PCB Corrosion Gold- Aluminum 1

[ManuelGG]

Hello,
I have a enquire, We are designing a PCB and we are not sure what is the better finish for it.
In the external sides of the PCB I have to areas in which I am going to fix to aluminum parts. The usual termination for the PCB is Nickel+ external gold plated surface. Like gold and aluminum are dissimilar metals, We are thinking on require this areas without gold (only nickel) What do you think?. I think it would be interesting to considered the following cases:
PCB termination:
- ENIG (Nickel+ gold)
- Nickel (without gold)
Protection:
- Nothing
-Conformal coating
Part in contact with PCB:
-Aluminum without treatment
-Anodized aluminum
-Aluminum with a conversion treatment (Iridite, Alodine)
The screws used to fix the aluminum part to the PCB will be stainless steel screw (is it necessary to isolate the head of the screw from the PCB? Fixation scheme: screw-PCB-aluminum part
The environemt for the PCB´s I am talking about is inside of a electronic rack, that could be in a building ( not outside exposition). This rack is not sealed from the ambient.
Regards

 

[MacGyverS2000]

Considering the two are at opposite ends of the reactivity table, you need a buffer of some form or another. Nickel coating, Iridite, etc. If you hook those two together and there is any moisture in the air, expect some severe corrosion over the years...

Dan - Owner

http://www.Hi-TecDesigns.com

 

[sreid]

Can you Hard Anodize the Aluminum?

 

[IRstuff]

Gold and aluminum are a bad mix; beware of the puule plague

TTFN

FAQ731-376

 

[ScottyUK]

'Purple', at least in the English language.


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If we learn from our mistakes I'm getting a great education!

 

[IRstuff]

arrgh, tried to fix it from "pruple"

TTFN

FAQ731-376

 

[ManuelGG]

Thank your for yours responses . Then if I treat the aluminum part (in conctact with gold)With some of the following treatment, the result will be O.K? Will not have corrosion?
-Hard anodized
-Iridite (is this treatment O.K) I´ll have direct electrical contact. What is the galvanic potential for aluminum with iridite?
- Nickel plated .
Could you mark me the preference order of these three treatments?
Regards