Printability Evaluation of Water-Soluble Type 7 Solder Paste for Fine Pitch Advanced Package Interconnects

This study evaluates the printability and solderability of water-soluble, Type 7 solder paste for fine-pitch interconnects in advanced packaging applications. Fluxes were formulated using sebacic acid and suberic acid as activators, and three fluxes and solder pastes were produced. From the wetting balance test and viscosity evaluations, the flux and paste containing sebacic acid (Paste-A) exhibited the highest flux activity, while the flux containing suberic acid (Paste-B), provided better stability with lower flux activity. Printability evaluations demonstrated that Paste-A and Paste-C which both sebacic and suberic acid was included showed excellent performance at fine pitches (down to 0.08 mm), with no slumping or bridging observed, whereas Paste-B showed dewetting and bridging at 0.08mm pitch. The results suggest that sebacic acid improves printability and wettability, but increases viscosity over time, while suberic acid enhances stability at the cost of reduced printability.