A high thermal conductivity porous thermal interface material that is easy to construct and a manufacturing method thereof

Abstract

The present invention discloses a highly thermally conductive porous thermal interface material that is easy to construct and a method for making it. The method comprises the following steps: S1. Using a porous metal foam film as a substrate and cleaning its surface; S2. Melting and liquefying a low-melting-point metal and / or alloy serving as a connecting layer; S3. Transferring and loading the low-melting-point metal and / or alloy onto the upper and lower surfaces of the substrate via contact transfer, the metal and / or alloy forms a eutectic alloy with the porous metal foam film, thereby producing a porous metal foam-based porous thermal interface material with a sandwich structure. The present invention achieves high thermal conductivity and low thermal stress interface interconnection at relatively low temperatures, reducing process temperatures and thereby improving efficiency and yield.

Description

Technical Field

[0001] The present invention relates to the technical field of thermal interface material preparation, and in particular to a highly thermally conductive porous thermal interface material that is easy to construct and a preparation method thereof. Background Art

[0002] The increasing integration of electronic circuits is accompanied by an increase in chip power density, making chip heat dissipation a pressing issue. Heat dissipation is particularly important for power devices such as insulated gate bipolar transistors (IGBTs) and metal oxide semiconductor field-effect transistors (MOSFETs). For example, the IGBT has become a widely used semiconductor power device in recent years. Its main power modules are IGBTs and other power modules. They generate large amounts of heat and dissipate heat in concentrated areas. If the heat dissipation capacity is insufficient, the local temperature will be too high, resulting in reduced chip reliability and even damage to the entire power module. Power devices based on silicon carbide, commonly known as third-generation semiconductors, are also experiencing rapid development. Their higher chip integration and higher heat dissipation requirements per unit area make thermal interface management a more prominent issue.

[0003] Thermal interface materials (TIMs) are components specifically designed to dissipate heat from chips. By filling the gap between the heat exchanger and chip, or between the heat exchanger and substrate, TIMs can reduce thermal resistance caused by air gaps at the interface and facilitate rapid heat transfer from the chip. For example, the second-class TIMs currently used in power devices are chopped carbon fiber thermal pads or solder layers, connecting copper-clad ceramic substrates to metal water-cooled heat sinks. However, their combined thermal conductivity and mechanical properties remain significantly limited. For example, vertically arranged chopped carbon fiber thermal pads can achieve a maximum vertical thermal conductivity of 80 W / mK, but their horizontal conductivity is very low. Lead-free solder requires high reflow temperatures, but large-scale application is prone to cold solder joints and delamination failure at the interface due to differences in thermal expansion coefficients. Indium, a TIM with excellent thermal conductivity, flexibility, and high reliability, has also been widely researched and adopted. However, indium readily forms a brittle eutectic with copper, causing some corrosion to the heat sink and the interface. Thermally conductive silver glue is also a widely studied thermal interface material, but its thermal conductivity is usually much lower than the above materials; the thermal conductivity of silver glue can be greatly improved by using high temperature and high pressure sintering, but the process is complex and costly.

[0004] Foam metal has a good metal electrical and thermal conductivity network, and its Young's modulus can be about 1 / 1000 of the Young's modulus of the metal body, so the interface thermal resistance and interface thermal stress are very low. At the same time, foam metal has certain mechanical properties and can release thermal stress through slight movements of the metal skeleton. It is a new type of material that can be used for chip heat dissipation in high-power semiconductor devices. However, the preparation of known foam metal thermal interface materials requires a higher temperature to achieve connection (for example, construction welding at the melting point of indium of 156°C or above), and electroplating is required to achieve indium plating of foam copper. For example, ZL201810254151.8 (A thermal interface material and its preparation method and application method) discloses a porous thermal interface material based on surface electroplated metal and its method. The preparation of thermal interface materials by electroplating will generate a large amount of wastewater discharge, and the thickness of the metal coating is not easy to accurately control, so there are application limitations. Summary of the Invention

[0005] In order to overcome the deficiencies of the prior art, the present invention provides a highly thermally conductive porous thermal interface material that is easy to construct and a method for making the same.

[0006] The present invention adopts the following technical solutions:

[0007] In a first aspect, a method for preparing a porous thermal interface material with high thermal conductivity and easy construction is provided, comprising the following steps: S1, using a porous foam metal film as a substrate and cleaning its surface; S2, melting and liquefying a low-melting-point metal and / or alloy serving as a connecting layer; S3, transferring and loading the low-melting-point metal and / or alloy respectively on the upper and lower surfaces of the substrate by contact transfer and forming a eutectic alloy with the porous foam metal film, thereby preparing a porous thermal interface material based on a porous foam metal with a sandwich structure.

[0008] In some embodiments of the present invention, step S3 includes: S31, spreading a first layer of molten low-melting-point metal and / or alloy on the first surface of the substrate with a scraper, cooling the first layer of molten low-melting-point metal and / or alloy to transfer to the first surface of the substrate; S32, spreading a second layer of molten low-melting-point metal and / or alloy on the second surface of the substrate with a scraper, cooling the second layer of molten low-melting-point metal and / or alloy to transfer to the second surface of the substrate, thereby obtaining the porous thermal interface material having a sandwich structure and a porous foam metal base;

[0009] The first surface is one of an upper surface and a lower surface of the substrate, and the second surface is the other of the upper surface and the lower surface of the substrate.

