Patent ID: 7188412

Claim:
A fabrication method for a printed wiring board, the method comprising: providing an insulator board made of thermoplastic resin and having a via-hole, a first surface and a second surface that is opposite the first surface; providing first and second conductor patterns that are respectively located on the first surface and the second surface to cover the via-hole, and that include a metal; packing an interlayer connecting material in the via-hole formed in the insulator board, the interlayer connecting material including a first metal and a second metal having a higher melting point than a healing temperature required for interconnecting the first and second conductor patterns; and interconnecting electrically the first and second conductor patterns with a unified conductive compound formed from the first and second metals sintered by hot-pressing the interlayer connecting material in the via-hole between the first and second conductor patterns, wherein, by the interconnecting, first and second solid phase diffusion layers are formed from the metal in the first and second conductive patterns and the first metal of the unified conductor compound diffused into the metal in the first and second conductor patterns and are located between the unified conductive compound and the first and second conductor pattern, and a volume of the unified conductive compound is reduced relative to a volume of the interlayer connecting material, a sidewall of the unified conductive compound in the via-hole becomes concave in shape and approaches a center axis of the via-hole approximatley halfway between the first surface and the second surface of the insulator board, and the first and second conductor patterns are electrically interconnected by the unified conductive compound and the first and second solid phase diffusion layers.