Repairing corrosion damage to PCBs

Wouldn't it be a multi-layer board with liquid conducted into the board by capillary action ?

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

Thus spake n cook:

So, the board's toast? No reason to attempt repair?

Opinions welcome.

On Sat, 22 Apr 2006 11:41:19 -0700, DaveC Gave us:

You may have to bake it at 60 C for an hour or so since there are things on the board that were not on it when it was soldered and water washed. A good vacuum cycle is good for evaporating those last little bits of remaining water as well.

On Sat, 22 Apr 2006 11:41:19 -0700, DaveC Gave us:

Use a fine child's tooth brush on it while you are doing the water wash.

BTW, if there are any transformers on the board, all bet are off. You would HAVE TO bake it or vacuum it out (the water).

On Sat, 22 Apr 2006 20:12:42 +0100, "n cook" Gave us:

The material PCBs are made from, regardless of the layer count, are hygroscopic and will absorb water.

If he cleans it with water, he will need to bake it out at the very least.

Toast. Not because of the above but because it stopped working whilst powered up with the contamination in place. The odds are that irreversible damage has been done.

No...... clean it and use a conductive ink pen .. i have fixed many laptop keyboards and mainboards using one of these .. you basically draw a new line on top of the old one with the pen which is silver conductive ink ... last i checked MCM electronics carries them .. i still have one from years ago and it is still half full ... hope this helps you out

cheers ..

I left my 10 year old VCR an afternoon in the rain after it failed to playback, considering it as garbage.I discovered after that some kid had tampered with the switches and set them to NTSC playback.I plugged it still wet, no on leds.After drying it out with a fan heater, it worked as new.Probably has 10 more years of life left.(Real story).

-- Tzortzakakis Dimitrios major in electrical engineering,freelance electrician

Another factor to contend with on multilayer PCB's are the VIA's (some call them feed-throughs) that rout traces through the board. If the metal has been etched out of the VIA by corrosive action, then you have to take a very small drill bit and clean out the thru-hole in the board an pass a small wire through and solder it to the traces, meaning a lot of work if many of them are bad. Also if the PCB is more than 2 layers it may be impossible to repair.

Also if you have heavy soil on a board or it is contaminated with Glycol (CRT Coolant for PJTV's) you can wash it with an ammonia based cleaner then rinse with distilled water. Windex works wonders :-)

Jammy

There is a difference between something that won't power up after getting contaminated, say because the psu shuts down, and something which powers up, works and then dies.

In the former case, almost all of the electronics has had no voltage applied at all. And power supply circuitry tends to be simpler, works with higher amplitude signals and lower impedances and with bigger track spacing than what is being powered.

In the latter, I believe that dendritic growth can occur very quickly between tracks with a voltage difference - once a ion-bearing liquid bridges the gap between them. The unit will continue to function "normally" whilst this growth is going on - until the gap is bridged and a much higher current flows. It is this current which does the destruction - hence the unit will work for some time before failing catastrophically.

The problem with attempting to clean a board is that contamination may exist in the gap under components,between components and board - which may also contain many tracks. If contamination has already started to crystalise out, it may not be readily soluble. Even an ultrasonic cleaning bath may not remove these. If high voltage components or sections of board have been contaminated, the currents that can flow when growth has allowed tracking to take place can be "exciting".

On Sun, 23 Apr 2006 23:31:28 +0100, Palindr?me Gave us:

Or simply failing to continue working, but not catastrophically.

I have repaired more than a few calculators that had soda or coffee spilled on them, and they only required removal of the foreign media and drying.

On Sat, 22 Apr 2006 11:41:19 -0700, DaveC wrote as underneath my scribble :

Some actual experience: I did a resurrect of a Sony MZ-R30 Minidisk Recorder/Player which had been dropped in seawater and this had stopped working immediately! This unit had been unwashed and returned around the world so had had about a month or more to corrode, seawater is unforgiving so I wasnt hopeful. I removed the 1/32" FG PTH 4 layer boards completely, then washed them in hot water, then blow dried with compressed air, you have to be sensible with this as physical damage is possible with compressed air, scanned them up to X10 for inspection then warmed boards (hot to touch) then coated with WD40 for about 30 minutes, compressed air again to remove most of the WD40 then baked in a warm oven for about 4 hours to flash off the remaining oil, repired some obviously corroded SM joints by flux/solder and iron reflow (under magnification!) and then reassembled. The point of the WD40 soak was to arrest any ongoing corrosive action, it is thin enough to wick anywhere the original liquid has gone. Worked like a champ ever since, about 3 years now. Your board has failed under power perhaps well after the event though and this points towards electrolytic corrosion and this may not be recoverable whatever you do, in a multilayered board. Whatever you do I would advise you against soaking a board in anything for a few days, imo that would be asking for trouble! Charlie+

Thus spake Charlie+:

I fully appreciate your creative technique of halting the corrosion. This is a concern for me, and until your post, I wasn't sure how to address that (other than using flux + solder on accessible lead corrosion), especially that hidden beneath components.

WD-40 -- while it may be effective in this application -- stinks! This is a laptop I'll be using (if I'm successful), which pretty much places my nose right above the logic board. Can't imagine smelling that awful smell for years.

Can someone offer an alternative for WD-40 to arrest corrosion on PC traces and component leads?

Thanks,

Your not going to smell it if its baked like he said until all oil is evaporated.

By the way, I usually coat the board or anything I have sprayed with water with WD-40.

Want something more aromatic, try some Bullfrog electronic contact cleaner. I think it smells pretty!

if not, get some stuff at The Home Depot, CRC 2-26 Lubricant, almost no smell, its plastic safe, multi purpose, presision lubricant, improves electrical properties, as read on can. Really cheap too, but slightl more than WD-40. They also have a no residue electronic contact cleaner which is also cheap for a large supersized can.

greg

why not soak the board for 20 minutes in DR99 solutiom at a ratio of

Thus spake GregS:

Thanks, Greg. I think WD-40 is great for most such applications (WD, I'm told, stands for "water displacer"), but if there's any chance I'll be sniffing that smell for years, I'll try the CRC route.

General Q: these products are water displacers. The reason these products stop corrosion is that they remove all traces of moisture? After that, if the green stuff (corrosion) is not causing a short, the corrosion should not continue, as long as moisture is not reintroduced?

Thanks,

Thus spake DaveC:

Should say: Then the water displacer product is evaporated (baked with high temperature). After that, if the green stuff (corrosion) is not causing a current path, the corrosion should not continue as long as moisture is not reintroduced?

(It seems weird to post a "reply" to your own post...)

On 24 Apr 2006 13:29:33 -0700, "bobs" wrote as underneath my scribble :

LOL! Charlie+

On Mon, 24 Apr 2006 09:35:30 -0700, DaveC wrote as underneath my scribble :

Sorry nearly missed this reply as you started a new thread! WD40 as well as being hygroscopic has corrosion inhibitors built in to a self wetting very thin liquid - that is the whole point. Also the point of putting the WD40 onto a preheated board is to help suck into any cavity as it cools. There is zero niff after baking off the volotiles leaving a very thin layer of inhibitors and wax behind, the compressed air has already removed practically all the visible WD40 anyway. That was my thinking in doing it this way! The visible corrosion is not the problem, as visible areas will have dried out quickly after the spill, coffee is I guess not particularly corrosive to metals but may make insulators conductive/resistive under certain conditions and this is probably the reason for failure. Post a followup how it goes with the laptop - you will probably have quite a job getting it down to just the boards in any case! Charlie+