[Nospam]

It's been many years since I've done any soldering, and I've never used any flux, other than what was in the rosin-core solder.

Going through the postings here, I've found a lot of recommendations to use liquid flux for soldering (especially for SMD), but I don't see much information on choosing a flux.

So, what should I look for in choosing a soldering flux?

Is Rosin-based flux preferable over organic/water-soluble?

What about a gel vs liquid flux?

A quick search turned up these:
http://www.ccis.com/home/hn/page3.htm
http://www.glassmart.com/soldering_flux.asp
http://www.circuitspecialists.com/prod.itml/icOid/2555

Would any of these work, or should I avoid any particular ones?

Any other recommendations?

 

[bg4533]

I use Kester Flux . It is the only type I have ever used, but it helps a little. I don't use it much and never really understood how it helps all that much. I mainly use it for interconnects.

 

[Edwood]

I only really need to use flux when desoldering parts.

I mainly use Cardas Quad Eutectic solder and Kester 44.

Cardas is so rich with flux, it splatters over the place, literally. Which makes soldering easy. Downside, is that it's difficult to control where the flux goes. You have to be careful when soldering small parts.

Careful with the liquid flux. Some kinds are acid based and need to be cleaned thoroughly afterwards.

One thing I liike about Cardas' rosin core is that it is fairly clear in color, and is fairly easy to clean. Although I have read somewhere that Cardas solder does not need to be cleaned off. Not sure if that's ture, But I clean anyways.

-Ed

 

[chillysalsa]

After working in the aerospace electronics industry, I noticed that RMA (rosin, mildly activated) in liquid form was the only one that was used, and very sparingly. You should also remove the flux thoroughly, because the ionic residue left behind can lead to shorting over 30 yrs.

 

[randytsuch]

I would stay away from water soluble flux.
We use it at work, because of environmental regulations, we need to use something that can be cleaned with water.
It is more conductive than the "standard" type of flux, so needs to be cleaned very well to make sure you get rid of all of it.

Randy

 

[pne]

i've actually never used flux at all until recently. i've noticed it does help solder flow quite a bit better, and seems to get rid of the impurities in a contaminated joint, allowing it to be melted/repaired.

 

[tangent]

Quote:

I don't see much information on choosing a flux.

For DIY electronics, rosin flux generally works best. You can get paste flux (usually in round tins) or liquid flux (usually in flux pens).

I prefer liquid flux, but I don't like flux pens or the bottles I've seen. It's hard to control the amount of flux you get from a flux pen and most squeeze bottles. You either get too little or too much, and too much usually means a mess builds up on the pen/bottle. So, I bought a gallon of Kester 1544 (same stuff as in Kester 44 solder) and some needle-tipped squeeze bottles, and that's working a lot better for me. I do have some surplus...PM me. <plug>

Quote:

never really understood how it helps all that much.

It helps the solder to flow better. (Thus the term "flux".)

I mainly use flux when I've burned off all the flux already on a joint. This happens to me a lot when prototyping, as I keep desoldering and resoldering connections, often reusing the solder already on the joint. Once the original flux is gone, you need to add more or you end up with a cold joint.

I also use it sometimes when desoldering, since desoldering relies on the solder flowing into the wick or the desoldering pump.

I've tried using it for SMT, but it's only rarely been necessary in my experience. Most of the time, the rosin already in the solder wire has been enough.

Quote:

seems to get rid of the impurities in a contaminated joint

I wouldn't put it that way. All flux does is helps the solder flow better. Without any flux, solder gets pasty and doesn't flow at all. Any impurities will tend to flow to the top of the joint when the solder is flowing well, so there's something to what you say, but it isn't "getting rid of" the impurities, just helping them stay separate out of the metal joint.

 

[aos]

Oh actually flux is one of the most important things to have when doing SMD. Without it some things get almost impossible to pull.

I never tried liquid flux though, haven't seen it being sold anywhere so I haven't even heard about it until a few months ago.

 

[Qpedejo]

Hi
I can highly recommend this : Multicore X32-10i flux...it's great!
Easy to clean and give u nice shiny solderings!

/PJ

 

[Nospam]

Thanks everyone for the feedback!

I ended up getting a small bottle of Kester 1544 from Tangent.

 

[Jugtree]

I can't seem to find Kester 1544 for shipping to or within Canada, in small quantities. Newark Canada has 1 gallon jugs, but I'll never need that much.

I need no more then 6-8 ounces.. really only 2 oz, but could give some to friends, if I have a bit extra left over.

Anyone have ideas?

.:..:::Jugtree

 

[cobaltmute]

I've used MG Chemicals No-clean Rosin flux from Sayal (around Toronto). While I like the way it helps me get the solder into the joint, it is a royal pain if you do want to clean it. It is available in pen or small bottle.

 

[BrianDonegan]

All I ever use is a Kester 951 (No Clean) flux pen. Easy to use, clean up is optional, depending on the situation. I either use the parts washer (big messy jobs) or just a quick rinse or Q-tip of isoprop. alcohol to clean up. Must small tasks need no clean up. It's great for touching up cold solder joints when repairing customers' work.

I also like Kester 245 No-Clean solder (.015", 28 gauge). Flows great, often needs no cleanup, super-small diameter.

 

[olblueyez]

Cant you buy solder with flux in it? I built test equipment and computers for years and never saw one person use separate flux. Is it because audiophile solder is not available with a flux core? Ive used wick to remove solder but thats it.

 

[BrianDonegan]

Quote:

Cant you buy solder with flux in it? I built test equipment and computers for years and never saw one person use separate flux. Is it because audiophile solder is not available with a flux core? Ive used wick to remove solder but thats it.

Yes, the solder I mentioned, and most others have flux inside them. Flux by itself has other uses, such as touching up cold solder joints. It also makes tining wire much easier... add flux, then heat, then solder. When I was soldering guitar pickups for a living, we used liquid flux extensively for this.