A Highly-Reliable and Cost-Effective Approach by Reducing Flux Cleaning in Flip-Chip Processes Through Underfill Curing in a Pneumatic Ambient

In this study, we introduced a new curing method to eliminate solder flux residue, allowing underfill to expel solder flux by varying pressure at specific temperatures, thereby increasing reliability. By implementing this method, the requirement for flux cleaning in the process is eliminated, resulting in enhanced throughput. To assess the efficacy of the streamlined procedures, the flip-chip lots in the production were utilized to evaluated. Standard samples underwent typical flip chip fabrication flow involving flux-dipping, soldering, water cleaning, baking, plasma cleaning, and underfill dispensing followed by curing in a pressure oven. Two additional sets of production lots omitted various cleaning steps. All lots underwent underfill curing with pneumatic agitation, the defluxing step, in an innovative pressure oven. The novel pneumatic configuration facilitates agitation of the underfill material and thereby enhances flux residue removal, resulting in reliable underfill films and increased flip-chip throughput without the need for cleaning flux. In summary, the novel pneumatic curing profile in a pressure oven presents a reliable flip chip assembly solution, eliminating the need for flux cleaning and leading to significant time savings and increased throughput.