PCB Cleaning after buildup

Thread Starter

fsonnichsen

Joined Jun 6, 2013
36
I have always cleaned PCB boards by hand after soldering up. I use a brush, swab and isopropyl followed by the compressor on "1 offs". If you spend enough time it works "OK" but I would rather do other things. Does anyone have experience of a better board cleaning method for "1 off" use (a few a day)? I am envious of the super clean boards I receive when I order them populated from vendors.

I have seen ultrasonics used and I guess these are fine for most applications without mechanical issues (crystals, piezos). I have personally soaked boards in isopropyl overnight and they come out clean. But in both cases I worry about what may leach into the chips, caps, resistors etc during long exposure. I thought maybe blasting with a spray for several minutes may be a better compromise.

I thought I would see some devices for this on the web but I do not see much other than ultrasonics
Open to any experience out there-
Thanks
Fritz
 

jpanhalt

Joined Jan 18, 2008
10,518
1) In earlier times, it was reported that some companies just used a household dishwasher.
2)The three main components of the Deoxit product are heptane, acetone, and ethyl alcohol. Heptane may be there only to retard evaporation.
3) The four main solvents in the Tech-Spray are isopropyl alcohol (IPA), ethanol, acetone, and THF (tetrahydrofuran = cyclotetramethylene oxide). THF is a good solvent. It has many of the properties of diethylether but boils at a higher temperature.

Personally, I just use ethyl alcohol (absolute, anhydrous) and acetone -- about 25% acetone. I leave the acetone out when I suspect some plastic parts may be affected. Nylon, epoxy, LPE, PP, etc. are generally safe with acetone, but polystyrene is not.

Anticipating that my supply of absolute ethanol may run out, I have investigated inexpensive alternatives. Alkoxy alcohols, e.g., 2-ethoxy ethanol, are a class of powerful, yet relatively non-toxic solvents called Cellosolves (https://en.wikipedia.org/wiki/Glycol_ethers ). Common versions are miscible in water yet retain their potency with a little water present.

Butyl Cellosolve is readily available and is used in many floor cleaners and strippers. I has a distinctive odor you may have experience with, but it also evaporates slowly. I have had good results with ethyl Cellosolve (2-ethoxy ethanol) with IPA, ethanol, and acetone. You can even add a little water to help get rid of any white residue. I used ethyl Cellosolve and IPA ( about 1:4) in my last project, and it worked well.
 

Thread Starter

fsonnichsen

Joined Jun 6, 2013
36
Thanks for the information on solvents. I've used a few concoctions with similar results. Much of the problem is that there are so many manifestations and combinations of solder, flux and paste out there these days: Flux,noflux, clean, noclean, water soluble, lead, silver, nolead etc. Each seems to favour a certain solvent and as you mention a combination may get them all. Maybe I should get away pure isopropyl and try some of the commercial solvents.
Do you guys soak it or use ultrasound? I find direct applications often still leave residue when viewed with a scope?
Thanks
fritz
 

jpanhalt

Joined Jan 18, 2008
10,518
I do not use ultrasound. I have a first wash and second wash, use a commercial tooth brush (not for teeth, nylon bristles), move 2nd wash to first and replace second wash with fresh as needed. Drain and use low pressure air to dry. Rarely any residue. What may remain is removed with a clean towel and solvent.

The boards end up are shiny and without smears. Residual oxides (?) removed by flux are the hardest to remove.
 
Top