A cos structure with low indium climbing and a preparation method thereof

Abstract

The present application relates to a COS structure with low indium climbing and a preparation method thereof, the COS structure comprising a heat sink, a transition layer arranged on the upper surface of the heat sink, and a semiconductor laser die welded on the transition layer through a solder layer; the N surface of the semiconductor laser die faces upward, the P surface faces downward, one end is an anti-reflection surface, and the other end is a high-reflection surface, and the high-reflection surface protrudes out of the heat sink. The COS structure is simple and easy to implement, can realize indium evaporation only at the bottom of the die, no indium on both sides, effectively reduces the alloy temperature, and avoids the "indium climbing" of the die disconnection surface after alloying.

Description

Technical Field

[0001] This invention relates to a low indium creepage COS structure and its preparation method, belonging to the field of semiconductor laser packaging technology. Background Technology

[0002] With societal and technological advancements, semiconductor lasers are gaining increasing prominence and wider applications. Their advantages, such as wide wavelength range, small size, light weight, and long lifespan, have led to their widespread use in lighting, projection, medical, military, and scientific research fields. However, the waste heat generated by the semiconductor laser chip during operation needs to be effectively dissipated promptly; otherwise, the laser chip temperature will become too high, reducing the device's luminous efficiency and potentially causing laser failure. Currently, a widely used technical solution is to sinter the semiconductor laser chip onto a heat sink with high heat dissipation capacity, effectively dissipating the heat generated during chip operation. For the heat sink and chip to be bonded together, a layer of solder must be deposited on the surface of the heat sink. The commonly used sintering solder is indium metal. Indium is widely used in semiconductor laser packaging technology due to its excellent ductility (plasticity), low vapor pressure and low electrical resistance, high thermal conductivity, strong and reliable properties, fatigue resistance, and ability to adhere to various materials.

[0003] The process of depositing an indium layer onto the surface of a heat sink is called indium evaporation. Currently, the commonly used method involves placing the heat sink sheet in a vacuum coating machine, heating it to melt indium granules, and then evaporating them onto the heat sink surface to create a layer of indium of a certain thickness. Next, a die is placed onto the heat sink using a bonding machine, and finally, an indium alloy is formed using an alloying machine, achieving heat dissipation and electrical conductivity. During the alloying process, because indium has good fluidity after melting, excess indium on both sides of the die has a certain probability of creeping to the die's dissociation surface, forming an "indium creeping" phenomenon. The higher the alloying temperature, the more severe the "indium creeping" becomes. This "indium creeping" problem can cause laser power failure, and the longer the laser is used, the greater the probability of "indium creeping," affecting the laser's lifespan. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a low-indium-climbing COS structure and its preparation method. This COS structure is simple and easy to implement, enabling indium to be evaporated only at the bottom of the die with no indium on the sides, effectively reducing the alloying temperature and avoiding indium climbing on the die's dissociation surface after alloying.

[0005] Terminology Explanation:

[0006] 1. COS (Chip on Submount): This is a pre-packaged semiconductor laser. The component includes a laser chip and a heat sink, wherein the laser chip is fixed to the heat sink by solder.

[0007] 2. N-side: The negative side of the semiconductor laser die that needs to be connected to the detection power supply.

[0008] 3. P-side: The positive side of the semiconductor laser die needs to be connected to the detection power supply.

[0009] The technical solution of this invention is as follows:

[0010] A low indium creepage COS structure includes a heat sink, a transition layer disposed on the upper surface of the heat sink, and a semiconductor laser die soldered to the transition layer via a solder layer; the N-side of the semiconductor laser die faces upward and the P-side faces downward, one end is an anti-reflection surface and the other end is a high-reflection surface, and the high-reflection surface protrudes from the heat sink.

[0011] According to a preferred embodiment of the present invention, the solder layer is made of an indium-silver composite structure, wherein the thickness of indium is 3-5 μm and the thickness of silver is 0.3-0.5 μm.

