SMT007 Magazine

SMT-July2014

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16 SMT Magazine • July 2014 by Dr. Jennie S. Hwang H-TECHnoLogiES gRoUP fEATURE Since lead-free implementation, concerns about tin whiskers have intensified. For the past 12 years, studies and research by various laboratories and organizations have delivered burgeoning reports and papers, and my column has devoted an entire series to this subject. This article aims to capsulize the important areas of the subject. (Note: For expression, "whisker" is used as both noun and verb.) The tin whisker issue and its potential mis- haps have been recognized for more than six decades in electronic, electrical and industrial applications. Some metals are prone to whisker- ing, or protruding from the surface of the sub- strate. In addition to tin, the metals that have exhibited whiskers include zinc, cadmium, sil- ver, gold, aluminum, copper, lead, and others. The whiskering phenomenon is distinct and unique. It is the result of a process differ- ent from other known phenomena (e.g., den- drites). And tin whisker and tin pest are separate metallurgical phenomena (SMT Magazine, May 2013). However, whiskers share commonality with dendrites in two aspects: Both are the re- sult of a physical metallurgical process, thus fol- lowing the science of physical metallurgy; and both could cause a product failure. Uncertainty about tin whisker growth is most insidious. Stock markets do not like un- certainty, nor does the electronics industry. Our effort is to alleviate the uncertainty. Practical Criteria As some metals can whisker when accom- modating conditions are met, the goal should be set with the differentiation between whisker- resistant and whisker-proof. Overall, for testing or evaluation of the whisker propensity of a system, the key ques- tions to be addressed are, is the system whisker- prone or whisker-resistant (not whisker-proof), and how does the system's whisker resistance stand in reference to the intended benchmark? Tin Whiskers: Capsulization

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