Shponglefan wrote on 2024-11-26, 22:48:
There is one that is still broken, but it only leads to an unpopulated pad so I'll probably leave it as is.
There's another board I've got one on like that. Heads off to a KBC footprint that isn't populated because it's in the chipset, wondering if I leave it completely alone whether corrosion will keep creeping until it finds something that is more vital. On the other hand to dig it out uglifies a few inches of board, and erases route of traces that have a tiny chance of being needed if there's a keyboard fault that fries the internal KBC.
I went on a little side quest, wondering why the corrosion doesn't just stop when everything is chemically exhausted.... that's because it's a three way thing... I don't have the exact reaction equations, but you get the potassium hydroxide leaking from the battery, then this reacts with the copper and oxidises it, and is all used up, right? ... um no, while the copper grabs the oxygen, the potassium grabs carbon dioxide from the air and becomes potassium carbonate salt, crusty white stuff. And does it just sit there? No, as soon as there's enough humidity in the air, it grabs water out of it and regenerates itself as potassium hydroxide again, oxidises the nearest copper and cycle repeats... This is apparently why it seems to creep, it's just the hydroxide and carbonate doing a shuffle step down the "fresh copper" interface, with rapidity determined by cycles of humidity. Cheaply made nicads may possibly have trace amounts of hydroxide on when new which can get this going without a leak.
Remedy seems to be neutralisation and copious amounts of water washing to dilute it down to nothing.
In theory then, if it's gone under mask or between layers, it's the interface between good and bad you most need to attack, as that should be where the carbonate/hydroxide seesaw is teeter-tottering away.
Edit: For stuff you can't get to fixing soon enough, it seems then that just closing it up in a bag doesn't even work as the carbon dioxide and whatever water vapor was enclosed will keep cycling, it seems that you want to put a desiccant in the sealed bag with it, that grabs hold of all the water and stops the cycle that way. I do not know if rice holds onto water strongly enough to be effective, but it's the cheapest to get hold of. Also desiccant packs that have been around a while are probably loaded up. What you may have to do with either thing is stick it in a low oven for an hour to drive out whatever it has grabbed from just being around and use freshly "regenerated" desiccant and/or rice to pack up your boards waiting on repair with.
Unicorn herding operations are proceeding, but all the totes of hens teeth and barrels of rocking horse poop give them plenty of hiding spots.
