ECC-Based Flux Cleaning Monitoring for Improved Reliability in High-Performance Computing (HPC) and Artificial Intelligence (AI)

Effective flux residue removal is critical to the quality and reliability of solder joints in advanced packaging. Even a PPM (part per million) level of residue can cause serious adhesion loss between underfill and solder joints, leading to potential reliability issues. With the emergence of 2.5D/3D IC packaging, particularly in high-performance computing (HPC) and artificial intelligence (AI) systems, the removal of flux residue has become more challenging and time-consuming with the large size of Chip-on-Wafer-on-Substrate (CoWoS) packages. This paper presents a new electro-chemical characterization (ECC) technique developed to monitor the flux residue removal process during advanced packaging fabrication. Compared to conventional lab mass spectroscopy approaches for residue detection, the ECC offers a much faster measuring time of less than one minute, making it suitable as the in-line production defense. Additionally, ECC has the resolution of residue detection down to ppb (part per billion) level so the chemical components in entire flux removal process can be closely monitored, which can provide significant amount of info for optimizing flux cleaning processes. Overall, the ECC proves to be a reliable method for monitoring flux removal process with high sensitivity and fast analysis, ultimately enhancing the yield and reliability of existing and future packaging products.