Circuit World, Vol. 33, No. 1, pp. 5-8, 2007

Assessment of Risk Resulting from Unattached Tin Whisker Bridging

Tong Fang, Sony Mathew, Michael Osterman, and Michael Pecht
University of Maryland
College Park, MD 20742


Purpose - This paper aims to present a methodology for estimating the risk of component level electrical bridging failures from unattached conductive (tin) whiskers.
Design/methodology/approach - Based on experimental data an algorithm was developed and assessed by further experiments. The risk estimate is based on whisker parameters, generated from experiments over a period of time. A bridging failure risk is defined as the probability of a conductive whisker landing between two isolated electrical conductors. A probabilistic estimate for electrical bridging failure risk is achieved by randomly sampling distributions of conductive whisker length, deposition angle, and density for a defined electrical structure. A fine pitch quad flat package attached to a printed wiring board is used as test vehicle to verify the risk estimate.
Findings - The estimated risk is found to be higher than planned in the experimental test. The lower experimentally determined risk was found to be the result of high contact resistance between the conductive whisker and the electrical conductors that form the unintended circuit. Contact resistance between the whisker and electrical conductors was found to mitigate the whisker shorting risk.
Originality/value - This is the first attempt to quantify the risk failure due to unattached conductive whiskers in electronic products. A methodology for estimating electrical bridging risk due to unattached conductive whiskers is provided. Contact resistance of conductive whiskers is found to be a critical issue that may be mitigate failure risks.

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