The quality of solder wire
largely determines the soldering effect, so it is very important to choose a good quality solder wire.
I believe everyone has heard that the quality of solder wire can be judged by the glossiness of solder joints. Comparing the whitening degree of solder joints, you can know the proportion of lead content in solder wire, so as to judge the quality of solder wire.
For example, in such a solder joint, only a small part of the central area is whitish, and the surrounding light occupies about 70% to 80% of the entire solder joint, so the lead content of the solder wire should account for at least half, and it should be a 40-degree solder wire; if The center of the solder joint is white, and accounts for 60%-65% of the entire solder joint, and the surrounding area is 35%-40%. This kind of solder wire has a higher lead content, and it should be 35-degree solder wire; The white center of the solder joint accounts for 80% of the entire solder joint, and only the bottom edge is slightly bright. Another example is the solder joint of 45-degree solder wire, only the top is whitish, accounting for only 5%-10%, and the rest is obviously bright.
Solder wire is pure tin, Sn, silvery white, shiny, ductile, not easily oxidized in air, and its melting point is 232°C. Tin can be melted with most metals to form alloys. But the material of pure tin is brittle. In order to increase the flexibility of solder and lower the melting point of solder, another metal must be fused with tin to ease the performance of tin.
So to sum up, the larger the central whitening area of the solder joint, the higher the lead content and the worse the quality.