Reliability of surface-mount PPTC circuit protection devices

Accelerated life tests were used to estimate s-failure rates for PolySwitch polymer-based positive temperature coefficient (PPTC) devices with a surface-mount configuration. Electrical tests were done on a lot inspection basis on production parts, and results were pooled. Using an exponential model, the estimated failure rate from the pooled data is about 0.8 to 3.0 failures in time (FIT). Product reliability is related to the effectiveness of FMEAs and process controls. Our experience in proliferating the use of failure modes effects analysis (FMEA) and statistical process control (SPC) is discussed. This includes the benefits, challenges, and lessons learned.