Preparation method of heat-conducting silica gel for power module chip packaging

Abstract

The invention discloses a preparation method of heat-conducting silica gel for packaging a power module chip, which comprises the following steps of: optimizing diamond micro-powder filling, surface etching and particle size compounding, so that the heat conductivity coefficient of the prepared heat-conducting silica gel can reach 3.8-4.5 W / (m.K) which is far higher than that of common silica gel (generally less than or equal to 3.0 W / (m.K)); meanwhile, the specific surface area of the diamond and the interface bonding force between the diamond and silica gel are improved through surface etching, the interface thermal resistance is reduced, a more efficient heat conduction path is formed, the packing stacking density is maximized through particle size compounding, air gaps are reduced, and a more stable and communicated heat conduction network is constructed; the SiC device is high in power density and high in switching speed, and the chip junction temperature is the key to restrict performance and reliability. The material can quickly and uniformly transfer heat of a chip to a heat dissipation substrate, obviously reduce junction temperature and temperature gradient in a module, and improve power density and long-term reliability.

Description

Technical Field

[0001] This invention relates to the field of silicone gel technology, and in particular to a method for preparing thermally conductive silicone gel for power module chip packaging. Background Technology

[0002] With the advancement of technology, electronic products are becoming smaller and smaller, and circuit integration is becoming increasingly sophisticated. This leads to greater power consumption in integrated circuits, resulting in higher heat flux density in electronic components. Simultaneously, rising temperatures in electronic devices double the probability of malfunction; for every 25°C increase in temperature, the failure rate increases tenfold. Therefore, solving the heat dissipation and cooling problems of electronic devices is crucial for their stable operation.

[0003] To address the aforementioned issues, filling the spaces between heat-generating components in electronic products with thermal interface materials can facilitate the timely dissipation of heat generated within the product. Current research on thermally conductive adhesives for power modules primarily utilizes hardened substrates, such as epoxy resins. However, hardened substrates exhibit relatively poor CTE matching capabilities, significantly impacting the lifespan of power modules. In existing technologies, fillers with medium thermal conductivity, such as alumina, boron nitride, or aluminum nitride (with thermal conductivity of 200-500 W / mK), require an addition amount exceeding 50% by volume to achieve the desired thermal conductivity. High thermal conductivity fillers, such as graphene, graphene nanosheets, and carbon nanotubes (with thermal conductivity of 1000-2000 W / mK), are typically expensive, and their high electrical conductivity limits their filler application. Therefore, a thermally conductive material with both good thermal conductivity and excellent insulation properties is needed. Summary of the Invention

[0004] In order to overcome the shortcomings of the prior art, the technical problem to be solved by the present invention is to propose a method for preparing thermally conductive silicon gel for power module chip packaging.

[0005] To achieve this objective, the present invention adopts the following technical solution: This invention provides a method for preparing thermally conductive silicone gel for power module chip packaging, which optimizes and improves the silicone gel from three aspects: surface modification, filler particle size, and filler ratio. Specifically, it includes the following steps: S00: Filler compounding. In terms of filler particle size, the proportion of fillers with different particle sizes can improve the space utilization inside the silicone gel and help improve rheological properties and reduce sedimentation. This case finds a better diamond micro powder ratio parameter by changing the mass ratio of diamond micro powder with different particle sizes, thereby increasing the packing density of diamond filler inside the silicone gel and thus improving the thermal conductivity of the silicone gel. At the same time, a suitable particle size distribution also helps to improve the maximum packing density and the connectivity of the thermal conductive network. Therefore, diamond micro powder with particle sizes of 50~70μm, 15~25μm, and 5~15μm is selected for compounding and filling. Preferably, diamond micro powder with particle sizes of 50~70μm, 15~25μm, and 5~15μm are mixed evenly at a mass ratio of 5~7:1.5~2.5:1 to form diamond micro powder filler, so as to make the thermal conductivity of the thermally conductive silicone gel perform optimally. Furthermore, from the perspective of surface modification, this invention improves the specific surface area of ​​diamond micropowder and its compatibility and bonding ability with the silica gel matrix by surface etching. This helps to increase the filling amount of diamond micropowder while ensuring good wetting and adhesion properties between the silica gel and the substrate. This allows the filler to form thermally conductive pathways within the silica gel more likely. At the same time, due to the increase in specific surface area, the contact area between the diamond micropowder and the matrix also increases accordingly, forming wider thermally conductive pathways. Therefore, in step S00, the diamond micropowder with a particle size of 50~70μm needs to undergo surface etching treatment before mixing. The etching treatment steps are as follows: S01: Surface pretreatment: Soak diamond micro powder with a particle size of 60μm in 1mol / L NaOH solution for 30min, then soak it in 1mol / L dilute sulfuric acid solution for 30min, filter, then rinse it with deionized water until neutral, and vacuum dry it at 80℃ for 2h. S02: Mixing: Washed diamond micro powder with a particle size of 50~70μm is mixed with nickel powder at a mass ratio of 1:5 and placed in a container; S03: Heating: First, place a container containing a mixture of diamond micro powder and nickel powder in a tube furnace. After purging the furnace with nitrogen for 5 minutes to completely remove the air, heat the mixture from room temperature to 600°C at a heating rate of 10°C / min. Then, heat it to 850°C at a heating rate of 5°C / min and hold it for 60 minutes. Then, cool it down to 300°C at a cooling rate of 10°C / min and then cool it down with the furnace. S04: Purification. The etched diamond micropowder is placed in a 40% (w / w) sulfuric acid solution, and a 30% (w / w) sulfuric acid solution is added. The solution was heated in an 80°C water bath for 60 minutes, then ultrasonically vibrated for 30 minutes. This process was repeated three times. The solution was then centrifuged at 3000 rpm, filtered, and repeatedly washed with deionized water until neutral to ensure no acid residue. Finally, it was vacuum dried at 80°C for 2 hours and then sealed for later use.

