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Registered Member #96
Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4062
Hi all. Just acquired a PCB from an industrial camera with serious water/corrosion damage.
So far the best thing I can find to de-corrode it is Oust (tm) with a dash of hydrogen peroxide 30 vols. It certainly stripped off the corrosion nicely, allowing me to see which through holes were borked. Has anyone got any better suggestions?
So far looks like about 5 damaged, at least now I can see which ones they are.
The chip inter-pin corrosion is history, that got eaten in the first 2 seconds of immersion.
btw tried my vinegar+peroxide trick, didn't help. Maybe its brand specific, it did some good but I think the sulphates might be the culprit here.
Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3141
In my opinion this is the WORST kind of damage to reliably repair, unless repair is vital, get new pcbs and copy or move over any programmed devices. Even if you find all corroded vias etc, you can't guarantee any level of reliability. If only double-sided you can poke a very fine tinned copper wire through the holes and re-insert components, if desperate. repair is very time consuming.
At work we use 'Fluxclene' solvent and 'Safewash' detergent, blow-dry and a drying cupboard. Not endorsing or comparing, just what wer'e provided with and it works.
Registered Member #3271
Joined: Mon Oct 04 2010, 02:29AM
Location: Canada
Posts: 159
Had some successful repairs in the past but it depends on the type of board you have.
A) Two layer pcb: pass a pre-tinned thin wire (wire wrap gauge for example) in the vias.
B) Three or four layer pcb, if they are the kind with a ground plane in the middle or the Vcc in the middle or both.
You need a good stereo binocular microscope (real 3D images such as a dissection microscope) with a small tilt platform. In those cases looking into the via hole will show if it is a simple through connection only to top-bottom.
At high binocular magnification you can "travel" the focused image by depth and locate the intermediate layers.
If it has ONE connection either to the Vcc or ground plane by the depth of the dimple ( also a typical about 1mm easement on the trace middle for the unconnected planes that will be visible through illumination.
Or in the case of a connection to one of the middle plane a bit of corroded metal in an opposed cross pattern at the right height in the hole. The focus depth will tell you which. Tricky but it works.
Do NOT put a bare wire through the via lest you might short or contact an unwanted intermediate layer if there is much damage to the via hole or the pcb is delaminated in that area. Locate a nearby component or trace that is obviously connected to it and route a thin wire to that point from the top. Much safer. you can access the other side using a wire wrap through the via (leave wire insulator on the wire, obviously)
Also some idea on how the circuit works and its layout will give you clues as to where it connects. For example multiple ground plane shorting vias are obvious for RF stuff. In the case of my FE rubidium atomic clock I ended up taking about 12 x-rays and located a few vias hidden under the chips that overlapped top and bottom!
C) Three or four layer pcb: you must be able to trans-illuminate or have a good x-ray machine to work it out I think. Looks easy to trasilluminate to pcb but I always find areas with thich and wide ground traces or, as mentioned above, with hidden vias under overlapping chips.
If it sound like a lot of work: it is. Sorry. depends a lot on the cost and availability of your component.
Never tried (ie: never had to) on a five and + layer pcb. Dont look forward to it either.....
Registered Member #96
Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4062
Hi, board mostly works now, at least the distance OSD chip is now doing something. Keyboard still not working but suspect problems on board 2, will update when I get it back.
EDIT: Power supply blew up, had to add external brick but it still works.
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Corroded through holes
