A method of reducing thermal interface material contact resistance

Abstract

The application discloses a method for reducing thermal contact resistance of thermal interface material, comprising: (1) grafting silane coupling agent containing active group I on the surface of a device; (2) coating thermal interface matrix containing active group II on the surface of the device obtained in step (1); (3) reacting the active group II and the active group I; wherein the reaction is at least one selected from the group consisting of thiol-alkenyl click reaction, amidation reaction of amino and carboxyl, condensation reaction of amino and aldehyde group, and addition reaction of hydroxyl and isocyanate. The application reduces the thermal contact resistance by the reaction between the silane coupling agent and the active group of the thermal interface matrix. The method provided by the application does not need additional modification process of the thermal interface material, and only relies on the inherent chemical groups to realize the chemical bond connection between the device surface and the thermal interface material, and the method is simple and effective.

Description

Technical Field

[0001] This invention relates to the field of manufacturing technology of non-metallic functional materials for electronic components, and in particular to a method for reducing the contact thermal resistance of thermal interface materials. Background Technology

[0002] Thermal interface materials are materials that reduce the thermal resistance between two interfaces by filling the gaps in the internal interface of a device [1], and are indispensable materials in the field of thermal management. With the miniaturization, high density and high power of integrated circuits, the heat flux density has increased dramatically, so the requirements for thermal interface materials are more stringent. The traditional research approach is to use high thermal conductivity fillers, such as graphene [2] and carbon fiber [3], and combine the orientation treatment of fillers to improve the intrinsic thermal conductivity of composite materials. However, such thermal interface materials with high intrinsic thermal conductivity are usually hard and have high contact thermal resistance. The applicant once tested a graphene-based thermal interface material (as shown in Figure 1), which has an intrinsic thermal conductivity of 20 W / (m·K). The thermal interface material was placed between a copper sheet and a silicon sheet (the most common application scenario), and the contact thermal resistance of the thermal interface material / copper interface, the thermal interface material / silicon interface and the intrinsic thermal resistance of the thermal interface material were measured. The intrinsic thermal resistance accounted for only 30%, while the contact thermal resistance was as high as 70%. It can be seen that the interface contact thermal resistance restricts the overall thermal conductivity of the thermal interface material. Therefore, reducing interfacial contact thermal resistance is one of the strategies for developing novel thermal interface materials.

[0003] At present, research on reducing the interfacial contact thermal resistance of thermal interface materials can be approached from both physical and chemical perspectives. Physical perspective: Prasher[4] studied the effect of surface roughness on interfacial contact thermal resistance. He used several copper substrates with different roughnesses as contact surfaces and thermally conductive silicone grease and phase change composite materials as thermal interface materials. He measured the interfacial thermal resistance of different combinations and found that as the roughness increases, the contact area between the device and the thermal interface material increases, thereby reducing the contact thermal resistance. Chemical perspective: Sumanjeet Kaur et al.[5] used chemical bonding to reduce the contact thermal resistance between carbon nanotube-based thermal interface materials and device interfaces. They used carbon nanotube arrays as the main body of thermal interface materials, grafted carboxyl groups (-COOH) at their ends, and grafted amino (-NH2) silane coupling agents on the metal surface. After amidation reaction, amide groups -CONH- were formed, reducing the contact thermal resistance. This method reduces the contact thermal resistance from the perspective of fillers. Since fillers do not contain carboxyl groups, an additional process of grafting carboxyl groups is required. Losego et al. [6] grafted silane coupling agents onto the surface of quartz to reduce the interfacial thermal resistance between quartz and gold films. By selecting silane coupling agents with different end-group functional groups, such as -SH, -NH2, and -Br, they studied the effect of different functional groups on the contact thermal resistance. Similar work was done by Zheng Kun et al. [7]. By grafting coupling agents with end-groups of -NH2, -Cl, -SH, and -H onto the surface of sapphire, they reduced the interfacial thermal resistance with polystyrene films. It should be noted that the interaction between the coupling agent and the polymer film is physical entanglement, and no covalent bond is formed.

