Patent ID: 6972070

Claim:
A method of making a printed wiring board comprising: packing via holes formed in an insulator material with an interlayer conducting material, wherein the interlayer conducting material includes a first metal material and a second metal material, and the second metal material melts at a temperature higher than a predetermined temperature; stacking layers of the insulator material with conductor patterns to form a stack such that the via holes are located between the conductor patterns in the stack; forming a solid conductive material in each of the via holes to electrically connect the conductor patterns by heating the stack to the predetermined temperature and pressing the stack; forming the interlayer conducting material as a paste prior to the packing, including adding a solvent to particles made of the metal materials; adding binder particles to the paste; and preheating the stack prior to the heating and pressing step and after the packing step to cause the binder particles to diffuse into the metal materials, wherein: the solid conductive material of each via hole includes a unified conductive layer and a solid phase diffusion layer, the solid phase diffusion layer is formed by the first metal material and a conductor metal, and the conductor metal is a metal of the associated conductor pattern.