In this study, we examined the interactions of three types of underfill materials with a Pb-Free solder paste. Underfill formulations cured by anhydride, base, and acid were assessed for changes in reactivity in the presence of Pb-free solder paste residue. An analysis of commercial Pb-free solder paste was conducted, and the effect on underfill reactivity of the primary components was explored. Reliability tests were conducted to correlate effect of solder paste residue on reliability. It was found that some types of underfill chemistry are affected more than others by solder paste residues, but good reliability can still be obtained. It also was found that the underfill flux interaction can be managed by formulation.
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