[0006] S10: The filler and silica gel matrix are compounded. An appropriate amount of liquid silica gel matrix is ​​taken, and the diamond micro-powder filler is slowly added to the silica gel matrix. During the addition process, low-speed mechanical stirring is performed. After preliminary mixing, the mixture is transferred to a planetary mixer for high-speed dispersion to form a high-viscosity silica gel mixture. The mixing process of the filler and silica gel matrix needs to be carried out under vacuum or immediately after mixing, with vacuum degassing treatment. The mass fraction of the diamond micro-powder filler in the high-viscosity silica gel mixture ranges from 65-75 wt%. Step S10 focuses on the filler ratio. Experiments have shown that the thermal conductivity of silica gel initially increases and then decreases with increasing diamond content. This is due to the limitations of the adhesive strength and viscosity of the silica gel matrix. The optimal filler content is usually lower than that of epoxy resin systems. When the diamond content is 65-75 wt.%, the thermal conductivity of silicone gel reaches its best state. As the diamond content increases, the density of the cured silicone gel shows a trend that is roughly the same as that of the thermal conductivity, that is, it first increases and then decreases. Therefore, when the diamond content is 65-75 wt.%, the density of silicone gel reaches a relatively high value. The gradual increase of diamond content will improve the volume resistivity of the cured silicone gel. At the filler content (65-75 wt.%) corresponding to the optimal thermal conductivity, its volume resistivity can still be maintained at the order of 1×10^14 Ω·cm or higher (such as 1.48×10^14 Ω·cm or higher), and it has good insulation properties.

[0007] S20: Degassing. Place the prepared high-viscosity silica gel mixture into a vacuum degassing mixer or transfer it to a vacuum drying oven. The vacuum degassing process is carried out at room temperature, and the speed of the vacuum degassing mixer is 1000-2000 rpm.

[0008] S30: Potting and curing. Apply a release agent to the mold beforehand, then pour the degassed silicone gel mixture into the prepared mold; after curing, perform a vacuum treatment for 10-15 minutes to remove any remaining micro-bubbles.

[0009] S40: Silicone gel curing, which involves the silicone gel mixture in the mold undergoing a pre-curing stage and a post-curing stage, followed by cooling to room temperature for demolding; the potting and curing steps are as follows: S41: Pre-curing stage, heating in a 60℃ oven for 30 minutes to initially shape the material; S42: Post-curing stage, heating at 100℃ for 1 hour to promote deep cross-linking (final cross-linking degree > 90%) and avoid "dry outside and wet inside"; the pre-curing stage involves placing the mold at room temperature for 30 minutes to allow the silicone gel to initially cross-link and gel, achieving a certain shape retention.

