Study of the Effect of Gravity Weight on Strip Warpage

Strip level warpage control is critical for the manufacturing and assembly of advanced packages. Unfortunately, it is very challenging to simulate strip level warpage accurately. One of the challenges is the strip gravity weight effect. In this paper, nonlinear simulations were performed using Ansys Workbench to observe the effect of gravity on strip warpage. The model consisted of the strip on top of a supporting surface, or table, to more closely resemble how the warpage was actually measured. To account for the gravity effect in simulations with various warpage shapes, contact conditions were included to capture the interactions between the strip and the supporting surface. Simulation results show the weight effect greatly reduced warpage on pre-mold strips, resulting in more accurate warpage simulation results when correlating to actual strip warpage measurement data. There was a significant difference in the weight effect at the chip-attach stage compared to the post-mold stage, with the post-mold stage showing less of a reduction in warpage. Other strip configurations and geometry effects were also studied in this paper, such as: strip size, number of blocks, a slot placed between blocks, and a cored vs. coreless substrate.