[sdiy] Ultrasonic Cleaning of PCBs

[Tom Bugs]

Hi list,
(I think the list wasn't working yesterday, but now it is back??!!)

I wondered if anyone has any experience / tips / tutorials for the 
ultrasonic cleaning of electronic bits'n'pieces.. I have been looking at 
how to make the job of PCB cleaning less hassle - I use so called 
NoClean solder, but there always remains quite a lot of residue, some of 
which tends to be very stubborn - I now use special cleaner as 
Iso-Alcohol doesn't seem to be quite up to the job often.

With this in mind I purchased a cheap Aoyue Ultrasonic cleaner - cheap, 
just to check things out really. The instructions it came with were, 
however, very poor and gave little useful info detail. I also got a 
bottle of 'ultrasonic cleaning fluid' (to be diluted 5-20%) from the 
vendor at the same time (again with little info). I've tried some google 
searching but haven't managed to find anything much useful, especially 
related to PCB cleaning.

The cleaner runs at either 33kHz (normal) or 50kHz (hi-speed) - one 
google reference said that a 'swept' frequency would be much more 
efficient and less prone to cause damage (!)
I've tried using the cleaning fluid - it seemed to leave the boards with 
a film a bit like fairy liquid and I haven't made up my mind yet as to 
whether the cleaning action is fully satisfactory.
I've also tried Iso-alcohol in there - this cleaned some but not all of 
the gunk.

Anyone got tips on types of liquid to use?
And also how long to run the process for -- the machine has an auto time 
of 99seconds (it is a basic machine!) (I think that question may be like 
asking 'how long is a piece of string'?!)
Another question is what is safe to clean with the machine -- I'm 
presuming that most standard passive components should be fine and 
likewise anything that is 'sealed'. The big question is what to do for 
standard, unsealed Pots and Switches -- will they be messed up by 
cleaning? (In current experiments I'm just cleaning once the board is 
stuffed expect for the switches and pots)

Any help would be greatly appreciated!
Cheers & best,
Tom / BugBrand