Abstract: A board consisting of a polyimide layer and copper foils is worked from one direction by etching to form through-holes, and the copper foils and inside of the through-holes are plated with copper, or the board is worked by etching or laser machining to form blind holes to expose the copper foils on the other side and through-holes simultaneously, and copper foils and insides of the blind holes and the through-holes are plated with copper. A metal ball plated with a noble metal is fixed on the copper foil by solidification of a metal paste to form an electric contact. Two superimposed plastic sheets are formed with holes each having a projection on inner wall of the hole, thereby vertically holding conductors by the projections of the holes of the superimposed plastic sheets. A laser beam machining method fabricates grooves or slits in a workpiece.

Abstract: A board consisting of a polyimide layer and copper foils is worked from one direction by etching to form through-holes, and the copper foils and inside of the through-holes are plated with copper, or the board is worked by etching or laser machining to form blind holes to expose the copper foils on the other side and through-holes simultaneously, and copper foils and insides of the blind holes and the through-holes are plated with copper. A metal ball plated with a noble metal is fixed on the copper foil by solidification of a metal paste to form an electric contact. Two superimposed plastic sheets are formed with holes each having a projection on inner wall of the hole, thereby vertically holding conductors by the projections of the holes of the superimposed plastic sheets. A laser beam machining method fabricates grooves or slits in a workpiece.