Influence of IMC surface geometry and material properties on micro-bump reliability of 3D Chip-on-Chip interconnect technology

This study aims at investigating the growth reaction of the Ni3Sn4 IMC during thermocompression bonding process, the anisotropic elastic constants of the IMC, and the effects of the material properties and surface geometry or morphology on the interconnect reliability of a three-dimensional (3D) Chip-on-Chip (CoC) interconnect technology with Cu/Ni/SnAg micro-bumps subject to accelerated thermal cycling (ATC) loading. The research starts from the investigation of the growth reaction of the Ni3Sn4 IMC during thermocompression bonding process through experiment and classical diffusion theory. The relationship between the Ni3Sn4 IMC thickness and bonding temperature/time is derived based on the predicted activation energy of the chemical reaction of the IMC layer by experiment. Next, the elastic stiffness coefficients of single crystal monoclinic Ni3Sn4 are calculated through molecular dynamics (MD) simulation using the polymer consistent force field (PCFF). The degree of anisotropy in the Ni3Sn4 crystal system is also confirmed by the electronic structure of single crystal Ni3Sn4 using first-principles calculation based on density function theory (DFT). For comparison with the published experimental data and also use in the subsequent reliability analysis, the effective elastic properties of polycrystalline Ni3Sn4 are derived using the Voigt-Reuss bound and Voigt-Reuss Hill average based on the calculated elastic stiffness coefficients. At last, 2D plane strain finite element (FE) analysis together with an empirical Coffin-Manson fatigue life prediction model are performed to predict the interconnect reliability of the 3D CoC interconnect technology. The computed results are compared with the ATC experimental data to demonstrate the effectiveness of these two FE models. The dependence of the interconnect reliability on the thickness, material properties and surface geometry or morphology of the Ni3Sn4 IMC is addressed.