Electrochemical fabrication of Formula C4s (controlled collapse chip connection) offers significant cost, reliability, and environmental advantages over the currently employed evaporation technology. A continuous seed layer is required for through‐mask electrodeposition of the solder alloy. This layer becomes the ball limiting metallurgy (BLM) for the solder pad after etching. The seed layer metallurgy and the BLM etching are crucial to obtaining mechanically robust C4s. In the present study, the issues related to the selection of seed layer metallurgy, uniformity of plating and etching, and mechanical integrity of C4s have been investigated. The results demonstrate the feasibility of electrochemically fabricating highly reliable Formula structures with a high degree of dimensional uniformity on a variety of wafer sizes ranging up to 200 mm.
Dr. Madhav Datta, Shenoy, R. V., Jahnes, C., Andricacos, P. C., Horkans, J., Dukovic, J. O., Romankiw, L. T., Roeder, J., Deligianni, H., Nye, H., Agarwala, B., Tong, H. M., and Totta, P., “Electrochemical fabrication of mechanically robust PbSn C4 interconnections”, Journal of the Electrochemical Society, vol. 142, pp. 3779–3785, 1995.