Comparison of Impact Properties of Sn-9Zn and Sn-3Ag-0.5Cu Lead-Free Solder Ball Joints

Impact properties of solder ball joints with Sn-9mass%Zn and Sn-3mass%Ag- 0.5mass%Cu lead-free solders were investigated under aging at 423 K. In the case of the joints with Cu electrodes, both Sn-9Zn and Sn-3Ag-0.5Cu joints have similar impact forces before aging. For the Sn-3Ag-0.5Cu joint, fracture occurred in an intermetallic compound (IMC) layer formed in a joint interface regardless of aging, and thus the impact force was stable upon aging at 423 K for 500 h. For the Sn-9Zn joint, fracture mode changed from solder fracture to other fracture upon aging and thus this change led a decrease in the impact force. In the Sn-9Zn joint with an electroless Ni/Au plated electrode, fracture occurred in the solder regardless of aging, and thus impact properties improved compared with the joint using the Cu electrode. The impact properties are superior to those of the Sn-3Ag-0.5Cu joints with the Cu and the electroless Ni/Au electrodes.