[0010] In some embodiments of the present invention, the step S3 includes: S3-1, spreading a first layer of molten low-melting-point metal and / or alloy on a first mold that is easy to peel off, and forming a first layer of low-melting-point metal and / or alloy foil by rolling; S3-2, spreading a second layer of molten low-melting-point metal and / or alloy on a second mold that is easy to peel off, and forming a second layer of low-melting-point metal and / or alloy foil by rolling; S3-3, placing the substrate between the first layer of low-melting-point metal and / or alloy foil and the second layer of low-melting-point metal and / or alloy foil, and transferring the first layer of low-melting-point metal and / or alloy foil and the second layer of low-melting-point metal and / or alloy foil to the upper surface and lower surface of the substrate by hot pressing to obtain the porous thermal interface material with a porous foam metal base having a sandwich structure.

[0011] In some embodiments of the present invention, the thickness of the connection layers on the upper surface and the lower surface of the substrate are respectively between 3 and 50 μm, and the total thickness of the two connection layers is 5% to 40% of the thickness of the substrate.

[0012] In some embodiments of the present invention, the porous metal foam membrane has a porosity of 20% to 80%, a thickness of 0.001-10 mm, and a pore size of 0.001-1 mm.

[0013] In some embodiments of the present invention, the connection layer is selected from one of Bi, Sn, Pb, In, Ga, Zn or an alloy thereof.

[0014] In some embodiments of the present invention, the material of the porous metal foam membrane is selected from one of copper, silver, nickel, zinc, copper-nickel alloy, nickel-chromium alloy, and copper-zinc alloy.

[0015] In some embodiments of the present invention, the porous foam metal film is prepared by the following steps: using a porous foam polymer film as a substrate, and sequentially performing chemical plating, electroplating thickening, high-temperature pyrolysis and reduction on the surface of the substrate.

[0016] In some embodiments of the present invention, the porous foam polymer film is one of polyvinyl acetate foam material, polyurethane foam material, polystyrene foam material and polyethylene foam material; the process adopted by the chemical plating is: immersing the porous foam polymer film in a metal salt (the metal in the metal salt refers to the metal of the material of the porous foam metal film, selected from one of copper, silver, nickel, zinc, copper-nickel alloy, nickel-chromium alloy, and copper-zinc alloy) 0.1-10g / L, potassium sodium tartrate 1-40g / L, sodium hydroxide 3-15g / L, and solvent 2-25g / L. L and stabilizer 0.01-0.5g / L, plating at 25-80 ° C for 5-40 minutes; the electroplating thickening process is: the porous foam polymer film treated by the above chemical plating is immersed in a metal salt (the metal in the metal salt refers to the metal of the material of the porous foam metal film, selected from one of copper, silver, nickel, zinc, copper-nickel alloy, nickel-chromium alloy, and copper-zinc alloy) 20-250g / L, potassium pyrophosphate 30-700g / L and ammonium citrate 4-40g / L, pH 8-9, 25-60 ° C at 0.05-3A / dm 2 The electroplating thickening is carried out at a cathode current density of ; the high-temperature pyrolysis is carried out in an air atmosphere at 350°C-600°C to remove the substrate; the reduction is carried out in a reducing atmosphere at 500°C-1400°C to remove the oxide layer formed by natural oxidation on the metal surface.

[0017] In some embodiments of the present invention, the porous foam metal film is obtained by mixing metal and / or alloy powder with a polymer binder, coating, high-temperature sintering, and reducing.

[0018] In a second aspect, a highly thermally conductive porous thermal interface material that is easy to construct and is obtained by the production method of the first aspect is provided.

[0019] The present invention has the following beneficial effects:

[0020] The present invention proposes a method for making a porous thermal interface material with high thermal conductivity that is easy to construct. The method uses a porous foam metal film as a substrate, melts and liquefies a low-melting-point metal and / or alloy as a connecting layer, and then transfers and loads the low-melting-point metal and / or alloy onto the upper and lower surfaces of the substrate by contact transfer, forming a eutectic alloy with the porous foam metal film. This achieves uniform coverage of the low-melting-point metal and / or alloy on the surface of the porous foam metal, thereby producing a soft porous foam metal-based porous thermal interface material with a sandwich structure. Compared with the existing method of loading by electroplating, the method of the present invention is easier, does not produce a large amount of wastewater, and the thickness of the connecting layer can be accurately controlled. At the same time, the low-melting-point metal and / or alloy used as the connecting layer for thermal connection is conducive to reducing the process temperature, thereby achieving high thermal conductivity and low thermal stress interface interconnection at a lower temperature, improving efficiency and yield (high temperature can easily lead to device failure). The porous thermal interface material with a sandwich structure prepared by the present invention is easy to construct and has high thermal conductivity. It can be used for heat dissipation of high-power, large-size chips in power devices such as MOSFET and IGBT.

