Cleaning Electronics: Advice, favorite methods, equipment, etc.

[tomizett]

Hi All,
This is a general question rather then one pertaining to a particular repair. As a repair technician by trade, I spend a lot of time cleaning things - but I sometimes wonder if there might be better ways of doing it.
Specifically, I'm interested in hearing peoples experiences and favorite methods of cleaning and drying entire PCBs contaminated with mostly "organic" type fluids such as oils and sugars (read smoke fluid and beer).

I have discussed with a colleague the possibility of using an ultrasonic cleaning bath - does anyone have experience of using one? What is the preferred cleaning medium - just (de-ionised?) water or something more fancy? Is there any possibility of damage, and what type/grade/power of machine would you recommend?

Cleaning with water of course raises the problem of thorough drying. I wonder if placing in an oven at a reasonably high (50-80 degC maybe?) for a few hours would be the most effective? What maximum temperature could be sustained without degrading component (particularly caps?) life? Drying has to be completely thorough and reasonably quick to stop any kind of corrosion or tarnishing setting in. If using an oven, would it be necessary (or beneficial) to remove the moisture be some means?

Anyway, I'd be interested in hearing what techniques others have used, particularly on the trade trade or in manufacturing.

 

[JimB]

On the (thankfully) few occasions that I have had to wash a circuit board to remove spilt "juices", plain tap water has generally done the trick.
If the juice is not miscible with water, iso-propyl alcohol (Propanol) has been successfull for me.

Horror stories:

A keyboard which had been showered with hydraulic fluid.
Luckily it was water based fluid, so soapy water did the trick.

An oscilloscope which had been showered in seawater.
Unfortunately the guys involved just dried it off by putting it in a warm oven. BAD mistake!
When it came on to my bench several days later, all the transistor bodies just dropped of their legs due to corrosion as soon as you touched them.
That scope was sent back to the manufacturer for refurbishment, it was OK when it came back, but in the following years it never was particularly reliable.

JimB

 

[tomizett]

Always good to hear the stories... I wouldn't like to have been the service agent for that 'scope.

I tend to work the other way, starting with isopropanol (thinking of it as easier to dry, non-conductive, non-corrosive etc) and use water as a last resort if that doesn't work. Sugar based things seem to respond better to water - if I rememember my chemistry right, that'd be to do with water being a polar molecule?
I think I also read that mixing isopropanol with water engorages the water to evaporate more readily (this really is beond my chemistry). Can anyone verify that?

Here's a cazy idea that came to me this afternoon though: How about placing your washed PCB in a vacuum chamber to lower the boiling point of the water - could that encorage it to dry out of all the crevises without excessive heat? I dare say too much vacuum would cause all your electrolytics to explode though...

 

[JimB]

Here's a cazy idea that came to me this afternoon though: How about placing your washed PCB in a vacuum chamber to lower the boiling point of the water - could that encorage it to dry out of all the crevises without excessive heat?

Yes, that is a good idea.

I dare say too much vacuum would cause all your electrolytics to explode though...

Maybe not.

Many years ago, I saw a circuit board mounted in a diecast box.
The idea was that this was to be used deep underwater, but it had to be quick and dirty and cheap.
To overcome the problems of water pressure which would have got in through the lid seal on the box or even crushed the box, the box was connected to an air supply via a divers breathing valve.
The diver breathing valve tracked the water pressure and gave air at very slightly above water pressure, and so the air pressure in the box kept out the water and prevented crushing.
The only problem was, what about the electronic components? Could they stand the pressure?
Phone calls to various manufacturers were no help, they said that their components could happily withstand very low pressure, as in up high in an aircraft, but no one had ever tested for high pressure deep underwater.

So, the circuit was built and tested in our departments pressure test tank.
The only thing that failed was an electrolytic capacitor which crushed under the pressure.
That capacitor was replaced with something a bit more robust, and the thing worked like a charm.

JimB

 

[KeepItSimpleStupid]

Tom:
Join the Tekscopes Yahoo group and look in the archives. There should be lots of discussions on how Tektronix used a dishwasher to clean PCB's. Yes there are requirements to make it work.

 

[tomizett]

Thanks... will do!