Patent ID: 7178233

Claim:
A process for producing a collapsed filled via hole comprising placing an insulating resin sheet with or without a conductive material sheet on at least one surface of the resin sheet, and a conductive metal sheet having a thickness larger than the resin sheet in this order on a die hole provided in a metal mold; punching the conductive metal sheet with a punch that does not reach the resin sheet thereby producing a chip of the conductive metal, the chip of conductive metal is pressed into the resin sheet by the punch, whereby a through hole is formed in the resin sheet and the chip is inserted and remains in the through hole to form a filled via hole with a first end and a second end; and collapsing the first end and the second end of the filled via hole to externally spread like an umbrella thereby producing the collapsed filled via hole, wherein the chip of conductive metal protrudes from both surfaces of the resin sheet by 10 to 500 μm.