CN113214583B - Thermal interface material with vertical sandwich structure and preparation method thereof - Google Patents

Abstract

The invention relates to a thermal interface material with a vertical sandwich structure and a preparation method thereof. In the polymer composite film with a vertical sandwich structure prepared by the method of the invention, the thermally conductive fillers are oriented and distributed in the film matrix, that is, the upper and lower surfaces are arranged in parallel, and the middle part is arranged vertically, which can form thermal conduction paths in the in-plane and out-of-plane directions. Effectively improve the thermal conductivity inside and outside the plane. The present invention includes the following steps: preparing a mixed solution of polymer gel containing thermally conductive filler, and dropping it onto a flat substrate. The ice-calendered gel solution containing calcium ions is used to form a film and freeze, and after the cryogel film is subjected to solvent exchange and normal pressure drying, a composite film with a vertical sandwich structure can be obtained. The thermal interface material prepared by the invention has two-way high thermal conductivity and excellent mechanical properties, and can effectively improve the heat dissipation performance.

Description

Thermal interface material with vertical sandwich structure and preparation method thereof

technical field

The invention relates to a thermal interface material with a vertical sandwich structure and a preparation method thereof, belonging to the technical field of thermally conductive composite materials.

Background technique

In recent years, with the development of microelectronic devices in the direction of miniaturization, light weight, high density and high integration, the heat generated during operation is difficult to dissipate quickly, which greatly shortens the service life of electronic devices, reduces the safety and performance of electronic devices. also greatly affected. Heat dissipation is critical to the life, safety, and performance of electronic devices, so exploring and developing new heat dissipation materials for thermal management of high-power-density electronic devices has become a research hotspot in the fields of electronic information and new materials. Thermal interface material (TIM) is a material used for heat dissipation and packaging of integrated circuits. It is mainly used to fill the microscopic gaps and uneven holes on the surface when the two materials are joined or contacted, and the electronic components are produced. The excess heat is quickly conducted and dissipated into the surrounding environment or cooling system. To maximize heat transfer efficiency, TIMs require not only high thermal conductivity, but also easy compression and flexibility to fill gaps. Polymer matrix composites are widely used as TIMs due to their good mechanical flexibility, but due to the mostly amorphous structure of polymers, the intrinsic thermal conductivity is low. In order to meet the requirements of the thermal conductivity of TIM, fillers with higher thermal conductivity, such as carbon materials, metal materials and ceramic materials, are usually added to the polymer. In order to improve the thermal conductivity of composite materials, it is a very effective means to arrange the fillers reasonably and build a thermal network in the matrix.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a thermal interface material with a vertical sandwich structure and a preparation method thereof. Due to the reasonable orientation and arrangement of the fillers in the composite material, an effective thermal conduction network can be formed at a relatively low content. It has excellent thermal conductivity in the in-plane and out-of-plane directions, and also has flexible properties, which is the best in the heat dissipation of electronic components. The application has laid a foundation, and the composite material of this system has good shape stability and small expansion coefficient at high temperature. It is easy to process and does not need complicated and expensive equipment and preparation technology, so it has good theoretical research and practical application value.

The present invention provides a thermal interface material with a vertical sandwich structure. The thermal interface material includes a thermally conductive filler and a polymer material with flexible properties, and the mass percentage of the thermally conductive filler and the polymer material is 2.5% to 25%.

In the present invention, the film thickness of the thermal interface material is 100-400 μm.

In the present invention, the cross-sectional structure of the thermal interface material is that the upper and lower surfaces are parallel structures, and the vertically oriented structures are embedded between the parallel structures.

In the present invention, the orientation structure of the thermally conductive filler of the thermal interface material is that the upper and lower surfaces are oriented in parallel, and the middle part is oriented vertically.

In the present invention, the polymer material with flexibility is a water-soluble polymer, including at least one of polyvinyl alcohol, water-based polyurethane or water-based polyacrylate.

In the present invention, the thermally conductive filler comprises at least one of graphene, hexagonal boron nitride, graphite sheet, MXene or carbon nanotube.

The present invention proposes a method for preparing a thermal interface material with a vertical sandwich structure, and the specific steps are as follows:

(1) Measure 10mL of deionized water, add 0.15~0.3g of sodium alginate and 0.1~1.2g of water-soluble polymer, fully stir and mix under corresponding dissolution conditions, add 0.01~0.2g of thermally conductive filler, and stir to obtain mixed gel solution;

(2), drop the mixed gel solution obtained in step (1) onto the flat substrate, place the ice containing calcium ions on the gel, roll it into a film and freeze it, remove the calcium ion ice, and obtain the frozen gel. adhesive film;

(3), soaking the frozen film obtained in step (2) in ethanol and acetone in turn; drying under normal pressure can obtain a thermal interface material with a vertical sandwich structure.

