Lowest Resistance Aluminum Finish

[j777]

Hello,

When purchasing aluminum standoffs you can get them with many different finishes. Which finishes have the lowest resistance and offer protection against corrosion?

The following link lists finishes available from a popular electronics hardware manufacturer.

 

[mgb_phys]

If you are that concerned about low resistance I would recommend using a separate ground strap instead or relying on grounding through stand-offs.

 

[j777]

I'm not necessarily "that" concerned I'm just looking for advice on common finishes like iridite, anodized, etc...

 

[mgb_phys]

Not really an expert but anodise is pretty high resistance, but without anodise you are going to form Al oxide which is also insulating.
Since the post only contacts the board at the top and the case at the bottom, you could just sand off the coating at the ends to make a good conducting path. Depending on how well the coating has been applied the screws will probably strip it out of the threads you are using tapped standoffs.

The main concern with no coating (or only a thin one ) would be that if the Al is in contact with copper on the circuit board and any moisture gets in you will have a corrosion cell.

 

[marcusl]

You have a tradeoff because the really hard protective coatings are non-conductive, and the conductive coatings are not so durable. Alodining is a conductive finish that offers some protection. Don't know how long it will hold up in a really corrosive environment.