Electrical Feedthroughs Formed in Silicon Wafers by Screen Printing Conductive Paste into Laser Drilled Holes

A programmable laser drill was used to produce an array of 5.8 mil diameter holes in a 20 mil thick silicon wafer. Capable of drilling through a wafer with a single 250Mus, 0.7 Joule pulse, the Nd:YAG laser is used in a two pulse mode. The first pulse is triggered when the beam is defocused in order to produce a tapered-wall crater, and the second pulse is triggered when the beam is focused on the wafer in order to produce a straight-wall through hole. The hole's tappered entrance facilitates its subsequent filling with a Ag sub (x) Pd sub (1-x) paste which is screen printed and fired to form an electrical feedthrough.