Effect of Joule heating on the reliability of microbumps in 3D IC

Due to the demand for high-performance electronic products, there has been a rapid development in three-dimensional integrated circuit (3D IC) packaging technology. The 3D stacking relies on microbumps and through silicon vias (TSVs) to connect multiple Si dies vertically. These high-performance electronic products usually need to consume high power, combined with limited heat dissipation due to dense packing, resulting in the issue of Joule heating. The problem of Joule heating impacts the reliability of products. This study investigated the factors contributing to Joule heating of microbumps and its subsequent reliability issues through experimental methods and finite element analysis (FEA) simulations. Joule heating was quantified by measuring the temperature increase at stable states using the temperature coefficient of resistance (TCR) equation. We first observed that environmental temperature influences Joule heating. Higher oven temperature can exacerbate the Joule heating effect and lead to higher temperature increase under the same current density. We also examined the effect of intermetallic compound (IMC) formation on Joule heating, with a 12.5% increase in heat generation after IMC formation. Furthermore, the adverse effect of voids induced by sidewall wetting during high-temperature storage (HTS) on Joule heating using FEA was demonstrated. Additionally, we discovered severe Joule heating to cause thermomigration (TM) in the microbumps at a system level. Finally, we proposed structural optimization of the microbump to mitigate Joule heating and enhance reliability.