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62 SMT Magazine • February 2015 by Scott Sentz aeM inc. The Unpredictability of Tin Whiskers Endures Feature Into decade number two of the European Union's RoHS and REACH restrictions for the use of lead in electronic components, the risk of tin whiskers in critical circuitry continues. The global environmental directives to implement lead-free initiatives resulted in the obsolescence of commercially available electronic compo- nents with tin-lead finishes. Even though some countries provide ex- emptions for special industry segments that re- quire lead, the reality is that there are fewer and fewer components available in the tin-lead ter- mination finish. Lead-free initiatives pose reliability issues due to tin whisker formation, which has re- sulted in failures due to electrical short circuits. Applications requiring high-reliability compo- nents have to identify solutions to either self- mitigate or fully mitigate RoHS components not available with tin-lead finishes. This article will explore a tin whisker mitiga- tion process for surface mount electronic com- ponents applicable to both passive and active components. Introduction The European Union (EU) RoHS 1 Direc- tive took effect July 1, 2006. This directive re- stricts the use of six hazardous materials in the manufacture of various types of electronic and electrical equipment including lead. It is closely linked with the Waste Electrical and Electron- ic Equipment Directive (WEEE) 2002/96/EC, which sets collection and recycling targets for electrical goods to minimize e-waste. The EU RoHS 2 Directive is the next generation of the original directive taking effect January 2, 2013. It deals with the same substances as the origi- nal directive, while gradually broadening its re- quirements to cover additional electronic and electrical equipment and parts. Adoption of no-lead finishes seem ideal from an environmental perspective if it were to be accomplished without risks to reliabil- ity of critical hardware. Pure tin, defined as tin with less than 0.1% lead, is a high reliabil- ity risk because of its propensity to form tin whiskers. Actually, there is a consensus in the Figure 1: Tin whisker at 6000X (photo courtesy of peter bush, SunY at buffalo).

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