Thermal-fatigue-resistant liquid cooling radiator, preparation process and IGBT (Insulated Gate Bipolar Translator) module

Abstract

The invention discloses a thermal fatigue resistant liquid cooling radiator, a preparation process and an IGBT module, and belongs to the technical field of radiators. According to the radiator, an interface layer, a stress adjusting layer and a hydrophilic protection layer sequentially cover the surface, where a copper needle array is welded, of a copper radiating bottom plate. The interface layer and the nano reinforcement form firm membrane-substrate combination through a silane coupling agent; the stress adjusting layer contains modified polyurethane resin and core-shell structure liquid crystal elastomer microspheres, volume shrinkage occurs in the temperature range of 80-125 DEG C, and heat stress concentration at the root of the needle is effectively dispersed in cooperation with a cross-scale stress transfer network formed by aminated nanocellulose and carbon nanotubes; and the hydrophilic protection layer and hydrophilic components cooperate to improve the heat exchange efficiency and the antibacterial performance through a micro-nano structure. According to the invention, the problem of interface cracking caused by thermal expansion coefficient mismatch and stress concentration of a welding pin fin structure in thermal circulation is solved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of heat sinks, and relates to an anti-thermal fatigue liquid cooling heat sink, a preparation process and an IGBT module. BACKGROUND

[0002] As a core component of new energy vehicles, rail transit and smart grids, the heat dissipation performance of a power semiconductor module (especially an IGBT module) directly determines the power density, efficiency and reliability of the system. The liquid cooling heat sink becomes the preferred solution for high-power scenarios due to its high heat exchange efficiency, and the needle-fin type copper heat dissipation bottom plate has become the mainstream design in the industry because of the high specific surface area brought by the needle-shaped fins. At present, there are mainly two technical routes for the manufacturing of the needle-fin type heat sink: one-piece forming process and welding assembly process. The one-piece forming process can avoid the connection interface and has a natural advantage in thermal fatigue resistance, but it is limited by the mold cost and structural complexity; and the welding assembly process is still adopted by more medium and high-end modules because of its design flexibility and controllable cost, and the process usually connects the independently processed copper needle array with the copper bottom plate through tin-based solder to form the heat dissipation core structure.

[0003] In actual application scenarios such as new energy vehicles and rail transit, the IGBT module is often in a dynamic working condition of "loading-unloading", and the frequent temperature rise and fall easily causes thermal fatigue, that is, the fatigue damage of materials or structures caused by repeated action of thermal stress under the action of cyclic temperature change, and this damage will continue to accumulate, which makes the connection interface formed by the welding assembly process naturally face severe tests.

[0004] Under the typical working conditions of the IGBT module, the solder joint area bears multiple stress actions, which further amplifies the risk of thermal fatigue damage: due to the significant difference in the thermal expansion coefficients of the copper matrix and the tin-based solder, a huge shear strain is generated at the interface during temperature cycling, which is the core driving force for the initiation of thermal fatigue cracking; at the same time, the geometric structure of the needle-bottom plate connection causes local stress to be highly concentrated, which accelerates the initiation of thermal fatigue cracks; in addition, the copper and solder interface will continuously generate a brittle intermetallic compound layer under the action of long-term thermal cycling, which sharply reduces the toughness of the solder joint and greatly attenuates the anti-thermal fatigue performance. The superimposed action of these factors greatly weakens the structural stability and bearing capacity of the welding interface, and finally leads to the cracking of the welding needle-fin structure, and the cracking position is mostly concentrated in the connection interface of the needle root and the bottom plate. SUMMARY

[0005] The purpose of the present application is to provide an anti-thermal fatigue liquid cooling heat sink, a preparation process and an IGBT module to solve the problem of thermal fatigue cracking of the welding assembly type needle-fin type copper heat dissipation bottom plate in the application of the IGBT module due to the mismatch of the thermal expansion coefficients of copper and solder, stress concentration at the needle root and embrittlement of the intermetallic compound.

[0006] The object of the present application can be achieved by the following technical solutions: In a first aspect, the present application provides a heat fatigue resistant liquid cooling radiator, comprising a copper heat dissipation bottom plate, a surface of the copper heat dissipation bottom plate is welded with a copper needle array, and the surface of the copper heat dissipation bottom plate welded with the copper needle array is sequentially covered with an interface layer, a stress adjusting layer and a hydrophilic protective layer. The raw materials of the interface layer include, by weight fraction: 3-aminopropyl triethoxysilane 4-6 parts, nanocellulose whisker 2.5-4 parts, aminated carbon nanotube 1.2-2 parts, isocyanate silane coupling agent 3-5 parts, anhydrous ethanol 80-100 parts and deionized water 8-12 parts. The raw materials of the stress adjusting layer include, by weight fraction: modified polyurethane resin 220-280 parts, liquid crystal elastomer microspheres 40-50 parts, organic montmorillonite 6-9 parts, nanometer zirconium oxide 10-15 parts, aminated nanocellulose 8-12 parts and silane coupling agent 4-6 parts. The raw materials of the hydrophilic protective layer include, by weight fraction: polyvinyl butyral resin 300-350 parts, hydrophilic modified nanosilica 30-40 parts, polyethylene glycol 20-30 parts, glutaraldehyde crosslinking agent 15-20 parts and nanosilver antibacterial agent 40-50 parts. The liquid crystal elastomer microspheres have a core-shell structure, and the core-shell structure includes a liquid crystal polymer core layer and a silica-based shell layer.

