Effect of Ti on the interfacial reaction between Sn and Cu

The effect of Ti on the solid state reactions between Sn and Cu has been investigated in this work. Based on the experimental results the following statements about the effect of Ti can be made: Firstly, the presence of Ti does not have measurable effect on the thickness of either Cu₆Sn₅ or Cu₃Sn during solid state annealing. However, the unevenness of both Cu₆Sn₅ and Cu₃Sn layers is increased by the addition of Ti. Secondly, there is no marked solubility of Ti to either Cu₆Sn₅ or Cu₃Sn. Rather Ti reacts with Sn to form large Ti₂Sn₃ platelets inside the solder matrix. These findings were subsequently rationalized with the help of the assessed Cu–Sn–Ti phase diagram. By utilizing this phase diagram information, the absence of any marked effects of Ti on the growth of Cu–Sn intermetallic compound (IMC) formation was rationalized. As there is a very low solubility of Ti to SnAg solder and to Cu–Sn IMC’s, Ti cannot change activities of components in the solder nor influence the stability of the IMC layers. Hence, these results throw significant doubts over the concept of trying to influence the Cu–Sn IMC layer thickness or quality by Ti alloying.