Solder Creep Fatigue for Lead-free Joints
Paper covers parameters for the SAC405/305, SAC205, SAC105 and SnAg to replace eutectic SnPb in the Engelmaier-Wild solder creep-fatigue model.
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Authored By:
Werner Engelmaier
Engelmaier Associates, L.C., Ormond Beach, FL USA
Summary
For many of the Pb-free solders required under the European RoHS directive, there is now sufficient information, primarily in the form of the results of accelerated thermal cycling of various levels of severity, to develop acceleration models for the creep-fatigue of these solders. In this paper the parameters for the SAC405/305, SAC205, SAC105 and SnAg to replace the parameters for eutectic SnPb in the well-established Engelmaier-Wild solder creep-fatigue model.
Conclusions
The solder alloys listed are far from all that are in use today; however, there is not enough information as yet for other Pb-free solders to propose model parameters.
Both the data base of the results of accelerated reliability tests as well as the model predictions shown for accelerated reliability testing and a typical product operational environment show relatively insignificant differences in the solder creep-fatigue for SnPb and SnAg solders; for benign loading conditions SAC 405/305 solders show a reduced life of up to a factor of 3.
SAC solders with reduced silver contents show a marked decline their mean cycles-to-failure relative to the other solder alloys.
Initially Published in the IPC Proceedings
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