinafter referred to as a temperature cycle, can occur because of different thermal expansion coefficients of the sink or of the ceramic mounting element, which lead to the fracture / shearing etc. of the layer made of a soft material and / or to indium migration , cause mechanical stress. Initially, these defects lead to increased temperatures of the diode. The layer of the soft solder is destroyed early, which leads to the decoupling of the ceramic mounting element from the heat sink and ultimately to the destruction of the laser diode due to overheating. This is particularly relevant for high-power laser diodes because they have a large contact area between the chip and the heat sink and a high temperature difference between on and off cycles.
    On the other hand, hard solder has a very high yield point and thus experiences an elastic instead of a plastic deformation under tension. Accordingly, it has good thermal conductivity and is free from thermal fatigue and creep. Unfortunately, the melting temperatures of known brazing alloys can be too high and endanger the integrity of the ceramic mounting element when heated for the purpose of heat sink mounting.
    [0009] There is thus a need for an improved laser diode assembly that is resistant to temperature cycling.
    DESCRIPTION OF THE INVENTION The object on which the invention is based is achieved on the one hand by the features of independent claim 1 and on the other hand by the features of independent claim 3. The laser diode assembly according to the invention according to claim 1 points towards the present prior art in FIG. 1 two additional warmth
    CH 711 148 B1 dissipative layers that are inserted between the heat sink and the ceramic mounting element. One of these two heat dissipation layers acts as a spacer between a layer of the soft solder and a layer of the hard solder, which in turn is bonded to the heat sink. The spacer is made of a material that is selected such that it has a coefficient of thermal expansion that is essentially matched to a coefficient of thermal expansion of the ceramic mounting element. Accordingly, the geometry of both the spacer and that of the ceramic mounting element changes substantially uniformly during a temperature cycle, which minimizes tensile / compressive forces which adversely affect the soft solder layer. However, the forces exerted on the spacers of the laser diode assembly according to the invention are not sufficient to endanger the integrity of the soft solder.
    The braze layer is used to bond the spacer to the heat sink. The braze is practically insensitive to the non-uniform deformation of the intermediate layers made of materials with different coefficients of thermal expansion, in this case the materials of the spacer or the heat sink. However, the elevated temperatures during connection of the spacer to the heat sink do not affect the integrity of the solder and the chip.
    In the inventive laser diode assembly according to claim 3, the layer of the spacer in the laser diode assembly is made of a highly plastic homogeneous metal, which is galvanized onto the ceramic mounting element or bonded directly before the spacer is bonded to the heat sink using a soft solder layer. In contrast to the known prior art, which usually has a thin metal layer that does not exceed 1 to 2 micrometers, the metal layer of the present laser diode assembly according to the invention is at least 10 micrometers thick and up to dozens of micrometers thick and has a coefficient of thermal expansion that is differs from that of the ceramic mounting element. However, the plasticity of the plated or directly bonded, highly plastic, homogeneous metal of the spacer compensates for thermally generated stresses, while its thickness significantly increases the service life.
    Brief Description of the Drawings The above and other features will be more readily apparent from the following specific description that is accompanied by the drawings, in which:
    1 shows an exploded view of a known laser diode assembly,
    2B and 2A show a sectional illustration and a side exploded illustration of a first laser diode assembly according to the invention, and
    3 shows a side view of a further laser diode module according to the invention.
    Specific Description The invention is discussed in detail below. Wherever possible, the same or similar reference numbers will be used in the drawings and the description to refer to the same or like parts or steps. The drawings are in a simplified form and not exactly to scale. Unless otherwise noted, the words and phrases in the description and claims are intended to be of normal and usual meaning to those of ordinary skill in the laser diode and fiber laser arts. The word "couple" and similar terms do not necessarily refer to direct and immediate connections, but also contain mechanical and optical connections via free space or via intermediate elements.
