A gallium-based liquid metal thermal interface material capable of low-temperature curing and a preparation method thereof

Abstract

The present invention discloses a gallium-based liquid metal thermal interface material capable of low-temperature solidification and a preparation method thereof, and belongs to the technical field of heat dissipation materials. The material is obtained by mixing smelted gallium-based liquid metal and a curing agent; in terms of mass percentage, the gallium-based liquid metal is 25% to 95%, and the curing agent is 5% to 75%; the gallium-based liquid metal is pure gallium, gallium-indium alloy, gallium-tin alloy, gallium-zinc alloy, gallium-indium-tin alloy, gallium-indium-zinc alloy or gallium-indium-tin-zinc alloy; the curing agent is a metal powder. The material of the present invention has a thermal conductivity much higher than that of a polymer-based thermal interface material, can greatly reduce the interface contact thermal resistance, and the material can be completely solidified after use, completely eliminating the risk of liquid metal causing short circuits in electronic devices; compared with metal-based thermal interface materials, it does not need to undergo a high-temperature welding process during use, which greatly reduces the difficulty of the material connection process. The present invention is suitable for high-power interface heat transfer applications such as high-performance computers, 5G communications, and electronic power.

Description

Technical Field

[0001] The invention relates to a thermal interface material, in particular to a gallium-based liquid metal thermal interface material capable of being cured at low temperature and a preparation method thereof, belonging to the technical field of heat dissipation materials. Background Art

[0002] The development trend of electronic systems today is miniaturization and high performance, which has caused a sharp increase in the thermal design power consumption of integrated circuits, seriously affecting the operating performance and service reliability of electronic devices. How to properly solve the heat dissipation problem of electronic devices has become increasingly important. The heat dissipation of high-end electronic devices usually adopts the method of adding a heat sink. Although the chip and the heat sink surface seem to be in full contact, the actual interface is composed of many point contacts surrounded by air gaps. Air is a poor conductor of heat, resulting in the heat sink's effectiveness being less than 30%. The material used to coat between the heating unit and the heat dissipation device to remove the interface air and improve the heat dissipation efficiency is called "thermal interface material".

[0003] Mainstream thermal interface materials are divided into two categories: one is polymer-based materials, represented by thermal grease, thermal gel, thermal pads, and phase change materials. These materials are easy to use and inexpensive, but have poor thermal conductivity; the other is metal-based materials, represented by low-melting-point solders. They have excellent thermal conductivity, but require high-temperature welding when used, and have disadvantages such as high welding temperature, flux residue, or hole defects. Therefore, commercial thermal interface materials are increasingly unable to meet the needs of high-power interface heat transfer in the field of microelectronics.

[0004] Gallium-based liquid metal has a much higher thermal conductivity than polymer-based materials, and compared with low-melting-point solder, liquid metal does not need to go through a high-temperature welding process when used, which greatly reduces the difficulty of the material connection process and is a potential ideal thermal interface material. However, the fluidity of gallium-based liquid metal is too strong, which can easily cause short circuits in electronic devices, seriously affecting its promotion and application in the field of microelectronics. Existing technologies usually use micro-powder doping technology to modulate liquid metal into a paste-like substance, or use polymer composite technology to constrain liquid metal. These measures can reduce the fluidity of liquid metal, but because the liquid metal is still in a fluid state, it is difficult to fundamentally eliminate the risk of liquid metal causing short circuits in electronic devices.

[0005] Chinese invention patent application 201710686955.0 discloses a liquid metal thermal conductive sheet and its preparation method, wherein the preparation method of the liquid metal thermal conductive sheet is: first prepare liquid metal, mix the liquid metal with polydimethylsiloxane PDMS; then add PDMS curing agent to cure and shape, to obtain a formed liquid metal-PDMS mixture; after stretching and cutting, obtain a thermal conductive sheet. In this technology, the thermal conductive sheet uses a polymer material as a matrix, and the thermal conductivity generally does not exceed 10W / (m·K), so this technology is not suitable for application scenarios with high heat generation, such as top-level CPUs, electric vehicle IGBT modules, etc.; moreover, in extreme cases, if the material breaks, the internal liquid metal still has the risk of overflow, which can easily lead to major problems such as short circuits in electronic components.

[0006] Chinese invention patent application CN202110178186.X discloses a liquid metal composite thermal interface material capable of low-temperature curing and a preparation method, wherein the low-temperature curing thermal interface material comprises liquid metal, a coupling agent, a toughening agent, an epoxy resin and a curing agent. A thermal conductive paste is made by filling surface-treated liquid metal micro-nano droplets and a toughening agent into an epoxy resin matrix, and a curing agent is added to make a liquid metal thermal conductive gasket capable of low-temperature curing. This technology is mainly used to solve the problem of heat transfer under liquid immersion. Due to the needs of special working environments, this technology uses epoxy resin as a matrix to make the thermal interface material have strong viscosity, but the thermal conductivity of thermal interface materials based on epoxy resin will be much lower than that of thermal interface materials based on metal. In extreme cases, such as material rupture, the liquid metal inside the solid material still has the risk of overflow. Summary of the invention

[0007] In view of the problems existing in the above-mentioned prior art, the present invention provides a gallium-based liquid metal thermal interface material capable of low-temperature curing and a preparation method thereof, which can completely eliminate the risk of short circuit of electronic devices caused by liquid metal.

