Anti-thermal fatigue liquid cooling radiator, preparation process and IGBT module

Abstract

The application discloses a kind of anti-thermal fatigue liquid cooling radiator, preparation process and IGBT module, belong to radiator technical field.The radiator is sequentially covered interface layer, stress adjustment layer and hydrophilic protective layer on the surface of copper needle array welded copper heat dissipation bottom plate.Interface layer is constructed firm film-base combination by silane coupling agent and nano reinforcing body;Stress adjustment layer contains modified polyurethane resin and core-shell structure liquid crystal elastomer microspheres, volume shrinkage occurs in 80-125 DEG C temperature interval, cooperate amino nano cellulose and carbon nanotube to form cross-scale stress transfer network, effectively disperses needle root thermal stress concentration;Hydrophilic protective layer improves heat exchange efficiency and antibacterial performance by micro-nano structure and hydrophilic component synergy.The application solves the interface cracking problem caused by thermal expansion coefficient mismatch and stress concentration in thermal cycle of welded needle fin structure.

Description

Technical Field

[0001] This invention belongs to the field of heat sink technology, and relates to a thermal fatigue resistant liquid-cooled heat sink, its manufacturing process, and an IGBT module. Background Technology

[0002] Power semiconductor modules (especially IGBT modules) are core components in new energy vehicles, rail transit, and smart grids, and their heat dissipation performance directly determines the system's power density, efficiency, and reliability. Liquid-cooled heat sinks have become the preferred solution for high-power applications due to their high heat transfer efficiency. Among them, the needle-fin copper heat sink base plate, with its high specific surface area provided by the needle-shaped fins, has become the mainstream design in the industry. Currently, the manufacturing of needle-fin heat sinks mainly adopts two technical routes: integral molding process and welding assembly process. Although the integral molding process can avoid the connection interface and has a natural advantage in terms of resistance to thermal fatigue, it is limited by mold cost and structural complexity. On the other hand, the welding assembly process is still used by many mid-to-high-end modules due to its flexible design and controllable cost. This process usually connects the independently processed copper pin array to the copper base plate with tin-based solder to form the core heat dissipation structure.

[0003] In practical applications such as new energy vehicles and rail transit, IGBT modules are often in a dynamic "loading-unloading" condition. Frequent temperature rises and falls can easily lead to thermal fatigue—that is, fatigue damage caused by repeated thermal stress on materials or structures under cyclic temperature changes. This damage will continue to accumulate, which makes the connection interface formed by the welding assembly process naturally face severe challenges.

[0004] Under typical operating conditions of IGBT modules, the solder joint area is subjected to multiple stresses, further amplifying the risk of thermal fatigue damage. Due to the significant difference in thermal expansion coefficients between the copper substrate and the tin-based solder, huge shear strain is generated at the interface during temperature cycling, which is the core driving force for thermal fatigue cracking. Simultaneously, the geometry at the pin-base connection leads to high local stress concentration, accelerating the initiation of thermal fatigue cracks. Furthermore, under long-term thermal cycling, a brittle intermetallic compound layer continuously forms at the copper-solder interface, causing a sharp decrease in solder joint toughness and a significant reduction in thermal fatigue resistance. The combined effect of these factors significantly weakens the structural stability and load-bearing capacity of the welded interface, ultimately leading to solder joint cracking in the welded pin-fin structure, with cracks mostly concentrated at the connection interface between the pin root and the base plate. Summary of the Invention

[0005] The purpose of this invention is to provide a thermal fatigue resistant liquid-cooled heat sink, its manufacturing process, and an IGBT module, in order to solve the problem of thermal fatigue cracking caused by the mismatch of thermal expansion coefficients between copper and solder, stress concentration at the root of the pin, and embrittlement of intermetallic compounds in the application of welded assembled pin-fin copper heat sink base plates in IGBT modules.

