Right off the bat, we’ll stipulate that what [Adrian] is doing in the video below isn’t actual hot air solder leveling. But we thought the results of his card-edge connector restoration on a CGA video card from the early 80s was pretty slick, and worth keeping in mind for other applications.
The back story is that [Adrian], of “Digital Basement” YouTube fame, came across an original IBM video card from the early days of the IBM-PC. The card was unceremoniously dumped, probably due to the badly corroded pins on the card-edge bus connector. The damage appeared to be related to a leaking battery — the corrosion had that sickly look that seems to only come from the guts of batteries — leading him to try cleaning the formerly gold-plated pins. He chose naval jelly rust remover for the job; for those unfamiliar with this product, it’s mostly phosphoric acid mixed with thickeners and is used as a rust remover.
The naval jelly certainly did the trick, but left the gold-plated pins a little worse for the wear. Getting them back to their previous state wasn’t on the table, but protecting them with a thin layer of solder was easy enough. [Adrian] used liquid rosin flux and a generous layer of 60:40 solder, which was followed by removing the excess with desoldering braid. That worked great and got the pins on both sides of the board into good shape.
[Adrian] also mentioned a friend who recommended using toilet paper to wick up excess solder, but sadly he didn’t demonstrate that method. Sounds a little sketchy, but maybe we’ll give it a try. As for making this more HASL-like, maybe heating up the excess solder with an iron and blasting the excess off with some compressed air would be worth a try.
look up what phosphoric acid (main ingredient of naval jelly) does to gold.
> blasting the excess off with some compressed air would be worth a try.
did you seriously just suggest to your readers that they blast molten solder with compressed air
yes pedants i realize that it will probably cool into a solid before it can make it into your eyeballs, but there’s still nothing about that which makes it a good idea.
the comments section is full of people with actually good suggestions for how to re-tin the contacts.
“look up what phosphoric acid (main ingredient of naval jelly) does to gold.”
Cool, you seem to know something, brag about it, but are not willing to tell it. Instead you instruct people to look it up themselves, that doesn’t help, does it? And how will we know if the answers we’ll find are the same as the answer you found, for all we know, you might have missed the point completely and might be referring to some other effect that has nothing to do with the article.
I’m pretty sure that the effect you failed mention could be described in a shorter sentence than that of both our comments together.
So I looked it up myself and this one thing I found:
The anodic dissolution of gold in concentrated phosphoric acid was investigated at 145–200°C. Gold dissolves in a narrow potential region (150 mV) about 300 mV positive to the oxygen potential in the same electrolyte. At higher potentials it passivates. At very high overvoltages dissolution, which increased rapidly with temperature, was also observed in the transpassive region. The product of the dissolution is finely divided gold, probably formed by immediate decomposition of the oxydation product. At 200°C, at which temperature pyrophosphoric acid is formed, the gold dissolution also yields a clear yellow solution of gold pyrophosphate
Regarding the cleaning of PCB pads, use an eraser, you know the ones you use in combination with a pencil. Just a gentle wipe or two should do the trick in most non severe cases. Don’t overdo it, erasers are abrasive. But whatever you do, never use sandpaper, never!
The card on the video, looks better. But how does it look after inserting/removing it a couple of times. there is a very good reason to use gold (of the hard type) for edge connectors.
“look up what phosphoric acid (main ingredient of naval jelly) does to gold.”
Probably SFA, under bench top conditions (room temperature, no electrolysis).
The only thing that dissolves gold under normal conditions is aqua regia.
Actually the smack or whack way isn’t much better. Rags, without synthetic fibers will work even on your iron tip. No plastics! Smoke alarms don’t work because of plastic cushions and coverings. MELT! Die.
Cellulose sponge, as used in soldering iron stands and kitchens, are also really useful for this.
Is it possible to use gold foil to add new gold to the contacts? Has anyone tried it?
I think you’ll need a lot of layers of goldfoil. And pure gold may be not hard enough and scraped away at the first try of inserting the card into a card socket. What you see as golden contacts is mostly copper with a tiny amount of gold in it.
Contacts are plated with a hard gold coating, soft gold like foil will rub off the first insertion into a socket.
Could the average hacker whip up a gold replating solder at home? Is there a mix of metals that along with gold foil have a low enough melting point to be applied but cool hard enough to stand up to repeated insertions?
Gold has a pretty high melting point and getting it in a usable state isn’t very safe. Mercury, cyanide, and aqua regia aren’t very kind. There seems to be a cyanide free version that’s out there, but it’s proprietary.
I saw something similar on a vintage computer restoration video. Can’t remember which one though.
Um, rust on gold-plated connectors? How?
Isn’t gold being used to exactly prevent corrosion from happening? Or was it dirt that changed to rust?
If merely conductivity was a thing, wouldn’t silver have been a better choice here?
silver oxidizes
I know, but it has higher conductivity than gold (there’s silver solder, too).
Gold is better than copper, though. And it doesn’t corrode, or so I thought.
If you know silver oxidizes, why are you still suggesting it?
Copper oxidizing is the reason it’s gold plated, putting a silver layer on the copper would just end in the same issue.
A silver alloy (like solder) may work well long term.
Gold doesn’t corrode but the oxidation can creep bellow from the sides.
“If you know silver oxidizes, why are you still suggesting it?”
Because it’s been in use in special RF applications were excellent conductivity is important. Microwave communications, for example, I guess.
Silver has highest* conductivity, better than gold.
(*among the standard materials, I mean)
Where there is frequent wiping action and/or sufficient current or voltage, silver can be a good plating choice for switch and connector contacts. Where you’re dealing with a ‘dry’ circuit where the contacts aren’t being moved against one another frequently, gold plating or flashing on top of the silver is common. The silver provides good conductivity, and the gold doesn’t corrode, ensuring good connections even in the absence of enough voltage, current, or wiping action.
“Um, rust on gold-plated connectors? How?”
No, rust on copper. Battery juice leakage on the gold, which removed it exposing the copper below. The copper needed the rust and oxidation removed and tinned to protect against future oxidation.
just don’t mate tin plated with gold plated connectors
Explain, please.
How is that different than a tinned DIP leg in a gold IC socket?
Asking for a friend…
Dissimilar metals have a tendency to oxidize when in contact. Tinned contacts are also known to be electrically noisy.
All that said, I doubt it will be a problem in this situation. The ISA bus has fairly large contacts. Not to mention a very slow clock rate.
I also remember some extra cheap ISA expansion cards would often use tinned card edges to save money anyway.
I get really fed up with the ‘retro experts’ who bollox up classic gear like this, they’ve somehow gotten themselves reputations way beyond their abilities, skills and knowledge.
I believe there’s some truth within, but on the other hand it’s “just” an IBM CGA card here.
I repeat, an C-G-A card – the worst graphics card ever made for PC.
If there’s anything good about it, it’s probably composite video output.
Both for 16c artifact colors and for compatibility with bog standard 60 Hz/15KHz TVs and monochrome monitors (green and amber screens used to be popular).
I can tell you didn’t watch any of the video then.
I remember an very old video about military training , they had a kit to restore the gold on those pins, it was about chemicals in small bottles, sadly that is all I remember…