Reliability of SAC Leadfree Solders in Automotive Underhood Temperature-Vibration

Leadfree solder interconnects accrue damage much faster when subjected to simultaneously elevated temperatures and vibration. Ultimate tensile strength has been shown to degrade upto 50-percent from initial fabricated value. Electronics in automotive underhood applications may be subjected to prolonged periods of high temperature vibration. This study presents a comparison of failure modes for various SAC alloy compositions at elevated test temperature and vibration. Test vehicle with lead-free SAC (SAC105 and SAC305) daisy chain CABGA packages have been tested to failure under harmonic vibration at the first natural frequency under multiple test temperatures. The test vehicles were subjected to three-test temperatures (25°C, 55°C and 155°C) and simple harmonic vibration with amplitude of 5g and 14g. Material properties of the printed circuit board at elevated temperatures have been measured using tensile tests. High-speed camera is also used to capture the vibration event during testing. Strain gauge was attached at the center of the board to extract the strain value. The vibration simulation is correlated with the system characteristics such as modal shapes and natural frequencies and displacement amplitudes for each test condition using global-local FE models. An imaging method has been used to extract the out of plane displacement of PCB, which is used to validate simulation results. Finite element method based global and local method has been used to extract hysteresis loop and plastic work density of critical solder joint. Anand Viscoplasticity material data from the prior studies by the authors have been used to capture the high-strain rate temperature dependent aging behavior of the solder joints. A comparison between simulation and experimental results is conducted. In this paper, a new model has been proposed for life prediction of electronics under simultaneous temperature-vibration.