[0008] In order to achieve the above-mentioned invention object, the present invention adopts the following technical solutions:

[0009] A gallium-based liquid metal thermal interface material capable of low-temperature solidification is obtained by mixing smelted gallium-based liquid metal and a solidifying agent; in terms of mass percentage, the gallium-based liquid metal is 25% to 95%, the solidifying agent is 5% to 75%, and the sum of the mass fractions of the two is 100%; the gallium-based liquid metal is pure gallium, gallium-indium alloy, gallium-tin alloy, gallium-zinc alloy, gallium-indium-tin alloy, gallium-indium-zinc alloy or gallium-indium-tin-zinc alloy; the solidifying agent is metal powder; the particle size of the metal powder is 0.1 to 100 μm; the metal is copper, nickel, iron, silver, copper alloy, nickel alloy, iron alloy or silver alloy.

[0010] To further achieve the purpose of the present invention, preferably, the copper alloy is an alloy with copper as a main component and one or more of zinc, tin and nickel.

[0011] Preferably, the nickel alloy is an alloy with nickel as a main component and one or more of manganese, copper, chromium, iron and silicon.

[0012] Preferably, the ferroalloy is an alloy with iron as a main component and one or more of chromium, silicon, molybdenum, nickel, manganese and boron.

[0013] Preferably, the silver alloy is an alloy with silver as a main component and one or more of tin, copper and indium.

[0014] Preferably, the smelting temperature is 50-120° C., and the smelting time is 0.1-1 h.

[0015] Preferably, the curing agent is pre-treated by degreasing, pickling, cleaning and drying before use.

[0016] Preferably, the pretreatment comprises the following steps:

[0017] (1) Chemical degreasing with NaOH solution, controlling the temperature to 20-80°C and the time to 10-60 min;

[0018] (2) Deionized water cleaning, the control time is 1 to 5 minutes;

[0019] (3) Use dilute sulfuric acid to remove rust at room temperature, and control the time to be 5 to 30 minutes;

[0020] (4) Deionized water cleaning, the control time is 1 to 5 minutes;

[0021] (5) Cleaning with anhydrous ethanol, the control time is 1 to 5 minutes;

[0022] (6) Vacuum drying at a temperature of 100 to 150° C. for a controlled time of 10 to 60 minutes.

[0023] Preferably, the concentration of the NaOH solution is 10-40 g / L; the concentration of the dilute sulfuric acid is 10-20 wt%.

[0024] The method for preparing a gallium-based liquid metal thermal interface material capable of low temperature curing comprises the following steps:

[0025] (1) Smelting to obtain gallium-based liquid metal;

[0026] (2) Pre-treating the curing agent surface;

[0027] (3) Adding a curing agent to the gallium-based liquid metal, stirring the mixture in a vacuum or protective gas environment, and obtaining a gallium-based liquid metal thermal interface material that can be cured at a low temperature.

[0028] Preferably, the stirring speed is 30 to 3000 rpm, and the stirring time is 0.1 to 100 min.

[0029] In the present invention, "degreasing, pickling, cleaning and drying" are conventional metal surface treatment methods, and only the concentrations of NaOH solution and dilute sulfuric acid used and related process conditions are slightly different for different metal materials.

[0030] The gallium-based liquid metal in the present invention includes gallium and an alloy of gallium with one or more of indium, tin and zinc; wherein the melting point of gallium is 29.7°C. Although the melting points of other metals are higher than 120°C, such as the melting point of indium is 156.5°C, the melting point of tin is 231.9°C, and the melting point of zinc is 419.5°C, they can still be dissolved in metallic gallium under a melting temperature of 50 to 120°C.

[0031] The gallium-based liquid metal thermal interface material capable of low temperature curing in the present invention is in liquid state when used. After implementation, it is cured after standing for a period of time. Therefore, the gallium-based liquid metal thermal interface material must be used before the material is cured.

[0032] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0033] (1) The present invention utilizes metal or alloy powders such as copper to solidify liquid metal, and the liquid metal can be completely converted into a solid intermetallic compound, effectively avoiding the problem in the prior art that the liquid metal still exists in a liquid form inside the thermal interface material, and can solve the problem of liquid metal overflow caused by the rupture of the sealing material, and completely eliminate the risk of liquid metal causing short circuits in electronic devices.

[0034] (2) The thermal conductivity of the thermal interface material obtained by the present invention is as high as about 100 W / (m·K), which is much higher than the thermal conductivity of mainstream polymer-based thermal interface materials. It can greatly reduce the interface contact thermal resistance and effectively improve the heat dissipation efficiency of the electronic system.

[0035] (3) Compared with traditional low melting point solders, the thermal interface material obtained by the present invention does not need to undergo a high temperature welding process when in use, which greatly reduces the difficulty of the material connection process.

