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How to wash off flux residue?

Migs

New Member
Thread starter #1
Friends:

After you solder a circuit board, what do you wash the flux residue off with? I am hesitant to use water for fear of subsequent corrosion, and have no clue as to what kind of flux is in my solder wire.

Thanks for your advice! -Migs
 
#2
Hi migs, i use a flux removing spray, you should get that from most electronic suppliers, i use maplin or rapid electronics here in the UK. I spray it on, leave for a few seconds and work it with an old toothbrush then spray it again to clean off any remaining residue. works every time.

billboard.
 

Migs

New Member
Thread starter #3
Thanks billboard, I will search for some. If I cant find some, do you think medicinal alcohol will work?

Migs
 

chemelec

Well-Known Member
#4
Migs said:
Thanks billboard, I will search for some. If I cant find some, do you think medicinal alcohol will work?

Migs
Most Solders use a Rosin type flux. This can be removed with Acetone and some other solvents.
But be careful, Acetone is Flammable and is definately also not good to Breathe.
This Rosin flux will NOT be removed with water.

I use a "Kester 331" Solder. It has a Water based flux built into it and just rincing the board Under Warm tap water Removes all the flux.

"Almost All electronic parts are quite Water Safe".

Just remember to dry the board completely before connecting to any power source.
 

Migs

New Member
Thread starter #5
Thanks chemelec!
I will try the water test at lunch to see if my solder flux clears off.
Migs
 
#6
Migs said:
Thanks billboard, I will search for some. If I cant find some, do you think medicinal alcohol will work?

Migs
I have used Isopropy Rubbing Alcohol, 91% for years. It works fine for me.
I rub it on with an acid brush that has its bristles cut short to give it a better scrubbing action. Then just dry with a paper towel. It is probably the safest of the usable solvents.
 

Migs

New Member
Thread starter #7
Good to know Rolf! I'll try that too. -Migs
 

Dean Huster

Well-Known Member
#8
Better yet, use the IPA found in home improvement, paint or hardware stores sold as "alcohol", designed for use as shellac thinner. It's 100% isopropyl alcohol and available in pint or gallon cans. Old toothbrushes work well for scrubbing and you can use floss to get underneath components on the other side (just kidding, just kidding!). For larger boards, fingernail brushes work well. Just remember that the brushes will cause splatter, so wear eye protection and keep your bench clear of things that you don't want splattered.

More dangerous because of explosion/fire and inhalation hazards, either lacquer thinner or acetone work much faster for non-water soluable fluxes. Two runs with the stronger solvents and a final rinse with IPA will leave your board clean as a whistle. Overall, I'd suggest doing it outside on the driveway just to be safer all around.

However, remember that flux removal, for the most part, is a cosmetic thing. Flux at room temperature is inactive and non-conductive, and as long as your circuit board is installed where you can't see the solder side, I wouldn't mess with it.

Dean
 
#10
Just don't use generic drug store rubbing alcohol, Most of them are only 30-70% alcohol (balance is water)
 

3v0

Coop Build Coordinator
Forum Supporter
#11
Liquid Flux Pens.

Dean Huster said:
...
However, remember that flux removal, for the most part, is a cosmetic thing.... I wouldn't mess with it.
Dean
Dean did say "for the most part".

A liquid flux pen can be a great aid when soldering, esp bare copper. Flux pens come with several different types of flux. Some pens like the Kester #2332-ZX are excellent at getting the solder to flow and make very nice joints. But it must be removed. What it leaves behind can keep you circuit from working. The residue from other flux pens can be left on the board with no ill effect. Check the datasheet on the pen you buy.


Often times when a "new and improved" way or product is mentioned, another person will post about how they do without. In this case look for a post like:
You do not need a stinkin liquid flux pen. I solder with a blowtorch and both hands tied behind my back.:p
Maybe you could learn to do so, but it is not required. Nor are you required to buy every tool mentioned here. What you should buy depends on the thickness of you wallet and what you are attempting.

 
Last edited:

Migs

New Member
Thread starter #12
Hi 3vO

The reason I ask is because I was building a Sumovore Sumo Robot kit with my son, and the instructions mentioned cleaning it off for better results.

I do appreciate all of you all's comments. As life goes on I have learned the great power of forums for enlightenment. You guys are all great! -Migs
 

Nigel Goodwin

Super Moderator
Most Helpful Member
#13
Migs said:
The reason I ask is because I was building a Sumovore Sumo Robot kit with my son, and the instructions mentioned cleaning it off for better results.
The only difference is cosmetic, and with reasonable soldering skills there shouldn't be any flux worth mentioning to remove?.
 

chemelec

Well-Known Member
#15
mneary said:
Corrosive fluxes are normally removed with water or IPA. It doesn't usually matter with the rest of them.
First, You should NEVER USE Corrosive Flux on any Circuit Board.

Secondly, Contrary to Manufacturers Claims, Most Rosin Fluxes are Somewhat Conductive.
** Especially in Sensitive Circuits and more so in a high humidity enviroment.

I Always Recommend Removing the flux on all Boards.
 

mvs sarma

Well-Known Member
#16
chemelec said:
First, You should NEVER USE Corrosive Flux on any Circuit Board.

Secondly, Contrary to Manufacturers Claims, Most Rosin Fluxes are Somewhat Conductive.
** Especially in Sensitive Circuits and more so in a high humidity enviroment.

I Always Recommend Removing the flux on all Boards.
Hi Chemelec,
But most solder wires sold contaon rosin inside and it is equally bad? -- I do agree cleaning with distilled water is done by many. Any other solution to get rid of left over rosin or such material as it is really posing problems in HF circuitry and oscillators.
 

3v0

Coop Build Coordinator
Forum Supporter
#17
chemelec said:
Secondly, Contrary to Manufacturers Claims, Most Rosin Fluxes are Somewhat Conductive.
** Especially in Sensitive Circuits and more so in a high humidity enviroment.

I Always Recommend Removing the flux on all Boards.
I agree. As the spacing between traces and parts decrease the ill effect of flux conductivity increases. It may be a waste of time if you never run a trace between pad or build on a protoboard. The nature of the flux makes a big difference.
 

Dean Huster

Well-Known Member
#19
If the circuit you're building is that terribly sensitive to flux residue, maybe you shouldn't be building it on G-10 glass epoxy board in the first place!

ALL flux is corrosive -- your usual rosin flux (vs an acid flux) is very corrosive at soldering temperatures and pretty inactive at room temperature. If it weren't corrosive, it wouldn't be very helpful with getting the surfaces to be soldered clean.

Yes, "cold" flux in high humidity and on high impedance PCBs (in excess of 10M ohms) could easily be a problem. I don't see any problems with it on digital, processor, audio and HF boards. Does it affect between-trace capacitance? Sure it would, but most the effect won't be that great as the dielectric constant of flux I'm sure is a lot lower that that of glass-epoxy.

Dean
 

Nigel Goodwin

Super Moderator
Most Helpful Member
#20
Why is there flux that needs removing in the first place?, I can see the reason for flow soldered boards, but for competent hand soldering there shouldn't be any excess flux to remove?.
 

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