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Is it recommended to tin PCBs before applying solder stop mask or should I apply the solder stop mask to the PCB and then apply the tinning?

Would tinning before applying the solder stop mask be wasteful in terms of the tin? Or is this a better practice than to tin after the solder stop mask has been applied (to only have the exposed pads be tinned, since the other traces are already covered with solder stop mask anyway)?

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  • \$\begingroup\$ I think it depends on what you are plating with and how your board will be soldered. Research SMOBC (solder mask over bare copper). SMOBC helps prevent flow of molten metal under solder mask. \$\endgroup\$
    – Tut
    Commented Sep 12, 2013 at 10:55
  • \$\begingroup\$ Meaning I should only tin the exposed pads after applying the soldermask ?? \$\endgroup\$
    – 1amtoo1337
    Commented Sep 12, 2013 at 11:47
  • \$\begingroup\$ Not my area of expertise, which is why I did not answer. It depends on the plating and your soldering process. If you hand solder, I think it doesn't matter; otherwise I think you may want SMOBC. I think the type of plating needs to match the process (SMOBC or not). \$\endgroup\$
    – Tut
    Commented Sep 12, 2013 at 12:00

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It is recommended to Apply solder stop mask first, then tin. If you do it the other way around, the solder will easily creep under the solder mask and cause "swelling". The solder stop mask is supposed to stop the solder!

When you order the board from a board house, you indicate this process with the word SMOBC, which means solder mask over bare copper.

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