Influence analysis of joint attributes on the fatigue progress of SnAgCu solder joints under thermomechanical loading

Abstract

With new technologies and the further development of vehicles, such as the electrification of the powertrain or autonomous driving, the proportion of electronics in vehicles continues to increase. The reliability of these electronic components is of the utmost relevance, especially in safety-relevant areas.One cause of failure of the electronics is thermo-mechanical fatigue of solder joints. This research investigates the thermomechanical fatigue of two-pole components. The attributes of solder joints are studied in high detail and with large number of samples to ensure the statistical significance. Here, the focus is not only on the correlations of the attributes themselves, but also on their influence on the damage behavior of the solder joints under temperature cycling load. 3D profilometry and radioscopy are used to investigate in detail the solder joint shape, the component position, the void ratio in the solder and the amount of solder paste applied. The degree of damage to the solder joints is determined using the shear test.This study shows the relationships between solder joint attributes of unstressed devices as well as the change of the attributes under thermal cycling. In addition, the dependencies between shear forces and attributes are investigated. Based on cross-section and X-ray images, an alternative failure limit to the commonly applied 50 % residual shear force, is presented.