[0007] Preferably, the liquid crystal elastomer microspheres are prepared from the following raw materials by weight fraction: 4,4'-bis(6-hydroxyhexyloxy) biphenyl 12-15 parts, bisphenol A type epoxy resin 8-10 parts, methacryloyl chloride 4-5 parts, 2-hydroxyethyl methacrylate phosphate ester 3-4 parts, N,N'-methylene bisacrylamide 1.5-2.5 parts, ammonium persulfate 0.4-0.6 parts, polyvinyl alcohol 6-8 parts, amino silicone oil 5-7 parts, tetraethoxysilane 8-10 parts and 25% ammonia water 3.0-5.0 parts.

[0008] Preferably, the thickness of the interface layer is 200-300 nm, the thickness of the stress adjusting layer is 25-80 μm, and the thickness of the hydrophilic protective layer is 20-30 μm.

[0009] Preferably, the modified polyurethane resin is a polyimide-polyurethane interpenetrating network structure, which is prepared from the following raw materials by weight fraction: 4,4'-oxobisphthalic anhydride 20-24 parts, 3,3'-diaminodiphenyl sulfone 12-15 parts, 1,4-butanediol 4-6 parts, isophorone diisocyanate 15-18 parts and polycaprolactone diol 30-40 parts.

[0010] Preferably, the hydrophilic modified nanosilica is prepared by reacting fumed nanosilica with 3-aminopropyl triethoxysilane.

[0011] Preferably, the particle size of the hydrophilic modified nanosilica is 20-30 nm.

[0012] Preferably, the stress adjustment layer further comprises 2.5-4 parts by weight of an antioxidant and 70-90 parts by weight of N,N-dimethylacetamide; the antioxidant is a complex of antioxidant 1010 and antioxidant 168.

[0013] In a second aspect, the present application provides a preparation process of the anti-thermal fatigue liquid cooling radiator as described in the first aspect, comprising the following steps: S1, pretreating the copper heat dissipation bottom plate; S2, mixing and dispersing the interface layer raw materials, then coating on the pretreated surface by dip-coating method and solidifying; S3, uniformly mixing the stress adjustment layer raw materials, then electrostatically spraying on the interface layer and performing gradient solidification treatment; S4, uniformly mixing the hydrophilic protective layer raw materials at ≤50℃, then coating on the surface of the stress adjustment layer by dip-coating method within 2 hours, and after surface drying, cross-linking solidification and deep solidification, performing room temperature water washing post-treatment.

[0014] Preferably, the pretreatment step comprises: using a mixture of 30% H2O2 and 5% H2SO4 to treat the surface of the copper heat dissipation bottom plate with copper needle array at 60℃ for 15 minutes, then rinsing clean with deionized water and drying.

[0015] In a third aspect, the present application provides an IGBT module comprising a power chip, a packaging structure and the anti-thermal fatigue liquid cooling radiator as described in the first aspect.

[0016] The present application has the following beneficial effects: (1) The core advantage of the anti-thermal fatigue of the present application is derived from the dual design of the synergistic construction of the functional network of the raw materials and the intelligent component response adjustment. A stable cross-scale stress transmission network will be formed inside the stress adjustment layer. The amino-nano cellulose itself has a natural three-dimensional network structure, and the amino groups on its surface can form hydrogen bonds with the end groups of the modified polyurethane resin, and at the same time, the amino groups on the surface of the amino-nano cellulose can have a synergistic effect with the amino groups on the wall of the amino-carbon nanotube, so that the amino-carbon nanotube is embedded in the three-dimensional skeleton of the amino-nano cellulose to form a composite network of "amino-nano cellulose network support and amino-carbon nanotube directional conduction". The network will also form a cross-layer stress transmission channel through the lapping of the nano-cellulose whiskers in the interface layer, and form a cross-layer stress transmission channel with the surface of the copper matrix, providing a structural basis for stress conduction. When the working temperature of the IGBT module rises to a certain interval (80-125℃), the liquid crystal elastomer microspheres in the stress adjustment layer will shrink in volume due to reaching the glass transition temperature, and this shrinkage force is transmitted to the copper needle root through the path of the liquid crystal elastomer microspheres, the three-dimensional network structure of the amino-nano cellulose, the directional conduction of the amino-carbon nanotube and the cross-layer connection of the nano-cellulose whiskers. At the same time, the organic montmorillonite in the stress adjustment layer is in a lamellar dispersed state, which can disperse the thermal stress concentrated at the needle root to a larger area, greatly reducing the stress concentration coefficient, thereby effectively weakening the interfacial thermal stress and stress concentration effect, and significantly prolonging the thermal cycle life of the heat sink.

[0017] (2) The interface layer forms a chemical bond with the surface oxide of the copper matrix through a silane coupling agent, and the nano-interlocking effect of the nano-cellulose whiskers significantly improves the film-base bonding strength; the modified polyurethane resin used in the stress adjustment layer has a polyimide-polyurethane interpenetrating network structure, and its unique molecular network gives the material excellent thermal stability and elastic recovery ability, providing a mechanical basis for stress adjustment; more importantly, the thermal expansion coefficient of the resin is 27-29 ppm / ℃ at 150℃, which is higher than the thermal expansion coefficient of Sn96.5Ag3.0Cu0.5 solder at room temperature (22-25 ppm / ℃), but within the actual working temperature range of the IGBT module (80-125℃), the thermal expansion coefficient of the solder will rise to 27-30 ppm / ℃, forming a temperature-dependent dynamic matching with the resin, thereby significantly reducing the interfacial strain difference during thermal cycling; the antioxidant compound system can capture high-temperature free radicals and decompose hydroperoxide, ensuring the stability of the mechanical properties of the film layer in a high-temperature environment.

