Liquid Metal Thermal Interface Material Having Anti-melt Characteristic and Preparation Method Thereof

Abstract

The present invention discloses a liquid metal thermal interface material having an anti-melt characteristic and a preparation method thereof. The liquid metal thermal interface material is characterized by comprising, in percentage by weight, 20-40 wt % of indium, 0-6 wt % of bismuth, 0-2 wt % of antimony, 0-3 wt % of zinc, 0-0.6 wt % silver, 0-0.3 wt % of nickel, 0-0.8 wt % of cerium, 0-0.6 wt % of europium and the balance of tin. The liquid metal thermal interface material has excellent thermal conductivity and chemical stability in an operating environment of an insulated gate bipolar transistor (IGBT), and thus is very suitable for IGBT devices in large-scale industrial production and practical applications.

Claims

1. A liquid metal thermal interface material having an anti-melt feature, the material comprising, in percentage by weight, the following constituents in proportions: 20-40 wt % of indium, 0-6 wt % of bismuth, 0-2 wt % of antimony, 0-3 wt % of zinc, 0-0.6 wt % of silver, 0-0.3 wt % of nickel, 0-0.8 wt % of cerium, 0-0.6 wt % of europium and the balance of tin.

2. The liquid metal thermal interface material according to claim 1, wherein the material comprises, in percentage by weight, the following constituents in proportions: 22 wt % of indium, 1.4 wt % of bismuth, 0.3 wt % of antimony, 1.6 wt % of zinc, 0.05 wt % of silver, 0.02 wt % of nickel, 0.02 wt % of cerium, 0.01 wt % of europium and the balance of tin.

3. The liquid metal thermal interface material according to claim 1, wherein the material comprises, in percentage by weight, the following constituents in proportions: 28 wt % of indium, 1.9 wt % of bismuth, 0.4 wt % of antimony, 1.8 wt % of zinc, 0.03 wt % of silver, 0.01 wt % of nickel, 0.01 wt % of cerium, 0.02 wt % of europium and the balance of tin.

4. The liquid metal thermal interface material according to claim 1, wherein the material comprises, in percentage by weight, the following constituents in proportions: 32 wt % of indium, 2.1 wt % of bismuth, 0.6 wt % of antimony, 2.9 wt % of zinc, 0.02 wt % of silver, 0.03 wt % of nickel, 0.02 wt % of cerium, 0.01 wt % of europium and the balance of tin.

5. The liquid metal thermal interface material according to claim 1, wherein an anti-melt temperature of the material ranges from 64 C. to 180 C.

6. The liquid metal thermal interface material according to claim 1, wherein the material is applicable to heat dissipation of an insulated gate bipolar transistor (IGBT) system within a temperature range of 60 C. to 180 C.

7. A preparation method of the liquid metal thermal interface material according to claim 1, the method comprising: using argon or nitrogen as a protective atmosphere and carrying out induction melting of the material mixed according to the proportions of the constituents in a graphite crucible to prepare an alloy melt; uniformly stirring the alloy melt at a temperature ranging from 400 C. to 500 C. to fine homogenization; pouring the uniformly-stirred alloy melt into a graphite mold for solidification; and performing heat treatment on solidified alloy ingots at a temperature ranging from 40 C. to 140 C. for 2 to 4 hours, and then carrying out cold rolling treatment.

8. The preparation method according to claim 7, wherein a rolling quantity per pass in the cold rolling treatment is 20-30%.

Description

[0013] FIG. 1 is a schematic diagram illustrating variations of a phase fraction of a foil-like liquid metal in a normal melting state with temperature (this system comprises only a liquid phase and a phase).

[0014] Through long-term study, the inventor has found an effective method to overcome side leakage of a liquid metal caused by an increased content of the liquid phase during melting, and thus designs a new liquid metal that has an anti-melt characteristic.

[0015] For the sake of convenient description of the anti-melt characteristic of the material, a schematic diagram in FIG. 2 is used as an example for description. The system comprises three phases, i.e., liquid phase, a phase and phase. The melting behavior of the alloy between T.sub.1 and T in this figure is consistent with that in FIG. 1. However, when the alloy continues to melt as the temperature rises, the fraction of the liquid phase decreases sharply with increasing temperature, accompanied by an increase in the fraction of the phase and phase. Generally, an anti-melt behavior is defined as a melting behavior in a temperature interval between T and T* in FIG. 2, i.e., the fraction of the liquid phase sharply decreasing with increasing temperature. Once the temperature exceeds T* in FIG. 2, the fraction of the liquid phase sharply increases with increasing temperature until the alloy melts completely. In addition, the decreased liquid phase between the temperatures T and T* may also can reduce the flowability of the liquid metal, and this characteristic is particularly significant for serving as a thermal interface material. The shadow area in FIG. 2 is a temperature interval where the material is suitable as the thermal interface material. Apparently, a foil-like liquid metal thermal interface material having an anti-melt characteristic may have a wider operating temperature range as compared to a common foil-like liquid metal.

