An investigation of tin whisker growth over a 32 year period

Purpose: This paper presents the results of a 32 year old laboratory study of whisker growth from tin electrodeposits that was originally undertaken to gain an increased understanding of the phenomenon of tin whisker growth. Design/methodology/approach: Whisker growth was evaluated using electroplated C-rings (both stressed and un-stressed) that were stored throughout in a desiccator at room temperature. Analysis has recently been undertaken to evaluate whisker growth and intermetallic growth after 32 years storage. SEM analysis has been performed to investigate whisker length and, using polished cross-sections, the morphology, thickness and type of intermetallic formation. Findings: Normal tin plated deposits on brass and steel with a copper barrier layer nucleated whiskers within 5 months and in each case these grew to lengths between 1 and 4.5 mm. For normal tin electroplated onto brass, a one or two month nucleation period was needed before whiskers developed. They reached a maximum length of about 1.5 mm after 6 months and little or no further growth occurred during the subsequent 32 years. Very few whiskers grew on the tin-plated steel samples and no intermetallic formation was observed. None of the fused tin-platings nucleated whiskers during the 32 year period. Practical implications: Knowledge about vintage whiskers is important in order that we can take steps to increase the resiliency of our space missions. Similarly, such knowledge is important to engineers engaged on products reaching their nominal end-of-life, but where for reasons of economy, these products cannot be replaced Originality/value: This study represents a unique insight into whisker growth and intermetallic formation over an extremely long time period.