Etch Rate Uniformity Enhancement for Plasma Drill Smear Removal
Original Publication Date: 1987-Jun-01
Included in the Prior Art Database: 2005-Feb-01
RF plasmas of oxygen and fluorine are commonly used to remove epoxy drill smear from through holes on printed circuit boards. Achieving uniform plasma etch rates, especially for large boards or multiple standard size panels in close proximity, can be difficult. A method for achieving uniform etch rates is described in the following. The primary etch species used are atomic oxygen and atomic fluorine. For a given amount of atomic oxygen in the plasma, there is an optimum amount of atomic fluorine required to achieve a maximum etch rate. Fluorine atoms in small concentrations enhance etch rates through reactions which generate radical surface sites. Fluorine present in excess, however, inhibits etching through competition with O atoms for sites leading to the formation of fluorocarbon compounds on the surface.