Warpage Optimization of Manufacturing Process for Fan-out Chip on Substrate-Bridge

Driven by the rapid progress in high-performance computing and heterogeneous integration, advanced packaging technologies are evolving to fulfill growing demands for high I/O density and enhanced electrical performance. ASE’s Fan-Out Chip on Substrate-Bridge (FOCoS-B) is a promising solution. This structure integrates multiple chiplets through an embedded bridge within a fan-out module, which is then mounted onto a high-density organic substrate. The architecture enables fine-pitch interconnects while offering excellent signal integrity and design flexibility.Due to the complex material stack and multi-layer assembly process, mechanical reliability especially warpage control has become a critical challenge in FOCoS-B packaging. This study investigates warpage behavior during two critical manufacturing stages: wafer-level processing and post-dicing fan-out module assembly. Finite Element Analysis (FEA) is used to simulate thermal-mechanical deformation and assess key contributing factors including structural and material conditions. In this study, the structural factors considered include the carrier thickness and the top epoxy molding compound (EMC) thickness, while the material factors involve the top and bottom EMC, wafer underfill (WUF), and the wafer carrier. A design of experiments (DOE) approach is applied to systematically analyze the impact and interaction of these variables.During the wafer process, the properties of the EMC and carrier are crucial and expectedly have a significant impact on warpage. After singulation into individual modules, the combination of the top and bottom EMC becomes even more important. Improper combinations of materials and structural parameters can result in significant warpage and stress concentrations, especially near the embedded bridge, thus threatening device reliability.This study provides key insights into warpage control and mechanical behavior in FOCoS-B structures and serves as a design guideline for improving process yield and long-term reliability in next-generation fan-out packaging.