If one boils water on a gas cooking-range, the gas flame temperature is so high that it should be able to melt the cooking pan. This does however not happen during normal cooking, while the pan and its content will divert so much heat to the direct area, that the spot where the flame hits the pan will only rise gradually in temperature.
In analogy with this example one should look to the making of single solder joints with a high temperature solder source with a relative small mass.
The joint and its surroundings are ‘cold’ and must be heated up to the solder temperature in a short time (2 – 3 s). Having a relative small mass of solder in the dedicated nozzle in comparison with common wave soldering, one needs a high temperature to realize the joint formation within the given time frame.
During the formation of the joint the solder temperature at the nozzle surface will drop, while at the same time the temperature of the joint area will rise. When the solder is just risen to the topside of the solder fillet, the temperature is thereabout 217 °C, when SAC-solder is used and assuming that the joint is well solderable. This is then also more or less the temperature that the solder at the nozzle surface, which is in contact with the joint, will have. The metal parts involved, like the component lead, the joint barrel and the solder, will transfer the temperature rather fast. That is why there is almost a thermal equilibrium when the joint formation is finished.
As soon as the solder source separates from the joint, the temperature of the solder surface of the flowing SelectWave will rise again to its set point within a short time.
Looking to the joint, the solder starts to solidify as soon as it is separated from the wave. During this process the solidification heat is emitted to the joint area. This will give at first an increase of the temperature in the direct vicinity of the joint. After that the temperature will gradually drop to the ambient temperature.
ITW EAE Support Center