Why choose our new TRI0121 solder? 63/37 ratio is a Eutectic alloy of Tin Lead solder. As such it melts at a temperature that is lower than each of its constituents, and at a very precise single temperature rather than a range of temperatures. In the case of 63/37 it is 183 degrees. 60/40 melts around 188 degrees C. As the melting point is a single temperature it will transition fast than non-Eutectic alloys which means lower chances of dry joints. In non-Eutectic alloys one metal will melt before the other, and the same is true when solidifying.