A thermal interface material and its preparation method and application

Abstract

This invention discloses a thermal interface material, its preparation method, and its applications, belonging to the field of microelectronic packaging and thermal management materials. The preparation method utilizes the synergistic effect of laser ablation and chemical deposition. First, laser etching forms micropores with high roughness and a large specific surface area. Then, a nano-silver catalyst layer is deposited, and combined with chemical copper plating and copper paste compaction technology, an axially penetrating metal channel composed of copper pillars is constructed within the polymer matrix, significantly improving the material's thermal conductivity. Furthermore, this invention directly and directionally etches a micropore array within a flexible polymer substrate, making the height of the vertical heat conduction channel adjustable. This provides sufficient macroscopic deformation margin to mitigate the thermally induced differential expansion at the chip and heat sink ends due to the mismatch in thermal expansion coefficients. The thermal interface material of this invention possesses high thermal conductivity, excellent compliance, and resistance to aging in harsh humid and hot environments, meeting the extreme heat dissipation and high reliability integration requirements of high-power semiconductor devices.

Description

Technical Field

[0001] This invention belongs to the field of microelectronic packaging technology and advanced thermal management materials, and specifically relates to a thermal interface material, its preparation method and application. Background Technology

[0002] In current semiconductor thermal management engineering, thermal interface materials serve as a bridge connecting heat sources and heat dissipation components, and their thermal conductivity and service reliability directly determine the lifespan of power devices.

[0003] Currently, the most common industrial approach is to randomly disperse high thermal conductivity fillers such as alumina, boron nitride, and carbon nanotubes within a highly compliant polymer matrix such as silicone rubber and epoxy resin. However, this traditional polymer-based composite thermal interface material suffers from significant microscopic interfacial thermal resistance between the thermally conductive particles, which are isolated from each other by the insulating and low-thermal-conductivity polymer matrix. This obstructs the heat conduction path, resulting in a thermal conductivity typically below 5 W / (m·K). Furthermore, to overcome the percolation threshold and establish a thermally conductive network, an extremely high volume fraction of particles must be filled, directly leading to a sharp deterioration in the intrinsic flexibility of the polymer.

[0004] To improve the inefficient heat transfer caused by random particle distribution, recent cutting-edge research has shifted towards ordered network design. This involves pre-constructing porous boron nitride nanosheet vertical arrays or graphene sponge frameworks using methods such as freeze casting, self-assembly, or porous framework templates, and then vacuum-infusing them with polymers. While this approach, employing vertically upright carbon fiber or metal nanowire arrays, significantly improves longitudinal thermal conductivity, its thermal framework is rigid and completely lacks longitudinal tensile strength. When large-size chips undergo significant warping due to thermal expansion and contraction at high temperatures, the chip edges exert enormous longitudinal tensile stress on the thermal interface material. This directly leads to physical fracture or detachment of the rigid vertical array at the interface, completely disrupting the heat conduction path.

[0005] Further research into microarray-type thermal interface materials has proposed processes for preparing copper or silver nanowire arrays using electrodeposition on sacrificial templates such as porous anodic alumina. Although vertical metal arrays prepared using the sacrificial template method exhibit a macroscopic modulus several orders of magnitude lower than bulk materials, they reveal serious inherent drawbacks in practical engineering applications. First, the traditional sacrificial template method is extremely cumbersome and lengthy, involving multiple independent steps such as porous template construction, surface activation, electrodeposition filling, selective chemical exfoliation of the template, and secondary polymer infusion. In these steps, the process parameters, such as temperature, voltage, and chemical environment, are extremely demanding to control; any tiny local defect can lead to overall array incompleteness. Second, due to the physical limitations of the fabrication process of sacrificial templates such as porous anodic alumina, the thickness of the obtained template-based metal arrays in the vertical direction is typically less than 50 micrometers. In practical high-power electronic packaging, due to the significant difference in the coefficients of thermal expansion between the materials on both sides of the heat source and heat sink, such ultra-thin arrays simply cannot provide sufficient macroscopic deformation to buffer thermal stress caused by temperature differences, making them highly susceptible to interfacial delamination and fatigue failure during service. Furthermore, the template method requires a large amount of specialized high-purity reagents to remove the sacrificial skeleton, resulting in high manufacturing costs and significant waste of raw materials and environmental pressure. Finally, although carbon-based ordered arrays have excellent intrinsic thermal conductivity, their microscopic affinity with the polymer matrix is ​​extremely weak, and the interfacial adhesion between the two phases is poor. During thermal expansion, it is extremely difficult to achieve a strong solid-phase or liquid-phase metallurgical weld between their ends and the metal heat sink, compromising long-term service reliability.