[0036] (4) Since the thermal interface material obtained by the present invention has high thermal conductivity and fully cured performance, the material of the present invention has broad application prospects in high-power semiconductor devices in the fields of high-performance computers, 5G communications, and electronic power. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 A preparation flow chart of a gallium-based liquid metal thermal interface material capable of low-temperature curing provided by the present invention;

[0038] Figure 2 This is a photo of the material before curing in Example 1;

[0039] Figure 3 This is a photo of the “copper sheet-liquid metal-copper sheet” overlap sample after the material solidified in Example 1;

[0040] Figure 4 This is a microstructure image of the material obtained in Example 1 after curing at 60°C for 36 hours, taken under a scanning electron microscope at 500 times magnification. At the same time, appropriate positions were selected in the photo to perform energy spectrum (EDS) point analysis and surface scanning analysis;

[0041] Figure 5 The results of EDS element point analysis of the material obtained in Example 1 after curing at 60°C for 36 hours;

[0042] Figure 6 This is the total distribution diagram of copper, gallium, indium and tin elements obtained by EDS surface scanning analysis after the material obtained in Example 1 was cured at 60°C for 36 hours;

[0043] Figure 7 This is the copper element distribution diagram obtained by EDS surface scanning analysis after the material obtained in Example 1 was cured at 60° C. for 36 hours;

[0044] Figure 8 This is the gallium element distribution diagram obtained by EDS surface scanning analysis after the material obtained in Example 1 was cured at 60° C. for 36 hours;

[0045] Fig. 9 This is the indium element distribution diagram obtained by EDS surface scanning analysis after the material obtained in Example 1 was cured at 60° C. for 36 hours;

[0046] Fig.10 This is the distribution diagram of tin element obtained by EDS surface scanning analysis after the material obtained in Example 1 was cured at 60° C. for 36 hours;

[0047] Fig.11 This is a schematic diagram of a “copper sheet-liquid metal-copper sheet” overlap sample after the material is solidified in Example 1;

[0048] Fig.12 The shear strength test results of the overlapped samples obtained in Example 1 at different curing times at curing temperatures of 20°C and 60°C are shown. DETAILED DESCRIPTION

[0049] The content of the present invention is further described below through the drawings and embodiments. These embodiments are only used to illustrate the present invention, but not to limit the present invention.

[0050] In the embodiments of the present invention, the copper alloy powder is taken as brass (copper-zinc alloy), the silver alloy powder is taken as Ag43 (brand), and the iron alloy powder is taken as Fe90 (brand).

[0051] Example 1

[0052] Figure 1 A method for preparing a gallium-based liquid metal thermal interface material capable of low-temperature curing comprises the following steps:

[0053] Step 1, using a precision electronic balance to weigh 68.5g of gallium, 21.5g of indium, and 10g of tin, and put them into a crucible in sequence, and then placing the crucible in a heating furnace to melt the gallium-based liquid metal, the furnace temperature is set to 120°C, the heating time is 1h, during which the mixture is stirred once every 15min using a glass rod, and the gallium-based liquid metal is melted to obtain the gallium-based liquid metal, and the gallium-based liquid metal is cooled to room temperature for use;

[0054] Step 2: Use pure copper metal powder (particle size of about 20 μm) as a curing agent and perform surface pretreatment on the metal powder according to the following steps:

[0055] (1) Chemical degreasing with 40 g / L NaOH solution, temperature 80 °C, time 60 min;

[0056] (2) Deionized water washing, time 5min;

[0057] (3) rust removal with 20wt% dilute sulfuric acid, room temperature, time 30min;

[0058] (4) Wash with deionized water for 5 min;

[0059] (5) Cleaning with anhydrous ethanol for 5 min;

[0060] (6) Vacuum drying at 150°C for 60 min.

[0061] Step 3, using a precision electronic balance to weigh 20g of gallium-based liquid metal and 20g of curing agent, put them into a stirring cup, and then load the stirring cup into a planetary high-speed mixer, set the stirring speed to 2000r / min, the stirring time to 15min, and use a mechanical pump to create a vacuum environment (vacuum degree less than 100Pa) to prevent material oxidation and the formation of pores inside during stirring, and then fully stir the mixture to finally obtain a gallium-based liquid metal thermal interface material that can be cured at low temperature.

[0062] Figure 2 This is a photo of the material in Example 1 before solidification. It can be seen that the material has good fluidity before solidification.

[0063] Figure 3This is a photo of the "copper sheet-liquid metal-copper sheet" overlap sample after the material solidified in Example 1. The overlap sample is made by coating the gallium-based liquid metal thermal interface material between two copper sheets, then overlapping the two copper sheets, standing at 60°C for 36 hours, and waiting for the material to be completely solidified. After the material is solidified, the two copper sheets are connected together and can lift a bucket weighing 20kg, which reflects that the material has been completely solidified.