[0018] (3) In the hydrophilic protective layer, the residual hydroxyl groups of polyvinyl butyral, the hydrophilic migration characteristics of polyethylene glycol, and the micro-nano rough structure constructed by hydrophilic modified nano-silicon dioxide form a synergy to accelerate the spreading of the cooling liquid, improve the effective heat exchange area and heat exchange coefficient; the nano-silver antibacterial agent can destroy the cell membrane of microorganisms to achieve efficient bacteriostasis and prevent biological fouling from blocking the needle-fin flow channel; the reaction of glutaraldehyde crosslinking agent and polyvinyl butyral improves the water resistance of the hydrophilic layer, solving the problem of poor water resistance of traditional hydrophilic coatings. DETAILED DESCRIPTION

[0019] In order to further illustrate the technical means and effects adopted by the present application to achieve the predetermined inventive purposes, the specific embodiments, structures, features and effects according to the present application are described in detail below in combination with examples.

[0020] The preparation process and basic information of the raw materials involved in the following examples and comparative examples are described as follows. The raw materials not specifically described are all conventional industrial-grade products, which can be obtained through market channels, and the purity is all ≥98%.

[0021] 1. The modified polyurethane resin is a polyimide-polyurethane interpenetrating network structure, and the raw materials are prepared according to the following weight ratio and preparation process: (1) Raw materials: 4,4'-oxybisphthalic anhydride 20-24 parts, 3,3'-diaminodiphenyl sulfone 12-15 parts, 1,4-butanediol 4-6 parts, isophorone diisocyanate 15-18 parts, polycaprolactone diol 30-40 parts, N-methyl pyrrolidone 120-150 parts, acetic anhydride 10-12 parts, and triethylamine 5-7 parts; (2) Preparation process: a, 4,4'-oxybisphthalic anhydride and N-methyl pyrrolidone were added to a 500 mL four-necked flask under nitrogen protection, stirred at 25°C for 30 minutes until completely dissolved, then 3,3'-diaminodiphenyl sulfone was slowly added, the dropwise rate was controlled at 1 drop per second, after the dropwise addition was completed, the temperature was raised to 60°C, and the stirring reaction was carried out at 300 r / min for 4 hours to prepare a polyamide acid prepolymer solution; b, polycaprolactone diol was added to a 250 mL three-necked flask, vacuum dehydration was carried out at 100°C for 2 hours, the temperature was lowered to 60°C, isophorone diisocyanate and 1,4-butanediol were added, and the stirring reaction was carried out at 200 r / min for 1.5 hours to prepare a polyurethane prepolymer solution (NCO content 3.2%); c, the polyurethane prepolymer solution was slowly injected into the polyamide acid prepolymer solution, and an interpenetrating network precursor was formed by stirring at 50°C for 2 hours; d, acetic anhydride and triethylamine were added in turn, stirring was carried out at 40°C for 30 minutes, then the temperature was raised to 150°C for imidization reaction for 2 hours; e, the temperature was lowered to room temperature, the product was poured into deionized water for precipitation, the solid was collected by filtration, and vacuum drying was carried out at 60°C for 24 hours to obtain the modified polyurethane resin.

[0022] 2. The liquid crystal elastomer microspheres are of a core-shell structure, the core of the core-shell structure includes a liquid crystal polymer core layer and a silica-based shell layer, and the raw materials are prepared according to the following weight ratio and preparation process: (1) Raw materials: 4,4'-bis(6-hydroxyhexyloxy)diphenyl 12-15 parts, bisphenol A type epoxy resin 8-10 parts, methacryloyl chloride 4-5 parts, 2-hydroxyethyl methacrylate phosphate 3-4 parts, N,N'-methylene bisacrylamide 1.5-2.5 parts, ammonium persulfate 0.4-0.6 parts, polyvinyl alcohol 6-8 parts, amino silicone oil 5-7 parts, tetraethoxysilane 8-10 parts, 25% ammonia water 3-5 parts, deionized water 180-220 parts, dichloromethane 40-60 parts; (2) Preparation steps: a, 4,4'-bis(6-hydroxyhexyloxy)diphenyl is dissolved in dichloromethane, placed in an ice bath (0-5°C) environment, slowly add methacryloyl chloride and triethylamine (deacidifying agent, the amount is 1.2 times of methacryloyl chloride), after dropping, warm up to 25°C for 2 hours, remove the solvent by distillation under reduced pressure to obtain liquid crystal monomer; mix the monomer with bisphenol A type epoxy resin, 2-hydroxyethyl methacrylate phosphate, add N,N'-methylene bisacrylamide and ammonium persulfate, ultrasonic dispersion for 15 minutes to prepare the oil phase; polyvinyl alcohol is dissolved in 80°C deionized water (aqueous phase), after cooling to 40°C, add the oil phase, emulsify at 800r / min for 30 minutes, warm up to 60°C for 4 hours, centrifugal collection of precipitate, deionized water washing 3 times, 60°C drying to obtain 2.5-3.5μm liquid crystal elastomer core microspheres; b, amino silicone oil is dissolved in ethanol / water (1:1) mixed solution, add liquid crystal elastomer core microspheres, stir and disperse at 500r / min for 30 minutes; mix tetraethoxysilane with ethanol uniformly, slowly drop into the above system, at the same time, add 25% ammonia water to adjust pH to 9-10, 40°C reaction for 6 hours; centrifugal collection of product, wash with ethanol / water mixed solution 3 times, 80°C vacuum drying for 12 hours, to obtain liquid crystal elastomer microspheres with core-shell structure.

[0023] 3. Hydrophilic modified nano-silica, the raw materials are in the following ratio by weight and the preparation process includes the following: (1) Raw materials: fumed nano-silica (specific surface area 200m² / g) 50 parts, 3-aminopropyl triethoxysilane 8 parts, deionized water 200 parts, anhydrous ethanol 100 parts; (2) Preparation steps: a, add fumed nano-silica into ethanol / deionized water (1:1) mixed solution, disperse for 30 minutes by ultrasonic cell disruptor (power 600W) to form a uniform suspension; b, dissolve APTES in 10 parts of anhydrous ethanol, slowly drop into the above suspension, warm up to 80°C, stir at 200r / min for 4 hours; c, after the reaction, centrifugal collection of precipitate at 8000r / min for 15 minutes, wash repeatedly with deionized water until the pH value of washing liquid is 7; d, dry the precipitate in a 60°C vacuum drying oven for 12 hours, grind to obtain hydrophilic modified nano-silica, the particle size is 25nm.

