Stress analysis of 3-dimensional IC package as function of structural design parameters

Solid Liquid Inter-Diffusion (SLID) is a technology that has recently been utilized to fabricate 3D ICs. Since application of this technology is in its infancy stages, manufacturability and reliability of these bonds are still under heavy investigations. This study presents an elastic-plastic finite element and analytical analyses that were implemented to evaluate effect of package design parameters on thermo-mechanical reliability of the SLID bonds and copper interconnects. A numerical experiment is designed in which several design parameters; die thickness, bond size, underfill stiffness and substrate thickness, are varied in 3 levels. Stress in SLID bonds and in copper interconnects were evaluated using the 3-dimensional finite element analysis as well as an analytical approach. The results show that die and substrate thicknesses are the most influential factors among the selected parameters on stress at the interface and on copper interconnects. Main effect results for stress analysis in SLID bonds using finite element shows that die thickness and underfill stiffness are the most influential factors in defining stress at SLID bonds. Results of the analytical approach confirm the finite element analysis. It is shown that effect of interconnect size and pitch is very small compared to die thickness. In average increasing die thickness increases both shear and peeling stresses at the interfaces and copper interconnects.