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Dissolution of Copper and Formation of IMC in Bulk Lead-Free Solders

Besides the popular reflow soldering practice, wave soldering is another established technique in the electronic packaging industry for obtaining the solder joints. In this study the dissolution behavior of copper and the growth of intermetallic compound (IMC) during wave soldering process have been investigated. The study involved two different solder compositions, viz. pure Sn and eutectic Sn–Ag solder. Dipping experiments were conducted for the temperature range of 221–300 °C and for dwell time starting form 5 s to 6 min. The average thickness of the intermetallic compound formed and the amount of copper dissolved was determined. Experimental results indicated that the amount and rate of copper dissolution were strongly affected by temperature of molten solder and dwell time. The initial rate of copper dissolution was very high but it decreased with time. Based on the experimental results, the kinetic parameters governing the dissolution of copper and growth of the IMC were determined for the two solders.