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Effect of Electromigration on Interfacial Reaction In Ni/Sn63Pb37/Cu BGA Solder Joints

In this paper, to investigate the effect of electromigration (EM) on interfacial reactions in BGA solder joints, the Ni/Sn63Pb37/Cu BGA daisy-chain flip chips were used and the experiment was conducted under a current density of 1.0X103 A/cm2at 125°C. It has been found that the Ni3Sn4 intermetallic compounds (IMCs) formed at the solder/Ni interface and the CU6Sn5 IMCs formed at the solder/Cu interface in the as-reflowed state. With increasing EM time, the IMCs formed at chip interface transformed into (Cu, Ni)6Sn5 type, while the IMCs at the PCB side didn't change. During EM, at the anode side the IMCs grew and the growth behavior was linear with t1/2. At the same side, the IMC thickness at the anode side was larger than that at the cathode side. However, the growth behavior of IMCs at the cathode side was complicated. Due to the initial IMCs in the as-reflowed were thin, under the current density, first the IMCs grew. While after the thickness of IMCs increased to a critical value, it decreased thereafter.