Cycle Life Prediction for SMT Solder Joints on TCE‐Mismatched Substrates

Abstract

A method for the prediction of solder joint cycle life in surface‐mount assemblies is presented, based on the conversion of plastic solder shear strain into cycle life by means of an equation derived by Engelmaier. The paper introduces a different analytical procedure for the determination of solder joint shear strain. Shear strain is normally calculated from temperature and TCE differentials between package and interconnect board without consideration of elastic deformations. The suggested method derives average plastic shear strain of the solder joint at maximum temperature excursion from finite‐element analysis of a simple model consisting of an interconnect board, a solder joint and a package. All materials in the model have linear (elastic) properties, except solder which has non‐linear (elastic/plastic) characteristics. The solder stress/strain curve is described to the finite‐element programme with temperature‐dependent bilinear approximations. The solder joint is modelled as a single finite element so that only one value is computed for the plastic shear strain in the solder joint. This value represents the average shear strain which is converted into solder joint cycle life. The cycle life predictions with the finite‐element method are confirmed by cycling results obtained on actual hardware. The described method can serve as a design tool in the optimisation of surface‐mount assemblies. The procedure can help to define accelerated temperature cycling conditions.

Citation

Riemer, D.E. (1990), "Cycle Life Prediction for SMT Solder Joints on TCE‐Mismatched Substrates", Soldering & Surface Mount Technology, Vol. 2 No. 3, pp. 52-57. https://doi.org/10.1108/eb037732