[0006] In addition, there is a scheme to prepare nano-spring arrays using grazing angle deposition technology. Although this scheme endows the material with a certain deformation ability, the process requires expensive and precise vacuum deposition equipment, resulting in extremely low production efficiency. Moreover, the thickness of the prepared spring array is only at the micrometer level, which has extremely limited buffering capacity in actual packaging, making it difficult to promote large-scale industrialization.

[0007] Therefore, improvements to existing technologies are still needed. Summary of the Invention

[0008] In view of the technical defects of the above-mentioned prior art, such as complex sacrificial template process, limited array thickness, high production cost and weak multiphase interface bonding, the purpose of this invention is to provide a vertical metal copper column array composite thermal interface material and its preparation method that does not require a sacrificial template, has a thickness that can be adjusted across macroscopic to microscopic scales and has adjustable height.

[0009] To achieve the above objectives, the present invention is implemented through the following technical solution: In a first aspect, the present invention provides a method for preparing a thermal interface material, comprising the steps of: Polymer substrates with vertical micropore arrays were prepared by laser ablation. A silver catalytic layer is formed by depositing silver on the inner surface of the micropores in the vertical micropore array of the polymer substrate; A copper plating layer is formed on the surface of the silver catalyst layer by electroless copper plating. Copper paste is filled into the micropores of the micropore array of the polymer substrate after chemical copper plating, and then cured to obtain a vertical copper pillar array penetrating the polymer substrate.

[0010] This preparation method utilizes the synergistic effect of laser ablation and chemical deposition. First, laser etching is used to form micropores with high roughness and large specific surface area, facilitating the subsequent deposition of the nano-silver catalyst layer. Combined with chemical copper plating and copper paste compaction technology, an axially penetrating metal channel composed of copper pillars is constructed in the polymer matrix. This channel has a high thermal conductivity. Moreover, the use of a flexible polymer substrate to prepare the array thermal interface material overcomes the limitation of the small thickness of the metal array prepared by the traditional template method. This allows the vertical heat conduction channel to be highly adjustable within the range of 10 μm to 2000 μm, providing sufficient macroscopic deformation margin to alleviate the thermal differential expansion caused by the mismatch of thermal expansion coefficients at both ends of the chip and the heat sink.

[0011] Further, the polymer substrate is one or more of a polydimethylsiloxane board, a nitrile rubber substrate, a polyurethane substrate, or an epoxy resin substrate. Preferably, the thickness of the polymer substrate is 10 μm to 2000 μm, more preferably 50 μm to 1000 μm.

[0012] Furthermore, the laser emission power of the laser ablation is 10 W to 20 W; the laser scanning speed is 10 mm / s to 50 mm / s; the processing method is a skip processing, such as drilling odd-numbered holes first and then even-numbered holes; the number of cycles is 1 to 30.

[0013] Furthermore, the micro-hole array is a micro-hole array with openings at both ends. When forming the micro-hole array by laser etching, one can choose to directly etch to form through holes, or etch through holes from both ends separately.

