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Author Topic: What I learned today: Flux is awesome!  (Read 1947 times)
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Silly-con Valley, Ca, U.S.
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I'm a total newb to all of this and have maybe made less than 100 solder joints in my life before this morning. I was using solder with a flux core and from what I heard though that would be good enough. But I was never happy with my solder joints. Enter flux. I bought flux gel or paste. (can't remember what it's called.) It's basically a thick deep amber colored goop. OMG it makes soldering SO much easier. So for any newb out there who is just getting into this my advise would be USE FLUX!

Sorry for all of you how probably know this already but I'd thought I'd share for any other newbs who are teaching themselves like I am.

P.S. I won't start a whole new thread for this but also buy desoldering braid. It comes in very handy as well.

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10 PRINT CHR$(7)
20 GOTO 10

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Quote
desoldering braid. It comes in very handy as well
Desoldering braid works even better if you wet it before hand with some flux.
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Silly-con Valley, Ca, U.S.
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Good to know. I applied more to the board before using it. Kind of the same idea I guess. I had a big blob connecting 2 pads and swiping the iron point wasn't clearing it. Braid fixed it right up.
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10 PRINT CHR$(7)
20 GOTO 10

Austin, TX
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Like you, I never saw the value in flux.  I was having trouble solder some old PCBs I found and decided to try it.  It was like watching magic.

There are also "Flux Pens" out there.  They are basically sponges soaked in a liquid flux, inside of a marker case.  More expensive than the jelly (in terms of volume) but very convenient.

I find it very easy to wet de-solder braid with the Pen.  (I never figured out a un-messy way to get the jelly on to the braid.)
« Last Edit: February 03, 2011, 09:36:04 am by James C4S » Logged

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Dallas, TX
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Another amazing product for desoldering is CHIPQUIK, in case you have to work on large surfaces.
That product basically slows down the soldering process. Great product.

« Last Edit: February 02, 2011, 12:27:26 pm by Staedtler » Logged

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The flux included in the solder core is enough to get you by if you don't have any flux at all, but it really only works if you truly heat the part and then feed the solder directly into the joint. Once that is done the tiny amount of flux that was in the solder is gone, so if you have to reflow anything or solder using less textbook techniques, you need flux.  I like the little tins of paste flux you get in the plumbing section of the hardware store. It's easy to dip the tip of the soldering iron or leads of through-hole parts into the flux, and a tin lasts a thousand suns. I never got along with liquid flux or the flux pens.
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I like the little tins of paste flux you get in the plumbing section of the hardware store. It's easy to dip the tip of the soldering iron or leads of through-hole parts into the flux, and a tin lasts a thousand suns. I never got along with liquid flux or the flux pens.

Plumbing flux is usually RA, while electronics flux is RMA. So you definitely should not use plumbing flux on electronics...it's corrosive enough that you have to clean it off copper pipes, and the tiniest amount left on a thin foil PCB copper layer can wreak havoc. You still need to clean RMA flux off PCBs (unless it's labeled as no-clean) because it can corrode and/or become conductive over time. I have fixed a lot of electronics with 99% isopropyl and a toothbrush.
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Dallas
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Do you have any suggestions on a proper electronics flux that is also pasty like plumbing flux?

What does RA and RMA mean?
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It's available from a number of sources:
http://www.jameco.com/webapp/wcs/stores/servlet/Product_10001_10001_2094258_-1
http://www.dealextreme.com/p/premium-quality-precision-soldering-paste-110g-26169

Probably Dealextreme is the best source for the actual tubs of it. I prefer the syringes of flux paste which are actually available a lot more places and in no-clean types. Rosin flux works great and smells great but I don't use it for fine pitch ICs; it tends to wick under the chip and can't be cleaned out, then causes problems later.

RA is fully activated (acidic) flux and RMA is mildly activated flux that is almost PH neutral when cooled down from soldering temperatures.
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I have fixed a lot of electronics with 99% isopropyl and a toothbrush
Nail polish remover and cotton swabs, from wife/girlfriend, work as well.
« Last Edit: February 02, 2011, 09:41:53 pm by florinc » Logged

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What does "activated" mean, in the context of flux? I never thought there was so much to learn about flux.

"Flux", by the way, is a very funny word.
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What does "activated" mean, in the context of flux? I never thought there was so much to learn about flux.

"Flux", by the way, is a very funny word.

Flux capacitor is not funny, it's the quick way to the future.  smiley-grin
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Like you, I never saw the value in flux.  I was having trouble solder some old PCBs I found and decided to try it.  It was like watching magic.

There are also "Flux Pens" out there.  They are basically sponges soaked in a liquid flux, inside of a marker case.  More expensive than the jelly (in terms of volume) but very convenient.

I find it very easy to wet de-solder braid with the Pen.  (I never figured out a un-messy way to get the jelly on to the braid.)

Took the words out of my mouth.  I dont tend to use flux anymore, I have some good solder.  Im not sure it thats the reason I dont need it or if its because Im just getting better with the iron smiley-wink
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Flux works by removing oxidation on the PCB and components on a board and allowing the solder to bond with the metal. If you have good solder and a clean circuit board and components, it won't be necessary. Of course we live in the real world. The metal on our parts and circuit boards will oxidize with time and sometimes using additional flux is a big help.
First of all, as others have said, don't use plumbing flux. That is acid and will corrode the joints.  It probably won't contribute to the life of your soldering iron either.
I use two types of flux pens.  First is the water soluble.  This is nice because it washes clean with warm water. Isopropyl alcohol and Q-tips are good for small jobs. It is important to wash it off when you are done soldering otherwise moisture in the air will cause corrosion over time. For this reason I also don't use it for soldering wires with insulation.  The flux will wick up under the insulation and over time cause the wires to corrode.
No-clean flux is good for wires and other areas I don't want to clean.  I avoid using no-clean on high impedance and precision analog circuits. Over time dirt can get accumulate that can result in leakage currents.
If you are having trouble soldering and don’t have flux, try cleaning with some alcohol. Scrubbing  a circuit board before building a kit with a paper towel and alcohol is not a bad idea. In fact, years ago when I used to hand solder NASA satellite circuit boards we cleaned every joint with alcohol and a brush just before we soldered it.
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As the previous post mentioned, flux removes the oxidation of the copper.

If it is a circuit board that you are sodering, try rubbing some steel wool lightly  over the pads you are soldering too.  It will expose fresh copper and the flux within the solder you are using should be sufficent.  Clean the board before soldering, you do not want a loose piece of steel wool shorting out a trace.  When soldering to larger component like switches, I'll use sand paper or a very light file to remove oxidation it oxidation is bad. I ran into one manufacture's cheap switches, the metal they were using was SO BAD, solder would not even flow with generous amounts of flux applied after cleaning with a file.

You can eventually tell when you do not have enough heat or oxidation is preventing the solder from flowing.

I use 12 gauge wire for a supply bus around my train layout, using Digital Command Control (DCC).  Using plumbers flux is sometimes the only way I can get the oxidation removed from the wire so the soler will flow when I aply take off taps from the 12 g wire.
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