Failure analysis on electrolytic Ni/Au surface finish of PCB used for wire bonding and soldering

摘要

Purpose - The purpose of this study is to address two kinds of printed circuit board (PCB) failures with electrolytic Ni/Au as the surface finish. One was the weak bondability of gold wires to Ni/Au pads and the other was "dull gold" and weak solder wettability, which both caused great loss for the PCB manufacturer. Design/methodology/approach - The failure samples were studied and analyzed in terms of macro- and micro-morphology of the surface finish, its element composition and thickness by various characterization techniques, such as three-dimensional stereo microscope, scanning electron microscope, energy dispersive spectroscopy and X-ray fluorescence spectrum. Findings - Then the causes of the two failures were both found to be the inadequate thickness of gold deposit and other surface finish defects, but these causes played different roles in either failure or the mechanisms differ. Finally, their failure mechanisms were discussed and corresponding countermeasures were put forward for prevention. Practical implications - This study not only addresses a practical failure problem but also provides some clues to a better and further understanding of the effect of PCB process and management on its quality and reliability in manufacturing practice. Originality/value - It sheds light on how the thickness and quality of surface finish affects its wire bonding and soldering performances.