[0010] The beneficial effects of this invention are as follows: (1) Significantly improve thermal management capability: By optimizing the diamond micro powder filling ratio (65-75wt.%) in thermally conductive silicone gel, diamond micro powder surface etching and particle size compounding (preferred, the particle size ratio is 60μm:20μm:10μm=6:2:1, and mixed evenly according to the mass ratio of 6:2:1), the thermal conductivity can reach 3.8~4.5W / (m·K), which is far superior to ordinary silicone gel (usually ≤3.0W / (m·K)); surface etching increases the specific surface area of ​​diamond and the interfacial bonding force with silicone gel, reduces interfacial thermal resistance, and forms a more efficient thermal conduction path; particle size compounding maximizes the filler packing density, reduces air gaps, and constructs a more stable and interconnected thermal conduction network; SiC devices feature high power density and fast switching speeds, making the chip junction temperature a key factor limiting performance and reliability. This material can rapidly and evenly transfer heat from the chip to the heat dissipation substrate, significantly reducing the junction temperature and internal temperature gradient of the module, thereby improving power density and long-term reliability.

[0011] (2) High volume resistivity: At a filler content of 65-75 wt.%, more preferably 70-75 wt.%, the volume resistivity is ≥ Maintaining electrical insulation and meeting the insulation requirements of high-voltage SiC modules (typically ≥1200V), diamond itself is a perfect insulator. Surface etching enhances the bonding with silicon gel, reducing local electric field distortion and potential leakage paths caused by filler agglomeration, ensuring the electrical safety of the module in high-voltage, high-dv / dt operating environments, and preventing insulation failure and short-circuit risks. (3) Effectively reduce thermomechanical stress: Despite being filled with a large amount of high-hardness diamond, the ultra-low elastic modulus of the silicon gel matrix is ​​preserved (superior to epoxy resin). The material can absorb and relax the stress caused by the mismatch of thermal expansion coefficients (CTE) between the chip (SiC), substrate (ceramic), and shell (metal), significantly reducing the risk of solder joint fatigue, chip cracking and interface delamination. It is especially suitable for high-reliability applications such as automotive-grade applications that are subjected to frequent power cycles and temperature shocks.

[0012] (4) Surface etching enhances interface bonding: The surface roughness of the diamond increases after etching, forming a stronger physical anchoring and chemical bonding with the silicon gel matrix, improving the wettability and adhesion of the interface with the chip / DBC substrate, etc. The strong interface bonding reduces the risk of interface delamination under high temperature operation or temperature cycling, ensuring the long-term integrity of the thermal interface and avoiding a sharp increase in thermal resistance due to interface degradation.

[0013] (5) Environmental protection and cost potential: The technology of artificial diamond micro powder is mature and the cost can be controlled after large-scale production; the optimized filling amount reduces the waste of expensive fillers; the silicone gel itself is non-toxic and its recyclability is better than some epoxy systems. Attached Figure Description

[0014] Figure 1 This is a process flow diagram of a method for preparing thermally conductive silicone gel for power module chip packaging according to a specific embodiment of the present invention. Detailed Implementation

[0015] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0016] To address the problems of existing chip interconnect technologies, specifically the need for a thermally conductive material with good thermal conductivity and insulation properties to facilitate the timely dissipation of heat generated within electronic products through the thermal interface material filled between heat-generating components, this project aims to overcome the shortcomings of traditional interconnect materials in terms of thermal performance, electrical performance, cost, and environmental friendliness. Based on this direction, this project selects silicone gel and diamond as materials. Silicone gel, due to its excellent elasticity, extremely low modulus (effectively reducing thermal stress), excellent weather resistance, chemical corrosion resistance, and wide temperature stability (-50℃ to 200℃), is commonly used as a matrix material for thermal interface materials in electronic devices. However, because silicone gel itself has a low thermal conductivity (approximately 0.15-0.2 W / mK), it is not suitable for direct use as a thermal interface material. To improve the thermal conductivity of silicone gel, a common method is to fill it with thermally conductive fillers. Meanwhile, diamond, as an electrically insulating material, has a thermal conductivity of 2000 W / mK, combining high thermal conductivity with high insulation properties. Diamond's thermal conductivity primarily relies on its lattice vibrations. Due to the high strength of the C-C bond and the relatively small mass of the C atom, C atoms vibrate primarily around a potential minimum, which is the main reason for diamond's high thermal conductivity. Furthermore, the valence electrons in diamond cannot move freely, resulting in excellent insulation properties. Diamond also exhibits other superior characteristics, such as good thermal stability and a low coefficient of thermal expansion. In addition, diamond micron powder can be synthesized artificially. Based on the above, this invention provides a method for preparing thermally conductive silicone gel for power module chip packaging, optimizing and improving the silicone gel from three aspects: surface modification, filler particle size, and filler ratio.