[0064] Figure 4 This is a backscattered image (500 times) of the material obtained in Example 1, which was cured at 60°C for 36 hours and then polished. Based on the color contrast difference, it can be judged that there are three substances inside the material after curing: copper particles, copper-gallium intermetallic compounds, and residual gallium-indium-tin alloy. In order to further determine the composition of these substances, EDS point analysis and surface scanning technology were used for testing. The EDS test results are shown in Figures 5 to 10 .

[0065] Figure 5 The EDS point analysis results of the material obtained in Example 1 ( Figure 4 The results show that the point analysis position is residual gallium-indium-tin alloy, in which the indium and tin contents are high and the gallium content is low. According to the gallium-indium-tin ternary phase diagram, the material is determined to be solid at room temperature.

[0066] Figure 6 The summary diagram of all elements in the EDS surface scanning results of the material obtained in Example 1 (for Figure 4 The dark grey circular substance contains only copper, which confirms that the substance is copper particles; the light grey substance contains only copper and gallium, which confirms that the substance is a copper-gallium intermetallic compound; the milky white substance contains indium, tin and a small amount of gallium, which confirms that the substance is a residual gallium-indium-tin alloy.

[0067] Figure 7 The distribution diagram of copper element in the EDS surface scanning result of the material obtained in Example 1. Figure 8 The distribution of gallium in the liquid metal matrix is ​​consistent, proving that most of the gallium in the liquid metal matrix reacts with copper to form copper-gallium intermetallic compounds, which are solid at room temperature.

[0068] Fig. 9 The distribution diagram of indium element in the EDS surface scanning result of the material obtained in Example 1. Fig.10 The distribution of tin element in the alloy is consistent, which proves that the main components of the residual gallium indium tin alloy are indium and tin elements, and the material is in a solid state at room temperature.

[0069] Fig.11Schematic diagram of the "copper sheet-liquid metal-copper sheet" overlap sample after the material is cured in Example 1. The sample is cured at 20°C and 60°C for 0 to 192 hours, and then the shear strength of the material is tested using a universal electronic mechanical testing machine with reference to the ASTM D5379 test standard. The test results are as follows: Fig.12 As shown. It can be seen that under 60℃, the material has a strength of 1MPa after 2h of curing, indicating that the material has gradually transformed from a paste to a solid state. As time goes by, the strength gradually increases, indicating that the material is gradually tending to be completely cured; under 20℃, the curing speed of the material is slower than 60℃, but the shear strength of the material reaches 1MPa at 24h, indicating that the material has gradually transformed from a paste to a solid state, and as time goes by, the strength gradually increases. After 192h, the strength is consistent with the highest strength of the 60℃ cured sample, indicating that the material can eventually be completely cured without heating and placed at room temperature.

[0070] Referring to the ASTM D5470 test standard, the thermal conductivity of the material cured at 60°C for 36 hours was measured using a thermal conductivity tester. After testing, the thermal conductivity of the material obtained in Example 1 was 101.5 W / (m·K). In addition, under this curing condition, the shear strength of the material obtained in this example was 7.0 MPa.

[0071] The testing methods for shear strength and thermal conductivity of the materials obtained in the following examples are the same as those in Example 1.

[0072] Example 2

[0073] like Figure 1 As shown, a method for preparing a gallium-based liquid metal thermal interface material capable of low temperature curing comprises the following steps:

[0074] Step 1, using a precision electronic balance to weigh 68.5 g of gallium and 21.5 g of indium, and put them into a crucible in turn, and then placing the crucible in a heating furnace to melt the gallium-based liquid metal, the furnace temperature is set to 120° C., the heating time is 1 hour, and the mixture is stirred once every 15 minutes using a glass rod to melt the gallium-based liquid metal, and the gallium-based liquid metal is cooled and set aside;

[0075] Step 2, using brass (particle size 10 μm) as a curing agent, the alloy powder is subjected to surface pretreatment according to the following steps:

[0076] (1) Chemical degreasing with 10 g / L NaOH solution, temperature 20 °C, time 10 min;

[0077] (2) Deionized water washing, time 1 min;

[0078] (3) rust removal with 10 wt% dilute sulfuric acid, room temperature, time 5 min;

[0079] (4) Wash with deionized water for 1 min;

[0080] (5) Cleaning with anhydrous ethanol for 1 min;

[0081] (6) Vacuum drying at 100°C for 10 min.

[0082] Step 3, using a precision electronic balance to weigh 20g of gallium-based liquid metal and 20g of curing agent, put them into a stirring cup in sequence, then load the stirring cup into a planetary high-speed mixer, set the stirring speed to 2000r / min, the stirring time to 15min, use a mechanical pump to create a vacuum environment, and then fully stir the mixture to finally obtain a gallium-based liquid metal thermal interface material that can be cured at low temperature.

[0083] The gallium-based liquid metal thermal interface material was applied between two copper sheets, and then the two copper sheets were overlapped to prepare a "copper sheet-liquid metal-copper sheet" sandwich structure sample, which was left at 60°C for 36 hours to wait for the material to fully solidify. The shear strength of the material was tested using a universal electronic mechanical testing machine in accordance with the ASTM D5379 test standard; the thermal conductivity of the material was measured using a thermal conductivity tester in accordance with the ASTM D5470 test standard.

