Interfacial reaction and mechanical properties of eutectic Sn-0.7Cu/Ni BGA solder joints during isothermal long-term aging

The interfacial reactions and growth kinetics of intermetallic compound (IMC) layers formed between Sn-0.7Cu (wt.%) solder and Au/Ni/Cu substrate were investigated at aging temperatures between 70 and 170 degrees C for up to 100 days. After reflow, the IMC formed at the interface was (Cu,Ni)(6)Sn-5. In addition, only this (Cu,Ni)(6)Sn-5 layer was observed in the samples aged at temperatures between 70 and 150 degrees C. On the other band, after isothermal aging at 170 degrees C for 50 days, the solder/Ni interface exhibited a duplex structure of (Cu,Ni)(6)Sn-5 and (Ni,Cu)(3)Sn-4. The time exponents (n) determined at temperatures below 150 degrees C were about 0.2. The determined n values are presumably related to a grain boundary diffusion-controlled mechanism. In the ball-shear tests, the shear strength significantly decreased after aging for initial 1 day, after which it remained nearly unchanged through further prolonged aging. In all samples, fracture occurred in the bulk solder. (c) 2004 Elsevier B.V. All rights reserved.