Chang-Chae Shur

Intermetallic compound layer formation between Sn–3.5 mass %Ag BGA solder ball and (Cu, immersion Au/electroless Ni–P/Cu) substrate

The growth kinetics of intermetallic compound layers formed between eutectic Sn–3.5Ag BGA (ball grid array) solder and (Cu, immersion Au/electroless Ni–P/Cu) substrate by solid-state isothermal aging were examined at temperatures between 343 and 443 K for 0–100 days. In the solder joints between the Sn–Ag eutectic solder ball and Cu pads, the intermetallic compound layer was composed of two phases: Cu6Sn5 (η-phase) adjacent to the solder and Cu3Sn (ε-phase) adjacent to the copper. The layer of intermetallic on the immersion Au/electroless Ni–P/Cu substrate was composed of Ni3Sn4. As a whole, because the values of the time exponent (n) are approximately 0.5, the layer growth of the intermetallic compound was mainly controlled by a diffusion-controlled mechanism over the temperature range studied. The growth rate of Ni3Sn4 intermetallic compound was slower than that of the total Cu–Sn(Cu6Sn5+Cn3Sn). The apparent activation energy for growth of total Cu–Sn(Cu6Sn5+Cu3Sn) and Ni3Sn4 intermetallic compound were 64.82 and 72.54 kJ mol−1, respectively.

Mechanical properties of copper to titanium joined by friction welding

This paper describes a fundamental investigation of friction welding pure copper to titanium. Friction welding was performed using a brake type friction welder. The effect of friction time and upset pressure on the mechanical and metallurgical properties were evaluated. Under constant upset pressure, the tensile strength made little difference with an increase in friction time, whereas at the constant friction time, the tensile strength increased with increasing upset pressure. Thus, the upset pressure plays a major role over the friction time and friction pressure on tensile strength. Though Cu3Ti intermetallic compound is formed at the copper/titanium interface during welding, the tensile strength of welded joint is not affected. It may be due to the thickness of intermetallic compound layer at interface being very thin and scattered. The tensile fracture of the welded joint occurred in copper side near the interface.