Tomoo Nishiyama

High thermal conductivity composite sheets with controlled nanostructures for electric devices

We have developed the novel network polymer with mesogen to improve the thermal conductivity of epoxy resins by controlling the higher order structure. To obtain the evidence for the higher order structure, we carried out direct observations at both mesoscopic and microscopic scales. The developed resin shows an obvious lattice structure in the transmission electron microscope (TEM) image and large domains with sizes of about several micrometers in the atomic force microscope (AFM) image and the polarized optical microscope (POM). On the other hand, no domains of order-structures can be recognized in the TEM, AFM images and POM of conventional resin. Furthermore, the formed nanostructure of composite is confirmed by the small-angle X-ray diffraction. Thermal conductivities of developed epoxy resins are 1.0 W/m·K at a maximum and five times higher than that of the conventional ones. We mixed these resins with conventional ceramic fillers, then the new epoxy composites (10 to 15 W/m·K) have been obtained. Fabricated B-stage (pre-cured) sheet is flexible and the cured one shows good electrical properties. Thus the developed high thermal conductive composites may be applicable to the insulating adhesive sheets for power devices, etc.