Development of simulation-approach for 3D chip stacking with fine-pitch array-type microbumps

A robust finite element analysis (FEA) is beneficial to quality the microbump assembly by using process-flow technique and to estimate subsequent thermo-mechanical reliability of critical microbump in a whole 3D-ICs packaging structure. However, the foregoing simulation work is time-consuming and becomes difficult to obtain a converged numerical result while thousands of microbumps with an array-type need to be taken into account simultaneously. For this reason, this research proposed a simulated technique to introduce an equivalent material composed of microbumps and their surrounding underfill. The mechanical properties of above-mentioned equivalent material, including Young´s modulus, Poisson´s ratio, and coefficient of thermal extension are directly obtained applying a tensile load and giving a increment in temperature during FEA, respectively. The analytic results indicate that at least five microbumps at the outermost region of chip stacking structure need to be considered as an accurate stress/strain contour in concerned region is achieved.