[0006] The objective of this invention can be achieved through the following technical solutions:

[0007] In a first aspect, the present invention provides a thermal fatigue resistant liquid cooling radiator, comprising a copper heat dissipation base plate, wherein a copper pin array is welded to one surface of the copper heat dissipation base plate, and the surface of the copper heat dissipation base plate with the copper pin array is sequentially covered with an interface layer, a stress adjustment layer and a hydrophilic protective layer.

[0008] The raw materials of the interface layer include, by weight, 4-6 parts of 3-aminopropyltriethoxysilane, 2.5-4 parts of nanocellulose whiskers, 1.2-2 parts of aminated carbon nanotubes, 3-5 parts of isocyanate silane coupling agent, 80-100 parts of anhydrous ethanol and 8-12 parts of deionized water.

[0009] The raw materials of the stress-adjusting layer include, by weight: 220-280 parts of modified polyurethane resin, 40-50 parts of liquid crystal elastomer microspheres, 6-9 parts of organomontmorillonite, 10-15 parts of nano-zirconia, 8-12 parts of aminated nanocellulose, and 4-6 parts of silane coupling agent.

[0010] The raw materials of the hydrophilic protective layer include, by weight: 300-350 parts of polyvinyl butyral resin, 30-40 parts of hydrophilic modified nano silica, 20-30 parts of polyethylene glycol, 15-20 parts of glutaraldehyde crosslinking agent, and 40-50 parts of nano silver antibacterial agent.

[0011] The liquid crystal elastomer microspheres have a core-shell structure, which includes a liquid crystal polymer core layer and a silicon dioxide-based shell layer.

[0012] Preferably, the liquid crystal elastomer microspheres are prepared from the following raw materials in parts by weight: 12-15 parts of 4,4'-bis(6-hydroxyhexyloxy)biphenyl, 8-10 parts of bisphenol A epoxy resin, 4-5 parts of methacryloyl chloride, 3-4 parts of 2-hydroxyethyl methacrylate phosphate, 1.5-2.5 parts of N,N'-methylenebisacrylamide, 0.4-0.6 parts of ammonium persulfate, 6-8 parts of polyvinyl alcohol, 5-7 parts of amino silicone oil, 8-10 parts of tetraethoxysilane, and 3.0-5.0 parts of 25% ammonia.

[0013] 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.

[0014] Preferably, the modified polyurethane resin is a polyimide-polyurethane interpenetrating network structure, prepared from the following raw materials in parts by weight: 20-24 parts of 4,4'-oxophthalic anhydride, 12-15 parts of 3,3'-diaminodiphenyl sulfone, 4-6 parts of 1,4-butanediol, 15-18 parts of isophorone diisocyanate, and 30-40 parts of polycaprolactone diol.

[0015] Preferably, the hydrophilic modified nano-silica is prepared by reacting fumed nano-silica with 3-aminopropyltriethoxysilane.

[0016] Preferably, the hydrophilic modified nano-silica has a particle size of 20-30 nm.

[0017] Preferably, the stress-regulating layer further includes 2.5-4 parts by weight of antioxidant and 70-90 parts by weight of N,N-dimethylacetamide; the antioxidant is a compound of antioxidant 1010 and antioxidant 168.

[0018] In a second aspect, the present invention provides a manufacturing process for the thermal fatigue resistant liquid-cooled heat sink as described in the first aspect, comprising the following steps:

[0019] S1. Pre-treatment of the copper heat sink base plate;

[0020] S2. After mixing and dispersing the interface layer raw materials, apply them to the pretreated surface using the dip-coating method and then cure them.

[0021] S3. After uniformly mixing the stress-adjusting layer material, electrostatically spray it onto the interface layer and then perform gradient curing treatment.

[0022] S4. Mix the hydrophilic protective layer material evenly at ≤50℃, apply it to the surface of the stress conditioning layer using the dip-coating method within 2 hours, and after surface drying, cross-linking curing and deep curing, perform room temperature water washing post-treatment.

[0023] Preferably, the pretreatment step includes: using a mixture of 30% H2O2 and 5% H2SO4 to treat the surface of the copper heat sink base plate with copper pin array at 60°C for 15 minutes, and then rinsing it with deionized water and drying it.