[0084] The main difference between this embodiment and embodiment 1 is that the gallium-based liquid metal in this embodiment is changed from gallium-indium-tin alloy to gallium-indium alloy, the curing agent is changed from pure copper powder (particle size 20 μm) to copper alloy powder (brass, copper-zinc alloy, particle size 10 μm), and the curing agent surface pretreatment parameters are changed appropriately. After testing, the shear strength of the material obtained in this embodiment is 13.6 MPa, and the thermal conductivity is 58.4 W / (m·K).

[0085] Example 3

[0086] like Figure 1 As shown, a method for preparing a gallium-based liquid metal thermal interface material capable of low temperature curing comprises the following steps:

[0087] Step 1, using a precision electronic balance to weigh 68.5g of gallium and 10g of tin, and put them into a crucible in turn, and then placing the crucible in a heating furnace to melt the gallium-based liquid metal, the furnace temperature is set to 120°C, the heating time is 1h, during which the mixture is stirred once every 15min with a glass rod, and the gallium-based liquid metal is melted to obtain the gallium-based liquid metal, which is cooled and set aside;

[0088] Step 2: Using Ag43 silver alloy powder (particle size 10 μm) as a curing agent, the alloy powder is subjected to surface pretreatment according to the following steps:

[0089] (1) Chemical degreasing with 20 g / L NaOH solution, temperature 50 °C, time 30 min;

[0090] (2) Deionized water washing, time 2min;

[0091] (3) rust removal with 15 wt% dilute sulfuric acid, room temperature, time 20 min;

[0092] (4) Wash with deionized water for 2 min;

[0093] (5) Cleaning with anhydrous ethanol for 2 min;

[0094] (6) Vacuum drying at 120°C for 30 min.

[0095] Step 3, using a precision electronic balance to weigh 20g of gallium-based liquid metal and 20g of curing agent, put them into a stirring cup in sequence, then load the stirring cup into a planetary high-speed mixer, set the stirring speed to 2000r / min, the stirring time to 15min, use a mechanical pump to create a vacuum environment, and then fully stir the mixture to finally obtain a gallium-based liquid metal thermal interface material that can be cured at low temperature.

[0096] Gallium-based liquid metal thermal interface material was coated between two copper sheets to prepare a "copper sheet-liquid metal-copper sheet" sandwich structure sample, which was left at 60°C for 36 hours to wait for the material to fully solidify. The shear strength of the material was tested using a universal electronic mechanical testing machine in accordance with the ASTM D5379 test standard; the thermal conductivity of the material was measured using a thermal conductivity tester in accordance with the ASTM D5470 test standard.

[0097] The main differences between this embodiment and embodiment 1 are that the gallium-based liquid metal in this embodiment is changed from gallium-indium-tin alloy to gallium-tin alloy, and the curing agent is changed from pure copper powder (particle size 20 μm) to silver alloy powder (grade Ag43, Ag 43 Cu 25 Sn 31 Zn1, particle size 10 μm), and the curing agent surface pretreatment parameters are changed appropriately. According to the test, the shear strength of the material obtained in this embodiment is 10.2 MPa, and the thermal conductivity is 70.2 W / (m·K).

[0098] Example 4

[0099] like Figure 1 As shown, a method for preparing a gallium-based liquid metal thermal interface material capable of low temperature curing comprises the following steps:

[0100] Step 1, using a precision electronic balance to weigh 68.5 g of gallium and 10 g of zinc, and put them into a crucible in turn, and then placing the crucible in a heating furnace to melt the gallium-based liquid metal, the furnace temperature is set to 50° C., the heating time is 0.1 h, and the mixture is stirred once every 15 min using a glass rod to melt the gallium-based liquid metal, and the gallium-based liquid metal is cooled and set aside;

[0101] Step 2: Using Fe90 ferroalloy powder (particle size 10 μm) as a curing agent, the alloy powder is subjected to surface pretreatment according to the following steps:

[0102] (1) Chemical degreasing with 40 g / L NaOH solution, temperature 80 °C, time 60 min;

[0103] (2) Deionized water washing, time 5min;

[0104] (3) rust removal with 20wt% dilute sulfuric acid, room temperature, time 30min;

[0105] (4) Wash with deionized water for 5 min;

[0106] (5) Cleaning with anhydrous ethanol for 5 min;

[0107] (6) Vacuum drying at 150°C for 60 min.

[0108] Step 3, using a precision electronic balance to weigh 20g of gallium-based liquid metal and 20g of curing agent, put them into a stirring cup in sequence, then load the stirring cup into a planetary high-speed mixer, set the stirring speed to 2000r / min, the stirring time to 15min, use a mechanical pump to create a vacuum environment, and then fully stir the mixture to finally obtain a gallium-based liquid metal thermal interface material that can be cured at low temperature.

