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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)?

  • Is your PCB running immersed in saltwater? – PlasmaHH Nov 06 '15 at 08:53
  • 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) – Arsenal Nov 06 '15 at 08:55
  • 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. – Mohammad Yousefi Nov 06 '15 at 19:28
  • 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. – user57037 Nov 06 '15 at 20:23
  • 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 – Mohammad Yousefi Nov 06 '15 at 21:03
  • When boards are fabricated, sometimes they are stored for a long time before components are soldered to the board. Boards finished with the ENIG process (electroless nickel, immersion gold) can be stored for a long time. Bare copper cannot be used for mass production. The solder process is not reliable on bare copper, especially if it is stored for any length of time. Other treatments are solder plating and "Organic Surface Protectant" (OSP). – user57037 Nov 07 '15 at 16:42
  • Thanks mkeith what about tin(HASL / Lead Free HASL), it has closer material to copper in galvanic chart. except the resistivity it has better galvanic action in compare to Gold and also we solder the component with tin and lead so they are close together ( gold and tin\lead are far from each other) – Mohammad Yousefi Nov 08 '15 at 07:44
  • I don't know much about HASL. Wikipedia says it is problematic for fine pitch components. Most of the boards I design are ENIG (and have fine pitch components). HASL might be a good choice for some boards. But I still say you are inventing problems. ENIG boards are very resistant to corrosion and work well. I am not sure if HASL has as long a shelf-life as ENIG. ENIG boards can be stored for a long time prior to assembly. – user57037 Nov 12 '15 at 07:59
  • I said before ENIG boards have perfect flat surface and because of that they are good for fine pitch components. – Mohammad Yousefi Nov 12 '15 at 17:50

1 Answers1

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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.

Dave
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