[0024] Thirdly, the present invention provides an IGBT module, including a power chip, a packaging structure, and a thermal fatigue resistant liquid cooler as described in the first aspect.

[0025] The beneficial effects of this invention are:

[0026] (1) The core advantage of the present invention in resisting thermal fatigue stems from the dual design of the synergistic construction of functional network by raw materials and the intelligent component response regulation. A stable cross-scale stress transmission network will be formed inside the stress regulation layer. Aminated nanocellulose itself has a natural three-dimensional network structure. Its surface amino groups can form hydrogen bonds with the end groups of modified polyurethane resin, and at the same time, it can synergize with the amino groups on the tube wall of aminated carbon nanotubes, so that the aminated carbon nanotubes are embedded in the three-dimensional skeleton of aminated nanocellulose, forming a composite network of "aminated nanocellulose network support and aminated carbon nanotube directional conduction". This network will also form a cross-layer stress transmission channel with the copper substrate surface through the overlapping of nanocellulose whiskers in the interface layer, providing a structural basis for stress transmission. When the operating temperature of the IGBT module rises to a specific range (80-125℃), the liquid crystal elastomer microspheres in the stress adjustment layer will shrink in volume due to reaching the glass transition temperature. This shrinkage force is efficiently transferred to the root of the copper needle through the directional conduction of the liquid crystal elastomer microspheres, the three-dimensional network structure of aminated nanocellulose, the aminated carbon nanotubes, and the interlayer connection of nanocellulose whiskers. At the same time, the organic montmorillonite in the stress adjustment layer is in a layered dispersion state, which can disperse the thermal stress concentrated at the root of the needle to a larger area, significantly reducing the stress concentration coefficient, thereby effectively weakening the interfacial thermal stress and stress concentration effect, and significantly extending the thermal cycle life of the heat sink.

[0027] (2) The interface layer forms a chemical bond with the oxide on the surface of the copper substrate through a silane coupling agent, and combined with the nano-interlocking effect of the nanocellulose whiskers, the film-substrate bonding strength is significantly improved; the modified polyurethane resin used in the stress adjustment layer is a polyimide-polyurethane interpenetrating network structure. Its unique molecular network gives the material excellent thermal stability and elastic recovery ability, providing a mechanical basis for stress adjustment; more importantly, the coefficient of thermal expansion of this resin at 150℃ is 27-29ppm / ℃, which is higher than the coefficient of thermal expansion of Sn96.5Ag3.0Cu0.5 solder at room temperature (22-25ppm / ℃). However, in the actual working temperature range of IGBT module (80-125℃), the coefficient of thermal expansion of solder will increase to 27-30ppm / ℃, forming a temperature-dependent dynamic match with the resin, thereby significantly reducing the interface strain difference during thermal cycling; the antioxidant compound system can capture high-temperature free radicals and decompose hydrogen peroxide, ensuring the stability of the mechanical properties of the film layer under high temperature environment.

[0028] (3) In the hydrophilic protective layer, the residual hydroxyl groups of polyvinyl butyral and the hydrophilic migration characteristics of polyethylene glycol, together with the micro-nano rough structure constructed by hydrophilic modified nano silica, accelerate the spread of coolant and improve the effective heat exchange area and heat transfer coefficient; the nano silver antibacterial agent can destroy the cell membrane of microorganisms, achieve efficient antibacterial effect, and avoid biological fouling from clogging the needle fin channels; the reaction between glutaraldehyde crosslinking agent and polyvinyl butyral improves the water resistance of the hydrophilic layer and solves the problem of poor water resistance of traditional hydrophilic coatings. Detailed Implementation

[0029] To further illustrate the technical means and effects of the present invention in achieving its intended purpose, the following detailed description of the specific implementation methods, structures, features, and effects of the present invention, in conjunction with embodiments, is provided below.

[0030] The preparation process and basic information of the raw materials involved in the following examples and comparative examples are described below. Unless otherwise specified, the raw materials are all conventional industrial-grade products that can be obtained through commercial channels, and their purity is ≥98%.

