SiC-filled polymers with high electrical resistivity and high thermal conductivity
A thermal interface material is made by dispersing in a polymer, such as epoxy, silicone, or urethane, silicon carbide particles which have been previously oxidized to form a strongly adherent insulating layer. The attractive combination of high thermal conductivity and high electrical resistivity is achieved by controlling the thickness of the oxide layer and the loading of the ceramic particles in the polymer matrix.
1. A thermal interface material comprising silicon carbide particles in a polymer matrix, wherein a majority of the silicon carbide particles are greater than one micrometer in diameter and have a sufficient surface oxide layer to obtain in the thermal interface material a volume electrical resistivity greater than 1×10 10 ohm-cm at 25° C. and 100 V, and wherein the thermal interface material comprises a volume loading of the silicon carbide particles sufficient to obtain a thermal conductivity greater than 2.0 W/mK at 25° C., and a porosity less than 5% by volume.
2. The thermal interface material of claim 1 wherein the surface oxide layer of at least a portion of the silicon carbide particles is greater than nm in thickness.
3. The thermal interface material of claim 1 wherein the volume electrical resistivity is greater than 1×10 11 ohm-cm at 25° C. and 100 V, and the thermal conductivity is greater than 2.5 W/mK at 25° C.
4. The thermal interface material of claim 1 wherein the thermal conductivity is greater than 3.0 W/mK at 25° C.
5. The thermal interface material of claim 1 wherein the thermal interface material is selected from the group consisting of bulk heat sinks, potting compounds, adhesives and high-temperature filled cements.
6. The thermal interface material of claim 1 wherein the polymer matrix is selected from the group consisting of epoxy, urethane and silicone polymers, and combinations thereof.
7. The thermal interface material of claim 1 wherein the silicon carbide particles have a bimodal size distribution.
8. The thermal interface material of claim 1 wherein the volume loading of silicon carbide particles exceeds 50%.
9. The thermal interface material of claim 1 wherein the surface oxide layer is a native oxide layer on the silicon carbide particles that has been increased by thermal oxidation.
10. The thermal interface material of claim 1 where the silicon carbide particles are comprised of alpha-SiC grits subjected to an oxidation treatment prior to mixing with the polymer.
11. The thermal interface material of claim 1 additionally comprising particles with a higher dielectric strength than the silicon carbide particles.
12. The thermal interface material of claim 1 additionally comprising particles of one or more from the group consisting of oxides, nitrides, oxynitrides and combinations thereof.
13. The thermal interface material of claim 1 additionally comprising aluminum nitride particles.
14. An adhesive material comprising thermally conductive silicon carbide particles in a polymer matrix, wherein:
(a) a majority of the silicon carbide particles are greater than one micrometer in diameter and have a sufficient surface oxide layer to (i) obtain in the adhesive material a volume electrical resistivity greater than 1×10 10 ohm-cm at 25° C. and 100 V, and (ii) retain in the silicon carbide particles having the surface oxide layer a thermal conductivity of at least 90% of the thermal conductivity of the silicon carbide particles without the surface oxide layer;
(b) the adhesive material comprises a porosity less than 5% by volume; and
(c) the adhesive material is characterized by a flowability sufficient to wet a surface during application to the surface at a volume loading of 50% or more of silicon carbide particles.
15. The adhesive material of claim 14 wherein the adhesive material comprises at least 50% by volume of the silicon carbide particles.
16. The adhesive material of claim 14 wherein the surface oxide layer on at least a majority of the silicon carbide particles is less than 10% by volume of the total volume of the silicon carbide particles.
17. The adhesive material of claim 14 further comprising additional particles with a higher dielectric strength than the silicon carbide particles.
18. The adhesive material of claim 17 wherein the additional particles are selected from the group consisting of oxides, nitrides, and oxynitrides and combinations thereof.
19. The adhesive material of claim 17 comprising at least 60% by volume of a combination of silicon carbide particles and additional particles, wherein the combination has a bimodal particle size distribution, a majority of the silicon carbide particles are less than or equal to 15 micrometers in diameter, and a majority of the additional particles are greater than or equal to 5 micrometers in diameter.
20. The adhesive material of claim 14 wherein the polymer matrix comprises at least one polymer selected from thermoset polymers and thermoplastic polymers and combinations thereof.
21. The adhesive material of claim 14 wherein the polymer matrix is selected from the group consisting of epoxy, urethane and silicone polymers, and combinations thereof.
22. An adhesive material comprising silicon carbide particles in a polymer matrix, wherein:
(a) a majority of the silicon carbide particles are greater than one micrometer in diameter and have a sufficient surface oxide layer to obtain in the adhesive material a volume electrical resistivity of the composite greater than 1×10 10 ohm-cm at 25° C. and 100 V;
(b) the adhesive material comprises a volume loading of the silicon carbide particles sufficient to obtain a thermal conductivity in the adhesive material greater than 2.0 W/mK at 25° C.; and
(c) the silicon carbide particles have a bimodal particle size distribution.
23. The adhesive material of claim 22 wherein the silicon carbide particles have a bimodal average particle size distribution resulting in a diameter ratio of at least 7:1 of coarse-to-fine size particles.
24. The adhesive material of claim 22 wherein the silicon carbide particles have a bimodal average particle size distribution resulting in a green density ratio of about 2.3:1 coarse-to-fine size particles.
25. The adhesive material of claim 22 wherein the adhesive material comprises at least 50% by volume of the silicon carbide particles.
26. The adhesive material of claim 22 wherein the polymer matrix comprises at least one polymer selected from thermoset polymers and thermoplastic polymers and combinations thereof.
27. The adhesive material of claim 22 wherein the polymer matrix is selected from the group consisting of epoxy, urethane and silicone polymers, and combinations thereof.
28. A radiation resistant adhesive comprising the adhesive material of claim 22 .