An Embrittlement Mechanism of Impact Fracture of Sn-Ag-Cu Solder Joints on BGA Using Electroplated Ni/Au Surface Finishes

The impact toughness evaluation and fracture mechanism analysis in board level of Sn-3mass%Ag-0.5mass%Cu solder joints of ball grid arrays (BGAs) using electrolysis Ni/Au plating were performed. The cause of impact toughness degradation of BGA solder ball joints is the segregation of impurities to the (Cu, Ni)(6)Sn-5 intermetallic compound grain boundary formed in the solder joints. The impurities, consisting of Cl and organic matters, are taken in the Ni plating film at the time of Ni plating. The organic matter impurities come primarily from the solder mask of the BGA interposer substrates. To improve the impact toughness of the Sn-3mass%Ag-0.5mass%Cu solder joint of the BGA, it is necessary, to lower the concentration of these impurities. This, in turn, places importance on solder mask material selection (to minimize Ni plating bath contamination) as well as contamination prevention and plating bath sanitization.