Effects of Solder Mask Application Method on The Reliability of An Automotive Flip Chip PBGA Microcontroller

Stringent requirements on semiconductor devices targeted for automotive mission profiles are challenging the thermomechanical performance of packaging materials. One typical failure mode is solder mask cracks, which is a significant concern for FCPBGA packages. Solder mask cracks may be more likely to be observed during component level AATC stress tests. In this study, solder mask cracks occurred in specific areas of the substrate with high copper trace density and were found to be dependent upon the application/cure method of the solder mask. Differences in the application/cure process resulted in different material properties. The following investigation included material characterization, Finite Element Modeling (FEM), and additional component level AATC stressing to characterize the fundamental material property changes of the solder mask. Nanoindentation was performed throughout the interim stress readpoints to characterize the stiffness and hardness of the solder mask as a function of the application/cure process. A global-local FEM simulation was performed to correlate the design sensitivity of the substrate to solder mask cracking. It was found that the solder mask manufacturing process has a significant effect on the material properties, which impacts the thermomechanical performance of the solder mask through extended AATC stressing.