Soft solder flux residue

For years I have used Fry's Power Flow Flux for general non electrical/electronic soft soldering. It is an acid based paste which, according to its data sheet, does not contain zinc chloride. I have found it ideal and have never had any problems using it.

I have just made a fine brass gauze oil filter using it with ordinary lead/tin (electrical) solder. The wire diameter of the gauze was about 0.005". A white solid has been left on the gauze which had been in contact with the paste. Cleaning in hot water and citric acid does not remove this sold.

What is this solid? I assume it is part of the paste.

JA

Hi JA

If it was cored solder that you were using then something like IPA (Isopropyl Alcohol) may clean it off. In the past I have used this to clean flux residue from circuit boards that I have made/repaired. You can get t from the likes of CPC/Farnell with free post, assuming you are UK based. You could also try meths this will sometimes remove flux residue,

Regards

Martin

Confused. If you used electrical (cored) solder, why would you add flux paste?

The fluxes used in electrical solder are traditionally resin-based and the best solvents to remove them are alcohols, as Martin suggests. In the good old days that would be trike (Genclene etc) or IPA nowadays. Nowadays the production fluxes are water soluble and increasingly "no clean" fluxes are used. They leave a small residue that is almost inert although if you insist on trying to clean them off with solvents, they will come away and contaminate the board.

The whole idea of fluxes is to remove any surface oxidation, which tends to require an acidic flux. The MSDS for this Fry's flux suggests it comprises "nonylphenoxydiglycol" as a surfactant (wetting agent) and hydrochloric acid to do the work. It's horrible stuff to get in your cuts and strips chrome plating. Best stick with the cored solder if you can get away with it for small stuff and keep Fry's for plumbing?

I have never found cored solder alone any good except for electrical/electronic work. Surely there is nothing stopping you using it for other work with a suitable flux (OK some are nasty).

Have I missed something here? I have not had any problems with this approach over the last 50 years.

JA