[mds33200]

Hi, at work we have an ultrasonic machine filled with isopropyl alcohol (91%) which we use to clean electronic devices (pc boards, about 2” by 5”). The chips we get have oxidation built up on them, so when we put them in the ultrasonic machine (has built in heater) and is filled with isopropyl and 40 minutes later, lots of the oxidation is removed. The board is removed from the isopropyl, where the board is patted dry with a lint free towel. Then the boards are dunked into another tub filled with solution, which is composed of odorless paint thinner and another chemical at a  ratio of 19:1 respectively. So the chemical in the tub is about 95% odorless paint thinner.

I asked my boss today why we pat the boards down after the ultrasonic cleaning with isopropyl, and it turns out its done so the odorless paint thinner solution doesn’t get contaminated (from the alcohol saturating the boards). I asked if it was a necessary procedure since it would save so much time to just remove the boards and dunk them in the other tank, and he said it would be something to consitter. So what are your opinions?

I know the odorless paint thinner solution evaporates relatively quickly (though it is sealed) but if we left the box open for 5-10 minutes and aired the room out, would that be enough to evaporate the alcohol that accumulates in the odorless paint thinner solution?  Or would other chemicals evaporate at the same rate the isopropyl evaporates?

[enahs]

It can. It depends on what that "another chemical", as well as what really constitutes the orderless paint thinner, and the goal of this step is.


You could save a lot of time and create a sacrificial bath. If the "another chemical" and odorless pain thinner is not to expensive, you could first dip the boards in that and use it to rinse away the isopropyl alcohol, and then from there go into the actual bath, for however long and whatever conditions and such, to do whatever it is to do (you were very vague, and I suspect on purpose!).

And again, depending on that second step (purpose, chemicals, conditions) you might could find another cheap intermediate chemical to do the same thing.

Even just the odorless paint thinner would probably work. As you can drip dry it for a few seconds, and whatever odorless paint thinner is left on it should be insignificant to the volume of the other bath (since odorless paint thinner is already in excess).

[mds33200]

Hi, actually I like that idea alot (the idea you mentioned about the  intermediate bath) the purpose of the 2nd bath is to do a final cleaning, because after the boards are cleaned with isopropyl, most of the debris is removed from the board. However within minutes after the boards are removed from the isopropyl, the chips on the board form a white oxidation arround them (looks like powder but does not flake off)  and the second solution removes any other impurities on the boards, as well as the residue that the isopropyl left behind.

I know the "other solution" that is mixed with the paint thinner is itself a mixture of chemicals, to be honest I dont know what they are, I am not at work right now to look them up. I do know that the chemical is very expensive though, about $75-$100 per 60 ML (something like that) and itself is a 100% concentrated solution. Now the final bath is only suposed to be a 5% solution (so its diluted with the paint thinner) but consittering how much it takes to fill a container, its pretty expensive. We do keep the solution on the more concentrated side though, I would estimate the final bath is a 10% solution, 50% more potent then required. So for sure if the boards were dipped in pure paint thinner, then drip dry for several minutes, then transfered to the "final solution", that would do the trick.

Thanks for the sugestion, that will really save some time, not to mention how bad the smell was when we blotted the alcohol covered boards, even in a well ventolated room- it just made the process so tedious.