A Lecture on Soldering By The Soldering Craftsman 2-3

A lecture on Soldering

Ⅱ. Pb-free Soldering

3. Differences between Pb-free solder and eutectic Sn-Pb solder


First, let’s look at the difference between Pb-free solder and eutectic Sn-Pb solder.
Workmen may not get used to the fusing point difference when they just begin to conduct Pb-free soldering. Actually, the fusing point difference is merely 34℃. People who get used to eutectic Sn-Pb soldering may be puzzled: Why hasn’t it got fused yet?! Pb-free solder refusing to fuse may be a problem for workmen just starting to use it, though, for most of them, they have not any problems in doing eutectic Sn-Pb soldering. As is known to all, fusing point carries much weight in deciding the thermal capacity of an iron. As it is impossible to raise the temperature at the iron head for 34℃ (It will be discussed later.), under-heat occurring is no surprise.
Second, some people ask, “If there is any content of plumbum?” Of course not, since it is called Pb-free solder.
Third, there exist the differences regarding wettability and fluidity. The wettability and fluidity of Pb-free solder are still not as good as those of eutectic Sn-Pb solder, though some improvement has been seen. In addition, it is stickier. All these give rise to the difficulty in Pb-free soldering operation.
Fourth, difference in material costs. The price of eutectic tin solder is so cheap that sometimes the material cost can be neglected. However, since Pb-free tin solder came into being, the silver price keeps going up and the material cost can no longer be neglected, especially the price of the rare metal, silver will never go down in the future because of its limited reserves. Perhaps tin solder containing no silver can be used extensively one day in the future.
Fifth, there may be slight difference on the soldering surface. If the soldering is done with qualified eutectic tin solder, the soldering surface shines and presents metal gloss; if the job is done with Pb-free tin solder, the soldering surface will appear matte and coarse.