2-DIMENSIONAL THERMAL CONDUCTIVE MATERIALS AND THEIR USE

Abstract

The development and manufacture of thermal interface materials including, among other forms, greases, pastes, gels, adhesives, pads, sheets, solders and phase change materials, with good through-plane thermal conductivity for thermal interface applications. The good through-plane thermal conductivity is achieved, through the formation of a conductive network by the use of thermal conductive material-coated fillers, combinations of thermal conductive material-coated fillers and uncoated fillers.

Claims

1. Thermal interface material containing a material selected from the group consisting of: a. fillers, b. coated fillers, wherein the coating is selected from the group consisting of i. graphene, and, ii. Boron nitride, and, c. mixtures of a. and b.

2. The thermal interface material as claimed in claim 1 wherein the thermal interface material is in a form selected from the group comprising of: a. grease, b. gel, c. adhesive, d. paste, e. solder, f. pad, and, g. phase change material.

3. The thermal interface material as claimed in claim 2 wherein the thermal interface material is in a form selected from the group consisting of: a. grease, b. gel, c. adhesive, d. paste, e. solder, f. pad, and, g. phase change material.

4. The thermal interface material as claimed in claim 1 wherein the filler is selected from, the group consisting of: a. a ceramic, b. a metal, c. polymers, d. carbonaceous materials, e. composite materials, and, f. mixtures of any of a.-d.

5. The thermal interface material as claimed in claim 4 wherein the ceramic filler is selected from the group consisting of: a. an oxide, b. a carbide, c. a boride, and, d. nitride.

6. The thermal interface material as claimed in claim 5 wherein the ceramic filler is selected from the group consisting of: a. alumina, b. zinc oxide, c. silica, d. boron nitride, e. silicon carbide, f. aluminum nitride, g. tin oxide, h. magnesium oxide, i. titanium oxide, and, j. beryllium oxide.

7. The thermal interface material as claimed in claim 4 wherein the metallic filler is a metal alloy.

8. The thermal interface material as claimed in claim 4 wherein the metallic filler is selected from the group consisting of: a. copper, b. aluminum, c. nickel, d. silver, and, e. gold.

9. The thermal interface material as claimed in claim 4 wherein the polymeric filler is selected from a group consisting of: a. thermoplastic polymers, b. thermoset polymers, and, c. elastomers.

10. The thermal interface material in claim 9 wherein the polymeric filler is selected from the group consisting of a. polyolefin, b. polyamide, e. polyimide, d. nylon, e. polyester, f. polystyrene, f. polyacrylate, g. polyvinyichloride, h. fluoropolymers, i. polyvinyl acetates, j. polybutadienes, k. polychioroprene, l. polyurethanes, and, m. copolymers of any of a.-m.

11. The thermal interface material as claimed in 4 wherein the carbonaceous filler is selected from the group consisting of a. graphite, b. carbon black, c. carbon fiber, d. amorphous carbon, and, e. diamond.

12. The thermal interface material as claimed in claim 1 wherein graphene coating is achieved by a method selected, from the group, consisting of: a. mechanical milling, b. slurry coating, c. spray drying, d. chemical vapor deposition, e. physical vapor deposition, and, f. graphifixation,

13. The thermal interface material as claimed in claim 12 wherein the graphene source is selected, from the group consisting of: a, graphene nanoplatelet, b. graphite, c. carbon black, d. activated carbon, and, e. pitch.

14. The thermal interface material as claimed, in claim 1 wherein, in addition, there is present an additional filler.

15. The thermal interface material as claimed in claim 14 wherein the additional filler is graphene nanoplatelets.

16. The thermal interface material, as claimed in claim 15 wherein the graphene nanoplatelets have a thickness below 100 nm.

17. The thermal interface material as claimed in claim 15 wherein the graphene nanoplatelets have a thickness below 50 nm.

18. The thermal interface material as claimed, in claim 15 wherein the graphene nanoplatelets have a thickness below 25 nm.