[0004] While the above technical solutions reduce contact thermal resistance to some extent, they also present other problems:

[0005] 1. The method of reducing contact thermal resistance by adjusting roughness has strong limitations. It is generally only applicable to thermal interface materials such as fluid thermal grease, but not to thermal pads that have been cured and molded. On the contrary, for thermal pads, increasing roughness may increase contact thermal resistance. In addition, the process required to change the surface roughness of the device is relatively complex and difficult to achieve large-scale industrialization.

[0006] 2. In the method of reducing interfacial thermal resistance by grafting active functional groups onto fillers to induce a reaction between the fillers and the coupling agents on the device surface, the fillers inside the thermal interface material cannot react with the coupling agents on the device surface, and the distribution of the fillers within the thermal interface material is uncontrollable. Therefore, this method also has significant limitations. Furthermore, modifying the fillers will reduce their intrinsic thermal conductivity, thereby reducing the overall thermal conductivity of the composite material.

[0007] 3. The method of reducing interfacial contact thermal resistance by physical entanglement generated by surface grafting coupling agents. However, since the coupling agent does not react with any component of the thermal interface material (such as polymer matrix or filler) and does not form covalent bonds, the effect of reducing interfacial contact thermal resistance is not as good as the effect of forming covalent bonds (or other non-covalent bonds, such as hydrogen bonds, coordination bonds, etc.).

[0008] References:

[0009] [1]Zweben C.Advances in High-Performance Thermal ManagementMaterials-Areview[J].Journal of Advanced Materials,2007,39(1):3.

[0010] [2]Shahil K,Balandin A A.Thermal properties of graphene and multilayer graphene:Applications in thermal interface materials[J].SolidState Communications, 2012,152(15):1331-1340.

[0011] [3]Uetani K,Ata S,Tomonoh S,Yamada T,Yumura M,Hata K.ElastomericThermal Interface Materials with High Through-Plane Thermal Conductivity fromCarbon Fiber Fillers Vertically Aligned by Electrostatic Flocking[J].AdvMater. 2014;26(33):5857-5862.

[0012] [4]Prasher R S.Surface chemistry and characteristics based model for the thermal contact resistance offluidic interstitial thermal interfacematerials.Journal of Heat Transfer, 2001,123(5):969-975.

[0013] [5]Kaur S,Raravikar N,Helms BA,et al.Enhanced thermal transport atcovalently functionalized carbon nanotube array interfaces.[J].NatureCommunications,2014,5.

[0014] [6] MD Losego, Grady ME, Sottos NR, et al. Effects of chemical bonding on heat transport across interfaces[J]. Nature Materials. 11, 502–506 (2012).

[0015] [7]Zheng K, Sun F, Zhu J, et al. Enhancing the Thermal Conductance of Polymer and Sapphire Interface via Self-Assembled Monolayer[J]. Acs Nano, 2016:7792. Summary of the Invention

[0016] To address the aforementioned technical problems, this invention provides a method for reducing the contact thermal resistance of thermal interface materials. This method involves grafting a silane coupling agent containing active groups onto the device surface and reacting it with the thermal interface material matrix to reduce the contact thermal resistance of the thermal interface material.

[0017] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0018] This invention provides a method for reducing the contact thermal resistance of thermal interface materials, comprising the following steps:

[0019] (1) Grafting a silane coupling agent containing active group I onto the surface of the device;

[0020] (2) Coating the thermal interface substrate containing active group II onto the surface of the device obtained in step (1);

[0021] (3) React the active group II and the active group I;

[0022] The reaction is selected from at least one of the following: mercapto-alkenyl click reaction, amidation reaction of amino and carboxyl groups, condensation reaction of amino and aldehyde groups, and addition reaction of hydroxyl and isocyanate groups.

[0023] In the technical solution of the present invention, the active group I is selected from at least one of vinyl, mercapto, amino, aldehyde, carboxyl, hydroxyl and isocyanate groups; the active group II is selected from at least one of vinyl, mercapto, amino, aldehyde, carboxyl, hydroxyl and isocyanate groups.

[0024] In the technical solution of the present invention, when the reaction is a mercapto-alkenyl click reaction, the reaction is carried out under light irradiation conditions, and the thermal interface matrix containing active group II is doped with a photocatalyst.