[0012] This invention forms an indium-silver solder layer on the heat sink by evaporating a thin layer of silver on the indium surface. This solder has a lower melting point than pure indium solder, thus allowing the COS alloy to be completed at a lower temperature. This reduces the "indium creep" on the die release surface without affecting the alloy quality.

[0013] According to a preferred embodiment of the present invention, the heat sink is made of copper alloy with a thickness of 200-300 μm, a length of 500-1200 μm, and a dissociation period of 600-1200 μm.

[0014] According to a preferred embodiment of the present invention, the transition layer is made of gold and has a thickness of 2-2.5 μm.

[0015] According to a preferred embodiment of the present invention, the semiconductor laser die is made of gallium arsenide, the die cavity length is 250-800 μm, the cleavage period is 300-500 μm, and the thickness is 90-120 μm.

[0016] According to a preferred embodiment of the present invention, the semiconductor laser die is welded to the center of the heat sink, with a left-right offset within the range of 50±10μm, and the high reflectivity surface protrudes from the heat sink by a distance of 10-40μm.

[0017] A method for preparing the above-mentioned low indium climbing COS structure includes the following steps:

[0018] (1) The heat sink, transition layer material and solder layer material are pretreated respectively, then the upper surface of the heat sink is polished and ground, and then a transition layer is prepared on the upper surface of the heat sink.

[0019] (2) Place the heat sink on the vapor deposition fixture, put the solder layer material into different tungsten boats, evacuate the chamber, heat the solder layer material for 30-40 seconds, and finally vapor deposit the solder onto the surface of the heat sink at 20%-30% of the rated power to obtain the solder layer.

[0020] (3) Using a semiconductor laser bonding device, the die is placed on the surface of the heat sink where the solder layer has been vaporized;

[0021] (4) Using vacuum reflow soldering equipment, in an inert gas atmosphere, the reflow soldering of the die and the heat sink is completed under conditions such as preheating, heat preservation and cooling to obtain a low indium creep COS structure.

[0022] According to a preferred embodiment of the present invention, in step (1), the pretreatment method is as follows: the heat sink, transition layer material and solder layer material are cleaned with deionized water for 20-30 minutes and then ultrasonically treated for 20-30 minutes.

[0023] According to a preferred embodiment of the present invention, in step (1), after the transition layer material is melted, it is prepared onto the upper surface of the heat sink by CVD chemical vapor deposition.

[0024] According to a preferred embodiment of the present invention, in step (2), indium is first vapor-deposited, and then silver is vapor-deposited onto the surface of indium to prevent indium oxidation.

[0025] According to a preferred embodiment of the present invention, in step (2), the vapor deposition fixture used in the present invention is customized according to different die sizes. Several vapor deposition holes are arranged in parallel on the vapor deposition fixture. The width a of the vapor deposition hole is the die dissociation period, the length b of the vapor deposition hole is the die cavity length, and the thickness c is 200-300μm. This ensures that after vapor deposition, a solder layer with the same shape as the die P surface is formed only in the central area of ​​the heat sink, and no solder layer is formed in other areas of the heat sink.

[0026] This invention uses a specially designed vapor deposition fixture to vapor deposit indium and silver onto the central area of ​​the heat sink, with the size matching that of the die. This results in a solder layer between the heat sink and the die, and the areas on both sides of the die are completely free of indium, thus effectively preventing indium from creeping onto the die's dissociation surface during alloying.

[0027] According to a preferred embodiment of the present invention, in step (2), the vacuum level needs to be maintained at 6 × 10⁻⁶. -6 Torr below.

[0028] According to a preferred embodiment of the present invention, in step (2), the solder layer evaporation rate is:

[0029] According to a preferred embodiment of the present invention, in step (3), the ASM bonding equipment is used to identify the vapor deposition area on the heat sink surface.

[0030] According to a preferred embodiment of the present invention, in step (3), when the die is placed on the surface of the heat sink that has been plated with solder, the center line of the vapor deposition hole needs to coincide with the center line of the heat sink.