In the present invention, the ice containing calcium ions in step (2) is frozen from a calcium chloride solution.

The beneficial effects of the thermal interface material prepared in the present invention are:

(1) In the present invention, since the thermally conductive fillers inside the composite film are reasonably oriented and arranged into a vertical sandwich structure, thermal conduction paths can be formed in the in-plane and out-of-plane directions, and the thermal conductivity is very excellent;

(2) In the present invention, due to being compounded with a flexible polymer material, it has good flexibility;

(3) In the present invention, the composite film has a simple preparation process, no pollution to the environment, low raw material and production costs, and is conducive to large-scale preparation;

(4) In the present invention, the composite film exhibits excellent heat dissipation effect when the CPU is fully loaded.

Description of drawings

FIG. 1 is an appearance photo and a scanning electron microscope photo of the thermal interface material with a vertical sandwich structure in Example 1. FIG. Among them (a) is the macro photo of the thermal interface material with vertical sandwich structure, the scale bar is 2 cm, (b) is the scanning electron microscope photo of the thermal interface material with vertical sandwich structure;

FIG. 2 is a Micro-CT photograph of the thermal interface material with a vertical sandwich structure in Example 1. FIG. where (a) is a photo of the film with a vertical sandwich structure, and (b) is a cross-sectional photo of the thermal interface material with a vertical sandwich structure;

FIG. 3 is the in-plane and out-of-plane thermal conductivity of the thermal interface material with a vertical sandwich structure in Example 1;

4 is a thermal expansion curve of a thermal interface material having a vertical sandwich structure in Example 1;

5 is the resistivity of the thermal interface material with vertical sandwich structure in Example 1;

FIG. 6 is an infrared image of the thermal interface material with a vertical sandwich structure in Example 1. FIG. Among them: (a) and (c) are the infrared images of the sample before heating, (b) and (d) are the infrared images of the sample after being heated on a 90°C hot stage for 90s;

FIG. 7 shows the temperature change of the CPU core when the thermal interface material with the vertical sandwich structure is used for heat dissipation in Example 1;

8 is a scanning electron microscope photograph of a thermal interface material with a vertical sandwich structure in Example 2;

FIG. 9 shows the in-plane and out-of-plane thermal conductivity of the thermal interface material with the vertical sandwich structure in Example 2. FIG.

Detailed ways

The present invention will be further described below with reference to specific embodiments and accompanying drawings, but the present invention is not limited to the following embodiments. The methods are conventional methods unless otherwise specified. The raw materials can be obtained from open commercial sources unless otherwise specified.

Example 1:

First, 5g of commercial hexagonal boron nitride (BN) powder was dispersed in 500ml of a mixed solution of isopropanol and water (volume ratio 1:1) and ultrasonicated for more than 12h, centrifuged at 3000rpm for 10min to take the supernatant, and continued to centrifuge at 15000rpm for 10min. The precipitates were collected and lyophilized for later use. Disperse 0.2g of sodium alginate and 0.18g of polyvinyl alcohol in 10mL of deionized water, stir and dissolve at 90°C for 30min, cool to room temperature and stir for more than 24h, add 0.07g of the lyophilized powder, and stir for more than half an hour to fully mix;

Next, the obtained mixed gel solution was dropped on a flat substrate, and ice (3wt% CaCl ₂ ) containing calcium ions was rolled on the gel solution for 10min to form a film and freeze. Remove the ice cubes, soak the frozen gel film in ethanol and acetone for 1 h, and dry at 60°C under normal pressure to obtain a polymer/BN composite film with a vertical sandwich structure;

As shown in Figure 1, the prepared polymer/BN composite film has a white appearance, no obvious damage after folding, and the cross-section has a vertical sandwich structure, and the vertical structure is embedded in the upper and lower parallel layered structure;

Figure 2 shows the photo of the distribution of filler BN in the polymer/BN composite film. It can be seen that the vertically arranged BN is embedded in the BN arranged in parallel on the upper and lower surfaces to form a vertical sandwich structure;