[0014] Furthermore, the vertical micropore array has a depth-to-diameter ratio of 2 to 5:1, a micropore height of 10 to 2000 μm, and a planar arrangement of micropores with a spacing and / or pitch greater than 100 μm.

[0015] The silver catalyst layer primarily serves as a transitional bonding layer between the copper and polymer substrate, providing dense nucleation sites for copper atoms. Furthermore, the thickness of the silver catalyst layer is 10–20 nm.

[0016] Further, the polymer substrate is immersed in a silver nitrate solution in ethanol and allowed to stand at room temperature in the dark to react, forming the silver catalyst layer. Using ethanol as a reducing agent to deposit the nano-silver catalyst within the microporous array of the polymer substrate is more conducive to obtaining silver nanoparticles with a narrower particle size distribution. Preferably, the concentration of silver nitrate in the ethanol-silver nitrate solution is 20-30 g / L. Preferably, the reaction time is 5-10 h.

[0017] A copper plating layer serves as a transition between the silver catalyst layer and the copper paste, enhancing the interfacial bonding strength between the copper pillars and the polymer and preventing voids. This ensures a tight bond. Furthermore, the copper content in the plating layer is ≥98wt%, and the high-purity and high-crystallinity electroless copper plating provides a good continuous thermal conductivity path. Further, the thickness of the copper plating layer is 20-100μm. Typically, the polymer substrate is immersed in a copper plating solution for copper plating. In one embodiment of the invention, the copper plating solution comprises: 15g / L copper sulfate pentahydrate, 15g / L sodium hydroxide, 20g / L disodium ethylenediaminetetraacetate, 7.5g / L potassium sodium tartrate, and 40g / L 37wt% formaldehyde aqueous solution.

[0018] Furthermore, the total copper content within the vertical copper pillar array is 50-70 vol%. This total copper includes both the copper in the copper plating layer and the copper paste filling the layer. By volume percentage, the total copper content is greater than 50-70% to ensure sufficient polymer matrix to buffer thermal stress, while also providing sufficient metal thermal conductivity.

[0019] Furthermore, in order to address the problem that copper is prone to oxidation and degradation during long-term humid and hot service, leading to the collapse of the thermal / electrical conduction network, the preparation method of the present invention further includes: plating tin on the upper and lower surfaces of the vertical copper pillar array to form a tin protective layer, so as to improve the structural integrity and electrothermal contact reliability of the thermal interface material under long-term thermal cycling and harsh humid and hot environment service.

[0020] Preferably, the thickness of the tin protective layer is 1 μm to 5 μm.

[0021] In a second aspect, the present invention also provides a thermal interface material prepared by the above-described preparation method.

[0022] A third aspect of the present invention also provides the application of the above-described thermal interface material in semiconductor devices.

[0023] Compared with existing technologies, The preparation method of this invention involves forming a roughened microporous array in a polymer substrate using laser etching, followed by the introduction of a nano-silver catalytic active layer, and then electroless copper plating and copper paste filling and curing. This constructs an axially penetrating metal channel composed of copper pillars within the polymer matrix, resulting in a thermal interface material with ultra-high longitudinal thermal conductivity and excellent compliance, achieving an effective thermal conductivity of 37 W·m. -1 ·K -1 Furthermore, this invention directly and directionally etches a micro-hole array inside a flexible polymer substrate, overcoming the limitation of small thickness in metal arrays prepared by traditional template methods. This allows the vertical heat conduction channel to be highly adjustable within the range of 10 to 2000 μm, thereby providing sufficient macroscopic deformation margin to alleviate thermal differential expansion caused by the mismatch of thermal expansion coefficients at both ends of the chip and the heat sink.

[0024] Furthermore, by introducing a tin protective layer with both oxidation resistance and solderability at both ends of the array, the present invention can significantly reduce the interfacial contact thermal resistance during device assembly and improve the thermal interface material's resistance to aging in harsh humid and hot environments.

