Kosuke Nakao, Atsushi Hiraizumi, Etsuko Iwasaki
From the standpoint of environmental protection, we cannot move forward without adopting Pb-free processes for the soldering of electronic components. Furukawa Electric, a leading manufacturer of reflow soldering systems, has now developed an oven designed for the Sn-Ag process, which at present seems to show the best chance of actual implementation. Compared to the Sn-Pb eutectic crystal solders used conventionally, the liquid phase temperature of Sn-Ag solder is about 30°C higher. The temperature for soldering must be at least 230°C. If the joints of the components having the highest thermal capacity are raised to this temperature, there is a major problem with the heat withstand properties of those with lower thermal capacity. The issue as far as the reflow oven is concerned is how small a temperature difference can be achieved between component joints. Other concerns addressed in the development work were bare-board temperature distribution, temperature profile reproducibility and obtaining wetting time, and satisfactory results were obtained. Results were especially good in terms of joint-to-joint temperature difference, which was reduced to about one-third of the former value.