[0016] FIG. 2 is a schematic diagram illustrating variations of a phase fraction of a foil-like liquid metal in an anti-melt state with temperature (this system comprises a liquid phase, phase and phase).

[0017] The melting and the phase content of an alloy are closely associated with the thermodynamic properties of the alloy. Therefore, theoretically, it is possible to design a foil-like liquid metal having the anti-melt behavior based on a phase diagram. Generally, a phase diagram of a c-component system is c-dimensional, and consists of a single-phase zone, a two-phase zone, a three-phase zone . . . a c-phase zone. By using a novel material design technique, appropriate alloy constituents may be found so that the alloy has the anti-melt behavior when used as a liquid metal, as shown in FIG. 2. In other words, the flowability of a foil-like liquid metal in a solid-liquid state may be customized to prevent side leakage of the liquid metal, and the thermal conductivity can be improved to an utmost extent. Besides, such a design method may provide a foil-like liquid metal having an anti-melt characteristic for use within a temperature range of 60 C. to 18 C. for an IGBT system.

[0018] Based on the above novel material design technique, the present invention provides a liquid metal thermal interface material having an anti-melt characteristic for heat dissipation of IGBTs. Operating temperatures of suitable IGBT heat dissipation systems range from 60 C. to 180 C. The liquid metal thermal interface material having the anti-melt characteristic is produced through alloy smelting, casting, heat treatment and cold rolling processes.

[0019] That is, the present disclosure includes the following invention: [0020] (1) A liquid metal thermal interface material having an anti-melt characteristic is characterized by comprising, in percentage by weight, 20-40 wt % of indium, 0-6 wt % of bismuth, 0-2 wt % of antimony, 0-3 wt % of zinc, 0-0.6 wt % silver, 0-0.3 wt % of nickel, 0-0.8 wt % of cerium, 0-0.6 wt % of europium and the balance of Sn. [0021] (2) The liquid metal thermal interface material according to above (1) has an anti-melt temperature ranging from 64 C. to 180 C. Such a material starts melting at a temperature ranging from 60 C. to 140 C., and keeps in a solid-liquid state between 60 C. and 200 C., with a related anti-melt temperature ranging from 64 C. to 180 C., depending on the selected alloy constituents. [0022] (3) The liquid metal thermal interface material according to above (1) or (2) is suitable for heat dissipation of an IGBT system within a temperature range of 60 C. to 180 C. [0023] (4) A method of preparing the liquid metal thermal interface material according to above (1) to (3) is characterized in that: using argon/nitrogen as a protective atmosphere, and performing induction melting of a material mixed according to the alloy composition of above (1) to (3) in a graphite crucible by using an induction smelting technique, and then stirring at a temperature ranging from 400 C. to 500 C. for about 10 minutes. The specific temperatures are selected according to the selected alloy constituents. The uniformly-stirred alloy melt is then poured into a graphite mold for solidification, and heat treatment is performed on the solidified alloy ingots at a temperature ranging from 40 C. to 140 C. for 2 to 4 hours. The purpose of the heat treatment is to achieve sufficient phase precipitation of the alloy, which is conducive to improving the mechanical properties of the material and facilitates further cold rolling. The further cold rolling is carried out afterwards. [0024] (5) In the preparation method of the liquid metal thermal interface material according to above (4), a rolling quantity per pass in the cold rolling is 20-30%. The heat treated alloy ingots may be cold rolled at the room temperature to a required thickness, such as 0.05 mm. The rolling quantity per pass is 20-30% depending on the selected alloy constituents.

[0025] The present invention has the following advantages: [0026] (1) The foil-like liquid metal thermal interface material in the present invention has sufficient temperature ranges and possesses an anti-melt characteristic. The material keeps in a solid-liquid state with a sufficient solid phase content within these temperature ranges. As enough viscosity is provided to prevent side leakage, short circuit of an electronic system can be avoided completely. An ultimate solution can be absolutely carried out for the heat dissipation requirements of IGBTs today with increasingly rigid heat dissipation requirements. [0027] (2) Such a foil-like liquid metal thermal interface material may be manufactured through simple steps, including induction smelting, casting, heat treatment and cold rolling. Despite low production cost, the product has excellent thermal conductivity and chemical stability in operating environments of IGBT. It is very applicable for IGBT devices in large-scale industrial production and practical applications. [0028] (3) The liquid metal thermal interface material having the anti-melt characteristic provides an effective solution at the top of a heat dissipation pyramid for heat dissipation in extreme conditions. It can promote rapid development in many new industrial fields in practice, especially for high heat-flow density electronic devices. It is expected that the related products of the present invention will certainly be applied on a large scale to the fields of information and telecommunications, advanced energy, photovoltaic industry, space application, advanced weapon systems and advanced electronics soon in the future.