[0025] The thermal interface material of this invention has ultra-high longitudinal thermal conductivity, excellent compliance and resistance to aging in harsh humid and hot environments, which can meet the extreme heat dissipation and high reliability integration requirements of high-power semiconductor devices. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the process flow according to an embodiment of the present invention; Figure 2 Optical photographs of the inner surfaces of the micropores formed after laser etching in Example 1 and Comparative Example 1; Figure 3 Optical photographs of the polymer substrates formed by laser etching in Examples 1-4; Figure 4 Scanning electron microscope and optical microscope images of the sample in Example 1: Figure 4 (a) is the surface morphology of the silver catalyst layer, (b) is the surface morphology of the copper plating layer, (c) is a digital photograph of the substrate surface after copper paste filling, and (d) is a digital photograph of the substrate surface after electroless tin plating. Figure 5 The images show a cross-sectional view of the TCPA-TIM sample prepared in Example 1 and its interface with the heat sink. Figure 5 (a) is an interface diagram, (b) is a magnified view of (a), and (c) is an interface diagram of the bonding between the tin-plated protective layer and the heat sink. Figure 6 This is a comparison of the heat dissipation performance of the thermal interface materials prepared in Example 1, Comparative Example 2, and Comparative Example 3. Figure 6(a) is a schematic diagram of the heat dissipation test device; (b) is a comparison of infrared thermal images of different samples after the LED lights are turned on. Figure 7 The thermal conductivity stability test results of TCPA-TIM, the thermal interface material prepared in Example 1, in the LED lamp switching cycle experiment; Figure 8 The graph shows the resistance change of the thermal interface materials prepared in Examples 1 and 7 during the double 85 aging test. Detailed Implementation

[0027] The technical solution of this invention utilizes the synergistic effect of laser ablation and chemical deposition to precisely construct a structurally complete embedded vertical copper-based array within a polymer matrix, forming a through-hole metal channel to serve as a thermal interface material. Specifically, the steps include: (1) A polymer substrate with a vertical micropore array was prepared by laser ablation.

[0028] Specifically, polymer substrates (such as epoxy resin, polyurethane, nitrile rubber, polydimethylsiloxane, etc.) can be placed in a laser engraving system (such as Ousay 4060), and selective precision ablation of one or both sides can be performed through a laser preset program. The laser power and scanning speed can be controlled to quickly process a regularly arranged vertical micro-hole array with a high aspect ratio within the polymer matrix.

[0029] In some embodiments, the laser emission power of the laser ablation is 10 W to 20 W; the laser scanning speed is 10 mm / s to 50 mm / s; the processing method is a skip processing, such as drilling odd-numbered holes first and then even-numbered holes; the number of cycles is 1 to 30.

[0030] The above-mentioned single-sided or double-sided ablation means that the micro-hole array can be directly etched to form through holes, or etched from both ends to form through holes.

[0031] In some embodiments, the depth-to-diameter ratio of the micropores in the vertical micropore array is 2 to 5:1, the height of the micropores is 10 μm to 2000 μm, and the planar arrangement of the micropores and / or the pitch is greater than 100 μm.

[0032] (2) Silver is deposited on the inner surface of the micropores of the vertical micropore array of the polymer substrate to form a silver catalyst layer.

[0033] Because laser ablation imparts extremely high microscopic roughness and a large specific surface area to the pore walls, silver ions can be reduced in situ and immobilized on the inner walls of the pores. This silver catalyst layer primarily serves as a transitional bonding layer between the copper and polymer substrates, providing dense nucleation sites for copper atoms.

[0034] In some preferred embodiments, ethanol is used as a reducing agent to deposit nano-silver catalysts within the etched polymer micropores. Specifically, the polymer substrate is immersed in a silver nitrate solution in ethanol and allowed to react at room temperature in the dark to form the silver catalyst layer. Ethanol is relatively mild and slowly reduces silver ions, resulting in a narrower particle size distribution of the silver nanoparticles. Preferably, the silver nitrate concentration in the ethanol-silver nitrate solution is 20-30 g / L. Preferably, the reaction time is 5-10 h.

