Fluxless flip-chip attachment techniques using the Au/Sn metallurgy

With the use of the Au/Sn system as solder metallurgy different fluxless flip-chip processes are possible. In the studies for this paper Au/Sn bumped chips are used for soldering in an infrared oven under activated atmosphere with the self-alignment mechanism. A new approach is the successful application of the Au/Sn metallurgy for vapor phase soldering which provides the self-alignment effect as well. Flip-chip bonding on rigid and flexible substrates using a pulse heated thermode is also demonstrated. The scope of this paper is to show the development of different fluxless flip-chip processes with Au/Sn metallurgy on thin film and thick film substrates. The wetting of the pads, the fillet formation and the growth of ζ-phase are the major subjects of the studies as they determine the bonding result. Shear tests were performed in order to quantify the quality of the interconnection. The results obtained by the different methods are compared and conclusions about the investigated processes drawn