Interfacial reactions between In-48Sn solder and electroless nickel/immersion gold substrate during reflow process

In this study, the interfacial reactions of In-48Sn solder balls on an electroless Ni/immersion Au (ENIG) ball grid array (BGA) substrate during reflow at 170 degrees C for up to 1800 s were investigated using SEM, transmission electron microscope (TEM) and energy dispersive X-ray spectroscope (EDS) analyses. During the initial 10 s of the reflow process, AuIn2 cubes and a continuous Ni-3(Sn,In)(4) intermetallic compound (IMC) layer were formed at the interface between the solder and the substrate. The thickness of the Ni-3(Sn,In)(4) layer was found to increase from approximately 140 nm to 1 mu m, as the reflow time increased from 10 to 1800 s, respectively. The transformation of Ni to form the Ni-3(Sn,In)(4) IMC led to the formation of a P-rich Ni (hereafter Ni3P) layer between the Ni-3(Sn,In)(4) IMC and the ENIG substrate, whose thickness increased with increasing the reflow time. Copyright (C)\ 2006 John Wiley & Sons, Ltd.