SMTA International Conference Proceedings

Strategic Environmental Research and Development Program (SERDP) Tin Whisker Testing and Modeling: Tin Whisker Growth on SAC305 Assemblies

Authors: Stephan Meschter, Ph.D., Polina Snugovsky, Jeff Kennedy, Zohreh Bagheri and Eva Kosiba
Company: BAE Systems and Celestica Inc.
Date Published: 9/28/2014   Conference: SMTA International

Abstract: Driven by European Union directives, most commercial electronics manufacturers began delivering lead-free electronic components, assemblies, and equipment in 2006. As a result of a global movement away from using lead (Pb), component manufacturers are increasingly applying tin-rich finishes to the leads of their devices and soldering with lead(Pb)-free solders. Unfortunately, this can create a risk of tin whisker formation that can result in electrical failures. Because of its unique requirements such as long service lifetimes, rugged operating environments, and high consequences of failure, the aerospace and defense industries must mitigate the detrimental effects that tin whiskers. The present paper provides a status on the effort associated with a multi-year Strategic Environmental Research and Development Program (SERDP) testing and modeling project that aims to assess tin whisker growth on lead-free manufactured assemblies and utilizes whisker short circuit statistical modeling to enable improved reliability assessments. The tin whisker growth of tin finished parts soldered with SAC305 (Sn-3.0Ag-0.5Cu) solder alloy under high temperature/high humidity and thermal cycling conditions were evaluated. In total, over 129,724 whiskers were observed to have grown from thin (less than 25 microns) regions of SAC305 solder alloy, with many whiskers growing long enough to bridge between typical electronic circuit conductors. It was also found that whisker growth occurred on thick solder alloy sections of SAC305 with rare earth elements (Ce, Y and La). Details of the whisker nucleation and growth results are provided.

Key Words: 

Tin Whiskers, Lead Free, Assembly, Testing, Humidity, Corrosion, Thermal Cycling

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