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Indium-lead solders are used for IBM controlled collapse chip connections (C-4s) to improve fatigue life in temperature cycling for large chip applications. Using 50% In-Pb alloy, which is expensive, has posed a number of manufacturing and reliability concerns. This paper presents the results of development studies leading to the use of a low-indium solder alloy for C-4 applications. This alloy overcomes all previous concerns while exceeding the fatigue life specification of the high-indium alloy. Also described are the variables and tests used to evaluate C-4 performance of In-Pb alloys over the 5% to 50% range. Results are presented graphically and mathematically to show the improvement obtained with indium-content solders over the conventional tin-lean alloys.
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