[0021] Other beneficial effects of the embodiments of the present invention will be further described below. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a flowchart of the steps of a method for making a highly thermally conductive porous thermal interface material that is easy to construct according to an embodiment of the present invention;

[0023] Figure 2 2 is a schematic structural diagram of a porous thermal interface material having a sandwich structure and a porous metal foam base according to an embodiment of the present invention;

[0024] Figure 3 3. This is an SEM image of the easy-to-construct, high-thermal-conductivity porous thermal interface material prepared in Example 5 of the present invention and its corresponding element distribution diagram. DETAILED DESCRIPTION

[0025] The present invention will be further described below with reference to the accompanying drawings and in combination with preferred embodiments. It should be noted that, unless there is a conflict, the embodiments and features in the embodiments of the present application can be combined with each other.

[0026] It should be noted that the directional terms such as left, right, up, down, top, and bottom in this embodiment are merely relative concepts, or are based on the normal use status of the product, and should not be considered as restrictive.

[0027] The embodiment of the present invention provides a method for manufacturing a highly thermally conductive porous thermal interface material that is easy to construct. Figure 1 and Figure 2, comprising the following steps: S1, using a porous metal foam film 1 as a substrate and cleaning its surface; S2, melting and liquefying a low-melting-point metal and / or alloy 2 as a connecting layer; S3, transferring and loading the low-melting-point metal and / or alloy 2 on the upper and lower surfaces of the substrate respectively through contact transfer and forming a eutectic alloy with the porous metal foam film, thereby preparing a porous thermal interface material with a porous metal foam base having a sandwich structure.

[0028] In a preferred embodiment, step S3 includes the following steps: S31, spreading a first layer of molten low-melting-point metal and / or alloy on the first surface of the substrate using a scraper, cooling the first layer of molten low-melting-point metal and / or alloy 2 to transfer to the first surface of the substrate; S32, spreading a second layer of molten low-melting-point metal and / or alloy on the second surface of the substrate using a scraper, cooling the second layer of molten low-melting-point metal and / or alloy 2 to transfer to the second surface of the substrate, thereby obtaining the porous thermal interface material having a porous foam metal base with a sandwich structure; wherein the first surface is one of the upper surface and the lower surface of the substrate, and the second surface is the other of the upper surface and the lower surface of the substrate. In this technical solution, the speed and angle of the scraper in steps S31 and S32 are controlled to prevent the liquefied low-melting-point metal and / or alloy from penetrating into the pores of the porous foam metal.

[0029] Preferably, the porous metal foam membrane 1 has a porosity of 20% to 80%, a thickness of 0.001 to 10 mm, and a pore size of 0.001 to 1 mm.

[0030] In order to avoid as much as possible the liquefied low-melting-point metal and / or alloy from penetrating into the pores of the porous metal foam, it is preferred that:

[0031] For porous foam metal with a porosity between 20% and 50%, a thickness between 0.001 and 0.3 mm, and a pore size between 0.001 and 0.20 mm, the scraper angle in step S31 is 20-60° and the scraper speed is 0.005-0.02 m / s.

[0032] For porous foam metal with a porosity of 40%-70%, a thickness of 0.01-0.7 mm, and a pore size of 0.08-0.30 mm, the scraper angle in step S31 is 30-70° and the scraper speed is 0.01-0.05 m / s.

[0033] For porous foam metal with a porosity of 50%-80%, a thickness of 0.2-1.0 mm, and a pore size of 0.05-0.50 mm, the scraper angle in step S31 is 30-80° and the scraper speed is 0.02-0.20 m / s.

[0034] For porous foam metal with a porosity of 50%-80%, a thickness of 0.2-1.0 mm, and a pore size of 0.2-1.0 mm, the scraper angle in step S31 is 60-90° and the scraper speed is 0.05-0.50 m / s.

[0035] For porous foam metal with a porosity of 70%-80%, a thickness of 0.4-10 mm, and a pore size of 0.4-1.0 mm, the scraper angle in step S31 is 70-90° and the scraper speed is 0.1-1.0 m / s.

[0036] In another preferred embodiment, step S3 includes the following steps: S3-1, spreading a first layer of molten low-melting-point metal and / or alloy 2 on a first, easily peelable mold, and forming a first layer of low-melting-point metal and / or alloy foil by rolling; S3-2, spreading a second layer of molten low-melting-point metal and / or alloy 2 on a second, easily peelable mold, and forming a second layer of low-melting-point metal and / or alloy foil by rolling; S3-3, placing the substrate between the first and second layers of low-melting-point metal and / or alloy foil, and transferring the first and second layers of low-melting-point metal and / or alloy foil to the upper and lower surfaces of the substrate by hot pressing, thereby obtaining the porous thermal interface material having a sandwich structure and a porous foam metal base. In this technical solution, the hot pressing temperature, pressing pressure, and contact time in step S3-3 are controlled to prevent the liquefied low-melting-point metal and / or alloy from penetrating into the pores of the porous foam metal.

