Fatigue life estimation of FBGA memory modules under harmonic excitation

Abstract

This paper predicts the fatigue life of fine-pitch ball grid array (FBGA) solder joints in memory modules due to harmonic excitation by the experiments and the finite element method. A global-local modeling technique was used in finite element simulation. A finite element model of the memory module with simplified solder joints was developed as a global model, and the natural frequencies and modes were calculated and verified by experimental modal testing. Displacement variations were calculated from the global model due to vibration excitation using the mode superposition method. A local model with detailed solder joints was developed in order to calculate stress magnitude concentrated on solder joints of the memory module under vibration. Stress versus life (S-N) curve was developed for memory modules under various vibration levels to derive solder material fatigue constants. Then the fatigue life of the memory module was determined by using the Basquin equation and Miner’s rule. It was experimentally verified that predicted fatigue life of the memory module under cumulative damage conditions matches with experimental results with reasonable accuracy.