Effect of Cleaning Process Parameters and Materials on Flux Residue for Flip Chip Assembly

ABSTRACT Flip chip assemblies are underfilled with the ultimate objective of achieving a higher life in service. Voiding and/or delamination of the underfill at interfaces with the adhering surfaces may subsequently lead to early solder joint failures. Such phenomena are caused by several factors, which include, but are not limited to, the interaction of the underfill with the flux residues from the reflow solder assembly process. Research efforts focus on understanding the interaction issues of underfills and fluxes, which would help in introducing compatible underfill and flux materials. Concurrently, researchers also focus on developing innovative cleaning processes that would result in pristine surfaces and high assembly throughputs. The objective of this research was to study the effect of process parameters and materials on cleaning the residues that are trapped between the silicon chip and the laminate of a high I/O very fine pitch flip chip assembly that is manufactured in-house. The study also included an investigation into the effectiveness of process parameters to clean residues from the lead free soldering process. Experiments were designed to compare the effect of a variety of cleaning procedures that were used independently or in combination with each other. This included methods such as acid solution cleaning, plasma cleaning, refluxing, immersion cleaning, and a surfactant impingement cleaning technique, all in combination with an in-line aqueous wash process. The results indicate that the most effective cleaning process was a multi-stage process that utilized the surfactant impingement technique.