[0037] Preferably, the porous metal foam membrane 1 has a porosity of 20% to 80%, a thickness of 0.001 to 10 mm, and a pore size of 0.001 to 1 mm.

[0038] In order to avoid as much as possible the liquefied low-melting-point metal and / or alloy from penetrating into the pores of the porous metal foam, it is preferred that:

[0039] For porous foam metals with a porosity between 20% and 50%, a thickness between 0.001 and 0.3 mm, and a pore size between 0.001 and 0.20 mm, the thickness of the two low-melting-point metal and / or alloy foils is 3-15 microns, and the bonding transfer is performed within a range of 5-40°C above their melting points. In step S3-3, the pressing pressure of the hot press is controlled to be 0.001-0.05 MPa, the contact time is 3-30 seconds, and the pressing material is a polymer sheet such as PTFE, PVDF, PP, HDPE, PVC, PMMA, PDMS, or an aluminum alloy or other alloy sheet coated with paint that is not wetted by it.

[0040] For porous foam metals with a porosity of 40%-70%, a thickness of 0.01-0.7 mm, and a pore size of 0.08-0.30 mm, the thickness of the two low-melting-point metal and / or alloy foils is 3-20 microns, and the bonding transfer is performed within a range of 5-50°C above their melting points. In step S3-3, the pressing pressure of the hot press is controlled to be 0.001-0.1 MPa, the contact time is 3-30 seconds, and the pressing material is a polymer sheet such as PTFE\PVDF\PP\HDPE\PVC\PMMA\PDMS, or an aluminum alloy or other alloy sheet coated with paint that is not wetted by it.

[0041] For porous foam metals with a porosity of 50%-80%, a thickness of 0.2-1.0 mm, and a pore size of 0.05-0.50 mm, the thickness of the two low-melting-point metal and / or alloy foils is 3-25 μm, and the bonding transfer is performed within a range of 5-60°C above their melting points. In step S3-3, the pressing pressure of the hot press is controlled to be 0.001-0.15 MPa, the contact time is 3-30 seconds, and the pressing material is a polymer sheet such as PTFE\PVDF\PP\HDPE\PVC\PMMA\PDMS, or an aluminum alloy or other alloy sheet coated with paint that is not wetted by it.

[0042] For porous foam metals with a porosity of 50%-80%, a thickness of 0.2-1.0 mm, and a pore size of 0.2-1.0 mm, the thickness of the two low-melting-point metal and / or alloy foils is 3-30 μm, and the bonding transfer is performed within a range of 5-80°C above their melting points. In step S3-3, the pressing pressure of the hot press is controlled to be 0.005-0.20 MPa, the contact time is 3-30 seconds, and the pressing material is a polymer sheet such as PTFE\PVDF\PP\HDPE\PVC\PMMA\PDMS, or an aluminum alloy or other alloy sheet coated with paint that is not wetted by it.

[0043] For porous foam metals with a porosity of 70%-80%, a thickness of 0.4-10 mm, and a pore size of 0.4-1.0 mm, the thickness of the two low-melting-point metal and / or alloy foils is 3-50 μm, and the bonding transfer is performed at 5-100°C above their melting points. In step S3-3, the pressing pressure of the hot press is controlled to be 0.005-0.30 MPa, the contact time is 3-60 seconds, and the pressing material is a polymer sheet such as PTFE\PVDF\PP\HDPE\PVC\PMMA\PDMS, or an aluminum alloy or other alloy sheet coated with paint that is not wetted by it.

[0044] In the embodiment of the present invention, when the low-melting-point metal and / or alloy is transferred to the porous metal foam membrane, the liquefied low-melting-point metal can be prevented from penetrating into the pores of the porous metal foam membrane, thereby preventing the porous metal foam from losing its softness and resilience.

[0045] Preferably, the material of the mold in step S3-1 and step S3-2 can be selected from polytetrafluoroethylene (PTFE), polyphenylene sulfide, polysulfone, polyetheretherketone, liquid crystal polymer, polystyrene, polycarbonate, polyacrylate, polypropylene, polyvinylidene fluoride, perfluoroethylene propylene copolymer, polyvinyl chloride, etc.

[0046] Preferably, the thickness of the connection layers on the upper surface and the lower surface of the substrate are respectively between 3 and 50 μm, and the total thickness of the two connection layers is 5% to 40% of the thickness of the substrate.

[0047] Preferably, the connection layer is selected from Bi, Sn, Pb, In, Ga, Zn or alloys thereof.

[0048] Preferably, the material of the porous metal foam membrane 1 is selected from one of copper, silver, nickel, zinc, copper-nickel alloy, nickel-chromium alloy, and copper-zinc alloy.

[0049] Preferably, the porous metal foam membrane 1 is prepared by the following steps: using a porous polymer foam membrane as a substrate, and sequentially performing chemical plating, electroplating thickening, high-temperature pyrolysis and reduction on the surface of the substrate.

