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What is the biggest concern about the growth of tin whiskers? A simple answer is “uncertainty.”
Electronic system failures attributing to or related to whiskers have been reported in the past before the electronics industry was converted to lead free. With the elimination of the use of lead (Pb) in electronics in compliance with worldwide RoHS regulations, Pb-free materials including pure tin (Sn) have been used as surface coating for component leads and metal terminals, and as solder materials in making solder joints.
Pure tin makes a practical replacement to Sn-Pb as a choice of surface coating because of its economics, availability, and performance in manufacturability, compatibility, and solderability. Today, most component manufacturers offer pure tin-coated components.
On electronic system failure, as an illustration, one of the well-studied and highly publicized incidents was the TOYOTA Camry 2003 model investigation. The unintended acceleration of the vehicle speed control was reported in 2009. National Highway Traffic Safety Administration (NHTSA) initiated an investigation with the technical support of NASA Engineering and Safety Center. Destructive physical analysis of a failed accelerator pedal position sensor assembly from a consumer vehicle that was identified with a diagnostic trouble code found the presence of tin whiskers. A tin whisker had formed a 248 Ω resistive short between two terminals of the accelerator pedal position sensor of its potentiometer accelerator pedal assembly. A second tin whisker of similar length grew from a 5-volt source terminal adjacent to a pedal signal output terminal, but this whisker did not make contact with any other terminals at the time of the analysis.
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Editor's Note: This column originally appeared in the November 2013 issue of SMT Magazine.