[0035] In some preferred embodiments, the thickness of the silver catalyst layer is 10-20 nm.

[0036] (3) Perform chemical copper plating on the surface of the silver catalyst layer to form a copper plating layer.

[0037] Specifically, the substrate is immersed in a chemical copper plating solution for copper plating. A commercially available chemical copper plating solution can be used. In a preferred embodiment of the present invention, the copper plating solution comprises: 15 g / L copper sulfate pentahydrate, 15 g / L sodium hydroxide, 20 g / L disodium ethylenediaminetetraacetate, 7.5 g / L potassium sodium tartrate, and 40 g / L a 37 wt% formaldehyde aqueous solution. Using this copper plating solution, copper plating is performed at 60°C for 15 minutes.

[0038] In some preferred embodiments, the copper plating layer has a thickness of 20~100 μm. The copper plating layer serves as a transition between the polymer substrate and the copper paste, enhancing the interfacial bonding strength between the copper pillars and the polymer and preventing void formation. Furthermore, the high-purity and highly crystalline electroless copper plating layer provides a good continuous thermal conductivity path; therefore, in some preferred embodiments, the copper content in the plating layer is ≥98 wt%.

[0039] (4) Fill the micropores of the micropore array of the polymer substrate after chemical copper plating with copper paste and cure it to obtain a vertical copper pillar array.

[0040] To further eliminate mass transfer limitations in deep holes and ensure complete compaction of the pore interior, commercial copper paste needs to be applied to the copper-plated micropores and cured. In some preferred embodiments, after copper paste filling, the total copper content (including the chemical plating and the filling copper paste) in the through-holes is 50-70% (volume percentage) to ensure sufficient polymer matrix to buffer thermal stress, while also providing sufficient metal thermal conductivity. That is, the total copper content in the cured copper pillar array is 50-70% (volume percentage).

[0041] In some preferred embodiments, curing is performed at 130-170°C.

[0042] After curing, excess polymer substrate at both ends of the copper pillar array is removed by laser secondary etching or mechanical grinding and peeling, resulting in an embedded vertical copper pillar array that completely penetrates and exposes both ends of the polymer matrix. This vertical copper pillar array can be directly used as a thermal interface material.

[0043] Furthermore, to address the problem of copper's susceptibility to oxidation and degradation during long-term humid and hot service, leading to thermal network collapse, the preparation method of this invention further includes: (5) Tin is plated on the upper and lower surfaces of the vertical copper column array to form a tin protective layer.

[0044] Specifically, the vertical copper pillar array is immersed in a commercial chemical tin plating solution, and a continuous and dense pure tin protective layer is grown at the exposed top and bottom of the vertical copper pillars, ultimately forming an embedded vertical copper pillar array with an outer layer covered by tin.

[0045] In some preferred embodiments, the thickness of the tin protective layer is 1 μm to 5 μm.

[0046] The preparation method of this invention introduces a nano-silver catalyst layer into the microporous inner wall of a polymer substrate, and combines it with chemical copper plating and copper paste dense filling technology to construct an axially penetrating metal channel composed of copper pillars in the polymer matrix. This results in a high thermal conductivity. Moreover, by using a flexible polymer as a substrate to prepare an array thermal interface material, the limitations of the small thickness of the metal array prepared by the traditional template method can be overcome. This allows the thickness of the vertical heat conduction channel to be highly adjustable within the range of 10 μm to 2000 μm, providing sufficient macroscopic deformation margin to alleviate the thermal differential expansion caused by the mismatch of thermal expansion coefficients at both ends of the chip and the heat sink.

