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We have developped a PCB with a battery holder.

PCB

As you can see the copper is covered by a tin layer. On older versions of our PCB it had a gold-plated layer.

Now on our recent boards we experienced that there was 'gunk' around the batteries. Is it corrosion or leakage? I'm no expert on chemical precesses.

We never saw it happen on the gold-plated PCBs. Could it be that this is caused by the tin layer?

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    \$\begingroup\$ Has the assembler also changed? Could be the new guy isn't washing the flux off properly. \$\endgroup\$
    – user_1818839
    Nov 15, 2019 at 11:03
  • \$\begingroup\$ Do you REALLY mean tin? Or solder (HASL?) or nickel or ... . Contact metalurgy is a black art. If the "gunk" is dry and solid and metalish it could be a metal-metal + current electrochemical reaction. I'd not expect and electrochemical reaction to extend into the cell proper. Are the cells "leaking" visibly. \$\endgroup\$
    – Russell McMahon ♦
    Nov 22, 2019 at 0:59
  • \$\begingroup\$ This recent PICList discussion has potentially relevant material. My posts are under 'RussellMc" and I have a number of possibly useful links there. \$\endgroup\$
    – Russell McMahon ♦
    Nov 22, 2019 at 1:04
  • \$\begingroup\$ Some of the topics here may be relevant (many aren't) \$\endgroup\$
    – Russell McMahon ♦
    Nov 22, 2019 at 1:05

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