Comparison of lead-free solder joints made by immersion gold plating with those produced by autocatalytic electroless gold plating

Electroless Ni/Au plating is presently in use with high-density Jisso technology in the manufacture of electrical appliances. Electroless Ni/Au plating is said to be less satisfactory than conventional electrolytic plating with respect to the quality of solder joints and lead-free solder in particular. The reason for this is considered the P-rich layer which forms at the interface of solder bulk and Ni layer but this has yet to be fully confirmed. Solder joints made by electroless Ni/Au plating and Sn-3 mass%Ag-0.5 mass%Cu lead-free solder balls were examined here for reliability assessment under high temperature storage, using an electroless Ni/Au layer made by autocatalytical deposition and another made by immersion Au plating. Interfacial structure and solder pull strength data for the two layers were compared as basis for this assessment and confirm if solder joints made by electrolytic plating is actually superior. At the interface of both layers, cavity formation was found to have occurred by Ni corrosion during An plating and the number of which appeared to be a factor determining solder joint reliability. Electrolytic Au plating not accompanied by Ni corrosion should provide solder joints with reliability exceeding that by electroless An plating.