[0109] Gallium-based liquid metal thermal interface material was coated between two copper sheets to prepare a "copper sheet-liquid metal-copper sheet" sandwich structure sample, which was left at 60°C for 36 hours to wait for the material to fully solidify. The shear strength of the material was tested using a universal electronic mechanical testing machine in accordance with the ASTM D5379 test standard; the thermal conductivity of the material was measured using a thermal conductivity tester in accordance with the ASTM D5470 test standard.

[0110] The main differences between this embodiment and embodiment 1 are: the gallium-based liquid metal in this embodiment is changed from gallium-indium-tin alloy to gallium-zinc alloy, the curing agent is changed from pure copper powder (particle size 20 μm) to iron alloy powder (grade Fe90, iron-carbon-chromium-silicon-boron alloy, particle size 10 μm), and the liquid metal smelting parameters are changed appropriately. After testing, the shear strength of the material obtained in this embodiment is 24.5 MPa, and the thermal conductivity is 105.5 W / (m·K).

[0111] Example 5

[0112] like Figure 1 As shown, a method for preparing a gallium-based liquid metal thermal interface material capable of low temperature curing comprises the following steps:

[0113] Step 1, using a precision electronic balance to weigh 68.5 g of gallium, 21.5 g of indium, and 10 g of tin, and put them into a crucible in sequence, and then placing the crucible in a heating furnace to melt the gallium-based liquid metal, the furnace temperature is set to 80° C., the heating time is 0.5 h, and the mixture is stirred once every 15 min using a glass rod to melt the gallium-based liquid metal, and the gallium-based liquid metal is cooled for standby use;

[0114] Step 2: Using pure copper metal powder (particle size 20 μm) as a curing agent, the metal powder is pretreated on the surface according to the following steps:

[0115] (1) Chemical degreasing with 40 g / L NaOH solution, temperature 80 °C, time 60 min;

[0116] (2) Deionized water washing, time 5min;

[0117] (3) rust removal with 20wt% dilute sulfuric acid, room temperature, time 30min;

[0118] (4) Wash with deionized water for 5 min;

[0119] (5) Cleaning with anhydrous ethanol for 5 min;

[0120] (6) Vacuum drying at 150°C for 60 min.

[0121] Step 3, using a precision electronic balance to weigh 20g of gallium-based liquid metal and 10g of curing agent, put them into a stirring cup in sequence, then load the stirring cup into a planetary high-speed mixer, set the stirring speed to 100r / min, the stirring time to 60min, use a mechanical pump to create a vacuum environment, and then fully stir the mixture to finally obtain a gallium-based liquid metal thermal interface material that can be cured at low temperature.

[0122] Gallium-based liquid metal thermal interface material was coated between two copper sheets to prepare a "copper sheet-liquid metal-copper sheet" sandwich structure sample, which was left at 60°C for 36 hours to wait for the material to fully solidify. The shear strength of the material was tested using a universal electronic mechanical testing machine in accordance with the ASTM D5379 test standard; the thermal conductivity of the material was measured using a thermal conductivity tester in accordance with the ASTM D5470 test standard.

[0123] The main differences between this embodiment and embodiment 1 are: the ratio of gallium-based liquid metal and curing agent is changed from 1:1 to 2:1; the mixing process parameters are changed, the stirring speed is changed from 2000r / min to 100r / min, the stirring time is changed from 15min to 60min, and the liquid metal smelting parameters are changed appropriately. After testing, the shear strength of the material obtained in this embodiment is 12.6MPa, and the thermal conductivity is 80.7W / (m·K).

[0124] Example 6

[0125] like Figure 1 As shown, a method for preparing a gallium-based liquid metal thermal interface material capable of low temperature curing comprises the following steps:

[0126] Step 1, using a precision electronic balance to weigh 68.5g of gallium, 21.5g of indium, and 10g of tin, and put them into a crucible in sequence, and then placing the crucible in a heating furnace to melt the gallium-based liquid metal, the furnace temperature is set to 120°C, the heating time is 1h, during which the mixture is stirred once every 15min with a glass rod, and the gallium-based liquid metal is melted to obtain the gallium-based liquid metal, which is cooled and set aside;

[0127] Step 2: Using pure copper metal powder (particle size 20 μm) as a curing agent, the metal powder is pretreated on the surface according to the following steps:

[0128] (1) Chemical degreasing with 40 g / L NaOH solution, temperature 80 °C, time 60 min;

[0129] (2) Deionized water washing, time 5min;

[0130] (3) rust removal with 20wt% dilute sulfuric acid, room temperature, time 30min;

[0131] (4) Wash with deionized water for 5 min;

[0132] (5) Cleaning with anhydrous ethanol for 5 min;

[0133] (6) Vacuum drying at 150°C for 60 min.

[0134] Step 3, using a precision electronic balance to weigh 20g of gallium-based liquid metal and 5g of curing agent, put them into a stirring cup in sequence, then load the stirring cup into a planetary high-speed mixer, set the stirring speed to 2000r / min, the stirring time to 15min, use a mechanical pump to create a vacuum environment, and then fully stir the mixture to finally obtain a gallium-based liquid metal thermal interface material that can be cured at low temperature.