[0017] Example 1: Preferably, the raw materials are diamond micro powders of 60μm, 20μm, and 10μm, and the mass ratio when they are mixed evenly is 6:2:1; silica gel matrix; The thermally conductive silicone gel was prepared using the following steps: (1) Etching is performed on 60μm diamond micropowder according to the above steps, while no etching is performed on 20μm and 10μm. (2) Diamond micro powders with particle sizes of 60 μm (after etching), 20 μm and 10 μm were mixed evenly in a mass ratio of 6:2:1; (3) The filler is compounded with the silica gel matrix, and the proportion of diamond filler is 65 wt.% to form a high viscosity silica gel mixture; (4) The prepared high-viscosity silica gel mixture is placed in a vacuum degassing mixer for degassing; (5) Pour the degassed silicone gel mixture into a pre-prepared mold for curing. Place the mold at room temperature for 30 minutes to allow the silicone gel to initially crosslink and gel, obtain a certain shape and maintain it for pre-curing. Then, heat it to 100°C under vacuum for 1 hour for post-curing treatment, and then cool it to room temperature for demolding. After the above steps, the thermal conductivity of the thermally conductive silicon gel prepared in this embodiment for power module chip packaging was measured to be 3.8~4.2 W / (m·K), and its resistivity per unit volume was: At this point, the resistivity is still relatively low.

[0018] Example 2: Unlike Example 1, the high-viscosity silica gel mixture uses a diamond filler ratio of 70 wt.%. After the above steps, the thermal conductivity of the thermally conductive silica gel prepared in this example for power module chip packaging was measured to be 4.2~4.5 W / (m·K), and its resistivity per unit volume was not less than: .

[0019] Example 3: Unlike Example 1, the diamond filler ratio in the high-viscosity silicone gel mixture is 75 wt.%. After the above steps, the thermal conductivity of the thermally conductive silicone gel prepared in this example for power module chip packaging was measured to be 4.5~5.0 W / (m·K), and its resistivity per unit volume is not less than... At this point, both thermal conductivity and resistivity are at relatively high values, but the risk of interface defects increases with high filler content, requiring enhanced surface treatment.

[0020] In relation to the above embodiments, the following three comparative examples are provided: Comparative Example 1: The results were largely the same as in Example 2, except that the 60μm diamond powder was not etched. The thermal conductivity of the thermally conductive silicon gel prepared in this example for power module chip packaging was measured to be 1.9-2.2 W / (m·K), and its resistivity per unit volume was: ; Comparative Example 2: The results were largely the same as in Example 1, except that the 60μm diamond powder was not etched. The thermal conductivity of the thermally conductive silicon gel prepared in this example for power module chip packaging was measured to be 2.1-2.5 W / (m·K), and its resistivity per unit volume was: ; Comparative Example 3: The results were largely the same as in Example 3, except that the 60μm diamond powder was not etched. The thermal conductivity of the thermally conductive silicon gel prepared in this example for power module chip packaging was measured to be 2.7-3.2 W / (m·K), and its resistivity per unit volume was: ; Therefore, it can be seen that after etching, the thermal conductivity of thermally conductive silicone gel can be effectively improved by diamond micropowder with a particle size of 50~70μm. When the proportion of diamond filler is low, the thermal conductivity is significantly improved while the resistivity per unit volume is not significantly improved. When the proportion of diamond filler is high, the thermal conductivity is not significantly improved while the resistivity per unit volume is significantly improved, but the risk of interface defects increases with high filler content, requiring enhanced surface treatment. Therefore, in practical applications, a diamond filler ratio of 70wt.% in the high-viscosity silicone gel mixture is preferred to ensure that the thermally conductive silicone gel has a relatively excellent and balanced thermal conductivity and resistivity per unit volume.

[0021] This invention has been described through preferred embodiments. Those skilled in the art will understand that various changes or equivalent substitutions can be made to these features and embodiments without departing from the spirit and scope of the invention. This invention is not limited to the specific embodiments disclosed herein; other embodiments falling within the scope of the claims are also within the protection scope of this invention.

