The Unpredictability of Tin Whiskers Endures


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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 components with tin-lead finishes.

Even though some countries provide exemptions for special industry segments that require lead, the reality is that there are fewer and fewer components available in the tin-lead termination finish.

Lead-free initiatives pose reliability issues due to tin whisker formation, which has resulted in failures due to electrical short circuits.

Applications requiring high-reliability components 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 mitigation process for surface mount electronic components applicable to both passive and active components.

Introduction

The European Union (EU) RoHS 1 Directive took effect July 1, 2006. This directive restricts 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 Electronic 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 original directive, while gradually broadening its requirements 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 reliability of critical hardware. Pure tin, defined as tin with less than 0.1% lead, is a high reliability risk because of its propensity to form tin whiskers. Actually, there is a consensus in the high-reliability industry that at least 3% lead is needed for best practice.

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Editor's Note: This article originally appeared in the February issue of SMT Magazine.

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