Figure 3 shows the thermal conductivity of pure polymer films and polymer/BN composite films. The vertical sandwich structure can form thermal conduction paths in both in-plane and out-of-plane directions to improve thermal conductivity;

As shown in Figure 4, compared with the pure polymer film, the polymer/BN composite film has less thermal expansion and better shape stability;

Figure 5 shows the resistivity of the polymer/BN composite film, and it can be seen that it has excellent electrical insulating properties;

Figure 6(a) and Figure 6(b) compare the thermal imaging photos of the pure polymer, Figure 6(c) and Figure 6(d) polymer/BN composite film, it can be seen that the polymer/BN composite film The surface temperature is significantly higher than that of pure polymer;

Figure 7 shows the core temperature curve of the CPU when the polymer/BN composite film with a vertical sandwich structure is used for heat dissipation. It can be seen that after using the polymer/BN composite film with a vertical sandwich structure, the core temperature of the CPU under full load operation can be reduced 27°C.

Example 2:

Disperse 0.2 g of sodium alginate and 0.6 g of polyvinyl alcohol in 10 mL of deionized water, stir and dissolve at 90°C for 1 h, cool to room temperature and stir for more than 24 h, add 0.04 g of graphene, and stir for more than half an hour to fully mix;

Next, the obtained mixed gel solution was dropped on a flat substrate, and ice (3wt% CaCl ₂ ) containing calcium ions was rolled on the gel solution for 10min to form a film and freeze. Remove the ice cubes, soak the frozen gel film in ethanol and acetone in turn for 1 h, and dry at 60°C under normal pressure to obtain a polymer/graphene composite film with a vertical sandwich structure;

Figure 8 shows the SEM photo of the polymer/graphene composite film, showing a vertical sandwich structure in cross section;

Figure 9 shows the thermal conductivity of the polymer/graphene composite films, with excellent thermal conductivity in the in-plane and out-of-plane directions.

Claims (6)

1. The thermal interface material with the vertical sandwich structure is characterized by comprising a heat-conducting filler and a polymer material with flexible performance, wherein the mass percentage of the heat-conducting filler to the polymer material is 2.5% -25%; the cross section structure of the thermal interface material is that the upper surface and the lower surface are parallel structures, and a vertical orientation structure is embedded between the parallel structures; the orientation structure of the heat conducting filler of the thermal interface material is that the upper surface and the lower surface are oriented in parallel, and the middle part is oriented vertically;

the preparation method of the thermal interface material comprises the following specific steps:

(1) weighing 10mL of deionized water, adding 0.15-0.3 g of sodium alginate and 0.1-1.2 g of polymer material, fully stirring and mixing under corresponding dissolving conditions, then adding 0.01-0.2 g of heat-conducting filler, and stirring to obtain a mixed gel solution;

(2) dripping the mixed gel solution obtained in the step (1) on a flat base material, placing ice containing calcium ions on the gel, calendering to form a film, freezing, and removing the calcium ion ice to obtain a frozen gel film;

(3) sequentially soaking the frozen film obtained in the step (2) in ethanol and acetone; drying under normal pressure to obtain the thermal interface material with a vertical sandwich structure.

2. A thermal interface material as defined in claim 1, wherein the thermal interface material has a film thickness of 100 to 400 μm.

3. A thermal interface material as claimed in claim 1, wherein the polymer material with flexible property is water soluble, specifically any one of polyvinyl alcohol, aqueous polyurethane or aqueous polyacrylate.

4. The thermal interface material of claim 1, wherein the thermally conductive filler is any one of graphene, hexagonal boron nitride, graphite flakes, MXene, or carbon nanotubes.

5. The method for preparing a thermal interface material with a vertical sandwich structure according to claim 1, comprising the following steps:

(1) weighing 10mL of deionized water, adding 0.15-0.3 g of sodium alginate and 0.1-1.2 g of polymer material, fully stirring and mixing under corresponding dissolving conditions, then adding 0.01-0.2 g of heat-conducting filler, and stirring to obtain a mixed gel solution;

(2) dripping the mixed gel solution obtained in the step (1) on a flat base material, placing ice containing calcium ions on the gel, calendering to form a film, freezing, and removing the calcium ion ice to obtain a frozen gel film;

(3) sequentially soaking the frozen film obtained in the step (2) in ethanol and acetone; drying under normal pressure to obtain the thermal interface material with a vertical sandwich structure.

6. The method according to claim 5, wherein the calcium ion-containing ice of step (2) is prepared by freezing a calcium chloride solution.

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