Precise Warpage Control Technology for 12-Inch Bumpless Via-Last Chip-on-Wafer (COW) by Finite Element Method (FEM)

To realize the advanced information society, high-density and multi-layered structures such as Wafer-on-Wafer (WOW) and Chip-on-Wafer (COW) are required in the near future. This paper describes the influencing factors in reducing warpage during the resin molding process for COW, utilizing the Finite Element Method (FEM). It was confirmed that resin thickness significantly impacts warpage. To make a comparison, we replaced the base wafer material from silicon (Si) to glass with a higher coefficient of thermal expansion (CTE) and simulated the results. Consequently, it was found that the warpage amount was reduced to one-sixth of the original value. Therefore, an effective approach to minimize wafer warpage is to reduce resin thickness as much as possible and then determine the required warpage amount through simulations, aiming to achieve the desired linear expansion of the substrate.