[0031] According to a preferred embodiment of the present invention, in step (4), the reflow soldering process is carried out in a nitrogen atmosphere to ensure the stability of the solder at high temperatures.

[0032] According to a preferred embodiment of the present invention, in step (4), the preheating temperature is 110-130°C and the preheating time is 80-120s.

[0033] According to a preferred embodiment of the present invention, in step (4), the temperature for heat preservation is 170-190°C and the heat preservation time is 70-120s.

[0034] According to a preferred embodiment of the present invention, in step (4), the cooling rate is 0.5-1℃ / s.

[0035] The beneficial effects of this invention are as follows:

[0036] The preparation method provided by this invention is simple to operate. By adding a thin layer of silver to the surface of indium, the melting point of the solder is reduced. Furthermore, by designing a special evaporation fixture, the evaporation area on the heat sink is controlled within a fixed size range and its size matches that of the die used. By using the above methods, while retaining only the solder layer under the P-side of the die and reducing the alloying temperature, the probability of indium creeping to the die dissociation surface during alloying can be effectively reduced. This solves the problem of laser leakage failure caused by "indium creeping" and effectively improves the service life and various electrical parameters of the semiconductor laser. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of the low indium creepage COS structure of the present invention;

[0038] Figure 2 This is a schematic diagram showing the position of the semiconductor laser die on the heat sink.

[0039] Figure 3 This is a rendering of the vapor deposition fixture;

[0040] Figure 4 This is a plan view of the vapor deposition fixture;

[0041] Figure 5 Front view of the vapor deposition fixture;

[0042] Figure 6 This is a side view of the vapor deposition fixture.

[0043] 1. Heat sink, 2. Transition layer, 3. Solder layer, 4. Semiconductor laser die, 5. Anti-reflective surface, 6. High reflective surface, 7. N-side, 8. P-side, 9. Evaporation fixture. Detailed Implementation

[0044] The present invention will be further described below with reference to the embodiments and accompanying drawings, but is not limited thereto.

[0045] Example 1

[0046] A low indium creep COS structure, such as Figure 1 and Figure 2 As shown, it includes a heat sink 1, a transition layer 2 formed on the upper surface of the heat sink 1, and a semiconductor laser die 4 soldered to the transition layer 2 by a solder layer 3. The N-side 7 of the semiconductor laser die 4 is on top, the P-side 8 is on the bottom, the front end is an anti-reflection surface 5, and the rear end is a high-reflection surface 6. The semiconductor laser die 4 is attached to the center position of the heat sink 1, and the high-reflection surface 6 protrudes from the heat sink 1 by a distance of 20 μm.

[0047] The heat sink 1 is made of copper alloy, with a thickness of 200μm, a length of 1000μm, and a width of 500μm.

[0048] The transition layer 2 is made of gold and has a thickness of 2 μm.

[0049] The solder layer 3 is made of an indium-silver composite structure, with an indium thickness of 3.5 μm and a silver thickness of 0.4 μm.

[0050] The semiconductor laser die 4 is made of gallium arsenide, with a die cavity length of 500 μm, a dissociation period of 300 μm, and a thickness of 100 μm.

[0051] Example 2

[0052] The difference between the low indium creepage COS structure provided in Example 1 and the one described in Example 1 is as follows:

[0053] The high reflectivity surface 6 of the semiconductor laser die 4 protrudes from the heat sink 1 at a distance of 30μm.

[0054] The heat sink 1 has a length of 1200 μm and a width of 800 μm.

[0055] The solder layer 3 is made of an indium-silver composite structure, with an indium thickness of 5 μm and a silver thickness of 0.4 μm.

[0056] The semiconductor laser die 4 has a cavity length of 800μm, a dissociation period of 500μm, and a thickness of 120μm.

[0057] Example 3

[0058] Example 1 provides a method for preparing a low-indium-climbing COS structure, comprising:

[0059] (1) After cleaning the heat sink 1, transition layer 2 and solder layer 3 with deionized water for 20 minutes, ultrasonic treatment was performed for 20 minutes. Then, the upper surface of the heat sink 1 was polished and ground. After the transition layer 2 was melted, it was prepared onto the heat sink 1 by CVD vapor deposition to obtain the heat sink 1 with transition layer 2.