Claims

1. A method for preparing thermally conductive silicone gel for power module chip packaging, characterized in that, Includes the following steps: S00: Filler compound, diamond micro powder with particle size of 50~70μm, 15~25μm and 5~15μm is selected, and the diamond micro powder with particle size of 50~70μm, 15~25μm and 5~15μm is mixed evenly in a mass ratio of 5~7:1.5~2.5:1 to form diamond micro powder filler; S10: The compounding of filler and silica gel matrix: Take an appropriate amount of liquid silica gel matrix, slowly add the diamond micro powder filler to the silica gel matrix, and perform low-speed mechanical stirring during the addition process. After preliminary mixing, transfer to a planetary mixer for high-speed dispersion to form a high-viscosity silica gel mixture. S20: Degassing, place the prepared high-viscosity silicone gel mixture into a vacuum degassing mixer or transfer it to a vacuum drying oven; S30: Potting and curing: A release agent is pre-applied to the mold, and then the degassed silicone gel mixture is poured into the pre-prepared mold; S40: Silicone gel curing, which allows the silicone gel mixture in the mold to undergo a pre-curing stage and a post-curing stage before being cooled to room temperature for demolding.

2. The method for preparing thermally conductive silicone gel for power module chip packaging according to claim 1, characterized in that: In step 10, the mass fraction of diamond micron filler in the high-viscosity silica gel mixture ranges from 65 to 75 wt%.

3. The method for preparing thermally conductive silicone gel for power module chip packaging according to claim 1, characterized in that: In step S00, the diamond micro powder with a particle size of 50~70μm needs to undergo surface etching treatment before mixing. The etching treatment steps are as follows: S01: Surface pretreatment: Soak diamond micro powder with a particle size of 60μm in 1mol / L NaOH solution for 30min, then soak it in 1mol / L dilute sulfuric acid solution for 30min, filter, then rinse it with deionized water until neutral, and vacuum dry it at 80℃ for 2h. S02: Mixing: Washed diamond micro powder with a particle size of 50~70μm is mixed with nickel powder at a mass ratio of 1:5 and placed in a container; S03: Heating: First, place a container containing a mixture of diamond micro powder and nickel powder in a tube furnace. After purging the furnace with nitrogen for 5 minutes to completely remove the air, heat the mixture from room temperature to 600°C at a heating rate of 10°C / min. Then, heat it to 850°C at a heating rate of 5°C / min and hold it for 60 minutes. Then, cool it down to 300°C at a cooling rate of 10°C / min and then cool it down with the furnace. S04: Purification. The etched diamond micropowder is placed in a 40% (w / w) sulfuric acid solution, and a 30% (w / w) sulfuric acid solution is added. The solution was heated in an 80°C water bath for 60 minutes, then ultrasonically vibrated for 30 minutes. This process was repeated three times. The solution was then centrifuged at 3000 rpm, filtered, and repeatedly washed with deionized water until neutral to ensure no acid residue. Finally, it was vacuum dried at 80°C for 2 hours and then sealed for later use.

4. The method for preparing thermally conductive silicone gel for power module chip packaging according to claim 1, characterized in that, In step S10, the mixing process of the filler and the silica gel matrix needs to be carried out in a vacuum environment or immediately after mixing, the vacuum degassing process needs to be performed.

5. The method for preparing thermally conductive silicone gel for power module chip packaging according to claim 1, characterized in that, In step S20, the vacuum degassing process is carried out at room temperature, and the speed of the vacuum degassing mixer is 1000-2000 rpm.

6. The method for preparing thermally conductive silicone gel for power module chip packaging according to claim 1, characterized in that, In step S30, after curing, a vacuum treatment is performed for 10-15 minutes to remove any remaining microbubbles.

7. The method for preparing thermally conductive silicone gel for power module chip packaging according to claim 1, characterized in that, In step S40, the pre-curing stage involves placing the mold at room temperature for 30 minutes to allow the silicone gel to initially crosslink and gel, thereby achieving a certain shape retention.

8. The method for preparing thermally conductive silicone gel for power module chip packaging according to claim 1, characterized in that, In step S40, the potting and curing steps are as follows: S41: Pre-curing stage, heat in a 60℃ oven for 30 minutes to preliminarily set the material; S42: Post-curing stage, heat at 100℃ for 1 hour to promote deep cross-linking (final degree of cross-linking > 90%).

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