Open circuit caused by inner-layer separation in printed circuit board

Plated through holes provide conductive connection among different copper layers, and mechanical support for components. Plated through hole process includes many steps such as drill, desmear, micro-etch and electroless copper plating. Improper control of any step will lead to plated through hole defects. In the present study, an open circuit failure caused by one of plated through hole defects, inner-layer separation, was found. The inner-layer separation existed in all of four copper layers. The root cause of the inner-layer separation defect was found and the defect could be duplicated. Corrective action was implemented.