Solder Filler Motion Driven by Interfacial Tension in Self-Organization Assembly Process

Abstract

Soldering and anisotropic conductive adhesives (ACAs) are widely used for assembling electronic devices with narrow-pitch terminals. Solder bump methods need a number of processes, while interconnects of ACAs are less reliable. The purpose of this study is to develop a novel assembling method. The Self-organization assembly method using active resin containing solder fillers may allow reliable interconnects by simple process. The focus of this paper is on the movement of fillers, one of the fundamental processes of the Self-organization assembly method. In-situ observations on the behavior of 40 µmφ molten fillers in the resin revealed irregular movement of the fillers at a velocity of several µm/s. Numerical analysis, using improved volume of fluid method, indicated that even 10% difference of interfacial energy between half sides of a 40 µmφ filler could move the filler at the velocity of several mm/s. The inhomogeneous distribution of the interfacial energy is thought to be caused by the remaining surfactant elements.