[0025] Preferably, the photocatalyst is selected from at least one of 2,2-dimethoxy-2-phenylacetophenone, thioxanthone, and benzophenone;

[0026] Preferably, the amount of photocatalyst is 1 to 5‰ of the mass of the thermal interface matrix, more preferably 2‰; excessive amount of photocatalyst can easily lead to small molecule residues, affecting the matrix properties of the thermal interface material.

[0027] In the technical solution of the present invention, when the reaction is amino and carboxyl amidation, the reaction is carried out under heating conditions, and the heating temperature is preferably 60°C to 120°C.

[0028] In the technical solution of the present invention, when the reaction is a condensation reaction of amino and aldehyde groups, the reaction is carried out at room temperature.

[0029] In the technical solution of the present invention, when the reaction is an addition reaction of hydroxyl and isocyanate groups, the reaction is carried out under heating conditions, and the thermal interface matrix containing active group II is doped with a catalyst.

[0030] Preferably, the heating temperature is 60℃~120℃;

[0031] Preferably, the catalyst is selected from at least one of organic tertiary amine catalysts and organometallic compound catalysts; wherein, the organic tertiary amine catalysts may include triethylenediamine, N,N-dimethylcyclohexylamine and quaternary ammonium salts, etc.; the organometallic compound catalysts may include dibutyltin dilaurate and stannous isooctanoate, etc.

[0032] Preferably, the amount of the organic tertiary amine catalyst is 0.2-1% of the mass of the thermal interface matrix, more preferably 0.5%. If the amount of catalyst is too high, it will affect the properties of the thermal interface material.

[0033] Preferably, the amount of the organometallic compound catalyst is 0.2-1% of the mass of the thermal interface matrix, more preferably 0.5%. If the amount of catalyst is too high, it will affect the properties of the thermal interface material.

[0034] As a preferred embodiment, the general structural formula of the silane coupling agent containing the active group I is shown in formula (I):

[0035]

[0036] In equation (I), m is an integer from 1 to 3, n is an integer from 1 to 21, and R 1 The active group I; R 3 Selected from any of the hydrolyzable groups; examples of hydrolyzable groups include methoxy, ethoxy, -Cl, and acetoxy; R 2 Selected from either methyl or ethyl; and in R 2 Or R 3 When multiple instances exist, they can be the same or different from each other.

[0037] In a preferred embodiment, in step (1), before grafting the silane coupling agent containing the active group I onto the surface of the device, it is necessary to perform plasma etching in an air or oxygen atmosphere to graft oxygen-containing functional groups.

[0038] In the technical solution of the present invention, the thermal interface material is selected from any one of silicone grease, silicone rubber, polyamide resin, Schiff base resin and polyurethane resin.

[0039] As a preferred embodiment, in step (2), the thermal interface matrix containing active group II can be listed as silicone oil containing active vinyl group, such as side vinyl silicone oil, single-end vinyl silicone oil, double-end vinyl silicone oil, polyamide resin containing active carboxyl group, Schiff base resin containing active aldehyde group or amino group, polyurethane resin containing active isocyanate group, etc. The above thermal interface matrix can be used alone or in any combination.

[0040] In a preferred embodiment, in step (2), the coating is selected from at least one of spin coating, vapor deposition, slot coating, scraping coating and screen printing.

[0041] The above technical solution has the following advantages or beneficial effects:

[0042] This invention provides a method for reducing the contact thermal resistance of thermal interface materials. The invention first grafts a silane coupling agent containing an active group I onto the device. Through the chemical reaction between the silane coupling agent and the thermal interface material matrix, the contact between the device and the thermal interface material is enhanced, thereby reducing the contact thermal resistance. This invention addresses the issue from the perspective of the thermal interface material matrix. Currently, the most commonly used matrix material on the market is one containing vinyl silicone oil. The contact thermal resistance is reduced through the reaction between the vinyl group and the silane coupling agent. The method provided by this invention does not require additional, deliberate modification of the thermal interface material; it relies solely on the inherent chemical groups of the material itself to achieve a chemical bond connection between the device surface and the thermal interface material. The method is simple and effective. Attached Figure Description

[0043] Figure 1 This is a thermal resistance analysis diagram of graphene-based thermal interface materials in existing technologies.

