PCB failure analysis related to the ENIG black pad problem

The purpose of this paper is to verify the principal conclusions, done during the implementation of FP7 ASPIS project objectives in fundamental research of ENIG‐related failures by investigating real problematic PCB samples of different suppliers.

SEM, EDS and XPS techniques were applied for morphology and composition studies of ENIG coatings of three PCB samples (A, B and C), while electrochemical measurements were used to determine the porosity of EN and IG layers.

The surface morphology analysis of the un‐soldered pads of PCB A disclosed the fact that the surface of substrate was not pre‐treated in a proper manner before EN deposition, which generated structural defects such as cracks and opening pores in the EN layer, which in turn could produce the voids in the solder layer during the soldering process. The results of PCB B analysis confirmed the authors' observation that Au layers deposited on EN substrate from IG solution contaminated with Cu ions are highly porous and loosely adhering to EN coating, which, in addition, undergoes serious corrosion damages and may be the principal reason for the black pad defect occurrence. High porosity of IG deposit and the presence of the intermediate layer between Au and Ni‐P, which was enriched in Cu and O, were the main reasons for the black pad issue in the case of PCB C.

The gained knowledge on the mechanism of ENIG‐related failures, which cause reliability problems in PCB manufacture, makes it possible to elaborate potential non‐destructive techniques for detecting ENIG problems.