Through-Hole Drilling Condition of FR-4 Printed Wiring Boards Based on Preventing Ion Migration

Abstract

In the printed wiring board manufacturing sector, methods have been developed to improve the circuit packaging density. A problem has emerged in that the quality of drilled through hole is deteriorating in the smaller diameter drilling of printed wiring boards (PWBs) with high packaging density, because the insulation is insufficient among through-holes after plating in finer circuit pattern. Thus, we have attracted attention to occurrence of delamination in the glass cloth around the drilled hole of FR-4 type PWBs, because it is considered that the poor insulation among through holes is caused by ion migration along the delamination of glass cloth. In the drilling hole to GFRP, Damage occurs from the drilled hole wall to the inside of material by peeling off between layers, it is defined as delamination in this study. In the present report, we describe the influence of drilling conditions on the width of delamination of glass cloth around the drilled hole. First, we made the FR-4 type PWBs (thickness 0.2 mm) reinforced by five kinds of glass cloths. We carried out the drilling experiments (spindle speed 33000rpm and feed rate 0.01–0.06 mm/rev) for these PWBs with diameter 0.4 mm drill tools. Second, we researched the relationship between delamination width and relative hole position for the glass cloth thickness by image processing method. As a result, we demonstrate two important factors (the feed rate conditions in drilling and the thickness of glass cloth at drilled hole wall) to prevent the delamination of glass cloth. The practical formula is proposed to predict the delamination width around the drilled hole by a multivariate analysis method.