The Great Underfill Race

Most Flip Chip assemblies require underfill to bestow reliability that would otherwise be ravished by stress due to thermomechanical mismatch between die and substrate. While underfill can be viewed as “polymer magic” and the key to modern Flip Chip success, many see it as the process “bottleneck” that must be eliminated in the future. Both views are accurate. A substantial amount of R&D is being focused on making underfill more userfriendly. Electronic materials suppliers, various consortia, government labs and university researchers are working diligently to shatter the bottleneck and fully enable Flip Chip the final destination for micropackaging. This paper will describe these efforts and provide a status report on state-of-the-art underfill technologies. We will also examine new processing strategies. Today, three distinctly different underfill systems vie for victory: capillary, pre-dispense and solid film. The incumbent capillary flow underfill manufacturers attempt to win by offering snap flow/snap cure materials and new features. Can the new 5-minute cure underfills deliver enough throughput and performance? Will the so-called “No Flow”, or pre-dispense liquids, win by eliminating flux even though dispensing equipment is still required? Which systems are REWORKABLE and how important is this feature? Perhaps the ultimate solution is solid underfill, but can the polymer chemists meet such a challenge wrought with paradox? How and where should solid underfills be applied and processed? Learn the status of the most unusual approach Reworkable Wafer-Level Flux-Underfill. Success at wafer-level can have a profound affect on Flip Chip by eliminating all steps and equipment now associated with the underfill process. We will try to determine if wafer-level underfill can deliver on the promise of making Flip Chip the Ultimate CSP!