High-speed SMT compatible dispenseless underfill process for CSP BGA flip chip assembly

Abstract

Fluxing underfill materials are widely used in electronics manufacturing to improve reliability performance. The prevailing process of applying fluxing underfill is by dispensing the desired volume onto the printed circuit hoard with optimized patterns. The underfill cure is accomplished concurrently with solder joint formation in the reflow process. Even thou& the processing time of applying underfill material by this method is much shorter than that of the conventional capillary flow underfill process, the processing time of underfill dispensing is much longer than other process steps (e.g., printing, chip placement, reflow, etc). The current underfill dispensing process is a bottleneck in the high-speed electronic assembly manufacturing. Besides the long processing time, the underfill dispensing process requires complicated and expensive dispensing machines, which increase the manufacturing cost. In this research, an innovative dispenseless fluxing underfill process and the associated module have been developed to achieve high-speed SMT compatible underfill processing [I]. The underfill application and chip placement are integrated into one process step that is accomplished by one placement machine. The prototyping of flip chip on board assemblies utilizing this innovative process shows dramatically reduced processing time. It also improves the reliability of electronic assembly systems. This invention enables remarkable cost savings from shortening processing time and eliminating the capital cost associated with underfill dispensing machines. The proposed process and module are fully compatible with the current SMT electronic manufacturing infrastructure. The dispenseless underfill process provides a high-speed and costeffective solution for flip chip, CSP, and BGA electronic packaging assembly.