[0047] Furthermore, in order to address the problem that copper is prone to oxidation and degradation during long-term humid and hot service, leading to the collapse of the heat conduction network, the preparation method of the present invention further includes: plating tin on the upper and lower surfaces of the vertical copper pillar array to form a tin protective layer, so as to improve the structural integrity and electrothermal contact reliability of the thermal interface material under long-term thermal cycling and harsh humid and hot environment service.

[0048] The thermal interface material of this invention can be used in semiconductor devices, such as LED heat dissipation.

[0049] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. The specific embodiments described herein are for illustrative purposes only and are not intended to limit the invention.

[0050] The raw materials and reagents used in the following examples (unless otherwise specified) were all commercially available; the techniques and methods used (unless otherwise specified) were all conventional means in the art.

[0051] Example 1 refer to Figure 1 This embodiment provides a thermal interface material, and the preparation method of the thermal interface material includes the following steps: 1. Laser engraving: Prepare a PDMS substrate with a thickness of 500 μm, place it in a laser engraving system (Osai 4060), adjust the laser power to 15W, the scanning speed to 20mm / s, adopt a skip processing method, and cycle 10 times to process a regularly arranged through-type vertical micro-via array with openings at both ends on the PDMS substrate. The through-hole spacing is 150 μm, the through-hole diameter is 150 μm, and the depth-to-diameter ratio is 3:10. The PDMS substrate is then ready for use.

[0052] 2. Silver ion activation: Immerse the PDMS substrate obtained in step 1 into an ethanol solution of 25 g / L silver nitrate and let it stand at room temperature in the dark for 8 hours to form a silver catalyst layer.

[0053] 3. Chemical copper plating: Immerse the PDMS substrate obtained in step 2 into the chemical copper plating solution and plate copper at 60 ℃ for 10 min to form a copper plating layer; the composition of the copper plating solution is: 15 g / L copper sulfate pentahydrate, 15 g / L sodium hydroxide, 20 g / L disodium ethylenediaminetetraacetate, 7.5 g / L potassium sodium tartrate, and 40 g / L formaldehyde aqueous solution with a mass fraction of 37 wt%.

[0054] 4. Copper paste filling: Copper paste (Shenzhen Huaneng Zhiyan Electronics Co., Ltd.) is applied by scraping into the through holes of the micro-via array after electroless copper plating. After copper paste filling, the total copper content (including electroless plating and filling copper paste) in the polymer vertical through holes is about 60% (volume percentage). The copper paste is heated to 150℃ and held for 30 minutes to solidify. Then, the residual polymer layer at the top and bottom ends is removed by laser secondary etching, thereby obtaining an embedded vertical copper pillar array that is completely penetrated and exposed at both ends of the polymer substrate.

[0055] 5. Chemical Tin Plating: Immerse the vertical copper column array obtained in step 4 into a chemical tin plating solution (Suzhou Zhiying Electronic Technology Co., Ltd.) and tin-plat for 15 minutes at room temperature to form a tin protective layer. The resulting thermal interface material is denoted as Through-Type Tin-Copper Array Thermal Interface Material, or TCPA-TIM for short.

[0056] Example 2 The only difference from Example 1 is that in step 1, the PDMS substrate is replaced with a polyurethane substrate; all other aspects are the same.

[0057] Example 3 The only difference from Example 1 is that in step 1, the PDMS substrate is replaced with a nitrile rubber substrate; all other aspects are the same.

[0058] Example 4 The only difference from Example 1 is that in step 1, the PDMS substrate is replaced with an epoxy resin substrate, the laser scanning speed is 15 mm / s, and the number of cycles is 15. All other aspects are the same.

[0059] Example 5 The only difference from Example 1 is that the laser power is 20W in step 1, and everything else is the same.

[0060] Example 6 The only difference from Example 1 is that the laser power is 10W in step 1, and everything else is the same.

[0061] Example 7 The only difference from Example 1 is that step 4, chemical tin plating, is omitted. The resulting thermal interface material is denoted as through-type copper array thermal interface material, or CPA-TIM for short.

