The Formation and Growth of Intermetallic Compounds in Sn-Zn and Sn-Zn-Al Solder with Ni/Au Surface Finish Bond Pad

摘要

In this study,we used microstructure evolution and electron microprobe analysis (EPMA) to investigate the interfacial reactions in Sn-Zn and Sn-Zn-AI solder balls with Au/Ni surface finish ball-grid-array (BGA) bond pad over a period of isothermal aging at 150 deg C.During reflow,Au dissolved into the solder balls and reacted with Zn to form gamma-Au_3Zn_7 and gamma_2-AuZn_3.As aging progressed,gamma and gamma_2 transformed into gamma_3-AuZn_4.Finally,Zn precipitated out next to gamma_3-AuZn_4.The Zn reacted with the Ni layer to form Ni_5Zn_(21).A thin layer (Al,Au,Zn) intermetallic compound (IMC) formed at the interface of the Sn-Zn-AI solder balls,inhibiting the reaction of Ni with Zn.Even after 50 days of aging,no Ni_5Zn_(21) was observed.Instead,fine (Al,Au,Zn) particles similar to Al_2 (Au,Zn) in composition formed and remained stable in the solder.The lower ball shear strength corresponded with the brittle fracture morphology in Sn-Zn-AI solder ball samples.