[0044] Figure 2 This is a reaction mechanism diagram in Example 1 of the present invention.

[0045] Figure 3 This is a diagram showing the water droplet angle test results in Embodiment 1 of the present invention. Detailed Implementation

[0046] The following embodiments are merely some, not all, of the embodiments of the present invention. Therefore, the detailed descriptions of the embodiments provided below are not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0047] In this invention, unless otherwise specified, all equipment and raw materials are commercially available or commonly used in the industry. The methods described in the following embodiments are conventional methods in the art, unless otherwise specified.

[0048] Example 1:

[0049] In this embodiment, to facilitate subsequent experimental characterization, aluminum is used to simulate the device, a mercapto-containing silane is used as the silane coupling agent, and vinyl silicone oil is used as the thermal interface matrix material to reduce the contact thermal resistance of the thermal interface material. Figure 2 As shown, it includes the following steps:

[0050] (1) Aluminum was sputtered onto a quartz plate by magnetron sputtering. The size of the quartz plate was 2cm*2cm*200 μm, and the thickness of the sputtered aluminum film was about 100nm. The plate was placed in a plasma generator, and the surface of the aluminum film was etched by plasma bombardment equipment. The plasma atmosphere was air, the inlet pressure was 30MPa, the plasma generator power was 750kW, and the bombardment time was 15min.

[0051] (2) Using (3-mercaptopropyl)trimethoxysilane as a silane coupling agent (structural formula shown in Formula II), ethanol, water and silane coupling agent are mixed in a mass ratio of 15:5:0.1 and stirred in a constant temperature water bath at 80°C for 5 hours to allow the silane coupling agent to be fully hydrolyzed; the aluminum film obtained in step (1) is placed in the hydrolyzed silane coupling agent solution, left to stand for 2 hours, and then dried at 120°C for half an hour to allow it to undergo a dehydration condensation reaction; finally, the ungrafted silane coupling agent on the surface is rinsed off by soaking in alcohol.

[0052]

[0053] (3) Using 2,2-dimethoxy-2-phenylacetophenone (chemical structure shown in Formula III) as a photocatalyst, vinyl silicone oil and photocatalyst were mixed at a mass ratio of 1000:2 and stirred evenly; wherein, the vinyl silicone oil was DY-V411 vinyl silicone oil (branched type) purchased from Qicaiguan, and its molecular structure is as follows: (CH3)3SiO[(CH3)2SiO] m [(CH2=CH)(CH3)SiO] n Si(CH3)3;

[0054]

[0055] (4) Spin coat the mixture obtained in step (3) onto the surface of the aluminum film obtained in step (2). During spin coating, the rotation speed is 2000 r / min, the time is 1.5 min, and the thickness of the spin coating is about 400 μm. Irradiate with ultraviolet light for 10 minutes. The ultraviolet light wavelength is 355 nm.

[0056] In this embodiment, the reaction mechanism between vinyl silicone oil and a thiol-containing silane coupling agent is as follows: Figure 2 As shown, the base is not drawn in the figure.

[0057] Effect test:

[0058] (1) Water droplet angle test

[0059] Test method: The contact angle of the droplet was measured 2 seconds after it fell using a miniature automatic angular contact measuring instrument OCA20 (Germany).

[0060] Test results are as follows Figure 3As shown: In step (1), the wettability of the unmodified aluminum film is between hydrophilic and hydrophobic; after plasma bombardment, the surface of the aluminum film becomes very hydrophilic because a large number of hydrophilic oxygen-containing groups are added to the surface; in step (2), after grafting a thiol-containing silane coupling agent on the basis of plasma modification, the hydrophilicity weakens, but it still exhibits hydrophilicity. Commonly used silane coupling agents are very hydrophobic, but the thiol-containing silane coupling agent used in this embodiment has a very strong hydrophilicity of thiol, which weakens the overall hydrophobicity of the coupling agent. Therefore, after grafting the coupling agent onto the surface of the aluminum film, the hydrophilicity weakens, but it still does not change from hydrophilic to hydrophobic.

