BGA Jointing Property of Sn-8.8 mass%Zn and Sn-8.0 mass%Zn-3.0 mass%Bi Solder on Electroless Nickel-Phosphorus/Immersion Gold Plated Substrates

The BGA joint properties including the joint strength and the interfacial structure have been investigated in detail between the lead-free solders containing Sn-8.8Zn and Sn-8.0Zn-3.0Bi with low melting temperature and the replacement gold plated film on the electroless nickel-phosphorus deposits. The results indicate that both Sn-8.8Zn and Sn-8.0Zn-3.0Bi solders can be readily jointed with the substrate in the same way as the conventional Sn-37Pb solder at the peak temperature of 230°C. The joint strength of Sn-8.8Zn solder is higher than that of Sn-8.0Zn-3.0Bi solder, and both of them are higher than that of Sn-37Pb under same surface finishing. Moreover, γ2(AuZn3) intermetallic compound occurs as the reaction layer at Sn-8.8Zn and Sn-8.0Zn-3.0Bi joints, and the bismuth crystals occur at Sn-8.0Zn-3.0Bi joint. The hot bump pull testing results clearly show that the fracture of solder ball occurs along the reaction layer of γ2(AuZn3) intermetallic compound since this reaction layer or bismuth crystals in the joint causes the decrease of jointing strength.