Design and Demonstration of Self-Healing Behavior in a Lead-Free Solder Alloy

Abstract

A critical review of self-healing behavior in metals and metal composites with a focus on the opportunities and challenges inherent to their design and application will be presented. In this work, a self-healing composite (SHC) is designed, consisting of carbon fiber microtubes filled with a low melting temperature alloy imbedded within a lead-free solder alloy having a higher melting point than the filler alloy. In this concept, when the SHC is damaged or cracked, heat can be applied to the affected area whereupon the low melting alloy will melt and flow into the crack. Once heat is removed, the filler will solidify, sealing the crack to effectively heal the damaged alloy. This will lead to a decrease in the electrical resistivity of the healed composite compared to the damaged material. The research described in this paper explores the concept of self healing to fabricate self healing lead-free solder matrix composites and to probe the healing agent as sealing material, with the aid of Computational Fluid Dynamics (CFD) models developed by the authors for the manufacturing processes and self-healing behavior. The simulation consists of healing a cracked SHC lead-free solder alloy reinforced with carbon fiber microtubes filled with a low melting solder alloy. The objective of this study is to find the influence and efficiency of this concept of self-healing for lead-free solder alloys and their composites. Experimental validation of the CFD analysis will be presented. Micro-electric soldered joints are subjected to very large amounts of thermo-mechanical cycling, in which large amounts of stress are produced from serving as both an electrical and mechanical connection; thus a self healing technology could be extremely useful in variety of applications.