[0031] 1. The modified polyurethane resin has a polyimide-polyurethane interpenetrating network structure, and its raw materials, by weight, and preparation process include the following:

[0032] (1) Raw materials: 20-24 parts of 4,4'-oxophthalic anhydride, 12-15 parts of 3,3'-diaminodiphenyl sulfone, 4-6 parts of 1,4-butanediol, 15-18 parts of isophorone diisocyanate, 30-40 parts of polycaprolactone diol, 120-150 parts of N-methylpyrrolidone, 10-12 parts of acetic anhydride, and 5-7 parts of triethylamine;

[0033] (2) Preparation process: a. Add 4,4'-oxo-diphthalic anhydride and N-methylpyrrolidone to a 500mL four-necked flask under nitrogen protection, stir at 25℃ for 30 minutes until completely dissolved, then slowly add 3,3'-diaminodiphenyl sulfone at a dropping rate of 1 drop / second. After the dropping is complete, raise the temperature to 60℃ and stir at 300r / min for 4 hours to obtain polyamic acid prepolymer solution; b. Add polycaprolactone diol to a 250mL three-necked flask, dehydrate under vacuum at 100℃ for 2 hours, cool to 60℃ and then add isophorone diisocyanate. Cyanate ester and 1,4-butanediol were reacted at 200 r / min for 1.5 hours to prepare a polyurethane prepolymer (NCO content 3.2%); c) the polyurethane prepolymer was slowly injected into a polyamic acid prepolymer and stirred at 50°C for 2 hours to form an interpenetrating network precursor; d) acetic anhydride and triethylamine were added sequentially, stirred at 40°C for 30 minutes, and then heated to 150°C for an imidization reaction for 2 hours; e) the product was cooled to room temperature, poured into deionized water to precipitate, filtered to collect the solid, and vacuum dried at 60°C for 24 hours to obtain a modified polyurethane resin.

[0034] 2. The liquid crystal elastomer microspheres have a core-shell structure. The core of the core-shell structure includes a liquid crystal polymer core layer and a silica-based shell layer. The raw materials and preparation process by weight are as follows:

[0035] (1) Raw materials: 12-15 parts of 4,4'-bis(6-hydroxyhexyloxy)biphenyl, 8-10 parts of bisphenol A epoxy resin, 4-5 parts of methacryloyl chloride, 3-4 parts of 2-hydroxyethyl methacrylate phosphate, 1.5-2.5 parts of N,N'-methylenebisacrylamide, 0.4-0.6 parts of ammonium persulfate, 6-8 parts of polyvinyl alcohol, 5-7 parts of amino silicone oil, 8-10 parts of tetraethoxysilane, 3-5 parts of 25% ammonia water, 180-220 parts of deionized water, and 40-60 parts of dichloromethane;

[0036] (2) Preparation steps: a. Dissolve 4,4'-bis(6-hydroxyhexyloxy)biphenyl in dichloromethane and place it in an ice bath (0-5℃). Slowly add methacryloyl chloride and triethylamine (acid-binding agent, the amount of which is 1.2 times that of methacryloyl chloride). After the addition is complete, heat the mixture to 25℃ and react for 2 hours. Remove the solvent by vacuum distillation to obtain the liquid crystal monomer. Mix the monomer with bisphenol A epoxy resin and 2-hydroxyethyl methacrylate phosphate, add N,N'-methylenebisacrylamide and ammonium persulfate, and ultrasonically disperse for 15 minutes to obtain the oil phase. Dissolve polyvinyl alcohol in deionized water (aqueous phase) at 80℃, cool the mixture to 40℃ and add it to the oil phase. Disperse the mixture at 800 r Emulsify at 500 rpm for 30 minutes, heat to 60℃ and react for 4 hours. Collect the precipitate by centrifugation, wash three times with deionized water, and dry at 60℃ to obtain 2.5-3.5 μm liquid crystal elastomer core microspheres; b. Dissolve amino silicone oil in an ethanol / water (1:1) mixture, add the liquid crystal elastomer core microspheres, and disperse by stirring at 500 rpm for 30 minutes; mix tetraethoxysilane with ethanol evenly, slowly add it dropwise to the above system, and simultaneously add 25% ammonia water to adjust the pH to 9-10, react at 40℃ for 6 hours; collect the product by centrifugation, wash three times with an ethanol / water mixture, and vacuum dry at 80℃ for 12 hours to obtain core-shell structured liquid crystal elastomer microspheres.