[0060] (2) Figure 3 , Figure 4 , Figure 5 and Figure 6 As shown, a corresponding vapor deposition fixture 9 is fabricated according to the die size, with a vapor deposition hole width a = 300 μm, a vapor deposition hole length b = 500 μm, and a vapor deposition fixture 9 thickness c = 200 μm;

[0061] (3) Place the heat sink 1 into the completed vapor deposition fixture 9, and then place it into the vapor deposition equipment at a temperature of 6×10. -6 In a vacuum environment, the indium layer thickness is 3.5 μm, the silver layer thickness is 0.4 μm, the deposition area size is 500 × 300 μm, and the solder layer 3 deposition rate is... When the die is placed on the surface of the heat sink 1 after the solder layer 3 has been plated, the center line of the vapor deposition hole needs to coincide with the center line of the heat sink 1.

[0062] Adjust the high-precision bonding machine's recognition area to the size of the heat sink 1 vapor deposition area (500×300μm), and bond the die to this position. The reflow soldering process is carried out in a nitrogen atmosphere to ensure the stability of the solder at high temperatures.

[0063] (4) Vacuum reflow soldering is used. Under a nitrogen atmosphere, the temperature is preheated at 120°C for 90s, held at 170°C for 80s, and then cooled to room temperature at a rate of 1°C / s.

[0064] The dissociation surface of the low indium creep COS structure die after welding in this embodiment was observed. No indium creep phenomenon was found. The thrust between the die and heat sink 1 was greater than 1.5N. During use, the failure rate caused by indium creep was reduced to less than 0.1%.

[0065] Example 4

[0066] Example 2 provides a method for preparing a low-indium-climbing COS structure, comprising:

[0067] (1) After cleaning the heat sink 1, transition layer 2 and solder layer 3 with deionized water for 20 minutes, ultrasonic treatment was performed for 20 minutes. Then, the upper surface of the heat sink 1 was polished and ground. After the transition layer 2 was melted, it was prepared onto the heat sink 1 by CVD vapor deposition to obtain the heat sink 1 with transition layer 2.

[0068] (2) Based on the core size and Figures 3-6Fabricate a corresponding vapor deposition fixture 9 with a vapor deposition hole width a = 500 μm, a vapor deposition hole length b = 800 μm, and a vapor deposition fixture 9 thickness c = 200 μm; d is the distance between two vapor deposition holes.

[0069] (3) Place the heat sink 1 into the completed vapor deposition fixture 9, and then place it into the vapor deposition equipment at a temperature of 6×10. -6 In a vacuum environment, an indium layer with a thickness of 5 μm and a silver layer with a thickness of 0.4 μm are deposited, and the deposited area is 800 × 500 μm in size.

[0070] (4) Adjust the recognition area of ​​the high-precision bonding machine to the size of the heat sink 1 vapor deposition area of ​​500×300μm, and bond the core to this position;

[0071] (5) Vacuum reflow soldering is used. Under a nitrogen atmosphere, the temperature is preheated at 130℃ for 100s, held at 180℃ for 100s, and then cooled to room temperature at a rate of 0.8℃ / s.

[0072] The dissociation surface of the low indium creep COS structure die after welding in this embodiment was observed. There was no indium creep phenomenon. The test strength thrust was greater than 2N. During use, the failure rate caused by indium creep was reduced to less than 0.1%.

[0073] Comparative Example 1

[0074] A conventional COS structure includes a heat sink, on which a transition layer and a solder layer are sequentially disposed. A semiconductor laser die is soldered to the transition layer through the solder layer. The N-side of the semiconductor laser die is on top and the P-side is on the bottom. The front end is an anti-reflection surface and the rear end is a high-reflection surface. The semiconductor laser die is attached to the center of the heat sink, and the high-reflection surface protrudes from the heat sink by a distance of 20 μm.