[0050] Preferably, the porous foam polymer film is one of polyvinyl acetate foam material, polyurethane foam material, polystyrene foam material and polyethylene foam material; the process adopted by the chemical plating is: immersing the porous foam polymer film in a metal salt (the metal in the metal salt refers to the metal of the material of the porous foam metal film, selected from one of copper, silver, nickel, zinc, copper-nickel alloy, nickel-chromium alloy, and copper-zinc alloy) 0.1-10g / L, potassium sodium tartrate 1-40g / L, sodium hydroxide 3-15g / L, a solvent (preferably formaldehyde and / or hydrazine hydrate) 2-25 g / L and 0.01-0.5g / L of stabilizer, plated at 25-80°C for 5-40 minutes; the electroplating thickening process is as follows: immerse the porous foam polymer film treated with the above chemical plating in 20-250g / L of metal salt (the metal in the metal salt refers to the metal of the material of the porous foam metal film, selected from one of copper, silver, nickel, zinc, copper-nickel alloy, nickel-chromium alloy, and copper-zinc alloy), 30-700g / L of potassium pyrophosphate and 4-40g / L of ammonium citrate, pH value 8-9, 25-60°C, 0.05-3A / dm 2The electroplating thickening is carried out at a cathode current density of ; the high-temperature pyrolysis is carried out in an air atmosphere at 350°C-600°C to remove the substrate; the reduction is carried out in a reducing atmosphere (such as an inert gas containing hydrogen or nitrogen) at 500°C-1400°C to remove the oxide layer.

[0051] Preferably, the porous metal foam film 1 is obtained by mixing metal and / or alloy powder with a polymer binder, coating (the material of the coating substrate is not limited, as long as the substrate can be removed after subsequent high-temperature sintering, or can be removed after the reduction step), high-temperature sintering (removing the polymer binder), and reducing (such as reducing the oxide formed by natural oxidation of the metal surface to the corresponding metal under a reducing gas such as hydrogen).

[0052] Preferably, in step S1, the surface of the porous metal foam film can be cleaned by physical methods such as ultrasonic cleaning, plasma cleaning, acid treatment such as sulfuric acid and hydrochloric acid, or organic solvent treatment such as alcohol and acetone, or a combination thereof, and then dried for later use. For example, ultrasonic cleaning can be used, and the cleaned porous metal foam is placed in a 50°C oven for 15 minutes for drying before use.

[0053] The porous thermal interface material with a porous foam metal base and a sandwich structure prepared by the present invention is easy to construct and has high thermal conductivity, and can be used for heat dissipation of high-power and large-size chips in power devices such as MOSFET and IGBT.

[0054] like Figure 2 As shown, as a method of using porous thermal interface materials, a porous thermal interface material with a porous foam metal base having a sandwich structure can be fixed to the interface between the heat source 4 (such as a substrate) at the heating end and the heat sink 3 at the heat dissipation end by means of screw reinforcement through a fixed torque. It can also be fixed by using a clamp to prevent movement during welding. The welding conditions can be selected and optimized according to the melting point characteristics of the low-melting-point metal and / or alloy itself. When the porous thermal interface material is used to connect the heat source 4 and the heat sink 3, the applied temperature depends on the melting point of the low-melting-point metal and / or alloy, which is generally about 0-80°C above the melting point temperature of the metal and / or alloy. For example, the porous foam metal thermal interface material can be constructed and connected by pressurized heating, with the applied pressure ranging from 0.5psi to 500psi and the heating temperature being 30°C to 300°C.

[0055] The present invention is further described below through more specific examples.

[0056] Example 1

[0057] The porous foam metal film 1 of this embodiment is a foam nickel with an average pore size of 200μm, a porosity of 20%, and a thickness of 0.3mm. The foam nickel is made by using polyvinyl acetate foam material as a substrate and sequentially undergoing chemical plating, electroplating thickening, high-temperature pyrolysis and reduction. Among them, the chemical nickel plating uses 0.8g / L nickel nitrate, 3g / L potassium sodium tartrate, 3g / L sodium hydroxide, 5g / L hydrazine hydrate, and 0.2g / L stabilizer, and is plated at 80°C for 20 minutes. After washing with a large amount of deionized water, the film is plated at 0.1A / dm 2 Electroplating thickening is performed at a cathode current density of 1000 nm. By controlling the electroplating thickening time, a nickel foam with a porosity of 20% can be obtained. The material is then pyrolyzed at 550°C in an air atmosphere to remove the organic components (i.e., the substrate). Subsequently, high-temperature reduction is performed at 1050°C in a reducing atmosphere (nitrogen containing 1.5% (volume fraction) hydrogen) to remove the oxide layer.

[0058] The low melting point metal and / or alloy 2 in this example is Bi2In3Ga 0.5 Alloy. Methods for transferring the load of low-melting-point metal and / or alloy 2 by contact include:

[0059] Bi2In3Ga 0.5 The alloy melts into a liquid state;

[0060] Spread Bi2In3Ga on the upper surface of nickel foam with a scraper 0.5 alloy, the construction temperature is 150℃ to ensure the Bi2In3Ga 0.5 The alloy is in a molten state, the scraper angle is 30°, the scraper speed is 0.008m / s, and then cooled to make the liquid Bi2In3Ga 0.5 The alloy is transferred to the upper surface of the nickel foam. The above steps are then repeated on the lower surface of the nickel foam to obtain a porous thermal interface material. In this example, Bi2In3Ga 0.5 The thickness of the alloy transferred to the nickel foam surface was 8 μm.

