Ultrasonic Washing Ceramic Power Resistors - Yes or No?

[donlisms]

In earlier days, Tektronix would routinely wash entire oscilloscopes in warm water and detergent.  The procedural details are documented with pictures in official Tek documents.

Yes, really.  :-)

(Sorry I don't have any links; there is at least some discussion at groups.io.)

[timeandfrequency]

Hi donlisms,

In earlier days, Tektronix would routinely wash entire oscilloscopes in warm water and detergent.  The procedural details are documented with pictures in official Tek documents.

Yes, really.  :-)

(Sorry I don't have any links; there is at least some discussion at groups.io.)

You are right.
Setup, required tools, chemicals and procedure is described here.

Nice TE wash station, probably including a lazy-susan to ease the handling of the displayed boat anchor.
Don't know if the two lights at the top are really waterproof...

[vk6zgo]

Those are pretty clean to be honest. These resistors were never made to look pretty. The "dirtiest" ones I would say are older and were never white to start with. These days they get made nice and white so I'd not worry too much about calling them dirty.

Yeah, the old ones looked like cement.
If you wash them by complete immersion, either in a ultrasonic cleaner or more traditional ways, it is a good idea to cook them in a normal domestic oven, which will dry them out.

Many years ago, we washed a unglazed porcelain insulator from a TV transmitter, then soaked it in alcohol to hasten its drying.
Unfortunately, even though it looked dry, when we turned the Tx on, it went "bang" & shut down, so in the end, we had to cook the insulator in the lunchroom oven.

We learned just how porous unglazed porcelain was, but I doubt that the ceramic coating on resistors would retain as much fluid.

[vk6zgo]

They are all low values, so no worry about leakage.
I am quite happy to leave them in the oven for hours to dry out afterwards.
They are not immediately going into use, I bought them for stock, so what with the oven baking and then leaving them naturally to further dry out over most likely several months before I have a need to use one, would that not be OK?

The oven baking should be quite sufficient.

[EPAIII]

If it it corrosion on the leads that you are worried about, you are probably going to need some form or abrasive. I always keep small pieces of extra fine (200, 320, 400 grit) sandpaper at my electronic benches. With the sandpaper folded in half it only takes a few seconds to have old leads cleaned down to bare metal. Then flux and tinning and you are set to go.

And there is no sense in doing this before you are ready to use them. If you are like me, you probably will never use 75% of your collection of e. parts.

[Gyro]

I would still just leave them alone. They are reasonably low value so any surface leakage isn't an issue, and they are designed to run hot. Just take them out of the newspaper, store them where they won't rub together to much and stop worrying about it.

[TimFox]

Some of the "dirt" on the rough surfaces may be just newspaper ink that rubbed off.

[TERRA Operative]

A friend of mine who was a very good teck, used to wash TV chassis with electronics intact. He did this in a quarter car wash.
Dried them in the sun.
No failures due to this Process.
Another highly regarded teck used to put boards in his dishwasher, good results, until his wife put a stop to it.

I sometimes put PCB's through the dishwasher. The latest one of note was PCB's from a nicotine flavoured TDS 700 series Tek scope.

Came out sparkly clean and after a good dry, and a blow with some compressed air and hairdryer to get water out from under the chips, it works fine.

[james_s]

Just keep in mind it can take surprisingly long to get all the water out from under large ICs. Also if you are in an area that has minerals in the water it's a good idea to give it a good rinse in alcohol or distilled water prior to drying.

[DavidKo]

If it it corrosion on the leads that you are worried about, you are probably going to need some form or abrasive. I always keep small pieces of extra fine (200, 320, 400 grit) sandpaper at my electronic benches. With the sandpaper folded in half it only takes a few seconds to have old leads cleaned down to bare metal. Then flux and tinning and you are set to go.
...

I use steel wool for such a purposes. In case of sandpaper, than 200 is still quite rough. With sandpaper I usually start with 600-800 grit and go down if the rust is deep.

[EPAIII]

No sense in arguing over the grit size. My point is abrasive is the best way to remove corrosion from the leads. 200, 400, 800, I even have 2000 grit. And perhaps a scrap of 10,000 grit. Start where you will.

As for steel wool, it can leave whiskers behind. Steel whiskers which will be conductors. Sand paper leaves dust which is an insulator. I will stick with the sandpaper.

If it it corrosion on the leads that you are worried about, you are probably going to need some form or abrasive. I always keep small pieces of extra fine (200, 320, 400 grit) sandpaper at my electronic benches. With the sandpaper folded in half it only takes a few seconds to have old leads cleaned down to bare metal. Then flux and tinning and you are set to go.
...

I use steel wool for such a purposes. In case of sandpaper, than 200 is still quite rough. With sandpaper I usually start with 600-800 grit and go down if the rust is deep.

[EPAIII]

A lot is being said about washing PCBs and even whole electronic devices in water and aqueous solutions. I have done this and probably worse.

BUT care must be used in the decision to do this. Boards or devices with electro-mechanical parts can be very difficult to dry. Relays, switches, variable resistors and capacitors can admit water to their interior where it can remain for days or longer. And membrane switches are almost impossible to dry out except by complete disassembly if that is even possible.

A high purity alcohol is your friend here. 91% or better.

Even the use of solvents intended for electrical or electronic use can carry foreign substances into the interior of these parts where those substances remain after the solvent itself has long since evaporated. I learned the hard way that flux remover would carry the flux into switches and relays where it coated the contacts turning them into insulators. It took many additional washings with the solvent to remove that flux from those components. The lesson is, if you use flux remover, be very careful where it flows.

One more point: ICs and other components in plastic packages are NOT hermetically sealed. Gasses and liquids can get inside and possibly cause damage. And the damage may not be immediately apparent. This is one reason why there are ceramic packages.

[DavidKo]

You can get similar result when you use solvent to remove the "fat" on the PCB. Fat will be only dissolved in the solvent and after evaporating it create thin fat film everywhere.

Our approach (for cleaning and degreasing) in ultrasonic cleaner was:
- clean with detergent (industrial - do not have "special" ingrediencies) which "breaks down" fat to be washable
- clean with distilled water
- clean with pure alcohol (99.9%) - probably can be replaced with IPA

After cleaning the last step was flushing the surface with pure alcohol.
We have used it to prepare substrate for vapor deposition.