Stress and strain distribution of lead-free solder joints with compliant layer in wafer level chip scale package under random vibration based on orthogonal design

The 3D finite element analysis models of lead-free solder joint with compliant layer in wafer level chip scale package (WLCSP) were developed. By using ANSYS the finite element analysis of the lead-free solder joints model was performed under random load. 1st compliant layer thickness, 2nd compliant layer thickness, die-side and substrate-side pad diameter were selected as four key configuration parameters, by using orthogonal array, the solder joints which have 16 different configuration parameters' levels combinations were designed. The maximum stress values within lead-free solder joints were obtained. Based on the values of stress the range analysis was performed. The results of study show that the stress and strain decreases with the increase of 1st and 2nd compliant layer thickness. With 99% confidence, the substrate-side pad diameter and die-side pad diameter have significant effect on the stress of solder joint under random vibration load, and with 95% confidence, the 1st compliant layer thickness and the 2nd compliant layer thickness have a certain effect on the stress of solder joint. The substrate-side pad diameter, the die-side pad diameter, the 1st compliant layer thickness and the 2nd compliant layer thickness affect the stress of solder joints in a descending order.