[0037] 3. Hydrophilic modified nano-silica, the raw materials and preparation process by weight are as follows:

[0038] (1) Raw material: 50 parts of fumed silica (specific surface area 200 m² / g), 8 parts of 3-aminopropyltriethoxysilane, 200 parts of deionized water, and 100 parts of anhydrous ethanol;

[0039] (2) Preparation steps: a. Add fumed silica nanoparticles to an ethanol / deionized water (1:1) mixture and disperse for 30 minutes using an ultrasonic cell disruptor (600W) to form a uniform suspension; b. Dissolve APTES in 10 parts of anhydrous ethanol and slowly add it dropwise to the above suspension. Heat to 80°C and stir at 200r / min for 4 hours; c. After the reaction is complete, centrifuge at 8000r / min for 15 minutes to collect the precipitate and wash repeatedly with deionized water until the pH of the washing solution is 7; d. Place the precipitate in a vacuum drying oven at 60°C and dry for 12 hours. After grinding, obtain hydrophilic modified silica nanoparticles with a particle size of 25nm.

[0040] 4. Other basic information about raw materials:

[0041] Antioxidant 1010 / 168: Mixing ratio 1:1;

[0042] Nano-zirconia: Particle size 50nm;

[0043] Nano silver antibacterial agent: 10nm aqueous dispersion, solid content 30%;

[0044] All other raw materials not specifically mentioned are conventional industrial-grade products and can be obtained through commercial channels. Example 1

[0045] 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:

[0046] (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.

[0047] (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;

[0048] (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.

[0049] A manufacturing process for a thermal fatigue resistant liquid-cooled heat sink includes the following steps:

[0050] 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℃.

[0051] 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.

[0052] 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.

[0053] 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

[0054] 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:

[0055] (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;

[0056] (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.

[0057] (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.

[0058] A manufacturing process for a thermal fatigue resistant liquid-cooled heat sink includes the following steps:

[0059] 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℃.

[0060] 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.

[0061] 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.

[0062] 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

[0063] 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:

[0064] (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;

[0065] (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.

[0066] (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.

[0067] A manufacturing process for a thermal fatigue resistant liquid-cooled heat sink includes the following steps:

[0068] 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℃.

[0069] 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.

[0070] 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.

[0071] 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.

[0072] Comparative Example 1

[0073] 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.

[0074] Comparative Example 2

[0075] The difference from Example 1 is that the stress-adjusting layer does not contain liquid crystal elastomer microspheres.

[0076] Comparative Example 3

[0077] 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.

[0078] Comparative Example 4

[0079] 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.

[0080] Performance testing

[0081] 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:

[0082] 1. Thermal cycling performance test

[0083] 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.

[0084] 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.

[0085] The thermal cycling performance test data are shown in Table 1.

[0086] Table 1

[0087] ;

[0088]

[0089] 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.

[0090] 2. Interface bonding strength test

[0091] 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.

[0092] 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.

[0093] The interface bonding strength test data are shown in Table 2.

[0094] Table 2

[0095]

[0096] 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.

[0097] 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.

