Patent ID: 8151455

Claim:
A method of manufacturing a printed circuit board for forming a through-hole for connecting a predetermined conductor-wiring layer of a multilayer printed circuit board having a plurality of conductor layers and insulating layers, applying conductive plating to the through-hole, and removing an overlong plated portion by drilling up to the vicinity of the conductor-wiring layer, the method comprising the steps of: preliminarily forming a plurality of test pattern layers for detecting the depth of an inner layer in the multilayer printed circuit board such that at least a part of a lower test pattern layer is not overlaid with any upper test pattern layer when viewed from a drill entrance side, and a surface conductor layer such that all the test pattern layers are overlaid with it; applying a voltage to two selected test pattern layers in the vicinity of a region subjected to the drilling, the depths of the two test pattern layers being near the depth of the conductor-wiring layer; performing a first drilling toward one of the selected test pattern layers by use of a drill for the drilling, and detecting a current produced when the drill comes into contact with the relevant test pattern to measure the depth of the layer (D 1 ); performing a second drilling toward the other test pattern layer by use of the drill, and detecting a current produced when the drill comes into contact with the relevant test pattern to measure the depth of the layer (D 2 ); and performing a third drilling by use of the drill up to just before the conductor-wiring layer based on a depth calculated from the D 1 and D 2 .