MANUFACTURE OF MULTILAYER WIRING BOARD

PROBLEM TO BE SOLVED: To keep the interlayer adhesive strength between an insulating layer and a conductor layer by forming a connection hole which passes through a thin part of the conductor layer and the insulating layer using a laser beam and then forming a Via conductor for connecting the conductor layer and a first wiring pattern, in the connection hole. SOLUTION: An insulating layer 1 is formed on a substrate 10 formed with a first wiring pattern 4 and then a conductor layer 6 is formed on the insulating layer 1. In part of the conductor layer 6 which is on the first wiring pattern 4, a thin part 8 is formed which is thinner than the other part of the conductor layer 6. Next, a laser beam having the diameter D2 smaller than the diameter D1 of the thin part 8 is cast to form a connection hole 3 which passes through the conductor layer 6 and the insulating layer 1. After removing smear, etc., in the connection hole 3, a Via conductor 5 is formed by electroless plating, etc., to connect the conductor layer 6 and the first wiring pattern 4 and then the conductor layer 6 is patterned to form a second wiring pattern 2.