3D IC assembly using thermal compression bonding and wafer-level underfill — Strategies for quality improvement and throughput enhancement

This paper examines the key aspects for quality improvement and throughput enhancement of thermal compression bonding (TCB) process using dry film laminated wafer-level underfill (WLUF) material. The WLUF material must have good compatibility with pre-assembly and assembly process steps. And all the process steps after and including WLUF lamination have to be co-optimized to ensure the integrity of the WLUF material, consequently leading to higher stacking yield. Good bump joining and underfill filling quality is achieved by optimization different stages of the TCB profiles. A new method enabled by WULF, termed vertical collective bonding (VCB), is applied to multi-layer 3D stacking, producing good bonding quality and significant process time saving. Multi-layer 3D stacks made by the VCB process show good thermomechanical reliability in high temperature storage and thermal cycling tests.