Flux/underfill compatibility study for flip-chip manufacturing

In flip-chip assembly processing, material compatibility is a key issue determining package quality and reliability. With the advent of no-clean fluxes, the elimination of the flux cleaning process introduced a compatibility concern between the flux residue and the underfill. To address this problem, various different types of fluxes have been introduced, ranging from epoxy fluxes designed to interact with the underfill to a low-residue system leaving almost nothing behind after the soldering process. In this study, the compatibility of various flux types with an underfill was investigated. Data from TGA and TMA revealed thermal and physical properties, such as flux residue amount and melting points. Surface characteristics analyzed through XPS were used in combination with thermal, chemical, and physical analysis to characterize the behavior of each material set. The advantages and disadvantages of the various flux systems were analyzed through these tests.