Recently, it has become more important to take the thermal dispersion of circuit boards into account. We have developed a new composite substrate with high thermal conductivity (HTC-CS) which is suitable for power modules. The main points of development of the substrate are: (1) newly developed composite materials with high thermal conductivity; (2) use of the lead frame (L/F) as a conductive layer; (3) use of thermally conductive sheets (TCSs) and realization of a simple procedure. Alumina and epoxy resin were mixed to make a slurry and were made into sheets by the doctor blade method. The sheet (TCS) was flexible while the resin was not hardened. The TCS was laid on the L/F and heated under pressure. The TCS moved into the gaps in the L/F patterns and the surface became flat; simultaneously, the resin in the TCS hardened to produce a rigid substrate. The substrate thermal conductivity was above 5 W/mK. The substrate was applied to intelligent power modules (IPM). These IPMs showed good reliability. In addition, it is simple to insert a shield layer in the substrate using the TCS procedure, and the substrate has high noise stability.
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