Would an ultrasonic cleaner filled with 99.9% anhydrous isopropyl alchohol be effective in cleaning rosin flux from hand soldered boards? I use the alchohol and a stiff brush now, but it seems to need 2 cleanings to get all the flux off.
Or would it just end up leaving a thinner coating of sticky rosin on everything?
I have found that also (needs two cleanings).
If you use a ultrasonic cleaner things may explode as there will be a cloud vapour given off.
POOF ! ! !
On th other hand, if you use "white lightning", you could have a great time while you clean your boards.
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Fill the tank of the ultrasonic cleaner with water.
Stand a laboratory type glass beaker, containing your alcohol and PCB in the water.
The ultrasonic energy is transferred through the beaker into the solvent.
You can have two beakers, with "dirty" and "clean" alcohol, Then you can do a 2 stage wash.
Start in the dirty solvent to get the majority of the flux off, then have a final rinse in the clean solvent.
When the solvents get too contaminated, you can dispose of the dirty one, then the clean becomes the new dirty, replenish the clean one.
@JohnLincoln
Sounds like you have done this.
You could still use white lightning instead of water though. 
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Thanks for the ideas. I'll have to see what I can find on ebay then.
CrossRoads:
Or would it just end up leaving a thinner coating of sticky rosin on everything
One way of avoiding this possibility is as follows:
Instead of allowing the newly washed PCB to dry naturally, use a high pressure airline to blow the PCB dry.
By blowing off the alcohol, you also blow off the dissolved flux that would form the thinner coating.
LarryD:
@JohnLincoln
Sounds like you have done this.You could still use white lightning instead of water though.
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Yes, I might have done this.
I have an alternative use for the white lightning
Instead of allowing the newly washed PCB to dry naturally, use a high pressure airline to blow the PCB dry.
By blowing off the alcohol, you also blow off the dissolved flux that would form the thinner coating.
I do this with an air compressor, it does require the second (some times third) washing, you can tell if there are streaks after drying.
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