Corrosion on unused PCB - still okay?

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MattiasC

Well-known member
Joined
Feb 14, 2006
Messages
53
Location
Austin, TX
I have an older PCB that I'm just getting around to populating now, and I've noticed very light corrosion across all of the contacts of the board.  I can still see silver, it's not heavy rust, and the traces all look fine.  Is it okay to still use or will I encounter problems down the line?

Thanks.
 
I thought once you have rust on metals, you have to remove it or else it will grow? Maybe the same rule applies for PCBs?
 
You mention silver.  Is it silver color (could be tin or silver), or is it actually silver plated?  Either way, it's not rust.  If it's actual silver, then it's silver sulfide (AKA tarnish).  You could use a silver cleaner, or just some 000 steel wool to polish off the corrosion.  If it's tin, then it's probably tin oxide.  Use the steel wool. 

You don't want to use it as-is since you are asking for cold solder joints.  Silver oxide is conductive, but silver sulfide is not.  Both oxides and sulfides are harder to wet with the solder than the clean metal underneath. Give it a cleaning regardless.
 
i've had this before with some la4 pcb's and gssl pcb's. They were left in one of my pcb boxes (read: shoe box) for a couple of months and started to oxidixe on the pads. I could easily sand it of with some steel wool and they solder perfectly, the steel wool doesn't affect the green solder mask. Funnily enough my home etched pcb's don't have these problems, and some of them are a few years old.

greetings,

Thomas
 
It's the "chemical silver" finish that reacts with sulfides in the air.

Best to keep these PCB's in an airtight bag.

A soft eraser removes the brown/black surface corrosion just fine..

Jakob E.
 

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