The Embrittlement Mechanism and Improvement of Impact Strength for Lead-Free Solder Joints in BGA Packages Using Electrolytic Ni/Au Plating

Abstract

The impact strength evaluation and fracture mechanism analysis in board level of Sn-3mass%Ag-0.5mass%Cu solder joints of BGAs using electrolytic Ni/Au plating were performed. The cause of impact strength degradation of BGA solder ball joints is the existence of low density defect, which contain organic materials, in the (Cu,Ni)₆Sn₅ intermetallic compound grain boundary formed in the solder joints. These organic materials are taken in by the Ni plating film at the time of Ni plating. To improve the impact strength of the Sn-3mass%Ag-0.5mass%Cu solder joint of the BGA, it is necessary to lower the concentration of these organic materials. The contamination prevention and Ni plating bath sanitization, solder mask material selection (to minimize Ni plating bath contamination) and higher current density of Ni plating are effective to keep lower concentration of organic materials in Ni plating film.