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It has been always said that having gold plating on a PCB has lots of advantages. Not only does it give a good clean low resistance contact, but the perfect flat surface. However based on the galvanic series table, gold and tin\lead (or even copper) placed farther apart from each other that leads to corrosion and noise voltage.

if it is true what would be better to take into account first, resistivity or corrosion (also noise voltage)?

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  • \$\begingroup\$ Is your PCB running immersed in saltwater? \$\endgroup\$ – PlasmaHH Nov 6 '15 at 8:53
  • \$\begingroup\$ Typically you won't get moisture across a tin/gold contact because the tin covers the whole gold surface and you try to keep your devices dry (I think you get in trouble with moisture before you get to corrosion) \$\endgroup\$ – Arsenal Nov 6 '15 at 8:55
  • \$\begingroup\$ Thanks Guys for your reply. Dear PlasmaHH No It doesn't. and Dear Arsenal I think just the rate of corrosion depends on the moisture content so we would have corrosion and noise voltage even in the absence of it. \$\endgroup\$ – Mohammad Yousefi Nov 6 '15 at 19:28
  • \$\begingroup\$ I don't think I understand this question. The actual question part is "what would be better to take into account first?" What does that mean? As a side note, I think what people are telling you is that ENIG board treatment has proven to be practical and successful for many types of PCB's. So I think we are all concerned that you are raising a theoretical problem which does not arise in the real world. If it IS a problem, then it will be a problem for IC's, also, because the leads always use dissimilar metals somewhere along the line. \$\endgroup\$ – mkeith Nov 6 '15 at 20:23
  • \$\begingroup\$ mkeith, you are right and I don't say it is a problem. in IC's we have gold (apparently the best) or aluminium and also copper as wire but I haven't found someone that compare them. I'm looking for a prove that explain why exactly the gold is better, just because of resistivity or the effect of galvanic action is too negligible, nothing to concern about \$\endgroup\$ – Mohammad Yousefi Nov 6 '15 at 21:03
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Galvanic series is entirely dependent on being immersed in water, mostly sea water. It has no bearing on much of anything else.

IF you were to take into account anything what-so-ever then I would take into account corrosion. It is true that some metals don't play well together. That really isn't the case here because these metals are all layered so that you don't have to worry about that. Resistivity is of no consequence here since the resistance added by either HASL or ENIG is extremely small either way. To be honest, your solder would add more resistance than either of these processes would. mKeith is correct and the only reason you pick one over the other is a cost/benefit analysis where you take into account that ENIG will keep a board's contacts free of detrimental oxides longer than HASL would. This improves solderability.

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