Usually, flipchip technology is based on either high-Pb or eutectic Sn/Pb solder forming the connections between the semiconductor chip and the carrier substrate. However decay of the 210Pb constituent, via 210Bi and 210Po, to 206Pb involves the emission of energetic alpha particles which have a tendency to cause soft errors in nearby active elements on the chip. Also, impending legislations in Europe and Japan on the elimination of Pb from electronic products have prompted the investigation of alternative solder alloys. This paper outlines an initial development effort focussed on the Sn/Ag/Cu (95.8/3.5/0.7) alloy. The study involved the development of a flip chip assembly process followed by a reliability evaluation comparing the fatigue resistance of the Sn/Ag/Cu alloy to that of eutectic Sn/Pb solder. The test vehicle used was a 225μm bump pitch, 11mm square die mounted on a ceramic substrate.

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