Interfacial Delamination Characterization and Thermo-mechanical Reliability of Stacked Die Package by Finite Element Analysis

Abstract

Stacked die packages are widely used in flash memory and solid-state drives (SSDs) due to high volume, low cost and flexibility. Die attach film (DAF) is popularly employed as the adhesive for chip-to-chip and chip-to-substrate connections owing to its excellent performance and reliability. However, because of the mismatch of coefficient of thermal expansion (CTE) of different materials in the package and so-induced high thermal stresses at interfaces, cracks may occur at the interfaces associated with the DAF, e.g., DAF/chip and DAF/substrate interfaces, which can have a serious impact on the reliability of the package. In the present work, the delamination characteristics of the interface between the DAF and the chip as well as the thermal stability of the package are studied by three-dimensional (3D) finite element analysis via virtual crack closure technique (VCCT). Based on the calculation of fracture mechanics parameters (e.g., energy release rate, G) along the crack front, the degree of danger of the interfacial crack at different directions (angles) and the effect of temperature on energy release rate are studied. In addition, some key geometric parameters affecting the stability of package are also investigated. The simulation results show that the thermal stress concentration occurs in the four corners of the interface between the chip and the DAF. The variation of G with the crack position (i.e., s, the distance from A to B) and the variation of Gmax with θ have the same trendency, and energy release rate curves have a good symmetry. Besides, temperature has a significant effect on the crack propagation driving force. The thermal stability of the package is enhanced with the increase of the thickness of the epoxy mould compound (EMC) cap and chip but degraded with the increase of the thickness of DAF