Thermo-mechanical modeling of stacked die flash memory package EMI shielding layer crack under thermal cycling test

Abstract EMI (Electromagnetic Interference) shielding is widely used in electronic modules to reduce the coupling of radio waves, electromagnetic fields, and electrostatic fields to enhance electric performance (Liu et al., 2016). Some flash memory products are also equipped with EMI shielding for the desired electric requirements. In this paper, TCT (Thermal Cycling Test) reliability of metallic thin film EMI (Electromagnetic Interference) shielding layer, which is deposited on stacked die flash memory package top and sidewalls is studied. A crack in the EMI layer is observed under TCT (Thermal Cycling Test) experiment. Three-dimensional thermo-mechanical FEA (Finite Element Analysis) modeling is used to determine the root cause of EMI shielding layer crack, that is, the two stacks of stacked NAND dies causes stress concentration and plastic strain accumulation at the EMI centerline region where the local metallic EMI structure gets fatigued and finally cracks. In addition, simulation results explain the difference in EMI layer fatigue behaviors between two stacks and one stack NAND package, which is verified by experimental warpage test data and crack occurrence. Lastly, methods to improve EMI layer fatigue life under TCT for two NAND stacks package are suggested.