Modeling of micro/nano-particle dissolution during reflow of lead-free composite solders

The ever increasing miniaturization of electronic devices has pressed the need to find the alternate solders that can deliver the necessary strength and reliability of the solder joints. In this view the development of composite solders has become the focus for many researchers in recent years. This paper presents a mathematical model to simulate the dissolution behavior of metal particles in composite solders during reflow process. The mathematical model is based on basic mass diffusion process and involves the actual physical properties of various species (particle, IMC, solder etc) of the system. Thermal effects and related thermodynamic constraints together with the non-equilibrium interface kinetics of dissolving micro and nano-size particles are also considered. The growth of intermetallic compound (IMC) and terminal size of embedded particles for various reflow conditions are analyzed using the model. Dissolution behavior of micro-size Cu particles in lead-free, Sn-Ag-Cu (SAC) alloy solder was studied. The end particle size and the thickness of the IMC layer around the particles are presented for various initial particle sizes and reflow conditions. Effects of initial copper content in Sn-Ag-Cu alloy solder and the interface reaction kinetics on the dissolution of copper particles and growth of intermetallic compound are also investigated. Results of the model show the interesting behavior of micron-size particle dissolution in liquid solders. The reaction kinetics at the IMC/solder interface was seen to play an important role in the dissolution of copper particles.