[0024] 4. Other basic information about raw materials: Antioxidant 1010 / 168: Mixing ratio 1:1; Nano-zirconia: Particle size 50nm; Nano silver antibacterial agent: 10nm aqueous dispersion, solid content 30%; All other raw materials not specifically mentioned are conventional industrial-grade products and can be obtained through commercial channels. Example 1

[0025] A thermal fatigue resistant liquid-cooled heat sink includes a copper heat sink base plate. One surface of the copper heat sink base plate is welded with an array of copper pins using Sn96.5Ag3.0Cu0.5 solder. The welded surface is sequentially covered with an interface layer, a stress-regulating layer, and a hydrophilic protective layer. The structure and weight proportions of each layer are as follows: (1) Interface layer: 5 parts of 3-aminopropyltriethoxysilane, 3 parts of nanocellulose whiskers, 1.6 parts of aminated carbon nanotubes, 4 parts of isocyanate silane coupling agent, 90 parts of anhydrous ethanol, and 10 parts of deionized water. (2) Stress-adjusting layer: 250 parts of modified polyurethane resin (the specific raw materials of the resin by weight are: 22 parts of 4,4'-oxophthalic anhydride, 13.5 parts of 3,3'-diaminodiphenyl sulfone, 5 parts of 1,4-butanediol, 16.5 parts of isophorone diisocyanate, 35 parts of polycaprolactone diol, 135 parts of N-methylpyrrolidone, 11 parts of acetic anhydride, and 6 parts of triethylamine; the modified polyurethane resin has an elastic modulus of 820 MPa at 150℃ and a coefficient of thermal expansion of 28 ppm / ℃), and 45 parts of liquid crystal elastomer microspheres (the specific raw materials of the liquid crystal elastomer microspheres by weight are: 13 parts of 4,4'-bis(6-hydroxyhexyloxy)biphenyl). 5 parts, bisphenol A type epoxy resin 9 parts, methacryloyl chloride 4.5 parts, 2-hydroxyethyl methacrylate phosphate 3.5 parts, N,N'-methylenebisacrylamide 2 parts, ammonium persulfate 0.5 parts, polyvinyl alcohol 7 parts, amino silicone oil 6 parts, tetraethoxysilane 9 parts, 25% ammonia water 4 parts, deionized water 200 parts, dichloromethane 50 parts; the glass transition temperature of liquid crystal elastomer microspheres is 78℃), organomontmorillonite 7.5 parts, nano-zirconia 12 parts, aminated nanocellulose 10 parts, silane coupling agent (KH-792) 5 parts, antioxidant (1010 / 168=1:1) 3 parts, N,N-dimethylacetamide 80 parts; (3) Hydrophilic protective layer: 325 parts of polyvinyl butyral resin (15% ethanol solution), 35 parts of hydrophilic modified nano SiO2, 25 parts of polyethylene glycol, 17.5 parts of glutaraldehyde crosslinking agent (50% aqueous solution), 45 parts of nano silver antibacterial agent (10nm aqueous dispersion), and 165 parts of ethanol / water (3:1) mixed solvent.

[0026] A manufacturing process for a thermal fatigue resistant liquid-cooled heat sink includes the following steps: S1. Pretreatment of copper heat sink base plate: Treat the surface of copper needle fins with a mixture of 30% H2O2 and 5% H2SO4 at 60℃ for 15 minutes, then rinse with deionized water and dry at 60℃. S2. Interface layer coating: After mixing the interface layer raw materials, ultrasonically disperse them for 30 minutes, coat them by dip-coating method (coiling speed 2mm / s), and cure them at 110℃ for 2 hours to form a 250nm thick film. S3, Stress-adjusting layer coating: After the stress-adjusting layer material is stirred evenly, it is electrostatically sprayed (voltage 45kV, distance 20cm). The gradient curing process goes through the following stages in sequence: 60℃ for 1.5 hours, then heated to 120℃ for 1 hour, then heated to 180℃ for 1.5 hours, and finally heated to 220℃ for 45 minutes. Nitrogen protection is used throughout the process and the furnace is cooled to form a 50μm thick film. S4. Hydrophilic Protective Layer Coating: a. Pre-dispersion: Add 35 parts of hydrophilic modified nano-SiO2 to 165 parts of ethanol / water (3:1) mixed solvent and ultrasonically disperse for 45 minutes until a transparent suspension is formed; b. Resin mixing: Add 325 parts of 15% PVB ethanol solution to the above suspension and stir at 250 r / min for 1 hour in a 50℃ water bath, ultrasonically dispersing for 5 minutes every 15 minutes to prevent agglomeration; c. Functional component addition: Add 25 parts of polyethylene glycol 600 and 45 parts of nano-silver antibacterial agent in sequence, stirring for 30 minutes after each addition; d. Crosslinking agent addition: Finally, add 1 7.5 parts of 50% glutaraldehyde aqueous solution, stir for 15 minutes, control the temperature of the mixture to ≤50℃ at all times, and ensure that the coating is completed within 2 hours; e. Coating and curing: use the dip-coating method (coating speed 1.2mm / s), ambient temperature 25±2℃, humidity 50±5%; after coating, first surface dry at 60℃ for 15 minutes to remove surface solvent, then crosslink and cure at 80℃ for 1 hour to promote acetal bond formation, and finally deep cure at 110℃ for 30 minutes to enhance the film density; after curing, immerse in deionized water at room temperature for 10 minutes to remove unreacted glutaraldehyde crosslinking agent, and air dry to form a 25μm thick hydrophilic protective layer. Example 2

