To meet the increasing demands upon soldered joints to provide structural integrity in electronic devices, fatigue-creep interactions in the most commonly used solder (37Pb-635n) have been investigated. At room temperature, homologous temperature (Th = 0.65), simultaneous interaction tests demonstrate the deleterious effect on fatigue endurance of dwells inserted at any location within the high strain cycle. Unbalanced tensile dwells produce the greatest life debit, which may exceed an order of magnitude at low strain ranges, and dwells lasting around one hundred seconds. A saturation effect in terms of dwell duration is observed for hold periods greater than this. The alloy cyclically softens under all conditions examined. Possible damage mechanisms are discussed from the evidence produced by metallographic examination. Reproducing some of the early experiments of Plumbridge & Miller (1972), the consequences of sequential fatigue-creep interaction tests are reported and compared with the influence of prior monotonic strain and prior ageing.
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