[0075] The heat sink is made of copper alloy, with a thickness of 200μm, a length of 1000μm, and a width of 500μm.

[0076] The transition layer is made of gold and has a thickness of 2 μm.

[0077] The solder layer is made of indium and has a thickness of 3.9 μm. Unlike Example 1, the solder layer completely covers the transition layer, meaning that indium is present not only between the P-side of the semiconductor laser die and the heat sink, but also in the regions on both sides of the die.

[0078] The semiconductor laser die is made of gallium arsenide, with a die cavity length of 500μm, a dissociation period of 300μm, and a thickness of 100μm.

[0079] The preparation method of the above-mentioned COS structure includes:

[0080] (1) After cleaning the heat sink, transition layer material and solder layer material with deionized water for 20 minutes, ultrasonic treatment was performed for 20 minutes. Then, the upper surface of the heat sink was polished and ground. After the transition layer material was melted, it was prepared onto the heat sink by CVD vapor deposition to obtain a heat sink with a transition layer.

[0081] (2) Place the heat sink in the evaporation fixture, then place it in the evaporation equipment, and heat it at 6×10 -6 Indium layer thickness of 3.9μm was deposited under vacuum, and indium was deposited on the entire surface of the heat sink.

[0082] (4) Adjust the high-precision bonding machine to identify the heat sink area and bond the core to the center area of ​​this heat sink block.

[0083] (5) Vacuum reflow soldering is used. Under a nitrogen atmosphere, the temperature is preheated at 130℃ for 100s, held at 200℃ for 90s, and then cooled to room temperature at a rate of 0.8℃ / s.

[0084] The alloyed products were tested, and the failure rate was 0.5% due to "indium creep" on the core separation surface. The test thrust was about 1.3N.

[0085] Comparative Example 2

[0086] Based on the standard COS structure provided in Comparative Example 1, the difference lies in:

[0087] The high reflectivity surface of the semiconductor laser die protrudes 30 μm from the heat sink.

[0088] The heat sink is 1200 μm long and 800 μm wide.

[0089] The solder layer is made of indium, and the thickness of the indium layer is 5μm.

[0090] The semiconductor laser die has a cavity length of 800μm, a dissociation period of 500μm, and a thickness of 120μm.

[0091] (1) After cleaning the heat sink, transition layer material and solder layer material with deionized water for 20 minutes, ultrasonic treatment was performed for 20 minutes. Then, the upper surface of the heat sink was polished and ground. After the transition layer material was melted, it was prepared onto the heat sink by CVD vapor deposition to obtain a heat sink with a transition layer.

[0092] (2) Place the heat sink in the evaporation fixture, then place it in the evaporation equipment, and heat it at 6×10 -6 In a vacuum environment, an indium layer with a thickness of 5μm is vapor-deposited, and the entire surface of the heat sink is vapor-deposited with indium.

[0093] (4) Adjust the high-precision bonding machine to identify the heat sink area, and the center line of the core tube must coincide with the center line of the heat sink.

[0094] (5) Vacuum reflow soldering is used. Under a nitrogen atmosphere, the temperature is preheated at 130℃ for 100s, held at 210℃ for 110s, and then cooled to room temperature at a rate of 0.8℃ / s.

[0095] The alloyed products were tested, and the failure rate was 0.5% due to "indium creep" on the core separation surface. The test thrust was about 1.8N.

[0096] By comparing Comparative Examples 1-2 and Examples 1-2, it can be seen that this application reduces the melting point of the solder by adding a thin layer of silver to the indium surface; and by developing a unique vapor deposition fixture, the vapor deposition area on the heat sink is controlled within a fixed size range and its size matches the die used. By using the above methods, while retaining only the solder layer under the P-side of the die and reducing the alloying temperature, the probability of indium creeping to the die dissociation surface during alloying can be effectively reduced, greatly solving the problem of laser leakage failure caused by "indium creep".

