Failure analysis of cathode filament formation in multilayer PWBs using combined electron spin resonance and micro-FTIR techniques

Multilayered Printed Wiring Boards (PWBs) typically fail in the field from electrical overstress (EOS) and from a time dependent conductive filament formation (CFF) resulting in excessive leakage currents or catastrophic shorts. CFF is caused by oxidation of the epoxy and by a metal ion migration processes. The oxidation of the epoxy in these boards is induced by the formation of organic free radicals. Under severe temperature and mechanical stress, or through manufacturing processes, organic free radicals can be formed by breaking the C-C covalent bond within the epoxide molecule. The oxidation process is enhanced by the presence of the metal and metal ions. In this work, electron spin resonance (ESR), micron-size Fourier transform infra red (/spl mu/-FTIR), and energy dispersive X-ray spectroscopy were used to elucidate the mechanism of failure.