Attachment reliability evaluation and failure analysis of thin small outline packages (TSOP's) with Alloy 42 leadframes

A series of studies designed to evaluate the long term surface mount reliability of Alloy 42 leaded thin small outline packages (TSOPs) using thermal cycling as an acceleration method is described. Visual inspections, pull strength, and scanning electron microscopy were used to characterize the solder joints. In addition, the solder plating, lead wetting, and aging characteristics were evaluated. Failure during thermal cycling was primarily caused by the coefficient of thermal expansion (CTE) mismatch between the package and the printed wiring board. By using acceleration factors based on solder joint strain energies induced by global and local mismatches during thermal cycling, the experimental results are extrapolated to various use conditions and life expectancies. The TSOP solder joint reliability depends on environmental conditions (cyclic temperature range, temperature maximum, and dwell time), board thickness and materials, product intended service life, and expected hazard rate limits.<
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