How to clean up and safely remove corrosion from a circuit board

[Elfen]

Thanks to a generous heart here at the forum, I'm getting a IIsi board to replace the one with the death chimes. If he wants to let himself know, that's up to him but I greatly appreciate it a lot.

But back to this board, before the recap it was dead, does not turn on, nothing. It's "twin" I successfully recapped and it works. But this one was brought back to a Zombie Life- it turns on and then Death Chimes. Considering neither board was dead, it is great to see some life in them.

As I wait for the donated board to arrive, I decided to put on my high powered magnification glasses - a moderate but powerful 5x. Damn thing gives me headaches when looking out into the distance! But looking at the board, I found corrosion on the RAM side of the board. RAM Chips, in UI7 - U7 and logic chips to RAM UH5 - UE5 have a white/grey rust on the solder and traces and UI6 has a dark grey 'rust' on the solder on the side closest to the PSU Jack. Only UI6 and UH5 are close to any leaked/replaced cap. In fact UE5 has a green corrosion on the top 2 right pins.

I washed the board so the rest of it is squeaky clean. It is just this area about the RAM that has corrosion. There is some corrosion around the Sony Sound chips but when I placed the 3 Caps there, their connections are OK (the IIsi is loud when it bongs and death chimes!).

How to remove this corrosion without damaging the board? Note, I washed both board with 3 parts distilled water/1 part ammonia, scrubbed with acetone and then rinsed with 70% isopropyl alcohol. This cleaned the board nicely, eliminating the cap goo. But finding "rust" on some components means that the bath did not clean it.

 

[archer174]

Use a liquid flux and reflow the solder. If the solder appears chunky then wick it away and apply fresh.

 

[raoulduke]

Scrubbing Bubbles.  Let it sit on the board for a while.  That's how I cleaned a pretty bad 3400c board - the corrosion eventually dissolves into the solution (I'm not sure if that's actually the mechanism, but if you leave the SB on the board for a half hour to an hour a few times it will basically float off.  Unity I think told me about it so he may have further observations on how to use it without risk.  When cleaning wires and plastic (stuff that can't really be 'damaged' like a board, I let it bathe for hours and even horrifying corrosion has totally come off with no harm to either plastic or metal.  It's pretty cool stuff.).

To wit, I reused my Kanga and 3400c power extender cables (like to the PRAM battery - technically they're part of the power boards in terms of the part numbers) despite the fact that they were totally corroded over when I started.  Left them in scrubbing bubbles in a cup and forgot about them.  The solution in the cup had a tinge of green and the metal prongs/leads and plastic connectors look like they're new.

 

[Elfen]

RaoulDuke:

I think I need to check this out. It is an interesting discovery. They might be using a very diluted chemical clamp to remove the corrosion. The product CLR could do the same thing but is probably too strong to pour onto a board.

BTW - on both boards, when I dunked, sloshed and soaked the boards in the water/ammonia, the liquid turned green when it removed the cap goo.

Archer174:

Though I do not have a hot air station, it would work otherwise. My iron tip is too big to fit in such tiny places between the RAM Chips.