Miyagi say: Frux-on Frux-off

[TrentO]

I just completed a soldering a project board, a few moments ago, to learn more about Pic32 microcontrollers and noticed all the ugly flux 'stains' near my solder joints. The flux residue wasn't too bad, mind you-- I consider myself a fairly decent solderer-- quick but wet solder joints, no burnt rosin, etc. But I hated seeing clear gobs of stuff here and there. I read somewhere that rubbing alcohol will make quick work of flux, so I tried it... And yes, it did get rid of much of the flux. Unfortunately, it also seem to melt the clear coating on the PCB board. So now, there are dull spots here and there on the board where the flux was. It didn't melt the silk-screening, but really soften up the shiny areas.

The question is-- is there anything that will take the flux off without dulling the surface at the same time? I know there's commercial-stuff that comes in a can, but I don't think I solder enough to make the purchase... And besides-- I'm suspicious that the stuff-in-a-can would also dull my boards.

What I'm using-- Kester "44" Rosin Core Solder, a green pcb board with ground-plane and all (seems like a pretty decent quality board,) and drug-store grade 70% isopropyl rubbing alcohol.

And guidance would be sincerely appreciated.

-Trent

P.S.: I also wanted to do a plug for Lucio Di Jasio's "Programming 32-bit Pic Microcontrollers in C" book-- it's good stuff.

[desolatordan]

The commercial stuff tends to be quite... volatile, to say the least, but it DOES work well.

The isopropyl alcohol should work fine. Use an acid brush and wipe it across the board, be liberal and remember you have to push the residue off the board. Helps to wipe up any residue with kimwipes or cotton cloth. I doubt it actually "melted" your coating, it's more likely that when it dried it left a matte finish because of flux residue?

The problem with using kimwipes and q-tips is that they sometimes leave little "hairs" around your board.

[Mastro Gippo]

I use a hard brush and "trichlorethylene" (that's what google translate says). It's cheap and, despite being a powerful solvent, it doesn't harm other parts (but don't let it touch shiny plastic surfaces as LCDs!!).

[74HC04]

With the uppermost respect, trichloroethylene is a bit of a nasty substance when it comes to health, especially since it's a carcinogen. My grandfather used to use it a lot as a general solvent when I was a kid but I wouldn't handle it myself (unless in a fume cupboard) these days. I can still remember the smell...

http://en.wikipedia.org/wiki/Trichloroethylene

[Valhallasmith]

Trichloroethylene works very well at removing stubborn flux deposits.  Unfortunately it is difficult for the hobbyist to use.  You would need a solvent rated mask and PVA coated gloves(expensive) to work safely with it.  A better alternative is to switch to water soluble flux, a no clean flux or use one of the commercial flux cleaners like G3 no clean flux remover.

[Andrew]

Isopropyl Alcohol http://en.wikipedia.org/wiki/Isopropyl_alcohol and a toothbrush.

[Mastro Gippo]

With the uppermost respect, trichloroethylene is a bit of a nasty substance when it comes to health, especially since it's a carcinogen. My grandfather used to use it a lot as a general solvent when I was a kid but I wouldn't handle it myself (unless in a fume cupboard) these days. I can still remember the smell...

http://en.wikipedia.org/wiki/Trichloroethylene

Well, reading that wikipedia link doesn't scare me at all... It was even used as an anesthetic in medicine, how bad would it be if I use it in a ventilated area? Soldering fumes are still the #1 concern for me. I must say that I use very small quantity of that stuff by the way, we have the same 0.75l bottle for almost 20 years and we cleaned a lot of PCBs, and it's still half full! I guess that bottle will outlive me. 

[KuchateK]

Isopropyl alcohol is very good at cleaning solder flux residue. I don't think there is anything on PCB that can be dissolved with isopropyl. Definitely not the solder mask. It was used commercially for cleaning flux. I think they banned it now because they had to recycle it. Water (when using water based flux) can be poured down the drain.

Thing is, Rubbing Alcohol (30% or more water content) is not good for cleaning. The problem is that alcohol evaporates quickly and you are left with sticky water and flux residue. Use pure Isopropyl alcohol. You can buy pretty big quantity (for hobby use 0.5-1l, about 16-32 oz, is a lot ) for few dollars online (I got mine from amazon).

Another thing, as mentioned, is that you have to "push" flux with alcohol away from PCB or wipe it with cotton swabs, paper towels, cotton cloth or something similar. If not, you will only spread it on bigger surface and board will be sticky. Usually several cycles of wetting, brushing, pushing/wiping are necessary for clean board. Brushes are very good for that purpose. Cut bristles to have stiffer brush, it will go better between or under components. It is also easier to "push" flux from board. I use regular flat "artists" paint brushes, from local dollar store, nothing special. Test the brush before first use. On one brush I got Isopropyl dissolved glue holding bristles.

[qno]

alcohol 80% and a toothbrush works for me.
After that conserve it with a protective coating of solder lacker, plastic spray (I use PRF202 from Taerosol) or the official Conformal Coating (this dry's only under UV light).

I also have heared of a brand called Humiseal but I have never used it.