[0061] In this example, when the porous thermal interface material obtained is constructed and connected by pressurized heating and applied to the interface between the heat source 4 (such as a substrate) at the heating end and the heat sink 3 at the heat dissipation end, the applied pressure range is 8psi and the heating temperature is 160°C.

[0062] Example 2

[0063] The porous metal foam membrane 1 of this embodiment is made of silver foam with an average pore diameter of 80 μm and a porosity of 70%, and a thickness of 0.2 mm. The silver foam is produced by mixing metal and / or alloy powder with a polymer binder, applying the mixture, sintering at high temperature, and then reducing it. Specifically, 20-micron diameter flake silver powder (99.99 wt%) and a polyurethane prepolymer (Desmodur 3390-propylene glycol, 1:1 equivalent) are thoroughly mixed in a mass ratio of 80:20. Methyl ethyl ketone is used as a solvent, and the mixture is degassed and stabilized using a planetary mixer. The mixture is then coated. The mixture is then pyrolyzed at 550°C in an air atmosphere to remove the organic component (polyurethane prepolymer). The resulting mixture is then reduced at 820°C in a reducing atmosphere (nitrogen containing 1.5% hydrogen) to remove the oxide layer.

[0064] The low melting point metal and / or alloy 2 in this example is InGa 0.3 Alloy. Methods for transferring the load of low-melting-point metal and / or alloy 2 by contact include:

[0065] InGa 0.3 The alloy melts into a liquid state;

[0066] Use a scraper to spread InGa on the upper surface of the foam silver 0.3 Alloy, the construction temperature is 70 ℃ to ensure that the InGa 0.3 The alloy is in a molten state, the scraper angle is 70°, the scraper speed is 0.04m / s, and then cooled to make the liquid InGa 0.3 The alloy is transferred to the surface of the silver foam. The above steps are then repeated on the lower surface of the silver foam to obtain a porous thermal interface material. In this example, InGa 0.3 The thickness of the alloy transferred to the silver foam surface was 6 μm.

[0067] In this example, the porous thermal interface material obtained is constructed and connected by pressurized heating to the interface between the heat source 4 (such as a substrate) at the heating end and the heat sink 3 at the heat dissipation end. The applied pressure is in the range of 2 psi and the heating temperature is 80°C.

[0068] Example 3

[0069] The porous foam metal film 1 of this embodiment is made of foam copper with an average pore size of 20 μm, a porosity of 30%, and a thickness of 0.3 mm. The foam copper is made by using polyvinyl acetate foam material as a substrate and sequentially undergoing chemical plating, electroplating thickening, high-temperature pyrolysis and reduction. Among them, chemical copper plating uses 0.2 g / L copper nitrate, 2 g / L potassium sodium tartrate, 2 g / L sodium hydroxide, 3 g / L formaldehyde, and 0.2 g / L stabilizer, and is plated at 60°C for 30 minutes. After washing with a large amount of deionized water, the film was plated at 0.2 A / dm 2 By electroplating at a cathode current density of 1000 nm, a copper foam with a porosity of 30% can be obtained by controlling the electroplating thickening time. The material is then pyrolyzed at 530°C in an air atmosphere to remove organic components. It is then reduced at 910°C in a reducing atmosphere (nitrogen containing 1% hydrogen) to remove the oxide layer.

[0070] In this example, the low-melting-point metal and / or alloy 2 is a SnIn alloy. The method of loading the low-melting-point metal and / or alloy 2 by contact transfer includes:

[0071] Melting the SnIn alloy into a liquid state;

[0072] Spreading a first layer of molten SnIn alloy on a first mold that is easy to peel off, and forming a first layer of low-melting-point metal and / or alloy foil with a thickness of 15 μm by rolling;

[0073] Spreading a second layer of molten SnIn alloy on a second easily strippable mold, and forming a second layer of low-melting-point metal and / or alloy foil with a thickness of 15 μm by rolling;

[0074] The foam copper is placed between a first layer of low-melting-point metal and / or alloy foil and a second layer of low-melting-point metal and / or alloy foil. At a construction temperature of 150°C, the first layer of low-melting-point metal and / or alloy foil and the second layer of low-melting-point metal and / or alloy foil are transferred to the upper and lower surfaces of the foam copper by hot pressing (pressing pressure of 0.03 MPa, contact time of 15 seconds, and pressing material of PTFE sheet) to obtain a porous thermal interface material.

[0075] In this example, the porous thermal interface material obtained is constructed and connected by pressurized heating to the interface between the heat source 4 (such as a substrate) at the heating end and the heat sink 3 at the heat dissipation end. The applied pressure is in the range of 3 psi and the heating temperature is 180°C.