19. The thermal interface material as claimed in claim 15 wherein the graphene nanoplatelets have a sloe below 500 nm.

20. The thermal interface material as claimed in claim 15 wherein the graphene nanoplatelets have a size below 10 nm.

21. The thermal interface material as claimed in claim 15 wherein the graphene nanoplatelets have a size below 10 nm.

22. A thermal interface material comprised of a filler coated with a thermally conductive material.

23. The thermal interface material as claimed in claim 22 wherein the thermally conductive material is 2-dimensional material.

24. The thermal interface material as claimed in claim 23 wherein the 2-dimensional material is graphene.

25. The thermal interface material as claimed in claim 23 wherein the 2-dimensional material is graphene nanoplatelets.

26. The thermal interface material as claimed in claim 23 wherein the 2-dimensional material is boron nitride platelets.

27. A method of providing a thermal interface composite, said method comprising: A. providing a first substrate that is a heat sink; B. providing a second substrate that is a heat source; C. placing a thermal interface material as claimed in claim 1 between said first substrate and said second substrate.

28. A method of providing a thermal interface composite, said method comprising: A. providing a first substrate that is a heat sink; B. providing a second substrate that is a heat source; C. placing a thermal interface material as claimed in claim 22 between said first substrate and said second substrate.

29. A composite structure comprising: a solid heat source; a solid heat sink; a thermal interface material as claimed in claim 1 contained between said solid heat source and said solid heat sink.

30. A composite structure comprising: a solid heat source; a solid heat sink; a thermal interface material as claimed in claim 22 contained between said solid heat source and said solid heat sink.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] FIG. 1 is an exemplary application illustration of thermal interface material showing a pad on an AIN board 1, LED chip 2, thermal interface material 3, silicon 4, AIN board 5, thermal interface material 6, and heat sink 7.

[0022] FIG. 2 is an illustration of a nanoplatelet coated filler particle showing the graphene coating 8 and the filler particles 9 and 9.

[0023] FIG. 3 is an illustration of a thermal interface material made with thermally conductive nanoplatelets and nanoplatelet coated fillers showing the resin matrix 10, the graphene coated filler particle 11, the graphene sheet or graphene nanoplatelet 12.

[0024] FIG. 4 is a microphotograph of graphene nanoplatelet coated alumina fillers for thermal interface materials.

[0025] FIG. 5 is a graph of thermal conductivity of alumina of the prior art compared to coated alumina of the instant invention.

[0026] FIG. 6 is a graph of thermal resistance of alumina of the prior art compared to coated alumina of the instant invention.

[0027] FIG. 7 is a graph of thermal conductivity showing dry coated alumina versus wet coated alumina.

[0028] FIG. 8 is a graph showing thermal conductivity for alumina A versus alumina treated according to this invention B and coated alumina C, and coated alumina and nanoplatelet blend D.

[0029] FIG. 9 is a graph showing thermal resistance of dry coated alumina versus wet coated alumina.

[0030] FIG. 10 is a graph showing thermal resistance of alumina and wet coated alumina.

[0031] FIG. 11 is a graph showing thermal conductivity of alumina and wet coated alumina.

THE INVENTION

[0032] Thus, in one embodiment of this invention, there is a thermal interface material containing a material selected from the group consisting of fillers, graphene coated fillers, and, mixtures of fillers and graphene coated fillers.

[0033] In another embodiment, there is a method, of providing a thermal interface composite, the method comprising providing a first substrate that is a heat sink and providing a second substrate that is a heat source, and placing a thermal interface material as described herein between the first substrate and the second substrate.

[0034] There is a further embodiment, which is a composite structure comprising a solid heat source, a solid heat sink, and, a thermal interface material as described, herein contained between the solid neat source and the solid heat sink.

[0035] In the instant invention, a through-plane thermal pathway can foe achieved through two approaches:

[0036] 1. Use of nanoplatelet-coated filler particles. For example, ceramic particles can be coated by a highly conductive nanoplatelet material such as graphene nanoplatelet and boron nitride platelet. The coating helps ensure a vertical heat, conducting pathway with a; minimum amount of graphene nanoplatelet addition. FIG. 2 illustrates this concept.