BRIEF DESCRIPTION OF THE DRAWINGS

[0029] FIG. 1 is a schematic diagram illustrating variations of a phase fraction of a foil-like liquid metal in a normal melting state with temperature, wherein the system comprises only a liquid phase and a phase.

[0030] FIG. 2 is a schematic diagram illustrating variations of a phase fraction of a foil-like liquid metal in an anti-melt state with temperature, wherein the system comprises a liquid phase, phase and phase.

DETAILED DESCRIPTION OF THE INVENTION

[0031] The present invention will be described in more details below through embodiments. However, the present invention is not limited to such embodiments.

Embodiment 1: Preparation of a Liquid Metal Thermal Interfacial Material 1 in the Present Invention

[0032] Alloy raw materials are prepared in the following percentages by weight: 22 wt % indium, 1.4 wt % bismuth, 0.3 wt % of antimony, 1.6 wt % of zinc, 0.05 wt % silver, 0.02 wt % of nickel, 0.02 wt % of cerium, 0.01 wt % of europium and the balance of Sn.

[0033] The above alloy constituents are subjected to induction smelting in a graphite crucible with argon or nitrogen as a protective atmosphere. The temperature is kept at 420 C., and the materials are electromagnetically stirred for 10 minutes to fine homogenization. Next, the molten alloy liquid is poured into a graphite mold for casting. After the alloy solidifies, the alloy ingots are subjected to heat treatment for 3 hours at 40 C. to ensure complete precipitation of a second phase in the alloy and excellent mechanical properties of the alloy. Cold rolling is carried out at a room temperature afterwards, and a thickness of 0.05 mm is obtained through several passes of rolling, wherein the rolling quantity per pass is 24%.

[0034] The alloy material obtained is a foil-like liquid metal that begins melting at about 60 C. and keeps a solid-liquid state between 60 C. and 74 C. The foil-like liquid metal has an anti-melt characteristic within a range of 62 C. to 68 C. and can be well applied to heat dissipation of a system of which an IGBT heat source temperature is below 68 C.

Embodiment 2: Preparation of a Liquid Metal Thermal Interfacial Material 2 in the Present Invention

[0035] Alloy raw materials are prepared in the following percentages by weight: 28 wt % indium, 1.9 wt % bismuth, 0.4 wt % of antimony, 1.8 wt % of zinc, 0.03 wt % silver, 0.01 wt % of nickel, 0.01 wt % of cerium, 0.02 wt % of europium and the balance of Sn.

[0036] The above alloy constituents are subjected to induction smelting in a graphite crucible with argon or nitrogen as a protective atmosphere. The temperature is kept at 420 C., and the materials are electromagnetically stirred for 10 minutes to fine homogenization. Next, the molten alloy liquid is poured into a graphite mold for casting. After the alloy solidifies, the alloy ingots are subjected to heat treatment for 3 hours at 80 C. to ensure complete precipitation of a second phase in the alloy and excellent mechanical properties of the alloy. Cold rolling is carried out at a room temperature afterwards, and a thickness of 0.05 mm is obtained through several passes of rolling, wherein the rolling quantity per pass is 28%.

[0037] The alloy material obtained is a foil-like liquid metal that begins melting at about 84 C. and keeps a solid-liquid state between 84 C. and 115 C. The foil-like liquid metal has an anti-melt characteristic within a range of 92 C. to 108 C., and can be well applied to heat dissipation of a system of which an IGBT heat source temperature is below 110 C.

Embodiment 3: Preparation of a Liquid Metal Thermal Interfacial Material 3 in the Present Invention

[0038] Alloy raw materials are prepared in the following percentages by weight: 32 wt % indium, 2.1 wt % bismuth, 0.6 wt % of antimony, 2.9 wt % of zinc, 0.02 wt % silver, 0.03 wt % of nickel, 0.02 wt % of cerium, 0.01 wt % of europium and the balance of Sn.

[0039] The above alloy constituents are subjected to induction smelting in a graphite crucible with argon or nitrogen as a protective atmosphere. The temperature is kept at 420 C., and the materials are electromagnetically stirred for 10 minutes to fine homogenization. Next, the molten alloy liquid is poured into a graphite mold for casting. After the alloy solidifies, the alloy ingots are subjected to heat treatment for 3 hours at 100 C. to ensure complete precipitation of a second phase in the alloy and excellent mechanical properties of the alloy. Cold rolling is carried out at a mom temperature afterwards, and a thickness of 0.05 mm is obtained through several passes of rolling, wherein the rolling quantity per pass is 30%.

[0040] The alloy material obtained is a foil-like liquid metal that begins melting at about 118 C. and keeps a solid-liquid state between 118 C. and 142 C. The foil-like liquid metal has an anti-melt characteristic within a range of 124 C. to 132 C., and can be well applied to heat dissipation of a system of which an IGBT heat source temperature is below 140 C.

[0041] The present invention may be used in an insulated gate bipolar transistor (IGBT) system