[0076] Example 4

[0077] The difference from Example 2 is that foamed silver with a porosity of 40% is used, and the rest is basically the same as Example 2.

[0078] Example 5

[0079] The porous foam metal film 1 of this embodiment is made of foam copper with an average pore size of 60 μm, a porosity of 70%, and a thickness of 1 mm. The foam copper is made by using polyvinyl acetate foam material as a substrate and sequentially undergoing chemical plating, electroplating thickening, high-temperature pyrolysis and reduction. Among them, chemical copper plating uses 0.2 g / L copper nitrate, 10 g / L potassium sodium tartrate, 10 g / L sodium hydroxide, 15 g / L formaldehyde, and 0.3 g / L stabilizer, and is plated at 60°C for 30 minutes. After washing with a large amount of deionized water, the film was plated at 0.2 A / dm 2 By electroplating at a cathode current density of 1000 nm, a copper foam with a porosity of 70% can be obtained by controlling the electroplating thickening time. The material is then pyrolyzed at 530°C in an air atmosphere to remove organic components. It is then reduced at 910°C in a reducing atmosphere (nitrogen containing 1% hydrogen) to remove the oxide layer.

[0080] The low melting point metal and / or alloy 2 in this example is Ga 0.8 In 0.5 Alloy. Methods for transferring the load of low-melting-point metal and / or alloy 2 by contact include:

[0081] Will Ga 0.8 In 0.5 The alloy melts into a liquid state;

[0082] Use a scraper to spread Ga on the upper surface of the foam copper 0.8 In 0.5 Alloy, the construction temperature is 80 ° C, the scraper angle is 70 °, the scraper speed is 0.05m / s, and then cooled to make the liquid Ga 0.8 In 0.5 The alloy is transferred to the surface of the copper foam. The above steps are then repeated on the other side of the copper foam to obtain a porous thermal interface material. In this example, Ga 0.8 In 0.5 The thickness of the alloy transferred to the foam copper surface is 6 microns. The SEM image of the porous thermal interface material prepared in this embodiment and its corresponding element distribution map are shown in FIG. Figure 3 shown.

[0083] In this example, the porous thermal interface material obtained is constructed and connected by pressurized heating to the interface between the heat source 4 (such as a substrate) at the heating end and the heat sink 3 at the heat dissipation end. The applied pressure is in the range of 2 psi and the heating temperature is 80°C.

[0084] Examples 6-13

[0085] The difference from Example 5 is that the porosity of the copper foam, the composition of the low-melting-point liquid metal, and the thickness of the low-melting-point metal in Examples 6-13 are respectively as shown in Table 2, and the rest are basically the same as in Example 5.

[0086] Examples 14-19

[0087] The difference from Example 2 is that the porosity of the foamed silver, the low-melting-point liquid metal composition, and the thickness of the low-melting-point metal in Examples 14-19 are respectively as shown in Table 2, and the rest are basically the same as Example 2.

[0088] As shown in Tables 1 and 2 below, Table 1 shows the thermal conductivity test results of porous metal foam-based thermal interface materials with sandwich structures of different porosities for Examples 1-4, using the laser flash point method. Table 2 shows the thrust test results of porous metal foam-based thermal interface materials with sandwich structures for Examples 5-19. The thrust test was performed using a Nordson Co. Dage 4000 thrust tester. The sample size was 5*5 mm. 2 , welded on the copper surface of the copper clad laminate. From the experimental results, it can be seen that the welding firmness is improved by adopting the method in the embodiment of the present invention.

[0089] Table 1

[0090] Porous thermal interface materials In-plane thermal conductivity Out-of-plane thermal conductivity Example 1: Porosity 20% <![CDATA[200W m -1 k -1 ]]> <![CDATA[189W m -1 k -1 ]]> Example 3: Porosity 30% <![CDATA[150W m -1 k -1 ]]> <![CDATA[120W m -1 k -1 <!-- 8 -->]]> Example 4: Porosity 40% <![CDATA[110W m -1 k -1 ]]> <![CDATA[100W m -1 k -1 ]]> Example 2: Porosity 70% <![CDATA[60W m -1 k -1 ]]> <![CDATA[63W m -1 k -1 ]]>

[0091] Table 2

[0092]

[0093]

[0094] In summary, the embodiments of the present invention achieve uniform coverage of the porous metal foam surface by heating and liquefying the low-melting-point metal and / or alloy and using contact transfer, significantly improving efficiency compared to known methods. Furthermore, coating the porous metal foam surface with the low-melting-point metal and / or alloy facilitates achieving high thermal conductivity and low thermal stress interface interconnection, and helps reduce process temperatures, thereby improving efficiency and yield (high temperatures can easily lead to device failure).

[0095] The above is a further detailed description of the present invention in conjunction with specific preferred embodiments, and the specific implementation of the present invention should not be considered to be limited to these descriptions. Those skilled in the art will recognize that several equivalent substitutions or obvious variations can be made without departing from the scope of the present invention, and that any equivalent performance or application should be considered to fall within the scope of protection of the present invention.