[0037] 2. Use of fillers with different sizes and morphologies. For example, in one embodiment, nano-platelet coated spherical filler particles are used together with graphene nanoplatelets to form a 3-D conductive network better than using spherical particles alone. The additional graphene nanoplatelets serve to better bridge the fillers with improved contact due to the 2-D and flexible feature of graphene nanoplatelets as illustrated in FIG. 3. For example, the contact between two spheres is theoretically a single point contact. Introduction of flexible and flake-like graphene nanoplatelets can significantly increase the contact area of conductive fillers.

[0038] In one embodiment, this invention comprises a TIM grease made with graphene-nanoplatelet coated alumina fillers. Alumina fillers were coated with graphene-nanoplatelet by a process using a mechanical milling machine. The coating process was designed to effectively attach graphene nanoplatelets onto alumina filler without significantly pulverizing the graphene nanoplatelets or producing amorphous carbon coating. The coated alumina filler is shown in FIG. 4. The TIM made with graphene coated alumina filler showed significant increase in thermal conductivity (FIG. 5) and decrease in thermal resistivity (FIG. 6) as compared with bare alumina

[0039] In another embodiment, graphene coating of fillers is achieved by a wet method. Graphene nanoplatelets and alumina are mixed together in a solution of appropriate organic solvent, where they are dispersed and agitated by ultrasonic mixing for 5 minutes. The solvent is then evaporated, leaving behind a homogeneous powder. The -powder is dispersed into silicone oil in order to create a thermal grease. The resulting thermal grease shows enhanced thermal conductivity compared to a grease made with an equal loading of unmodified alumina, as shown in FIGS. 7 and 8.

[0040] In yet another embodiment, graphene nanoplatelets are added to a TIM grease together with graphene-coated alumina fillers. The additional graphene nanoplatelets serve to better bridge the fillers due to the 2-D and flexible features of graphene nanoplatelets. The flexible and flake-like graphene nanoplatelets can significantly increase the contact area of conductive fillers as illustrated in FIG. 3.

[0041] The term graphene as used in this invention shall include graphene nanoplatelets from fully exfoliated graphite to particles with thicknesses of less than 100 nm and/or number of layers less than 300, and preferably with thicknesses of less than 20 nm and/or number of layers less than 60.

EXAMPLES

Example 1

Milling

[0042] Graphene nanoplatelets and alumina were added together into a canister with nailing media, and ball milled for 20 minutes. The resulting homogeneous powder was dispersed into silicone oil in order to create thermal grease. The resulting thermal grease showed substantially increased thermal conductivity and lower thermal resistance compared to grease made with an equal loading of unmodified alumina. The grease also showed equal thermal conductivity and lower thermal resistance and viscosity compared to grease made by a simple mixture of the same graphene nanoplatelet and alumina mixture.

Example 2

Solution Processing

[0043] Graphene nanoplatelets and alumina were mixed together in a solution of appropriate organic solvent, where they were dispersed and agitated by ultrasonic mixing for 5 minutes.

[0044] The solvent was evaporated, leaving behind a homogeneous powder. The powder was dispersed into silicone oil in order to create a thermal grease. The resulting thermal grease showed enhanced thermal conductivity compared to a grease made with an equal loading of unmodified alumina.

Example 3

[0045] Graphene nanoplatelet coated alumina powder was prepared as described in example 1. This powder was dispersed into silicone oil together with unprocessed graphene nanoplatelet powder. The resulting thermal grease showed superior thermal conductivity compared to thermal greases prepared with an equal filler content of unmodified alumina, a mixture of unmodified alumina and unprocessed graphene nanoplatelet powder with the same graphene nanoplatelet to alumina ratio, or graphene nanoplatelet coated alumina with the same graphene nanoplatelet to alumina ratio. Shown in table I.

TABLE-US-00001 TABLE I Unpro- Sili- Uncoated cessed Coated Alumina cone Thermal Alumina GnP Alumina GnP Oil Resistance Sample (g) (g) (g) (g) (g) (cm{circumflex over ()}2*K/W) Control 1 17 0 0 0 3 1.20 Control 2 16.8 0.2 0 0 3 0.39 Example 1 0 0 16.8 0.2 3 0.17 Example 2 0 0 16.8 0.2 3 0.27 Example 3 0 0.1 16.702 0.198 3 0.29 Total Sample Mass Thermal Conductivity (g) (W/mK) 20 2.22 20 3.65 20 3.61 20 4.76 20 4.27