[0027] A thermal fatigue resistant liquid-cooled heat sink includes a copper heat sink base plate. One surface of the copper heat sink base plate is welded with an array of copper pins using Sn96.5Ag3.0Cu0.5 solder. The welded surface is sequentially covered with an interface layer, a stress-regulating layer, and a hydrophilic protective layer. The structure and weight proportions of each layer are as follows: (1) Interface layer: 4 parts of 3-aminopropyltriethoxysilane, 2.5 parts of nanocellulose whiskers, 1.2 parts of aminated carbon nanotubes, 3 parts of isocyanate silane coupling agent, 80 parts of anhydrous ethanol, and 8 parts of deionized water; (2) Stress-adjusting layer: 220 parts of modified polyurethane resin (the specific raw materials of the resin, by weight, are: 20 parts of 4,4'-oxo-bis(phthalic anhydride), 12 parts of 3,3'-diaminodiphenyl sulfone, 4 parts of 1,4-butanediol, 15 parts of isophorone diisocyanate, 30 parts of polycaprolactone diol, 120 parts of N-methylpyrrolidone, 10 parts of acetic anhydride, and 5 parts of triethylamine; the modified polyurethane resin has an elastic modulus of 805 MPa at 150℃ and a coefficient of thermal expansion of 27 ppm / ℃), 40 parts of liquid crystal elastomer microspheres (the specific raw materials of the liquid crystal elastomer microspheres, by weight, are: 12 parts of 4,4'-bis(6-hydroxyhexyloxy)biphenyl). The following components were used: 8 parts bisphenol A epoxy resin, 4 parts methacryloyl chloride, 3 parts 2-hydroxyethyl methacrylate phosphate, 1.5 parts N,N'-methylenebisacrylamide, 0.4 parts ammonium persulfate, 6 parts polyvinyl alcohol, 5 parts amino silicone oil, 8 parts tetraethoxysilane, 3 parts 25% ammonia, 180 parts deionized water, 40 parts dichloromethane; the glass transition temperature of the liquid crystal elastomer microspheres was 76℃, 6 parts organomontmorillonite, 10 parts nano-zirconia, 8 parts aminated nanocellulose, 4 parts silane coupling agent (KH-792), 2.5 parts antioxidant (1010 / 168=1:1), and 70 parts N,N-dimethylacetamide. (3) Hydrophilic protective layer: 300 parts of polyvinyl butyral resin (15% ethanol solution), 30 parts of hydrophilic modified nano SiO2, 20 parts of polyethylene glycol, 15 parts of glutaraldehyde crosslinking agent (50% aqueous solution), 40 parts of nano silver antibacterial agent (10nm aqueous dispersion), and 150 parts of ethanol / water (3:1) mixed solvent.

[0028] A manufacturing process for a thermal fatigue resistant liquid-cooled heat sink includes the following steps: S1. Pretreatment of copper heat sink base plate: Treat the surface of copper needle fins with a mixture of 30% H2O2 and 5% H2SO4 at 60℃ for 15 minutes, then rinse with deionized water and dry at 60℃. S2. Interface layer coating: After mixing the interface layer raw materials, ultrasonically disperse them for 30 minutes, coat them by dip-coating method (coiling speed 2mm / s), and cure them at 110℃ for 2 hours to form a 200nm thick film. S3, Stress-adjusting layer coating: After the stress-adjusting layer material is stirred evenly, it is electrostatically sprayed (voltage 45kV, distance 20cm). The gradient curing process goes through the following stages in sequence: 60℃ for 1.5 hours, then heated to 120℃ for 1 hour, then heated to 180℃ for 1.5 hours, and finally heated to 220℃ for 45 minutes. Nitrogen protection is used throughout the process and the furnace is cooled to form a 25μm thick film. S4. Hydrophilic Protective Layer Coating: a. Pre-dispersion: Add 30 parts of hydrophilic modified nano-SiO2 to 150 parts of ethanol / water (3:1) mixed solvent and ultrasonically disperse for 45 minutes; b. Resin mixing: Add 300 parts of 15% PVB ethanol solution to the above suspension and stir at 250 r / min for 1 hour in a 50℃ water bath, with auxiliary ultrasonic dispersion 3 times during the period to prevent agglomeration; c. Functional component addition: Add 20 parts of polyethylene glycol 600 and 40 parts of nano-silver antibacterial agent in sequence, stirring for 30 minutes after each addition; d. Crosslinking agent addition: Finally, add 15 parts of 50% pentylene glycol... Dialdehyde aqueous solution, stir for 15 minutes, control the temperature of the mixture to ≤50℃ at all times, and ensure that the coating is completed within 2 hours; e. Coating and curing: use the dip-coating method (coiling speed 1.2mm / s) for coating, ambient temperature 25±2℃, humidity 50±5%; after coating, first surface dry at 60℃ for 15 minutes to remove surface solvent, then crosslink and cure at 80℃ for 1 hour to promote acetal bond formation, and finally deep cure at 110℃ for 30 minutes to enhance the film density; after curing, immerse in deionized water at room temperature for 10 minutes to remove unreacted glutaraldehyde crosslinking agent, and air dry to form a 20μm thick hydrophilic protective layer. Example 3