Claims

1. A method for preparing a highly thermally conductive porous thermal interface material that is easy to construct, characterized in that: The steps include: S1. Using a porous metal foam film as a substrate, cleaning its surface; S2. Melting and liquefying the low melting point metal and / or alloy serving as the connecting layer; S3. The low-melting-point metal and / or alloy is transferred and loaded on the upper and lower surfaces of the substrate respectively by contact transfer to form a eutectic alloy with the porous metal foam film while preventing the liquefied low-melting-point metal from penetrating into the pores of the porous metal foam film, thereby preparing a porous thermal interface material having a sandwich structure and a porous metal foam base; wherein: The step S3 comprises: S31, spreading a first layer of molten low-melting-point metal and / or alloy on the first surface of the substrate using a scraper, and cooling the first layer of molten low-melting-point metal and / or alloy so that the first layer of molten low-melting-point metal and / or alloy is transferred to the first surface of the substrate; S32, spreading a second layer of molten low-melting-point metal and / or alloy on the second surface of the substrate with a scraper, and cooling the second layer of molten low-melting-point metal and / or alloy to transfer to the second surface of the substrate, thereby obtaining the porous foam metal-based porous thermal interface material having a sandwich structure; the first surface is one of the upper surface and the lower surface of the substrate, and the second surface is the other of the upper surface and the lower surface of the substrate; Preventing the liquefied low-melting-point metal and / or alloy from penetrating into the pores of the porous foam metal by controlling the speed and angle of the scraper in steps S31 and S32; Alternatively, step S3 includes: S3-1, spreading a first layer of molten low-melting-point metal and / or alloy on a first easily peelable mold, and forming a first layer of low-melting-point metal and / or alloy foil by rolling; S3-2, spreading a second layer of molten low-melting-point metal and / or alloy on the second easily peelable mold, and forming a second layer of low-melting-point metal and / or alloy foil by rolling; S3-3, placing the substrate between the first layer of low-melting-point metal and / or alloy foil and the second layer of low-melting-point metal and / or alloy foil, and transferring the first layer of low-melting-point metal and / or alloy foil and the second layer of low-melting-point metal and / or alloy foil to the upper surface and the lower surface of the substrate by hot pressing to obtain the porous foam metal-based porous thermal interface material having a sandwich structure; The temperature, pressing pressure and contact time of the hot pressing in step S3-3 are controlled to prevent the liquefied low-melting-point metal and / or alloy from penetrating into the pores of the porous foam metal.

2. The production method according to claim 1, wherein The thickness of the connecting layers on the upper surface and the lower surface of the substrate are respectively between 3 and 50 μm, and the total thickness of the two connecting layers is 5% to 40% of the thickness of the substrate.

3. The production method according to claim 1, wherein: The porous foam metal film has a porosity of 20% to 80%, a thickness of 0.001 to 10 mm, and a pore size of 0.001 to 1 mm.

4. The production method according to claim 1, wherein: The connecting layer is selected from one of Bi, Sn, Pb, In, Ga, Zn or an alloy thereof.

5. The production method according to claim 1, wherein: The material of the porous foam metal film is selected from one of copper, silver, nickel, zinc, copper-nickel alloy, nickel-chromium alloy and copper-zinc alloy.

6. The production method according to claim 5, wherein: The porous foam metal film is prepared by the following steps: taking the porous foam polymer film as a substrate, and sequentially performing chemical plating, electroplating thickening, high-temperature pyrolysis and reduction on the surface of the substrate.

7. The production method according to claim 6, characterized in that: The porous foam polymer film is one of polyvinyl acetate foam material, polyurethane foam material, polystyrene foam material and polyethylene foam material.

8. The production method according to claim 6, wherein: The chemical plating process is as follows: immersing the porous foam polymer film in 0.1-10 g / L of metal salt, 1-40 g / L of potassium sodium tartrate, 3-15 g / L of sodium hydroxide, 2-25 g / L of solvent and 0.01-0.5 g / L of stabilizer, and plating at 25-80° C. for 5-40 minutes.

9. The production method according to claim 6, wherein: The electroplating thickening process is as follows: the porous foam polymer film treated by chemical plating is immersed in 20-250g / L of metal salt, 30-700g / L of potassium pyrophosphate and 4-40g / L of ammonium citrate, at a pH of 8-9, 25-60°C and a flow rate of 0.05-3A / dm 2 Electroplating thickening is carried out at a cathodic current density of .

10. The production method according to claim 6, wherein: The high-temperature pyrolysis is performed in an air atmosphere at 350° C.-600° C. to remove the substrate.

11. The production method according to claim 6, wherein: The reduction is carried out in a reducing atmosphere at 500° C.-1400° C. to remove the oxide layer.

12. The manufacturing method according to claim 5, characterized in that: The porous foam metal film is obtained by mixing metal and / or alloy powder with a polymer binder, coating, high-temperature sintering and reducing.

13. A highly thermally conductive porous thermal interface material that is easy to construct and is obtained by the preparation method according to any one of claims 1 to 12.

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