    Thermal management, mechanical tension and material defects introduced by the assembly / assembly process are critical problems that must be solved in order to achieve reliable laser performance at higher power levels. In addition to the operating temperature itself, the thermal-mechanical voltage is an important factor that is responsible for the aging of laser diodes. High thermal-mechanical voltage levels are caused by the assembly process and are minimized by the laser diode assemblies according to the invention, which are explained in detail below in connection with FIGS. 2 and 3.
    2A and 2B show the inventive laser diode assembly 20 according to claim 1. A laser diode ("DL") 22 is bonded to a metal layer which is plated on the diode support surface of a ceramic mounting element 18. A layer of soft solder 16 provides reliable contact between the metallized side of the ceramic mounting element 18 and a spacer 14. The material of the spacer 14 is selected to have a coefficient of thermal expansion that is substantially matched to that of the ceramic mounting element 18, while the geometry of the spacer 14 is similar to that of the ceramic mounting element 18, which is several hundred micrometers thick. Furthermore, the spacer 14 is bonded to a heat sink 10 by means of a brazing layer 12.
    In general, the temperature of the laser diode 22 increases when current is passed through it. If the bond between the ceramic mounting element 18 and the heat sink 10 is good, the temperature rise is smaller because the heat is conducted away from the laser diode 22; if the bond is bad, the temperature rise is comparative
    CH 711 148 B1 larger because the heat in the chip increases. The materials commonly used to manufacture the ceramic mounting element 18 in high power laser diode applications include BeO and AIN ceramics. Typically, the heat sink 10 is made of copper or other metal with thermal conductivity properties and electrical conductivity properties close to those of copper.
    Regardless of the materials used for the heat sink 10 or for the ceramic mounting element 18, there is a mismatch between their respective coefficients of thermal expansion. This can cause large amounts of thermal mechanical stress on the soft solder 16. Common ductile solders are lead, tin and indium and their respective alloys such as indium-tin, which are classified as soft solders because of their plasticity. Accordingly, the elongation properties of soft solders such as indium are used to compensate for the mismatch caused by the plastic deformation (creep).
    However, the soft solder interface materials develop voids because of the repeated on / off temperature cycles, each lasting dozens of minutes. The main concerns with cavities include the loss of thermal conductivity within the soft solder interface. Cavities can create hotspots by creating areas with poor heat dissipation paths. Accordingly, voids in the soft solder interface not only limit heat dissipation, but also degrade the electrical and mechanical properties of the connection. This in turn can lead to the separation of the ceramic mounting element with the laser diode thereon from the rest of the laser diode assembly and to the destruction of the laser diode.
    2A, 2B minimizes the undesirable stresses on the soft solder 16 and the formation of cavities in the interface by introducing additional intermediate layers 14 and 12. The layer 14, which is referred to below as the spacer, is also included selected a coefficient of thermal expansion that is essentially matched to that of the ceramic mounting element 18. The spacer 14 is preferably made of the same material as the ceramic mounting element 18. Thus, the relative displacement between the spacer 14 and the ceramic mounting member 18 is minimal during temperature cycles. As a result, the soft solder interface 16 has a life that is significantly longer than that of the soft solder in the prior art laser diode assembly of FIG. 1.
    [0021] Of course, the spacer 14 has a coefficient of thermal expansion that differs from that of the heat sink 10. In contrast to soft solder materials, hard solder has a very high yield strength and thus experiences an elastic instead of a plastic deformation under tension. Numerous alloys including Au-Sn, Au-Ge, Au-Si, etc., e.g. Au80Sn20 eutectic alloys used to overcome reliability problems. Accordingly, as one of ordinary skill in the semiconductor art knows, the braze interface 12 is relatively free of thermal fatigue and creep.
