Influence of Joint Formation Process on the Electromigration in High Bandwidth Memory (HBM)

Abstract

3D IC packaging technology has emerged as a promising solution to realize low power consumption, small form factor, multi function, and high speed as the device's scaling down limit has been met beyond Moore's Law. Because electronic devices require higher performances, high density of input/output interconnects (I/Os) and fine-pitch are needed to successfully meet the criteria for multi-functional and miniaturization of next-generation electronics. The increase in current density due to the miniaturization of the solder bump and pitch can cause serious electromigration (EM) failure issues. In case of controlled collapse chip connection (C4) and flip chip bumps, where the thickness of under bump metallization (UBM) is thinner compared to the solder, EM induced failure mainly occurred in UBM. However, new types of EM failure such as solder necking and formation of porous type IMC due to migration of Sn in micro-bumps was observed that was not found in C4 and flip chip bumps in case of micro-bumps with increased UBM thickness. Therefore, EM characteristics of the micro-bumps should be investigated further. In this work, we tested the electromigration lifetime using one high stacked high bandwidth memory (HBM) consisting of TSVs and micro-bumps made by thermo-compression bonding (TCB) and mass-reflow (MR). We performed electrical test for resistance change with the time and analyzed microstructure and metallurgical evolutions on the failure sample. As a result of cross-sectional analysis on the EM failure sample, we identified dissolution at the metal line and void at the TSV. Also, we confirmed migration of Sn at the solder that was not found in C4 and flip chip bumps. This phenomenon was not a critical failure site, but it was confirmed to be caused by EM. Also, we conducted high temperature storage (HTS) tests to identify thermal effect affecting HBM. Failure behavior in HBM according to HTS test was not confirmed.