Strategic Environmental Research and Development Program (SERDP) Tin Whisker Testing and Modeling: Long Term Low Temperature High Humidity Testing
Authors: Stephan Meschter, Evan Ekstrom, Polina Snugovsky, Jeff Kennedy, Zohreh Bagheri, and Eva Kosiba Company: BAE Systems and Celestica Inc. Date Published: 5/19/2015
ICSR (Soldering and Reliability)
Abstract: Commercial electronics manufacturers began a global movement away from using lead (Pb) in 2006 to meet European Union Reduction of Hazardous Substances (RoHS) legislation. Component manufacturers are for the most part applying tin-rich finishes to the leads of their devices and soldering with lead (Pb)-free solders. Unfortunately, this increases the risk of tin whisker formation that can result in electrical failures. Aerospace, defense, and high performance electronics have a long history of utilizing commercial-off-the-shelf parts and assemblies. However, due to its unique requirements such as long service lifetimes, rugged operating environments, and high consequences of failure, the high performance electronic industries must mitigate the detrimental effects of tin whiskers. This paper provides a status on the effort associated with a multi-year testing and modeling program 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 25°C/85 percent relative humidity (RH) conditions over three years was evaluated. Significant whisker nucleation and growth from the SAC305 solder alloy occurred where the solder was less than 25 microns thick with alloy 42 lead terminations. In contrast to the previous 85°C/85 percent RH testing, many whiskers with diameters less than one micron were observed. Many sub-micron diameter whiskers were observed require scanning electron microscope magnifications of 500 to 1,000x or more to be detected.
Tin Whiskers, Lead Free, Assembly, Testing, Thermal Cycling, Statistics