Cleaning Challenge of Die Attach Process in FCBGA with Larger Die Sizes and Finer Bump Pitches

With the rapid growth in demand for data center, artificial intelligence, high-performance computing and autonomous vehicles, FCBGA (Flip Chip Ball Grid Array) technology is advancing toward larger die sizes and finer bump pitches. The need for higher I/O counts has driven the demand for smaller bump pitches to increase I/O density. The traditional bump pitches of 150μm are being reduced to 80μm or less. Finer bump pitch introduce significant cleaning challenges as it increases the likelihood of flux residue, affecting product performance and reliability. This article mainly explored the major factors of flux cleaning, including concentration of cleaner, clean speed and wash tank temperature. In this experiment, highly active halogen flux was used for the cleaning test. Due to its chlorine compounds and corrosive, the effects of flux residue can be easily observed through reliability testing. FCBGA packages were subjected to several reliability tests, including: JEDEC Level 3 preconditioning (MSL3); uHAST (96 hours); bHAST (264 hours); HTSL (1000 hours). After these, the functionality of the packages was evaluated using I/V tests. SAT (Scanning Acoustic Tomography) to examine internal structural integrity. If structural issues such as white bumps were detected, SEM (Scanning Electron Microscopy) and TEM (Transmission Electron Microscopy) were employed to observe package interface delamination. EDS (Energy Dispersive Spectroscopy) was used to analyze the elemental composition at delamination position. Overall, the findings of this study indicate that cleaner concentration and clean speed are key factors in flux cleaning process after die attach, that can be adjusted to effectively clean flux residues, thereby enhancing the reliability and performance of FCBGA packages.