Entry overlay sheet and method for drilling holes

Abstract

An overlay sheet having a first thin layer of a polymer material, a second thin layer of a hard material such as a phenolic, melamine or metal foil, and a third thin layer of a polymer material, the first and third layers sandwiching the second layer. The sheet is applied to a surface of a printed circuit board such that the third layer is against the board surface, and the first layer is exposed to receive the drill bit. During drilling operations, the drill bit is advanced initially through the softer first layer of the polymer material, immobilizing the tip of the drill bit against lateral movement, then through the harder layer, then through the softer third layer, and finally through the printed circuit board. The harder layer prevents formation of burrs, and the polymer material inhibits drill bit wander.

Dependencies are inferred from the claim text.