Failure mechanism of brittle solder joint fracture in the presence of Electroless Nickel Immersion Gold (ENIG) interface

Electroless Nickel and Immersion gold (ENIG) plating has been successfully used for many electronic products as an alternative metal finish on printed circuit board (PCB). Brittle, interfacial solder joint fracture of solder joints on an ENIG metallization presents a problem despite major initiatives by electronics industry consortia and individual companies to study the interfacial fracture phenomena. The current studies will focus primarily on the failure mechanism of the brittle fracture of ENIG plating on the BGA and PCB type packages. The details of this failure mechanism will be discussed using results obtained from Scanning Electron Microscopy (SEM)/Energy Dispersive Spectroscopy (EDS), Focused Ion Beam (FIB), Transmission Electron Microscopy (TEM) and Electron Diffraction analyses. The current studies have successfully identified the failure mechanism for the brittle solder joint fracture with ENIG plating process and Sn/Pb solder balls. Kirkendall voids formed during solder reflow at the phosphorus rich Ni layer (Ni-P+) and Sn-Ni IMC interface, concentration of P in the Ni-P+ layer and density of mudflat cracks in the Ni-P+ layer have been identified as the key contributors to the brittle fracture.