Influence of multiple reflows and thermal shock on interfacial IMC of solder joints between Sn0.3Ag0.7Cu solder/pads(HASL, OSP, electrolytic Ni/Au and ENIG PCB finishes)

The effects of multiple reflows and thermal shock on interfacial reaction of the solder joints between Sn-0.3Ag-0.7Cu solder/pads (HASL, OSP, electrolytic Ni/Au and ENIG PCB finishes) were systematically investigated in this work. The results showed that the scallop Cu₆Sn₅ phase were formed in HASL and OSP finish pads during reflows, whereas the cylinder-type (Cu, Ni)₆Sn₅ near the solder and needle-type (Ni, Cu)₃Sn₄ adjacent to the Ni layer were formed in electrolytic Ni/Au and ENIG finish pads. For all the four kinds of finishes, the thickness of IMCs increased with reflow times increasing, and the interfacial IMCs growth was controlled by grain boundary diffusion; the growth rate at Cu surface was faster than at Ni surface. Furthermore, it was also indicated that the interfacial IMCs growth were not notable with thermal shock cycle numbers increasing, but Kirkendall voids could be observed in the Sn-Cu-Ni intermetallic compounds layer for electrolytic Ni/Au and ENIG Finish Under thermal shock tests.