Sanka Ganesan, Ji Wu, and Michael Pecht
University of Maryland
College Park, MD 20742
Ricky Lee and Jeffery Lo
Hong Kong University of Science and Technology
Yun Fu, Yonghong Li, and Ming Xu
Aero Combined Environment Laboratory
China Aero-Polytechnology Establishment,
Beijing 100028, P.R.China
Abundant data exist on the short-term reliability (i.e. less than 5 years) of lead-free solder joints under single loading conditions. Data on combined loading conditions and long-term reliability is scarce. The lead-free electronics will be deployed in many products that serve markets where long-term (greater than 5 years) is a critical requirement. In many applications, electronics will be subjected to long-term exposure to temperature extremes (high and low), humidity, atmospheric contaminants, and combined thermo-mechanical loading (temperature cycling and vibrations).
To assess long-term reliability, an experimental plan includes assessing the interactions among the applications conditions. The interacting influences include the growth of intermetallics at the solder joints due to high temperature exposure, electro-chemical degradation of electronics assemblies due to the exposure to humidity and atmospheric contaminants, formation of tin pest due to extended exposure to low temperature and the effects of combined thermo-mechanical loading conditions on the electronics assemblies. The test vehicle designs incorporate commercial variations in PCB pad finishes, component lead finishes. Three PCBs designs were developed to assess reliability of surface mount assemblies and single sided through-hole assemblies. The PCB materials include FR4, polyimide for SMT assemblies and paper-phenolic type (CEM-1) for through-hole assemblies.
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