[0029] A thermal fatigue resistant liquid-cooled heat sink includes a copper heat sink base plate. One surface of the copper heat sink base plate is welded with an array of copper pins using Sn96.5Ag3.0Cu0.5 solder. The welded surface is sequentially covered with an interface layer, a stress-regulating layer, and a hydrophilic protective layer. The structure and weight proportions of each layer are as follows: (1) Interface layer: 6 parts of 3-aminopropyltriethoxysilane, 3.5 parts of nanocellulose whiskers, 2.0 parts of aminated carbon nanotubes, 5 parts of isocyanate silane coupling agent, 100 parts of anhydrous ethanol, and 12 parts of deionized water; (2) Stress-adjusting layer: 280 parts of modified polyurethane resin (the specific raw materials of the resin, by weight, are: 24 parts of 4,4'-oxo-bis(phthalic anhydride), 15 parts of 3,3'-diaminodiphenyl sulfone, 6 parts of 1,4-butanediol, 18 parts of isophorone diisocyanate, 40 parts of polycaprolactone diol, 150 parts of N-methylpyrrolidone, 12 parts of acetic anhydride, and 7 parts of triethylamine; the modified polyurethane resin has an elastic modulus of 830 MPa at 150℃ and a coefficient of thermal expansion of 29 ppm / ℃), and 50 parts of liquid crystal elastomer microspheres (the specific raw materials of the liquid crystal elastomer microspheres, by weight, are: 15 parts of 4,4'-bis(6-hydroxyhexyloxy)biphenyl). The following components are included: 10 parts bisphenol A epoxy resin, 5 parts methacryloyl chloride, 4 parts 2-hydroxyethyl methacrylate phosphate, 2.5 parts N,N'-methylenebisacrylamide, 0.6 parts ammonium persulfate, 8 parts polyvinyl alcohol, 7 parts amino silicone oil, 10 parts tetraethoxysilane, 5 parts 25% ammonia water, 220 parts deionized water, 60 parts dichloromethane; the glass transition temperature of the liquid crystal elastomer microspheres is 80℃, 9 parts organomontmorillonite, 15 parts nano-zirconia, 12 parts aminated nanocellulose, 6 parts silane coupling agent (KH-792), 4 parts antioxidant (1010 / 168=1:1), and 90 parts N,N-dimethylacetamide. (3) Hydrophilic protective layer: 350 parts of polyvinyl butyral resin (15% ethanol solution), 40 parts of hydrophilic modified nano SiO2, 30 parts of polyethylene glycol, 20 parts of glutaraldehyde crosslinking agent (50% aqueous solution), 50 parts of nano silver antibacterial agent (10nm aqueous dispersion), and 180 parts of ethanol / water (3:1) mixed solvent.

[0030] A manufacturing process for a thermal fatigue resistant liquid-cooled heat sink includes the following steps: S1. Pretreatment of copper heat sink base plate: Treat the surface of copper needle fins with a mixture of 30% H2O2 and 5% H2SO4 at 60℃ for 15 minutes, then rinse with deionized water and dry at 60℃. S2. Interface layer coating: After mixing the interface layer raw materials, ultrasonically disperse them for 30 minutes, coat them by dip-coating method (coiling speed 2mm / s), and cure them at 110℃ for 2 hours to form a 300nm thick film. S3, Stress-adjusting layer coating: After the stress-adjusting layer material is stirred evenly, it is electrostatically sprayed (voltage 45kV, distance 20cm). The gradient curing process goes through the following stages in sequence: 60℃ for 1.5 hours, then heated to 120℃ for 1 hour, then heated to 180℃ for 1.5 hours, and finally heated to 220℃ for 45 minutes. Nitrogen protection is used throughout the process and the furnace is cooled to form an 80μm thick film. S4. Hydrophilic Protective Layer Coating: a. Pre-dispersion: Add 40 parts of hydrophilic modified nano-SiO2 to 180 parts of ethanol / water (3:1) mixed solvent and ultrasonically disperse for 45 minutes; b. Resin mixing: Add 350 parts of 15% PVB ethanol solution to the above suspension and stir at 250 r / min for 1 hour in a 50℃ water bath, with auxiliary ultrasonic dispersion 3 times during the period to prevent agglomeration; c. Functional component addition: Add 30 parts of polyethylene glycol 600 and 50 parts of nano-silver antibacterial agent in sequence, stirring for 30 minutes after each addition; d. Crosslinking agent addition: Finally, add 20 parts of 50% pentylene glycol... Dialdehyde aqueous solution, stir for 15 minutes, control the temperature of the mixture to ≤50℃ at all times, and ensure that the coating is completed within 2 hours; e. Coating and curing: use the dip-coating method (coiling speed 1.2mm / s) for coating, ambient temperature 25±2℃, humidity 50±5%; after coating, first surface dry at 60℃ for 15 minutes to remove surface solvent, then crosslink and cure at 80℃ for 1 hour to promote acetal bond formation, and finally deep cure at 110℃ for 30 minutes to enhance the film density; after curing, immerse in deionized water at room temperature for 10 minutes to remove unreacted glutaraldehyde crosslinking agent, and air dry to form a 30μm thick hydrophilic protective layer.

[0031] Comparative Example 1 The difference from Example 1 is that the copper heat sink base plate is not coated with any functional film layer. Only the copper heat sink base plate is pretreated, that is, the surface of the copper needle fins is treated with a mixture of 30% H2O2 and 5% H2SO4 at 60°C for 15 minutes, then rinsed with deionized water and dried at 60°C.

[0032] Comparative Example 2 The difference from Example 1 is that the stress-adjusting layer does not contain liquid crystal elastomer microspheres.

[0033] Comparative Example 3 The difference from Example 1 is that no hydrophilic protective layer was coated, only the interface layer and stress-regulating layer were retained, and the remaining raw material ratios and preparation processes were completely consistent with Example 1.

[0034] Comparative Example 4 The difference from Example 1 is that no interface layer was coated. Instead, a stress-adjusting layer and a hydrophilic protective layer were directly coated on the surface of the pretreated copper heat sink base plate. The remaining raw material ratios and preparation processes were completely consistent with those of Example 1.

