The Influence of the Pb-Free Solder Alloy Composition and Processing Parameters on Thermal Fatigue Performance of a Ceramic Chip Resistor

This paper presents the results of a thermal fatigue study of a 2512 ceramic chip resistor assembled with various Pb free solders including SnCu, SAC105, SAC205, SAC305 and SAC405. The test matrix also includes a SnPb eutectic control cell. The resistor test vehicle provides an expedient and self-consistent method for evaluating the relative fatigue performance of the various alloys. A study of the "as-received" solder joints was completed to characterize the microstructure of the solder joints with varying silver content. Thermal fatigue was evaluated using an accelerated temperature cycle of 0/100 degrees C with dwell times of 10, 30, and 60 minutes. The test results show a direct relationship between characteristic fatigue life and Ag content, with the higher Ag content alloys outperforming those with the lowest Ag content. A smight be anticipated, there also is a consistent inverse relationship between fatigue life and dwell time for the Pb free solders. The failure anaysis and microstructural evolution is characterized with optical metallography and scanning electron microscopy and the fatigue reliability of the PB free solders is discussed in terms of the microstructures.