Question: What is the thumb rule for soldering iron temperature for RoHS & Non-RoHS manual soldering?
Answer: Thanks for the question regarding solder iron temperature selection for manual soldering operations.
There are two factors involved in making this selection, one being the mass of the metal being joined and second the size of the soldering iron tip.
As for the alloy being used, the 63/37 is liquidus at 183C and the new RoHS alloys, such as SAC305 and Sn100C have a liquidus temperature around 215C. With the soldering iron set at between 371C [700F] and 398C [750F], one should be able to solder most joints. If the mass of the joints is very small then the temperature of the solder iron could be reduced to 343C [650F].
It is recommended to use the lowest possible temperature which will reflow the total joint, as using higher temperatures will create more damage to the tip of the soldering iron which will increase tooling cost.
These temperatures are satisfactory for all alloys, be it either the standard Sn/Pb or the new Lead-free alloys such as SAC 305 and Sn100C.