EM 388F Term Paper: Low-Cycle Fatigue Behavior of Lead-Free Solder

   Tin-based lead-free solders have been widely used in microelectronic packages today. In electronic packages, solder joints provide not only electrical connection, but also mechanical attachment between the semiconductor devices and substrates. Therefore, the mechanical properties of the solder joints have become critical to the reliability of electronic packaging. Under normal usage, electronic devices are exposed to cyclic temperature load. The thermal expansion coefficient (CTE) difference among materials will transform to a cyclic strain, hence facilitate the commonly seen low-cycle fatigue (LCF) of solder joints.

    Under a cyclic load, it has been observed the loading rate and temperature play important roles in LCF of lead-free solders. Further investigation indicated the fatigue life could be represented by a modified Coffin–Manson relationship. In this term paper, the LCF behavior of Sn-Ag lead-free solder alloys will be briefly reviewed, and the LCF properties of bulk lead-free solder and eutectic Sn-Pb solder will be compared as well.

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