What are the reasons why the double-sided PCB board pad is not tinned?
 There are several cases in which the PCB board is not tinned.
        1. The PCB circuit board is oxidized, and the PCB board is not tinned.
        2. The temperature of the furnace is too low, or the speed is too fast, and the tin does not melt.
        3. Solder paste problem, you can replace another solder paste try.
        4. Battery problem, this is the most common problem, because the battery is generally stainless steel, to be plated with a layer of chromium to tin.
        If the plating layer is oily or poorly plated, it will not be tinned. You can use a soldering iron to see if it can be soldered. Or put some solder paste on the battery, and then use the desoldering station or the electric heating table to see if the battery can be tinned.
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