[0062] Comparative Example 1 The steps in this comparative example are basically the same as those in Example 1, except that the laser power is adjusted to 30W.

[0063] Comparative Example 2 Commercially available spherical copper powder with a diameter of 1 micrometer (Guangzhou Metallurgy) was ground and mixed with PDMS and curing agent (Dow Corning, model DC184). After vacuum degassing, it was hot-pressed and cured at 80°C for 2 h to obtain a comparative sample, denoted as CPFP. The copper content in CPFP was similar to that in Example 1, approximately 60 vol.

[0064] Comparative Example 3 PDMS was mixed with curing agent (Dow Corning, model DC184) at a mass ratio of 10:1. After vacuum degassing, it was hot-pressed and cured at 80°C for 2 h to obtain the comparison sample PDMS.

[0065] Characterization test (1) The polymer substrates with microporous arrays prepared in Example 1 and Comparative Example 1 were characterized using an optical microscope, and the results are as follows: Figure 2 As shown. Among them Figure 2 In the diagram, 'a' represents a cross-sectional view of the micropores in Example 1. Figure 2 In the diagram, b is a cross-sectional view of the micropores in Comparative Example 1. Figure 2 It is known that when the laser etching power is too high, it can easily cause thermal damage or even carbonization of the micropores, affecting the subsequent electroless copper plating process. Therefore, it is preferable to limit the laser etching power to 10W-20W.

[0066] (2) The polymer substrates with microporous arrays of different substrates prepared in Examples 1-4 were characterized using an optical microscope, and the results are as follows: Figure 3 As shown. By Figure 3It is known that after laser processing, a regular array of micropores can be formed on polymer substrates such as PDMS, nitrile rubber, polyurethane and epoxy resin.

[0067] (3) The samples prepared in Example 1 were characterized using scanning electron microscopy and optical microscopy, and the results are as follows: Figure 4 As shown. By Figure 4 As shown in 'a', a silver catalyst layer with a particle size of approximately 15 nm was formed on the inner surface of the micropores of the PDMS substrate through silver ion activation. Figure 4 As shown in b, after chemical copper plating, a dense and continuous copper plating layer is formed, with a thickness of approximately 60 mm. m. Energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy analysis jointly confirmed that the copper content in the coating was close to 99 wt%. Figure 4 As shown in 'c', the micropores of the PDMS substrate are tightly filled with copper paste, exhibiting a metallic copper luster. Figure 4 As indicated by 'd', after chemical tin plating, the resulting tin protective layer is smooth, exhibiting a uniform, bright, silvery-white metallic luster, and has a thickness of approximately 2 mm. m.

[0068] (4) The cross-section of the TCPA-TIM sample prepared in Example 1 and the interface formed by welding with the copper-based heat sink were characterized using an optical microscope. The results are as follows: Figure 5 As shown. By Figure 5 As can be seen from 'a', the copper paste tightly fills the through-hole without any obvious gaps. Figure 5 As can be seen from b, the tin protective layer is also tightly bonded to the vertical copper pillar. From Figure 5 As can be seen from 'c', under the reflow soldering process, an alloy interface is formed between the tin protective layer of TCPA-TIM and the copper-based heat sink above, which can minimize the interface thermal resistance.

[0069] (5) The thermal conductivity of the thermal interface materials obtained in Examples 1 and 7 and Comparative Examples 2 and 3 was tested using a laser thermal conductivity meter.

[0070] The thermal conductivity of the thermal interface material TPCA-TIM in Example 1 was measured to be as high as 37 W / (m·K); the thermal conductivity of the thermal interface material CPA-TIM in the tin-free protective layer in Example 7 was 39 W / (m·K); the thermal conductivity of the thermal interface material CPFP in Comparative Example 2 was 1.8 W / (m·K); and the thermal conductivity of the thermal interface material PDMS in Comparative Example 3 was 0.2 W / (m·K).

