Thermal performance of conventional printed circuit materials can be increased with the use of heat sinks. Even better thermal dissipation can be achieved with the use of insulated metal boards as substrates. However, this technology is limited in the number of circuit layers and the circuit density. A novel material based on transient liquid phase sintering (TLPS) was developed and used to make additive multilayer circuits on metal substrates. The partial sintering operation of the polymer-based conductive composite is akin to that of Cermet materials, but processing is at temperatures of < 250° C. A metallurgically alloyed web is formed by TLPS, providing good conductivity and stability with respect to humidity and heat exposure. An interpenetrating polymer network provides adhesion to a variety of substrates.
Photoimageable dielectrics have been used to image circuit traces (as fine as 50 μm) and vias (down to 75 μm). The conductive composite is filled into the grooves and cured to form circuits. Sequential building of circuit and via layers yields the desired planarized circuit with blind and buried solid vias throughout the multilayer structure. Metal substrates have been chosen to achieve high thermal dissipation. The thermal conductivity of the polymer-based conductive composite itself was measured to be 25 W/mK, comparable to that of solder materials. Thermally resistive adhesive interfaces have been minimized in the fabricating the structure, resulting in a high thermal dissipation, as well as high density substrate.