IBM Corporation Ohlandt, Greeley, Ruggiero & Perle, LLP
Flip-Chip interconnections using lead-free solders
 An interconnection structure suitable for the connection of microelectronic circuit chips to packages is provided by this invention. In particular, the invention pertains to the area-array or flip-chip technology often called C4 (controlled collapse chip connection). The structure comprises an adhesion/barrier layer deposited on a passivated substrate (e.g., a silicon wafer), optionally an additional adhesion layer, a solderable layer of a metal selected from the group consisting of Ni, Co, Fe, NiFe, NiCo, CoFe and NiCoFe on the adhesion/barrier layer, and a lead-free solder ball comprising tin as the predominate component and one or more alloying elements selected from Bi, Ag, and Sb, and further optionally including one or more elements selected from the group consisting of Zn, In, Ni, Co and Cu. 
International Business Machines Corporation
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Gangadhara Swami Hariklia Sung Kwon Leathen Panayotis Constantinou Keith Thomas Wilma Jean Sampath Ho-Ming Madhav
Mathad Deligianni Kang Shi Andricacos Kwietniak Horkans Purushothaman Tong Datta