Effects of Metal Frame and Adhesive on Thermally-Induced Warpage and Stress of 2.5D Packages: Experimental and Numerical Studies

This paper aims to investigate the thermally induced warpage and stress of 2.5D packages with and without a reinforced metal frame experimentally and numerically. The consistent results between shadow moiré experiment and the finite element method (FEM) show that thermally induced warpage for 2.5D packages can be reduced by using a metal frame. The underfill stresses responsible for interfacial delamination and cracking in this package under thermal cycling are further analyzed using the validated FEM model. The location of underfill singular-feature stress corresponding to the delamination and crack has been identified. The results suggest that the low coefficient of thermal expansion (CTE) of substrate can reduce both package warpage and the underfill stress. And metal frame CTE, more pronounced than its modulus, increases with decreasing package warpage, but with increasing underfill stress. This paper also found that the selection of elastic modulus of metal frame adhesive below 50 MPa can significantly decrease the package warpage. Therefore, the CTE of the metal frame and the modulus of its adhesive are found to play important roles on controlling warpage of the packages and underfill stress, and should be carefully selected for improving both manufacturing and service reliabilities.