Claims

1. A low indium creepage COS structure, characterized in that, It includes a heat sink, a transition layer disposed on the upper surface of the heat sink, and a semiconductor laser die soldered to the transition layer by a solder layer; the N-side of the semiconductor laser die faces upward and the P-side faces downward, one end is an anti-reflection surface and the other end is a high-reflection surface, and the high-reflection surface protrudes out of the heat sink. The solder layer is made of an indium-silver composite structure. The solder layer is formed by evaporation using a evaporation fixture. The evaporation fixture has several evaporation holes arranged in parallel. The width of the evaporation hole is the die dissociation cycle, and the length of the evaporation hole is the die cavity length. This ensures that after evaporation, a solder layer with the same shape as the P-side of the die is formed only in the central area of ​​the heat sink, and no solder layer is formed in other areas of the heat sink.

2. The low indium creepage COS structure according to claim 1, characterized in that, The thickness of indium is 3-5 μm, and the thickness of silver is 0.3-0.5 μm.

3. The low indium creepage COS structure according to claim 1, characterized in that, The heat sink is made of copper alloy with a thickness of 200-300μm, a length of 500-1200μm, and a dissociation period of 600-1200μm.

4. The low indium creepage COS structure according to claim 1, characterized in that, The transition layer is made of gold and has a thickness of 2-2.5 μm; the semiconductor laser die is made of gallium arsenide, with a die cavity length of 250-800 μm, a cleavage period of 300-500 μm, and a thickness of 90-120 μm.

5. The low indium creepage COS structure according to claim 1, characterized in that, The semiconductor laser die is welded to the center of the heat sink with a left-right offset of 50±10μm, and the high reflectivity surface protrudes from the heat sink by a distance of 10-40μm.

6. A method for preparing a low-indium-climbing COS structure, used to prepare a low-indium-climbing COS structure as described in any one of claims 1-5, characterized in that, The steps include the following: (1) The heat sink, transition layer material and solder layer material are pretreated respectively, then the upper surface of the heat sink is polished and ground, and then a transition layer is prepared on the upper surface of the heat sink. (2) Place the heat sink on the vapor deposition fixture, put the solder layer material into different tungsten boats, evacuate the chamber, heat the solder layer material for 30-40 seconds, and finally vapor deposit the solder onto the surface of the heat sink at 20%-30% of the rated power to obtain the solder layer. (3) Using a semiconductor laser bonding device, the die is placed on the surface of the heat sink where the solder layer has been vaporized; (4) Using vacuum reflow soldering equipment, in an inert gas atmosphere, the reflow soldering of the die and the heat sink is completed through preheating, heat preservation and cooling conditions to obtain a low indium creep COS structure.

7. The method for preparing a low-indium-creeping COS structure according to claim 6, characterized in that, In step (2), indium is first vapor-deposited, and then silver is vapor-deposited on the indium surface.

8. The method for preparing a low-indium-creeping COS structure according to claim 6, characterized in that, In step (2), the thickness c of the vapor deposition hole of the vapor deposition fixture is 200-300μm.

9. The method for preparing a low indium creepage COS structure according to claim 6, characterized in that, In step (1), the pretreatment method is as follows: after cleaning the heat sink, transition layer material and solder layer material with deionized water for 20-30 minutes, ultrasonic treatment is performed for 20-30 minutes. In step (1), the transition layer material is melted and then prepared onto the upper surface of the heat sink using CVD chemical vapor deposition.

10. The method for preparing a low-indium-creeping COS structure according to claim 6, characterized in that, In step (2), the vacuum level needs to be maintained at 6×10⁻⁶. -6 Torr below; solder layer evaporation rate is ; In step (3), the ASM bonding equipment needs to identify the vapor deposition area on the heat sink surface; when the die is placed on the heat sink surface that has been coated with solder layer, the center line of the vapor deposition hole needs to coincide with the center line of the heat sink. In step (4), the reflow soldering process is carried out in a nitrogen atmosphere; the preheating temperature is 110-130℃ and the preheating time is 80-120s; the holding temperature is 170-190℃ and the holding time is 70-120s; the cooling rate is 0.5-1℃ / s.

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