[0035] Performance testing The performance of the copper heat sink base plates of Examples 1-3 and Comparative Examples 1-4 was tested. The test methods and results are as follows: 1. Thermal cycling performance test Test Basis and Conditions: This test was conducted in accordance with GB / T 2423.22-2012 "Environmental Testing Part 2: Test Methods Test N: Temperature Change". To accurately simulate the actual "load-unload" dynamic operating conditions of the IGBT module, the temperature cycle range was set from -40℃ to 125℃, with the low temperature and high temperature segments each held for 30 minutes. The heating and cooling rates were both controlled at 5℃ / min. Performance monitoring was conducted at 500, 1000, and 2000 cycles as key cycle nodes. At the same time, the actual liquid cooling operating environment was simulated by continuously circulating deionized water at a flow rate of 1.5L / min inside the heat sink as the circulation medium to ensure that the test conditions were highly matched with the actual application scenario.

[0036] Test methods and indicators: In accordance with the evaluation requirements of GB / T 2423.22-2012 standard, during the test, before each cycle and after each critical cycle node, an optical microscope with a magnification of 500x was used to observe the crack initiation and propagation state of the weld interface at the root of the copper pin and each functional film layer. At the same time, an infrared thermal imager was used to collect the surface temperature distribution data of the heat sink and calculate the thermal resistance change rate (i.e., ΔR / R0, where R0 is the initial thermal resistance). The failure judgment criteria were the appearance of cracks with a length ≥50μm at the weld interface or a thermal resistance change rate ≥20%. When either criterion was met, the corresponding failure cycle number was recorded to comprehensively evaluate the thermal fatigue crack resistance of the heat sink weld interface and functional film layer.

[0037] The thermal cycling performance test data are shown in Table 1.

[0038] Table 1 ;

[0039] As shown in Table 1, Examples 1-3 exhibited excellent thermal fatigue resistance, with thermal resistance changes controlled within 10% after 2000 thermal cycles and no obvious cracks observed. All examples exceeded 2000 cycles. In contrast, Comparative Example 1 (without a functional layer) reached the failure standard after 850 cycles, with a thermal resistance change rate of 25.8% and a 65μm long crack appearing after 1000 cycles. This demonstrates the significant effect of the three-layer film structure of the present invention on thermal fatigue resistance. Comparative Example 2 (without liquid crystal elastomer microspheres) had 1350 failure cycles, significantly lower than the examples, confirming the crucial role of the liquid crystal elastomer microspheres in stress regulation—their volume shrinkage behavior within the 80-125℃ temperature range effectively offsets thermal stress. Comparative Examples 3 (without a hydrophilic protective layer) and 4 (without an interface layer) failed after 1750 and 1200 cycles, respectively, indicating that the synergistic effect of each functional layer is crucial to the overall thermal fatigue resistance, especially the enhancing effect of the interface layer on the film-substrate bonding. In summary, Example 1 exhibits the best thermal cycling stability, with a thermal resistance change rate of only 8.5% after 2000 cycles, confirming the optimization effect of the group allocation ratio and process parameters in this example.

[0040] 2. Interface bonding strength test Test Basis and Conditions: This test is conducted in accordance with ASTM D4541 "Coatings Pull-Off Method for Bond Strength Test". During sample preparation, the heat sink is cut into 25mm×25mm square pieces. Epoxy resin and a stainless steel pull-off tool are used to bond the samples to the back of the copper substrate. After bonding, the samples are placed in an 80℃ environment for 2 hours to complete curing. The test is divided into two categories: the film-substrate bond strength between the copper substrate and the interface layer, and the interlayer bond strength between the interface layer and the stress-regulating layer, and between the stress-regulating layer and the hydrophilic protective layer, to ensure comprehensive coverage of all key bonding interfaces.

[0041] Test methods and test indicators: A universal tensile testing machine was used for testing. The loading speed was set to 1 mm / min. Tensile force was applied perpendicular to the film surface until peeling or breakage occurred. The maximum destructive load during the process was recorded. The bonding strength was calculated using the formula σ = F / S (where F is the maximum destructive load and S is the effective area of ​​the test sample). After the test, the failure interface was observed to determine whether the failure mode was interface separation or film cohesion failure. This was used to comprehensively evaluate the bonding stability between each functional film layer and the copper substrate, as well as between the film layers.

[0042] The interface bonding strength test data are shown in Table 2.

[0043] Table 2

[0044] As shown in Table 2, the membrane-substrate bonding strength of Examples 1-3 all reached 17.2-18.6 MPa, and the interlayer bonding strength was in the range of 14.2-16.8 MPa. Furthermore, the failure mode was cohesive failure, indicating that the three-layer membrane structure of the present invention has excellent interfacial bonding performance. The membrane-substrate bonding strength of Comparative Example 4 (without an interfacial layer) was only 7.8 MPa, and the failure mode was interfacial separation. This proves that the components in the interfacial layer, such as 3-aminopropyltriethoxysilane, nanocellulose whiskers, and aminated carbon nanotubes, significantly improved the membrane-substrate bonding strength through chemical bonding and nano-interlocking effects. The bonding strength of Comparative Examples 2 and 3 was comparable to that of Example 1, indicating that the liquid crystal elastomer microspheres and the hydrophilic protective layer had little impact on the interfacial bonding strength. In Example 1, the bonding strength of each layer reached the highest value (18.6 MPa for the film base, 16.8 MPa for the interface layer / stress-modifying layer, and 15.5 MPa for the stress-modifying layer / hydrophilic layer), which is consistent with the result of its optimal thermal cycling performance, confirming that high-strength interface bonding is the fundamental guarantee for long-term thermal fatigue resistance.

