Gold doesn't tarnish. Where is this dirt coming from?

[NexusX]

So I unpacked the majority of my Neo collection recently. My seldom played games. All in some sort of case or box. Clean equipment is a bit of my OCD behavior I have. So I KNOW before they were packed in boxes within boxes within within a climate controlled storage space... That the contacts were damn near polished and cleaned to perfection. So when took them out and played them on a clean Neo board I had the signs of dirty contact pads. So after taking it out and cleaned it with Q-tips and my cleaner of choice I noticed that it was still picking up what looks like black tarnishing. Contacts of course look clean to the naked eye though before cleaning.

My questions are. Where is this coming from? What material is tarnishing? Is it the underlayer Metal under the gold? I would be more understanding if I didn't have them in a few different layers of dust protection either. I'm really more curious and interested in why this is happening and understanding the cause of it rather than having to deal with it. That's not a big deal at all. But it's just like an unanswered question in my brain.

 

[skate323k137]

When it comes to fabrication of the circuit boards themselves, two of the main PCB finishes are HASL which is basically a solder bath, or ENIG

ENIG

(Electroless Nickel Immersion Gold) is a surface plating that is applied over the copper pads on a Printed Circuit Board

Either way it's a plating over copper, so if something abrasive had been used to clean them or they just get worn over time, it would be expected to see some sort of oxidation etc over time.

This is off the top of my head, but I seem to recall being told if you get PCB's made with an ENIG finish you're supposed to solder them right away before they're exposed to the elements for many days. IDK why this is coming to mind but just a thought.

 

[Neodogg]

Sell them, they are no good meow…

 

[maki]

This is off the top of my head, but I seem to recall being told if you get PCB's made with an ENIG finish you're supposed to solder them right away before they're exposed to the elements for many days. IDK why this is coming to mind but just a thought.

You're mixing ENIG up with copper, which would get stained after while.

Please never ever tin the gold plated module contacts, it would do damage over time to the actual slot, whose contacts are also hard gold plated.

Clean equipment is a bit of my OCD behavior I have.

I hope you're talking about a leather cloth?

No need to use anything abrasive there, just smooth out the surface. Most abrasive thing I use is a brass brush (brass, not steel!), then polish it.

Using chemicals etc. can leave a residue that keeps "working" it if not removed 100%.

Lots of old PCB have a layer of rosin flux over them, that will get dissolved by IPA for example, and can then move around, maybe thats what covered your contacts, or its leftovers from whatever you used to polish (if you used anything).

 

[skate323k137]

You're mixing ENIG up with copper, which would get stained after while.

Please never ever tin the gold plated module contacts, it would do damage over time to the actual slot, whose contacts are also hard gold plated.


I hope you're talking about a leather cloth?

No need to use anything abrasive there, just smooth out the surface. Most abrasive thing I use is a brass brush (brass, not steel!), then polish it.

Using chemicals etc. can leave a residue that keeps "working" it if not removed 100%.

Lots of old PCB have a layer of rosin flux over them, that will get dissolved by IPA for example, and can then move around, maybe thats what covered your contacts, or its leftovers from whatever you used to polish (if you used anything).

No, I don't have them confused, my point was either way it is copper underneath the finish. And I would not tin a ENIG contact / edge connector ever.

Edit: My reference to soldering ENIG boards ASAP was to installing/soldering any components onto the newly fabricated PCB as soon after fabrication as possible, in case that was confusing.

 

[NexusX]

You're mixing ENIG up with copper, which would get stained after while.

Please never ever tin the gold plated module contacts, it would do damage over time to the actual slot, whose contacts are also hard gold plated.


I hope you're talking about a leather cloth?

No need to use anything abrasive there, just smooth out the surface. Most abrasive thing I use is a brass brush (brass, not steel!), then polish it.

Using chemicals etc. can leave a residue that keeps "working" it if not removed 100%.

Lots of old PCB have a layer of rosin flux over them, that will get dissolved by IPA for example, and can then move around, maybe thats what covered your contacts, or its leftovers from whatever you used to polish (if you used anything).

Q-tips and a fresh felt tip. No no hard abrasives or anything like that or any other harsh chemicals. Occasionally I'll take some distilled water (neutral pH) to dampen a q-tip though to act as a dust magnet. Thank you for the information by the way.

 

[maki]

Q-tips and a fresh felt tip. No no hard abrasives or anything like that or any other harsh chemicals.

Sounds good!

Occasionally I'll take some distilled water (neutral pH) to dampen a q-tip though to act as a dust magnet.

Distilled water isn't really pH neutral, its acidic, not stable though.
I'd recommend 99% IPA over water tbh, it will take care of grease and not interact with the metals