    [0022] As discussed above, the prior art discloses numerous packaging configurations. Of course, every configuration is subject to strict tests. It is usually tested how the wavelength of emitted light varies in response to thermal stress over a predetermined number of temperature cycles, which typically contains hundreds of times and can occasionally reach more than a thousand times. Within each temperature cycle, a temperature difference between the highest and the lowest temperature exceeds 100 ° C. The dependence of the wavelength on the temperature increase of a pn junction is well known for any particular operating wavelength. For example, for a laser diode that emits light at 970 nm, each degree Celsius corresponds to a wavelength shift of 0.3 nm in the direction of longer wavelengths. As one of ordinary skill in the art knows, power consumption is a function of the injection current applied to a laser diode, the voltage across the laser diode, minus the optical power loss. Accordingly, the temperature change of the active connection is a reliable indicator of the loss in quality of the connection between the ceramic mounting element, which faces a heat sink, and an adjacent layer. In the laser diode assembly according to the invention in FIGS. 2A and 2B, this connection is the soft solder interface 16.
    Although there is no universal standard compulsory test that requires a predetermined number of repeated on / off cycles sufficient to call a laser diode assembly tested "good", common practice in the semiconductor industry is well known. That is, the temperature-based behavior of the pn junction in question during the number of temperature cycles that vary between 300 and 1000 times is accepted as a reliable indicator of the quality of an assembly.
    3 shows a further laser diode assembly 30 according to the invention, which comprises a heat sink 10 which is bonded via a soft solder interface 16. However, in contrast to the laser diode assembly of the prior art from FIG. 1, this laser diode assembly 30 has a lower surface 32 on the ceramic mounting element 18, which is galvanized with a relatively thick, pure metal layer 34 made of a highly plastic, homogeneous metal. Conventional practice in the packaging industry involves providing a metal layer that is as thin as possible, the thickness of which is usually about 1 micron. In contrast, the metal layer 34 of the laser diode assembly 30 according to the invention is at least 10 times thicker than that of the prior art and can be up to dozens of micrometers thick. Because of the plasticity of the
    CH 711 148 B1 clad or directly bonded, highly plastic homogeneous metal and the described thickness of the metal layer 34, thermally generated stresses are compensated according to the invention and the service life is significantly increased.
    权利要求:
    Claims (3)
    [1]
    claims
    1. laser diode assembly comprising:
    a ceramic mounting member (18) having a first surface that supports a laser diode (22);
    a heat sink (10) spaced from and facing a second surface of the ceramic mounting member (18) opposite the first surface, the ceramic mounting member (18) and the heat sink (10) having different coefficients of thermal expansion;
    a spacer (14) which is arranged on the second opposite surface of the ceramic mounting element (18) by means of a soft solder layer (16);
    a braze layer (12) bonded to the spacer (14) by means of which the spacer (14) is coupled to the heat sink (10), the spacer (14) made of a material with a coefficient of thermal expansion that matches that of the ceramic -Mounting element (18) is adapted, is manufactured.
    [2]
    2. The laser diode assembly of claim 1, wherein the spacer (14) is several hundred microns thick.
    [3]
    3. A laser diode assembly comprising a ceramic mounting member (18) having a first surface that supports a laser diode (22);
    a heat sink (10) spaced from and facing a second surface of the ceramic mounting member (18) opposite the first surface, the ceramic mounting member (18) and the heat sink (10) having different coefficients of thermal expansion;
    a spacer (34) arranged on the second opposite surface of the ceramic mounting element (18), the spacer (34) being formed as a metal layer consisting of a highly plastic, homogeneous metal, and a thickness of at least ten micrometers up to a few dozen micrometers, and wherein a soft solder layer (16) is bonded to the spacer (34) and couples this spacer (34) to the heat sink (10).
    CH 711 148 B1
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    法律状态:
    2020-09-30| PFA| Name/firm changed|Owner name: IPG PHOTONICS CORPORATION, US Free format text: FORMER OWNER: IPG PHOTONICS CORPORATION, US |
    优先权:
    申请号 | 申请日 | 专利标题
    US201461973237P| true| 2014-03-31|2014-03-31|
    US201461973225P| true| 2014-03-31|2014-03-31|
    PCT/US2015/022367|WO2015153208A1|2014-03-31|2015-03-25|High-power laser diode packaging method and laser diode module|
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