[0098] 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-cooled heat sink resistant to thermal fatigue, comprising a copper heat sink base plate, wherein an array of copper pins is welded to one surface of the copper heat sink base plate, characterized in that, The copper heat dissipation base plate, on which the copper pin array is welded, is sequentially covered with an interface layer, a stress adjustment layer, and a hydrophilic protective layer. The raw materials of the interface layer include, by weight, 4-6 parts of 3-aminopropyltriethoxysilane, 2.5-4 parts of nanocellulose whiskers, 1.2-2 parts of aminated carbon nanotubes, 3-5 parts of isocyanate silane coupling agent, 80-100 parts of anhydrous ethanol and 8-12 parts of deionized water. The raw materials of the stress-adjusting layer include, by weight: 220-280 parts of modified polyurethane resin, 40-50 parts of liquid crystal elastomer microspheres, 6-9 parts of organomontmorillonite, 10-15 parts of nano-zirconia, 8-12 parts of aminated nanocellulose, and 4-6 parts of silane coupling agent. The raw materials of the hydrophilic protective layer include, by weight: 300-350 parts of polyvinyl butyral resin, 30-40 parts of hydrophilic modified nano silica, 20-30 parts of polyethylene glycol, 15-20 parts of glutaraldehyde crosslinking agent, and 40-50 parts of nano silver antibacterial agent. The liquid crystal elastomer microspheres have a core-shell structure, which includes a liquid crystal polymer core layer and a silicon dioxide-based shell layer. The liquid crystal elastomer microspheres are prepared from the following raw materials in parts by weight: 12-15 parts of 4,4'-bis(6-hydroxyhexyloxy)biphenyl, 8-10 parts of bisphenol A epoxy resin, 4-5 parts of methacryloyl chloride, 3-4 parts of 2-hydroxyethyl methacrylate phosphate, 1.5-2.5 parts of N,N'-methylenebisacrylamide, 0.4-0.6 parts of ammonium persulfate, 6-8 parts of polyvinyl alcohol, 5-7 parts of amino silicone oil, 8-10 parts of tetraethoxysilane, and 3.0-5.0 parts of 25% ammonia water; The modified polyurethane resin has a polyimide-polyurethane interpenetrating network structure and is prepared from the following raw materials in parts by weight: 20-24 parts of 4,4'-oxophthalic anhydride, 12-15 parts of 3,3'-diaminodiphenyl sulfone, 4-6 parts of 1,4-butanediol, 15-18 parts of isophorone diisocyanate, and 30-40 parts of polycaprolactone diol.

2. The anti-thermal fatigue liquid-cooled radiator according to claim 1, characterized in that, 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.

3. The anti-thermal fatigue liquid-cooled radiator according to claim 1, characterized in that, The hydrophilic modified nano-silica is prepared by reacting fumed nano-silica with 3-aminopropyltriethoxysilane.

4. The thermal fatigue resistant liquid-cooled radiator according to claim 1, characterized in that, The hydrophilic modified nano-silica has a particle size of 20-30 nm.

5. The anti-thermal fatigue liquid-cooled radiator according to claim 1, characterized in that, The stress-regulating layer further includes 2.5-4 parts by weight of antioxidant and 70-90 parts by weight of N,N-dimethylacetamide; the antioxidant is a compound of antioxidant 1010 and antioxidant 168.

6. A manufacturing process for an anti-thermal fatigue liquid-cooled heat sink as described in any one of claims 1-5, characterized in that, Includes the following steps: S1. Pre-treatment of copper heat sink base plate; S2. After mixing and dispersing the interface layer raw materials, apply them to the pretreated surface using the dip-coating method and then cure them. S3. After uniformly mixing the stress-adjusting layer material, electrostatically spray it onto the interface layer and then perform gradient curing treatment. S4. Mix the hydrophilic protective layer material evenly at ≤50℃, apply it to the surface of the stress conditioning layer using the dip-coating method within 2 hours, and after surface drying, cross-linking curing and deep curing, perform room temperature water washing post-treatment.

7. The manufacturing process of an anti-thermal fatigue liquid-cooled heat sink according to claim 6, characterized in that, The pretreatment steps include: using a mixture of 30% H2O2 and 5% H2SO4 to treat the surface of the copper heat sink base plate with copper pin array at 60°C for 15 minutes, and then rinsing it with deionized water and drying it.

8. An IGBT module, characterized in that, It includes a power chip, a packaging structure, and a thermal fatigue resistant liquid cooling heat sink as described in any one of claims 1-5.

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