Excluding inclusions [PCB inspection]

The authors look at the causes of a persistent annoyance for manufacturers of printed circuit boards, and suggest some steps that would help to speed inspection and reduce both genuine faults and false rejects from the visual inspection system. This article goes into one detail of the problem: the inclusions in laminates that can cause false rejection in PCB manufacture. Laminate inclusions are now becoming prevalent because of the higher resolution needed to inspect reduced track and gap widths. Tests on rejected PCBs show that contamination inside laminates accounts for a large percentage of rejects. There are four main types of inclusions: tadpoles, burnt resin, metal and others. The most efficient way of spotting them is using visual methods