Cleaning a crusty, failing old PCB

[Tony_G]

Hey all,

I picked up a 9122D that has been sitting in a barn for some time (I'm working on getting a full 9122D going so I'm collecting units looking for working drives).

Anyway, this unit is in bad shape but surprisingly it works fine. I'd really like to keep it around but the PCB (and components) are in such bad shape that I have no idea of how to even start cleaning, repairing and sealing it all back up.

I did a short (2 min) video showing the condition here:

https://youtu.be/SQ3A_-j2ars

Any suggestions on how to address would be appreciated.

Look forward to hearing from you,

TonyG

[Shock]

Remove the source of the contamination i.e. piss, leaking, rusting component, metal. Remove components that don't play well with cleaning or that you need to get under such as electrolytic caps.

If the corrosion is sensitive to abrasion or ultrasonic cleaning then clean the PCB carefully with a electronics safe detergent diluted in demineralised and steam distilled water. Then do a clean rinse and then pure IPA. If you think there is a chance of further contamination you can also try neutralizing it before or during cleaning.

Where corrosion has eaten into the tin surface of the track your only choice really is to carefully take it back to copper and apply solder or another tinning method. Then apply conformal coating over the top.

For wrecked traces you can buy a repair kit or make your own. It depends on how much time you have and the level of the restoration.  For half munched on traces you can add solder to restore some of the current carrying ability. Obviously if contamination is under the traces then you are only prolonging the inevitable but adding some "meat" to them and protecting them from further exposure with conformal coat can be quite effective.

[Tony_G]

Thanks - Any suggestions on what to use to clean off the corrosion on the component leads? It looks a lot like what you'd get from a failed battery but there isn't one in the unit.

Thanks again,

TonyG

[helius]

Some capacitors can leak corrosive liquids (boric acid from aluminum electrolytics, sulfuric acid from wet tantalums). Chlorine or ozone in the air—if the equipment was kept near the ocean, salt ingress is also a possibility. In some cases old paper or rubber materials can also decay with corrosive end-products. There are also cases where electronics are attacked by mold.

[Shock]

At 1:47 it looks a lot like DNA. Something could have crawled inside and died.

Component leads are the same just clean them and prevent them from rusting further, if possible tin them and you can use clear conformal coating to protect them. The only other alternative is to replace them.

It could be the reaction of that metal plate being eaten away as well worsening things. If possible remove it clean it and coat it (aside from parts that need to be conductive) to prevent it reacting with the rest of the pcb.

[PKTKS]

I've seen  worst than that....

Although they look bad it may be cleaned.

The "problem" is that **IF** it is working (as it should)
and **IF** it will work after  all procedure done..

As suggested there are several methods each target a specific
type of cleaning.

Components are the easiest part - ULTRA SONIC BATH (w/proper solution)
After that the vast majority of rust and deteriorated rusty crap will be removed

Worst part are the PCB traces and solder mask rebuild
I would try brushing (softly) w/IPA the corroded traces as far as the bad parts gone
If they require service - probably just wire jumpers would do.

After that reapply the solder mask on all parts cleaned (UV curable) to prevent
corrosion and protect the already good ones

Components really crappy rusted should be replaced...
Components cleaned but exposed I WOULD *NOT* USE TIN -  instead
solder mask *OR*   SILICONE GLUE over the exposed parts.

I rather prefer solder mask nowadays.. very clean results

ULTRA SONIC BATH SOLUTION and mild soft IPA brush are top list options
Paul

[PKTKS]

more 2 cents i think worthy mention...

**IF** you need to replace components or any part with rusty
solder - and probably all the solder joint are  crap by now...

Regular flux ( RMA or even RA ) will not  do the job.. really
I have wasted a large amount of hours with crappy joints that
just won't be any good....

SOLUTION?  you need a rather powerful METAL FLUX (not regular TIN/LEAD  flux)
That kind of flux in general contains AMMONIA of some sort to activate
the de-oxidation process ..

A really crappy smelly and nasty stuff ... but it works.
Oxidation is removed and joints are cleaned like magic

Drawbacks:
- is conductive
- requires extensive cleaning
- it does left residues
- it is toxic and proper FUMME extraction required.

