Most joints soldered with lead-free solders get a less shiny appearance. While tin-lead surfaces are smooth and bright, SAC joints look dull and rougher. (SAC = tin-silver-copper solder alloy) The reason for this can be of different origins. One of them is the fact that these lead-free alloys contain often three elements that can give three eutectics during solidification of the solder. These eutectics have each their own melting point and solidification behaviour. After wave soldering, especially when using lead-free solders, joints on the same PCB may not have the same glossy appearance, although they are soldered under the same conditions.
The reasons for these effects will be explained in the attached document.
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