Abstract: A differential diameter hole drilling method by which through-holes having improved major surface quality are formed in a target material involves drilling a pilot hole having a diameter that is less than the desired diameter of the through-hole and then drilling a through-hole having the desired diameter. The pilot hole forms a channel from which thermal energy produced during laser drilling can diffuse into the environment, thereby reducing the amount of thermal energy diffusing into the surrounding target material matrix and the degree of thermal damage to the heat affected zone of the target material matrix. The pilot hole also forms a channel through which ablated target material may be removed, thereby increasing overall through-hole throughput. Pilot hole formation reduces the thermal energy required to form the remaining portion of the through-hole and thereby results in less thermal damage to the surrounding target material matrix.

Abstract: A method of fabricating a printed wiring board (1) and a printed wiring board module (17) by providing a first board (1) having a pair of major opposing surfaces, a via (3) having walls extending between the surfaces and a layer of copper (5) disposed on at least one surface and extending along the walls of the via. The copper disposed in the via is protected against a subsequent etching of the copper on the surface by filling the remaining portion of the via with an epoxy (7) and then reducing the thickness of the layer of copper on the surface. The layer of copper and the epoxy are then planarized. A core layer and a second board are then provided and the first and second boards are secured to opposing sides of the core layer. A second via having walls and extending through the first and second boards and the core layer is then formed and a layer of copper is disposed on the walls of the second via and the surface.