Warpage, Stresses and KOZ of 3D TSV DRAM Package During Manufacturing Processes

The objective of this paper is to measure and simulate the warpage of 3D TSV (through-silicon via) die-stacked DRAM (dynamic random access memory) packages subject to thermal loading (from the room temperature to 260 degrees C, solder reflow temperature) during manufacturing processes. The related die stresses and keep-out zone (KOZ) for the dies in the packages at the room temperature are further calculated with this validated simulation model. In the experiments, a full-field shadow moire is used to measure the out-of-plane deformation (warpage) of packages under thermal heating conditions. A finite-element method (FEM) is applied for analyzing the thermally-induced deformation, stresses and KOZs in the packages to gain insight into their mechanics. The full-field warpages of the packages from the shadow moire have been documented under temperature loading and compared well with FEM results. The stresses and KOZs at the proximity of a single TSV for each die in the package at the room temperature have been calculated with validated FEM model. It is found that the sizes of KOZs in four-die stacked DRAM package at the room temperature are dominated by the horizontal pMOS device and are almost double as large as the size in wafer-level die. And the sizes of KOZs are pretty much similar for each die in this four-die stacked DRAM package, even through the stresses at each die are apparently different.