[0045] In summary, the thermal fatigue resistant liquid-cooled heat sink of the present invention successfully solves the problem of interface cracking of welded needle-fin structures under thermal cycling conditions through the synergistic effect of the interface layer, stress adjustment layer, and hydrophilic protective layer. The interface layer establishes a strong film-substrate bond with the nano-reinforcement through a silane coupling agent; the intelligent response behavior of the liquid crystal elastomer microspheres in the stress adjustment layer at high temperatures, combined with the cross-scale stress transfer network formed by aminated nanocellulose and aminated carbon nanotubes, effectively disperses and counteracts the thermal stress concentration at the needle root; the hydrophilic protective layer improves heat dissipation efficiency and extends service life through the synergy of micro / nano structures and hydrophilic components. Experiments demonstrate that the integrity of the three-layer film structure and the optimization of the component ratio (especially in Example 1) are crucial to the thermal fatigue resistance of the heat sink. It maintains structural integrity and low thermal resistance characteristics after 2000 thermal cycles from -40°C to 125°C, with the failure cycle count more than 2.35 times higher than the uncoated sample.

[0046] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A liquid cooling heat sink against thermal fatigue, comprising a copper heat dissipation base plate, a copper needle array is welded on a surface of the copper heat dissipation base plate, characterized in that, The surface of the copper heat dissipation base plate welded with the copper needle array is sequentially covered with an interface layer, a stress adjusting layer and a hydrophilic protective layer; The raw materials of the interface layer include, by weight fraction: 3-aminopropyl triethoxysilane 4-6 parts, nanocellulose whisker 2.5-4 parts, aminated carbon nanotube 1.2-2 parts, isocyanate silane coupling agent 3-5 parts, anhydrous ethanol 80-100 parts and deionized water 8-12 parts; The raw materials of the stress adjusting layer include, by weight fraction: modified polyurethane resin 220-280 parts, liquid crystal elastomer microspheres 40-50 parts, organic montmorillonite 6-9 parts, nanometer zirconium oxide 10-15 parts, aminated nanocellulose 8-12 parts and silane coupling agent 4-6 parts; The raw materials of the hydrophilic protective layer include, by weight fraction: polyvinyl butyral resin 300-350 parts, hydrophilic modified nanosilica 30-40 parts, polyethylene glycol 20-30 parts, glutaraldehyde crosslinking agent 15-20 parts and nanosilver antibacterial agent 40-50 parts; The liquid crystal elastomer microspheres have a core-shell structure, and the core-shell structure includes a liquid crystal polymer core layer and a silica-based shell layer.

2. The liquid cooling heat spreader of claim 1, wherein, The liquid crystal elastomer microspheres are prepared from the following raw materials by weight fraction: 4,4'-bis(6-hydroxyhexyloxy) biphenyl 12-15 parts, bisphenol A type epoxy resin 8-10 parts, methacryloyl chloride 4-5 parts, 2-hydroxyethyl methacrylate phosphate ester 3-4 parts, N,N'-methylene bisacrylamide 1.5-2.5 parts, ammonium persulfate 0.4-0.6 parts, polyvinyl alcohol 6-8 parts, amino silicone oil 5-7 parts, tetraethoxysilane 8-10 parts and 25% ammonia water 3.0-5.0 parts.

3. The liquid cooling heat sink of claim 1, wherein, The thickness of the interface layer is 200-300 nm; the thickness of the stress adjusting layer is 25-80 μm; and the thickness of the hydrophilic protective layer is 20-30 μm.

4. The liquid cooling heat sink of claim 1, wherein, The modified polyurethane resin has a polyimide-polyurethane interpenetrating network structure and is prepared from the following raw materials by weight fraction: 4,4'-oxobisphthalic anhydride 20-24 parts, 3,3'-diaminodiphenyl sulfone 12-15 parts, 1,4-butanediol 4-6 parts, isophorone diisocyanate 15-18 parts and polycaprolactone diol 30-40 parts.

5. The liquid-cooled heat sink of claim 1, wherein, The hydrophilic modified nanosilica is prepared from fumed nanosilica and 3-aminopropyl triethoxysilane.

6. The liquid-cooled heat sink of claim 1, wherein, The particle size of the hydrophilic modified nanosilica is 20-30 nm.

7. The liquid-cooled heat sink of claim 1, wherein, The stress adjusting layer further includes 2.5-4 parts by weight of an antioxidant and 70-90 parts by weight of N,N-dimethylacetamide; and the antioxidant is a compound of antioxidant 1010 and antioxidant 168.

8. A process for the preparation of a liquid-cooled heat sink against thermal fatigue as claimed in claims 1-7, characterized in that, The method comprises the following steps: S1, pretreating the copper heat dissipation base plate; S2, mixing and dispersing the raw materials of the interface layer, coating the pretreated surface by dip coating method and solidifying; S3, mixing the raw materials of the stress adjusting layer uniformly, electrostatically spraying the interface layer, and gradient solidifying; S4, mixing the raw materials of the hydrophilic protective layer uniformly at ≤50°C, coating the surface of the stress adjusting layer by dip coating method within 2 hours, and performing surface drying, crosslinking solidification and deep solidification, and then performing room temperature water washing aftertreatment.

9. The process for preparing a liquid cooling heat sink against thermal fatigue according to claim 8, characterized in that, The pretreatment step includes: using a mixture of 30% H2O2 and 5% H2SO4 to treat the surface of the copper heat sink bottom plate with copper needle array at 60 DEG C for 15 minutes, and then rinsing with deionized water and drying.

10. An IGBT module, characterized by, The application relates to a liquid cooling radiator with heat fatigue resistance, which comprises a power chip, a packaging structure and the liquid cooling radiator with heat fatigue resistance as claimed in any one of claims 1-7.

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