[0071] Performance testing: (1) The thermal conductivity of the TCPA-TIM prepared in Example 1 and the CPFP and PDMS samples prepared in Comparative Examples 2 and 3 were tested using a high-precision infrared thermal imager. First, according to Figure 6 The diagram in Figure a shows the assembly of the test device. Figure 6 Image b shows a comparison of infrared thermal images after LEDs with different thermal interface materials are turned on. Figure 6 As can be seen from b, pure PDMS polymer has the worst thermal conductivity and significant heat accumulation; copper powder-filled PDMS (CPFP) has better thermal conductivity, which helps dissipate heat; TCPA-TIM provided in Example 1 of this invention exhibits excellent thermal conductivity, allowing the heat generated by the LED to be dissipated quickly.

[0072] (2) The thermal conductivity stability of the TCPA-TIM prepared in Example 1 during LED switching cycles was characterized using a high-precision infrared thermal imager, and the results are as follows: Figure 7 As shown. By Figure 7 It can be seen that the thermal conductivity of TCPA-TIM is stable during 1000 switching cycles, and the surface temperature of the LED hardly fluctuates.

[0073] (3) The aging resistance of the TCPA-TIM samples prepared in Example 1 and the CPA-TIM samples prepared in Example 7 were characterized using a double 85 aging test chamber and a resistance meter. The results are as follows: Figure 8 As shown. By Figure 8 It can be seen that the resistance of CPA-TIM began to rise rapidly after 5 hours of testing, and its conductivity degraded significantly under high temperature and high humidity conditions. In contrast, the resistance increase of TCPA-TIM was very small during the 20-hour test, indicating that the tin protective layer can significantly improve the material's aging resistance.

[0074] The embodiments of the present invention have been described in detail above, but the present invention is not limited to the described embodiments. For those skilled in the art, various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and these variations still fall within the protection scope of the present invention.

Claims

1. A method for preparing a thermal interface material, characterized in that: Including the following steps: Polymer substrates with vertical micropore arrays were prepared by laser ablation. A silver catalytic layer is formed by depositing silver on the inner surface of the micropores in the vertical micropore array of the polymer substrate; A copper plating layer is formed on the surface of the silver catalyst layer by electroless copper plating. Copper paste is filled into the micropores of the micropore array of the polymer substrate after chemical copper plating, and then cured to obtain a vertical copper pillar array penetrating the polymer substrate.

2. The preparation method according to claim 1, characterized in that, The polymer substrate is one or more of polydimethylsiloxane board, nitrile rubber substrate, polyurethane substrate or epoxy resin substrate.

3. The preparation method according to claim 1, characterized in that, The laser ablation process uses a laser emission power of 10-20 W, a laser scanning speed of 10-50 mm / s, a skip processing method, and a cycle count of 1-30 times.

4. The preparation method according to claim 1, characterized in that, The micropore array is a micropore array with openings at both ends; The vertical micropore array has a depth-to-diameter ratio of 2 to 5:1, a micropore height of 10 to 2000 μm, and a planar arrangement of micropores with a spacing and / or pitch greater than 100 μm.

5. The preparation method according to claim 1, characterized in that, The thickness of the silver catalyst layer is 10~20 nm.

6. The preparation method according to claim 1, characterized in that, The polymer substrate is immersed in a silver nitrate solution in ethanol and allowed to stand at room temperature in the dark to react, thereby forming the silver catalyst layer.

7. The preparation method according to claim 1, characterized in that, The total copper content in the vertical copper column array is 50-70 vol.

8. The preparation method according to claim 1, characterized in that, Also includes: Tin is plated on the upper and lower surfaces of the vertical copper pillar array to form a tin protective layer.

9. A thermal interface material, characterized in that, It is prepared by the preparation method according to any one of claims 1-8.

10. The application of the thermal interface material as described in claim 9 in semiconductor devices.

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