[0135] Gallium-based liquid metal thermal interface material was coated between two copper sheets to prepare a "copper sheet-liquid metal-copper sheet" sandwich structure sample, which was left at room temperature for 96 hours to wait for the material to fully solidify. The shear strength of the material was tested using a universal electronic mechanical testing machine in accordance with the ASTM D5379 test standard; the thermal conductivity of the material was measured using a thermal conductivity tester in accordance with the ASTM D5470 test standard.

[0136] The main differences between this embodiment and embodiment 1 are: the ratio of gallium-based liquid metal to curing agent is changed from 1:1 to 4:1; the curing conditions are changed from 60°C / 36h to room temperature / 96h. After testing, the shear strength of the material obtained in this embodiment is 15.6MPa, and the thermal conductivity is 94.8W / (m·K).

[0137] Example 7

[0138] like Figure 1 As shown, a method for preparing a gallium-based liquid metal thermal interface material capable of low temperature curing comprises the following steps:

[0139] Step 1, using a precision electronic balance to weigh 68.5g of gallium, 21.5g of indium, and 10g of tin, and put them into a crucible in sequence, and then placing the crucible in a heating furnace to melt the gallium-based liquid metal, the furnace temperature is set to 120°C, the heating time is 1h, during which the mixture is stirred once every 15min with a glass rod, and the gallium-based liquid metal is melted to obtain the gallium-based liquid metal, which is cooled and set aside;

[0140] Step 2: Using pure copper metal powder (particle size 20 μm) as a curing agent, the metal powder is pretreated on the surface according to the following steps:

[0141] (1) Chemical degreasing with 40 g / L NaOH solution, temperature 80 °C, time 60 min;

[0142] (2) Deionized water washing, time 5min;

[0143] (3) rust removal with 20wt% dilute sulfuric acid, room temperature, time 30min;

[0144] (4) Wash with deionized water for 5 min;

[0145] (5) Cleaning with anhydrous ethanol for 5 min;

[0146] (6) Vacuum drying at 150°C for 60 min.

[0147] Step 3, using a precision electronic balance to weigh 20g of gallium-based liquid metal and 20g of curing agent, put them into a stirring cup in sequence, then load the stirring cup into a planetary high-speed mixer, set the stirring speed to 100r / min, the stirring time to 60min, use a mechanical pump to create a vacuum environment, and then fully stir the mixture to finally obtain a gallium-based liquid metal thermal interface material that can be cured at low temperature.

[0148] Gallium-based liquid metal thermal interface material was coated between two copper sheets to prepare a "copper sheet-liquid metal-copper sheet" sandwich structure sample, which was left at room temperature for 96 hours to wait for the material to fully solidify. The shear strength of the material was tested using a universal electronic mechanical testing machine in accordance with the ASTM D5379 test standard; the thermal conductivity of the material was measured using a thermal conductivity tester in accordance with the ASTM D5470 test standard.

[0149] The main differences between this embodiment and embodiment 1 are: the mixing process parameters are changed, the stirring speed is changed from 2000r / min to 100r / min, the stirring time is changed from 15min to 60min; the curing conditions are changed from 60℃ / 36h to room temperature / 96h. After testing, the shear strength of the material obtained in this embodiment is 18.2MPa, and the thermal conductivity is 88.7W / (m·K).

[0150] Comparison example

[0151] The commercially available Shin-Etsu 7921 thermal grease was coated between two copper sheets to make a "copper sheet-thermal grease-copper sheet" sandwich structure sample. Referring to the ASTM D5470 test standard, a thermal conductivity tester was used to measure the thermal conductivity of the material. The test showed that the thermal conductivity of the material was 5W / (m·K).

[0152] The test results of thermal conductivity and shear strength performance of the materials of the embodiment and the control example are shown in Table 1. By comparison, it is found that the material involved in the present invention has a thermal conductivity much higher than that of the polymer-based thermal interface material, which can greatly reduce the interface contact thermal resistance and effectively improve the heat dissipation efficiency of the electronic system.

[0153] Table 1

[0154]

[0155] Thermally conductive silicone grease represented by Shin-Etsu 7921 silicone grease is one of the most common thermal interface materials. It is widely used in the heat dissipation of computer chips due to its universality and convenience. However, despite the many studies and improvements on polymer-based thermal interface materials by researchers in recent years, there is still no substantial improvement in its thermal conductivity, which is only about 5W / (m·K). The present invention proposes a gallium-based liquid metal thermal interface material that can be cured at low temperature. Since liquid metal is used as the matrix, the thermal conductivity of the thermal interface material obtained by the present invention can reach about 100W / (m·K). Under the same conditions, the temperature difference between the chip and the radiator can be greatly reduced, thereby achieving the purpose of improving the heat dissipation efficiency.

[0156] The application method of the present invention is similar to thermal grease, which is applied evenly on the outer surface of the heat source using tools such as scrapers and screens, and then the heat sink is pressed on it and pressure is applied. There are only two points to note when applying the material of the present invention: first, apply it within the material's operable time to avoid curing and resulting in failure to apply; second, control the material to be evenly applied, and control the coating thickness of the thermal interface material to about 100μm.

