Simple Techniques To Mitigate Tin Whiskers On RoHS-Compliant Printed Circuit Assemblies
by Michael Hundt, STMicroelectronics, Inc.
Lead-free soldering technologies have increased electronics manufacturers' awareness of a metallurgical phenomenon referred to as whiskers. Whiskers occur most commonly in circuits where tin is used as a final finish on printed circuit boards (PCBs) and electronic components. In certain cases, microscopic single-crystal filaments (or hair-like protrusions) of the metal grow outward from the surface. Electrical system failures caused by short circuits between PCB traces or component leads are attributed to these growths.
Tin whiskers could be easily avoided by adding small amounts (as little as 3%) of lead to the plating. But since Europe's RoHS regulations required the elimination of lead from nearly all electronics products, there has been a renewed interest in the mechanisms causing whisker growth and how to control them. Many semiconductor companies, including STMicroelectronics (ST), have undertaken extensive programs to develop and certify processes that mitigate or eliminate whisker growth in most applications.
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