Failure analysis of ENIG surface finish pad

This paper investigated the root cause of component fell-off from hand-held products after drop test. Failure modes are cracks at solder joints. Microstructure and fracture morphology of ENIG pad and solder joint were investigated through optical microscope (OM), scanning electron microscope (SEM), and energy dispersive spectrometer (EDS). The solder alloy used for assembly is SAC305 (SnAg3.0Cu0.5). The inter-metallic compound (IMC) at both PCB and component pads of the failed component is characterized through cross-section analysis. Through appearance observation on the failed components, fracture interface was smooth and appeared black and grey colour. Moreover, fracture contained high phosphors concentration (16~24 wt. %) and the flux residue covered on fracture surface. Compared with survived components, the failed samples show a thicker P-rich layer. Several obvious V-sharp spiked into Ni layer and some of them almost penetrated into 50% of the Ni layer thickness. Based on the results of drop test, appearance observation, composition analysis, and cross-section analysis, we concluded that the root cause of this failure maybe related to the black pad issue.