[0061] (2) Thermal conductivity of the test interface based on TDTR

[0062] Test method: Time-domain thermoreflectance (TDTR) method, which uses a femtosecond laser to excite an extremely high instantaneous heat flux density on the material surface, thereby generating a strong thermal reflection signal. By detecting the reflection signal, temperature information is obtained, and the thermal properties of the material are fitted. It is one of the most important means to study interfacial thermal resistance.

[0063] In this embodiment, the contact thermal conductivity of three groups of samples was tested using the TDTR method:

[0064] ① The contact thermal resistance between the unmodified aluminum film (without surface treatment) and the thermal interface material;

[0065] ② The contact thermal resistance between the aluminum film grafted with silane coupling agent after plasma treatment and the thermal interface material before it has been exposed to light and reacted.

[0066] ③ The contact thermal resistance between the aluminum film grafted with silane coupling agent after plasma treatment and the thermal interface material after photo-irradiation reaction.

[0067] The TDTR method can simultaneously obtain the intrinsic thermal conductivity of the thermal interface material matrix and the interfacial contact thermal resistance between the thermal interface material matrix and the aluminum film. During the test, four different locations were measured for each sample, and the average value was taken.

[0068] Test Results: The test results for the three groups are shown in Table 1. Based on the intrinsic thermal conductivity measurements, the thermal conductivity of the three groups is almost identical, which is in line with expectations. However, there is a significant difference in interfacial thermal conductivity. After grafting the silane coupling agent, the interfacial thermal conductivity increases significantly, indicating improved interfacial thermal conductivity. Furthermore, comparing the un-illuminated and illuminated cases, the interfacial thermal conductivity is further improved after the silane coupling agent and polymer matrix form bonds, indicating that this method, compared to traditional hybrid modification, is more effective in improving interfacial heat transfer and helps to further reduce interfacial thermal resistance.

[0069] Table 1

[0070]

[0071]

[0072] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for reducing the contact thermal resistance of thermal interface materials, characterized in that, Includes the following steps: (1) Grafting a silane coupling agent containing active group I onto the surface of the device; (2) Coating the thermal interface substrate containing active group II onto the surface of the device obtained in step (1); (3) React the active group II and the active group I; The reaction is a mercapto-alkenyl click reaction; The active group I is a vinyl or mercapto group; the active group II is a mercapto or vinyl group; The reaction is carried out under light irradiation conditions, and the thermal interface matrix containing active group II is doped with a photocatalyst. Before grafting the surface of the device with a silane coupling agent containing active group I, it needs to be plasma etched in an air or oxygen atmosphere to graft oxygen-containing functional groups. The method for grafting a silane coupling agent containing an active group I is as follows: the silane coupling agent containing an active group I is fully hydrolyzed and then subjected to a dehydration condensation reaction with the surface of the device.

2. The method according to claim 1, characterized in that, The photocatalyst is selected from at least one of 2,2-dimethoxy-2-phenylacetophenone, thioxanone, and benzophenone.

3. The method according to claim 1, characterized in that, The amount of the photocatalyst used is 1 to 5‰ of the mass of the thermal interface matrix.

4. The method according to claim 3, characterized in that, The amount of the photocatalyst used is 2‰ of the mass of the thermal interface matrix.

5. The method according to claim 1, characterized in that, The general structural formula of the silane coupling agent containing the active group I is shown in formula (I): （I） In equation (I), m is an integer from 1 to 3, n is an integer from 1 to 21, and R 1 The active group I; R 3 Selected from any of the hydrolyzable groups; R 2 Selected from either methyl or ethyl; and in R 2 or R 3 When multiple instances exist, they can be the same or different from each other.

6. The method according to claim 1, characterized in that, The thermal interface material is selected from any one of silicone grease, silicone rubber, polyamide resin, Schiff base resin, and polyurethane resin.

7. The method according to claim 1, characterized in that, In step (2), the coating is selected from at least one of spin coating, vapor deposition, slot coating, scraping coating and screen printing.

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