An investigation of copper dissolution and formation of intermetallic compound during soldering /

Abstract

Soldering is the predominant and established technique in electronic packaging industry for joining electronic components. During soldering of (Sn-rich solders), a SnCu interaction takes place at the Cu/solder interface. Copper is dissolved into molten solders and subsequently the intermetallic compound (IMC) would be formed at the interface as well as in the solder matrix. Understanding of copper dissolution and the growth of IMC at the Cu/solder interface is critical in achieving reliable soldered joints. This thesis presents an experimental investigation of Cu-Sn interaction kinetics. Two types of experiments, dipping and reflow have been performed. In dipping experiments, copper (99.9% pure) samples, coated with RMA flux, were dipped vertically in molten solders. In reflow experiments, solder buttons were reflowed in furnace. The dwell time (time for which the molten solder remains in contact with the substrate) in these experiments ranged from 5 seconds to lO minutes. The experiment temperature varied from the melting point of the solder up to 300°C. The samples were then cut, cleaned and cold mounted in epoxy at room temperature. Regular grinding, polishing, etching, and optical metallurgical process was utilized through all samples. The average thickness of IMC and thickness reduction in copper substrates was then measured from the optical microscopy photographs. Experimental results indicated that the temperature of molten solder and the dwell time controlled the copper dissolution rate and growth of IMC at the interface. For a given process temperature, the dissolution rate of copper into solder, showed a rising trend with increasing dwell time. The rate of formation of IMC layer revealed a similar trend. The experimental data can be used to estimate the kinetics of copper dissolution and the thickness of the resulting IMC formed during soldering.