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SMD soldering flux.
SMD soldering flux.
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Old 13th January 2021, 05:02 PM   #1
edbarx is offline edbarx  Europe
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Default SMD soldering flux.

What SMD soldering/desoldering flux do you use and suggest? I have watched YouTube videos by Louis Rossman doing literally next to impossible SMD desoldering/soldering work, but I have no idea what flux is used. I remember several years ago, I tried to repair an SMD PCB and failed miserably. The FLUX seems to be of paramount importance, and the internet is a nest of vipers ready to bite the innocent. The flux I ordered online was fake. It was much like wax used to steady components in old radios, rather than SMD flux!

SMD soldering would be a feat, but I am daunted by the thought alone!
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Old 13th January 2021, 05:21 PM   #2
rayma is online now rayma  United States
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Stay with major producers, like Kester. You can buy flux in small or large quantities. Use it liberally.
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Old 13th January 2021, 05:54 PM   #3
JMFahey is offline JMFahey  Argentina
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I always use simple homemade flux, just a "stone" of plain pine rosin, bought at the corner hardware store, inside an old jam jar and covered in alcohol which dissolves it in a few days.

I boight 1 kilo some 10 years ago, must have over 900 grams left.

Works like a charm, *bright shiny* solder joints every time.
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Old 13th January 2021, 06:19 PM   #4
JonSnell Electronic is offline JonSnell Electronic  United Kingdom
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Amtech NC-559 is by far the best. Low mess residue and easy to whipe up with Isopropanol.
I put some from the 100g tub in a small syringe for accurate application.
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Old 13th January 2021, 06:55 PM   #5
chris719 is online now chris719  United States
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SMD soldering flux.
I agree with the tacky flux in syringe recommendation, though I think I have some ChipQuik brand stuff.
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Old 13th January 2021, 07:54 PM   #6
Mark Tillotson is offline Mark Tillotson
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I've got 20g of "Termopasty", a Polish brand, comes in a little snuff tin as solid resin,
so for surface mount I scrape powder off the surface sometimes. But most of my SMT work
is toaster-oven reflowing of PCBs, for which I use ChipQuik lead-free no-clean solder paste SMD291SNL10 which comes in a handy 35ml syringe.
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Old 20th January 2021, 09:56 PM   #7
nigelwright7557 is online now nigelwright7557  United Kingdom
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I find the "wax" type good at also sticking down pins as well as being a flux.
I sometimes put a dab behind the IC body to hold it to the pcb.
Trying to solder a wandering IC isnt much fun !

I have soldered pins down to 0.5mm pitch but it takes care and patience and a good eye for shorts/bridges.

For a QFP I put solder flux on all pads and a little behind where body goes to suck it down.
I then solder a couple of pins very gently.
I then check if it is still aligned and fix if not.
I can then drag solder other pins.
Finally drag solder over original pins that were soldered.
Next a good visual inspection for shorts.
I find with stubborn shorts add some flux, remove all solder from iron and drag iron away from pin and that usually fixed it.

The more you do it the better you get.
But use good quality solder not cheap rubbish that just blobs.
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Old 23rd January 2021, 06:07 AM   #8
H713 is offline H713  United States
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I've been using Kester 186 for a long time and it works fine, but cleanup is a mess.

FWIW, Louis Rossmann always recommends Amtech NC-559-V2-TF. I may try it at some point since the Kester 186 is unbelievably sticky and is difficult to clean.

The most potent flux I've ever used is Kester 2222. That stuff is fantastic. You do need to clean it off however, but it is water soluble. Unfortunately, I don't know of anywhere to buy it in small quantities.
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Old 24th January 2021, 05:24 AM   #9
ouimetnick is offline ouimetnick  United States
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Send a message via AIM to ouimetnick SMD soldering flux.
I use Kester 186 at work and I hate it. It works well, but like you said, it's very sticky and annoying to clean. It cleans up well with Acetone, but we have to use a product called "Flux Off" it smells a bit like denatured alcohol and takes a bit of scrubbing.
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Old 24th January 2021, 06:07 AM   #10
suzyj is offline suzyj  Australia
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I make my own. It’s very easy. Mix pine rosin, Vaseline, a dab of isopropyl alcohol, and heat a little. You can dial in whatever consistency you desire. It’s the pine rosin that does all the heavy lifting in flux. Everything else is just to modify its consistency and stickiness.

See Suzy's Blog: Suzy's Super Rosin Paste Flux.

Last edited by suzyj; 24th January 2021 at 06:10 AM.
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