Influence of copper addition on adhesive strength of Sn-3Ag-1·5Sb solder joints

The present work investigates the effects of adding a small amount of Cu to Sn-3Ag-1·5Sb solders. The present results indicate that adding 0-5 and 1·0 wt-%Cu to Sn-3Ag-1·5Sb solders causes the liquidus temperature to decrease from its original value of 233·4°C to 231·6°C and to 231·4°C, respectively. Furthermore, it is noted that the addition of 1·0 wt-%Cu reduces the difference between the liquidus and solidus temperatures. It is shown that the added Cu reacts with the Sn content of the solder to form Cu₆Sn₅ particles in the β-Sn matrix, which are distributed non-uniformly since the Cu content is low. The experimental results also reveal that the growth rate of the solder joint interfacial intermetallic compound layers increases at higher levels of Cu addition. Finally, it is established that adding Cu to the Sn-3Ag-1·5Sb solder not only improves the adhesive strength of the solder joints, but also reduces the rate of degradation of the adhesive strength of the joints during thermal storage.