Dry lubricant drilling of thru-holes in printed circuit boards

Abstract

Thru-holes are drilled in a printed circuit board panel having alternating dielectric layers and electrically conductive layers. A water soluble dry film lubricant sheet is placed adjacent an electrically conductive outer layer of the panel prior to drilling thru-holes through the panel with a rotary drill. The drill surface is lubricated while forming a clean thru-hole from contact between the drill and the lubricant. The dry film lubricant generally may comprise a water soluble lubricant hardened to a solid or semi-solid dry film-form and impregnated in a carrier such as a porous paper sheet. In one embodiment, the dry film lubricant includes a water soluble lubricant such as dipropylene glycol, a non-ionic surfactant, and a wax-like hardener. Following drilling of the thru-holes, the dry film lubricant sheet is removed, and the thru-holes can be rinsed in an aqueous alkaline solution. The thru-holes are then plated with an electrically conductive metal for forming electrical contacts between the metalized thru-holes and the electrically conductive layers of the panel. The dry film lubricant extends drill life and produces a clean thru-hole that prevents epoxy smear and avoids the prior art use of harsh chemical treatment following drilling to otherwise remove dielectric smear or fibers that might extend into the thru-hole and disrupt the continuity of the later-formed electrical contact.

Dependencies are inferred from the claim text.