Why use that?  IT WORKS.

in 1 second the bad joint is not only good again but all oxide vanish
with the vapors... What would take hour of frustration will be ok in 1 second

Try the available metallic joint flux available in your store
kinda of a smelly orange paste for metallic solders.

Paul

[Ian.M]

The trouble with that is many ammonia compounds attack copper and can cause long-term corrosion, as do chlorides, so if you do use an ammonium chloride based (or other high activity) flux, you *MUST* clean the board thoroughly afterwards - initial defluxing with flux remover (solvent) to remove water resistant residue, then repeated washing with hot water and detergent, or heated ultrasonic cleaning, followed by rinsing with distilled or deionised water, and finally a thorough clean with IPA.   If you don't, you are likely to have trouble with the tracks to the pad you reworked corroding through months or years later.  However the same four stage cleaning process would be good for cleaning up the general contamination on the board, and for removing loose soldermask, so if you have the facilities to do so, it may be worth considering.

If you hope to get away with less thorough board cleaning, its a lot simpler to just scrape the solder surface of the joint you are reworking with a scalpel, or for large areas, abrade with a fibreglass pencil, to expose clean metal, then add some fresh rosin cure solder, with extra RMA flux, which will remelt the joint and break up the surface corrosion where you haven't scraped, so you can wick or solder-suck the joint normally without leaving significantly corrosive flux residue.


On the subject of water for board washing - as long as it doesn't dry, any potable water that doesn't contain excessive free chlorine or chlorides is fine.  Its only if your local water supply smells strongly off chlorine, tastes like bleach or tastes salty, that its not suitable.  However the final water rinse *must* be distilled/deionised to avoid leaving ionic contaminants on the board as it dries, and should be by spray (e.g using a sprayer bottle) rather than bath or tank if you are cleaning multiple boards as contaminant buildup in the rinse bath would defeat the purpose of using pure water.

[PKTKS]

TRUE.  You must clean that crap ASAP the best you can

I use a mild brush w/IPA at first (gross removal) and ULTRASONIC IPA ASAP.

The trick is to apply minimal flux and remove asap.

What would take several hours can be done in several minutes.

If you do need to mess the rusty solder joints the more you
need to mess the more useful that crap will be.

But it does require an extra effort to be cleaned

[Ian.M]

High % IPA and most other organic solvents aren't much good at removing ionic contaminants like ammonium salts and chlorides.   That's why I recommended a hot aqueous wash step.

Maybe you are using 70% IPA?  If not, I'm surprised you haven't run into trouble with on-going corrosion, though if your IPA bottle has been open long enough it *may* have adsorbed enough atmospheric moisture to be effective on ionic contaminants.

[PKTKS]

I got all this stuff locally from http://implastec.com.br/

They advertise their IPA as 99.99% (ouch)

They also have flux in paste for that purpose

Generally that flux is highly soluble in IPA and a good brush
followed by the bath in pure IPA will remove that crap enough
to rest worth using it.

And most of that flux vaporizes in a really nasty cloud of oxides quite fast
the left residue in small amounts is not so hard to wipe out

Not problems whatsoever so far..  but we are dealing
with  ALREADY HIGH CORRODED STUFF..  1 bit more 1 bit less

I really don't care that much -
the job is done in seconds instead of hour

I used to bother - at first...  not anymore

PS. i have also tested and can say that paste works as good as well
http://www.soldabest.com.br/produtos_pasta_soldar.htm

Paul

[james_s]

I've had good luck using a brass bristled brush to clean that sort of thing, I got the ones I'm using at the Dollar store, they look a bit like toothbrushes.

[Tony_G]

Thanks everyone for the feedback. Here is the cleaned board:

https://youtu.be/SDUeFI4K1fE

Not sure what, if anything, I should do about the track corrosion,

TonyG

[helius]

Is that a Dolch PAC on the left? Nice machines.
The acrylic overcoat pen should provide a lot of protection from corrosion, even though it does not seem to include active corrosion inhibitors. One thing you can do is to scour the exposed metal with sodium bicarbonate (baking soda) paste, it will neutralize any acid residues present and polish the metal somewhat. Then rinse with distilled water and dry before overcoating.

