Interfacial reaction and elemental redistribution in Sn3.0Ag0.5Cu–xPd/immersion Au/electroless Ni solder joints after aging

Sn3.0Ag0.5Cu solder doped with 0, 100, and 500 ppm Pd was reflowed with electroless Ni/immersion Au substrate. As Pd concentration increased in the solder, formation and growth of (Cu,Ni)6Sn5 were suppressed. After thermal aging, Cu4Ni2Sn5 and Cu5NiSn5 were observed at interface of Sn3.0Ag0.5Cu–xPd/Au/Ni systems. As compared to Cu4Ni2Sn5, more Pd dissolved in Cu5NiSn5. In addition, Pd doping enhanced the growth of Cu4Ni2Sn5 and slowed the formation of Cu5NiSn5, which would stabilize the intermetallic compound. Based on quantitative analysis by field emission electron probe microanalyzer, the correlation between Pd doping and elemental redistribution in solder joints was probed and discussed. This study described a possible mechanism of the formation of different intermetallic compounds in Pd-doped lead-free solder.