[0157] Chinese invention patent application 201710686955.0 has achieved the purpose of limiting the overflow of liquid metal, but the invention uses polymer-based materials to constrain liquid metal, and the general thermal conductivity of polymer-based materials does not exceed 10W / (m·K), so this technology is not suitable for application scenarios with huge heat generation, such as top-level CPUs, electric vehicle IGBT modules, etc. The present invention uses metal or alloy powders such as copper to solidify liquid metal, and the thermal conductivity of the resulting thermal interface material is as high as about 100W / (m·K), which can be adapted to the above application scenarios; in addition, in Chinese invention patent application 201710686955.0, the liquid metal still exists in the form of liquid inside the thermal interface material. In extreme cases, such as material rupture, the liquid metal still has the risk of overflow, which may cause major problems such as circuit short circuits.

[0158] The technical problem to be solved by the Chinese invention patent application CN202110178186.X is mainly the heat transfer problem in the liquid immersion state. Due to the needs of the special working environment, this technology uses epoxy resin as the matrix, which makes the thermal interface material have strong viscosity, but the thermal conductivity of the thermal interface material based on epoxy resin is much lower than that of the thermal interface material based on metal; and there is also the risk of liquid metal overflow inside the solid material, which may cause major problems such as circuit short circuit once overflowed. In the present invention, the liquid metal has been completely converted into a solid copper-gallium intermetallic compound. After the material is completely solidified, there is no liquid metal inside, and the safety is fundamentally guaranteed.

Claims

1. A gallium-based liquid metal thermal interface material capable of low temperature curing, characterized in that: The gallium-based liquid metal and the curing agent are stirred and mixed in a vacuum environment after smelting; in terms of mass percentage, the gallium-based liquid metal is 50% to 80%, and the curing agent is 20% to 50%; the gallium-based liquid metal is pure gallium, gallium-indium alloy, gallium-tin alloy, gallium-zinc alloy, gallium-indium-tin alloy, gallium-indium-zinc alloy or gallium-indium-tin-zinc alloy; the curing agent is metal powder; the particle size of the metal powder is 0.1 to 100 μm; the metal is copper, nickel, iron, silver, copper alloy, nickel alloy, iron alloy or silver alloy; the low-temperature curing refers to standing at 60°C for 36 hours or standing at room temperature for 96 hours to achieve complete curing.

2. The gallium-based liquid metal thermal interface material capable of low temperature curing according to claim 1, characterized in that: The copper alloy is an alloy composed of copper as a main component and one or more of zinc, tin and nickel.

3. The gallium-based liquid metal thermal interface material capable of low temperature curing according to claim 1, characterized in that: The nickel alloy is an alloy composed of nickel as a main component and one or more of manganese, copper, chromium, iron and silicon.

4. The gallium-based liquid metal thermal interface material capable of low temperature curing according to claim 1, characterized in that: The ferroalloy is an alloy composed mainly of iron and one or more of chromium, silicon, molybdenum, nickel, manganese and boron.

5. The gallium-based liquid metal thermal interface material capable of low temperature curing according to claim 1, characterized in that: The silver alloy powder is an alloy composed of silver as a main component and one or more of tin, copper and indium.

6. The gallium-based liquid metal thermal interface material capable of low temperature curing according to claim 1, characterized in that: The melting temperature is 50-120°C, and the melting time is 0.1-1h; the curing agent is pre-treated by degreasing, pickling, cleaning and drying before use.

7. The gallium-based liquid metal thermal interface material capable of low temperature curing according to claim 6, characterized in that: The pretreatment comprises the following steps: (1) Chemical degreasing with NaOH solution, controlling the temperature to 20-80°C and the time to 10-60 min; (2) Deionized water cleaning, the control time is 1 to 5 minutes; (3) Use dilute sulfuric acid to remove rust at room temperature, and control the time to be 5 to 30 minutes; (4) Deionized water cleaning, the control time is 1 to 5 minutes; (5) Cleaning with anhydrous ethanol, the control time is 1 to 5 minutes; (6) Vacuum drying at a temperature of 100 to 150° C. for a controlled time of 10 to 60 minutes.

8. The gallium-based liquid metal thermal interface material capable of low temperature curing according to claim 7, characterized in that: The concentration of the NaOH solution is 10-40 g / L; the concentration of the dilute sulfuric acid is 10-20 wt%.

9. A method for preparing a gallium-based liquid metal thermal interface material capable of low temperature curing according to any one of claims 1 to 8, characterized in that The following steps are involved: (1) Smelting to obtain gallium-based liquid metal; (2) Pre-treating the curing agent surface; (3) Adding a curing agent to the gallium-based liquid metal, stirring the mixture in a vacuum environment, and obtaining a gallium-based liquid metal thermal interface material that can be cured at a low temperature.

10. The method for preparing a gallium-based liquid metal thermal interface material capable of low temperature curing according to claim 9, characterized in that: The stirring speed is 30-3000 rpm, and the stirring time is 0.1-100 min.

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