[james_s]

That looks pretty good. I wouldn't worry too much about it, I've cleaned up boards years ago and just left bare copper that has been fine, but it can't hurt to brush on some kind of varnish.

[coromonadalix]

Even nails clear coat  will provide enough protection for pcb's

[Smith]

I would start by removing all the loose debris, an use some glass fiber or brass brush to cleanup in places where the corrosion went under the coating. Then a rinse with IPA, while cleaning it with a brush. An ultrasonic bath would help a  lot here.

This is the part where I remove most of the oxidized solder, and replace it with new fresh solder, just to make sure it didn't creep in anywhere. Simple component can simply be replaced, from the expensive/more difficult to replace components I look at the oxidation per component. If any severe oxidization looks to be creeping from the pin into the case (especially plastic DIP / diode packages, seen this before) I would replace them too.

Traces can be "repaired"by cleaning them with a glass fiber or brass brush. If there is any damage, or they  become very thin, some fresh solder can do wonders. I use some copper wire or just loose strands to repair very severer traces or high current traces. A nice layer of conformal coating should prevent future oxidation, of help regain some isolation.

I've done this on multiple boards with some places that went bad (much, much worse than this), but never on a whole board.

[coromonadalix]

i've done it on an friend vcr board,  an 6x8 pcb in an expensive HI-FI vcr who was cracked in half,  still dont know how it happened loll

Took me one week to do so,  working with fine strand helped a lot, the only problem left was an hybrid ceramic chip who had an small malfuction in the Dolby audio.

An fiber glass tooth brush works very well,  not sure i would use an brass one ??  even an pink / blue eraser can do an fine job.

[Tony_G]

Is that a Dolch PAC on the left? Nice machines.

Yes it is - I got it because it has an ISA slot in it and I could put my Viper card (HP card that is a stripped down series 300 machine I think) to use original HP code without converting it to HP Basic for Windows. Did a video on upgrading it with more memory and a compact flash drive.

I just picked up a Finistar machine that was built by Dolch as it had a PIII in it but unfortunately the board doesn't have an ISA slot so I'm not yet sure what I'll do with it.

TonyG

[Tony_G]

Thanks again for the suggestions everyone - I'll grab a glass fiber brush and see what that does.

TonyG

[martinr33]

I use tin plating solution for all kinds of corrosion cleanup. mostly battery contacts but I've been using it on old multilmeters as well (the leaky batteries mess up the range switch).

It works really well at removing  most forms of corrosion, and leaving a decent tin coating behind. It is just dip plating, so you can use a brush or q-tip.

(I don't know if anybody else has noticed this - but a certain major brand of batteries, formerly prized for its leakproof integrity, is now just about certain to leak into anything. I find this method the best way of dealing with the mess left behind)


I also use silver dip, of the kind intended to replate small spots on silver plated products. It isn't a strong as the tin plate solution.

[Bashstreet]

Like many have said i would just brush off the loose stuff and use the pen/lakka you ordered to give a bit of protection to the exposed traces.
I do not think using anything that can take material off (like brass brush etc) is warranted although it will make things look pretty.
Most cases in restoration the most important thing is to know when leave things be rather than overtry and damage something.

And yes i overdone... many many times. 

Any left over tarnish and small bit of corrosion will be fine under the coating long as you given the board good clean with IPA and brush.

[coromonadalix]

You have liquid tin plating,  but be careful for the vapors, smell awfull,  we did a test this week at my job ... works very well if you follow instructions.

https://www.mgchemicals.com/products/prototyping-and-circuit-repair/prototyping/liquid-tin-421

[Tony_G]

Did you apply that to a fully populated board? I tried using the MG Chemical repair pens and they're not going to work for this so I was thinking of just masking up the connectors and spraying with acrylic lacquer conformal coating.

TonyG

[martinr33]

I rub the MG tin plating solution on with a cotton bud. It works fast, and will take you from corroded and nasty to clean tin. You do need to clean it well afterwards, as the residue from the solution has no good business near electricity.