Bromine induces corrosion in reliability test

Abstract

The Ball grid array (BGA) product fixed on the PCB under Highly Accelerated Stress Test (HAST) reliability test and its relevant corrosion phenomenon are reported. In this article, BGA performed HAST with the socket which individually interconnect between BGA device and PCB test board is subjected to provide moisture path and transfer the applied bias to the PCB. Oxidation and corrosion are found on the SnAgCu solder balls. Moreover, Br contained byproduct on some specific solder ball surface is observed, too. Those phenomenon is examined by 3D microscope, high kV Energy dispersive spectrometer (EDS) and Xray photoelectron spectroscopy (XPS). The Br ion source mainly migrates from PCB solder mask to solder balls, so the PCB without solder mask does not present corrosion and the corresponding Br byproduct. It is also found that different electrical bias/current configurations applied on the solder balls will impact the solder ball corrosion and by product formation. It is suggested that electron chemical migration take place in this case.