The Formation and Growth of Intermetallic Compounds in Sn-Zn and Sn-Zn-Al Solder with Ni/Au Surface Finish Bond Pad
نویسندگان
چکیده
In this study, we used microstructure evolution and electron microprobe analysis (EPMA) to investigate the interfacial reactions in Sn-Zn and Sn-Zn-Al solder balls with Au/Ni surface finish ball-grid-array (BGA) bond pad over a period of isothermal aging at 150°C. During reflow, Au dissolved into the solder balls and reacted with Zn to form g-Au3Zn7 and g2-AuZn3. As aging progressed, g and g2 transformed into g3-AuZn4. Finally, Zn precipitated out next to g3-AuZn4. The Zn reacted with the Ni layer to form Ni5Zn21. A thin layer (Al, Au, Zn) intermetallic compound (IMC) formed at the interface of the Sn-Zn-Al solder balls, inhibiting the reaction of Ni with Zn. Even after 50 days of aging, no Ni5Zn21 was observed. Instead, fine (Al, Au, Zn) particles similar to Al2 (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-Al solder ball samples.
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