Effect of La on the Growth of Cu_6Sn_5 Intel-metallic Compound for Improved Sn-Pb Solder Joints

摘要

Small amount of rare earth element La were added into the traditional Sn60-Pb40 solder alloy in order to improve the reliability of solder joints. The results of aging tests of solder joints showed that, the growth of interface Cu_6Sn_5 intermetallic compound was depressed by La addition. Furthermore, the thermal fatigue life of solder joints was improved by 3 times. Thermodynamic analysis indicated that La had higher affinity with Sn in the Sn-Pb-La system, and then the driving force for Cu_6Sn_5 formation was reduced since the activity of Sn was lowered.