A lecture on Soldering
11. Temperature at an iron head
The optimum temperature of an iron head for best use is about 350. When the mother metal is in large size, the tin solder will not fully melt. In this case, most workmen will raise the head temperature to speed up the fusing. However, if the temperature at the head goes up too high, the high temperature will pass rapidly to the tin solder which is contacting the iron head. As a result, the solder flux will evaporate instantly along with slight vapor explosions and the splashing of tin ball and tin flux. Meanwhile, the solder flux evaporates so fast under high temperature that it gets no time to work before evaporation and, as a result, cold soldering occurs. What is worse is that the process of oxidization at the iron head quickens. Even if the head is cleaned up, oxidized film will formed again in just seconds. Working efficiency will be greatly dragged. So in order to avoid the fault like that, iron heads of identical profile but different in diameter (different in thermal capacity) should be selected according to the statement in Section 8 (Iron head selection).
One thing more, Although an advanced iron with temperature display and temperature control is more convenient to use, it may present big errors after the head has been worn out or changed. Sometimes the error can be as high as 50, so far to my personal knowledge.
In order to maintain a proper temperature in soldering operation, a thermometer can be used. A thermal coupler is installed in a temperature transducer and easy to be changed. It should be a practice rule to measure the iron before each operation and in case of any abnormal scenario.