Effect of Design Parameters on Thermo-Mechanical Stresses in 3D ICS

Abstract

Solid Liquid Inter-diffusion (SLID) bonds have been recently utilized to fabricate 3-dimensional integrated circuits (3D ICs). Introduction of this new technology in the production of electronic devices has enabled the electronic industry to produce super high density interconnects and vertical integration of ICs without manufacturing and environmental limitations of conventional solder interconnects. The properties of these bonds however are completely different from conventional solder joints. This manuscript presents a microstructural characterization of these bonds. This analysis shows that the bond mostly consist of intermetallic material, therefore may not behave visco-plastically under thermo-mechanical loading. A numerical experiment is conducted to evaluate the effect of design parameters such as underfill properties, die thickness, interconnect size and substrate thickness on stress level in SLID bonds and copper interconnects. A finite element model was built for all the treatments of the experiment and von mises stress at the copper interconnects and SLID bonds were obtained from finite element. Statistical analysis of the results was conducted to determine the main effects of selected parameters. This analysis shows that die and substrate thicknesses and underfill stiffness are the most influential factors among the selected parameters on stress 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. Both factors show higher stress at higher levels.