Characterization of the growth of intermetallic interfacial layers of Sn-Ag and Sn-Pb eutectic solders and their composite solders on Cu substrate during isothermal long-term aging

Single shear lap joints were made with four different solders, Sn-Pb and Sn -Ag eutectic solders, and their composites containing about 20 vol.% in-sit u Cu6Sn5 intermetallic phases about 3-8 micrometers in diameter. Two sets o f experiments were performed: In the first set, all of the above four solde r joints were aged at 150 degrees C for periods ranging to 5000 h and the i ntermetallic growth was monitored periodically. In the second set, each of the above four solder joints was aged at five different temperatures for 40 00 h. The interfacial layers between solders and the Cu substrate were exam ined using optical and scanning electron microscopy. The growth kinetics of intermetallic interfacial layers formed between solder and Cu substrate wa s characterized. The effect of in-situ Cu,Sn, intermetallic phases on the g rowth rate is discussed. The growth rate of the intermetallic layers in the eutectic Sn-Pb composite was slower for the first 150 h as compared to the eutectic Sn-Pb non-composite. The growth rate of the intermetallic layers were similar for both the eutectic Sn-Ag and eutectic Sn-Ag composite throu ghout the aging duration. The activation energies for Cu6Sn5 layer growth f or the eutectic Sn-Pb and Sn-Ag solder joints are evaluated to be 111 kJ/mo l and 116 kJ/mol, respectively. The eutectic Sn-Pb and Sn-Ag composite sold er joints exhibit higher activation energies of 161 kJ/mol and 203 kJ/mol.