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Old 23rd March 2007, 10:21 AM   #1
Stuey is offline Stuey  Australia
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Default How to use liquid solder flux

Hi all,

A very simple question; how do you use liquid solder flux on older amp boards when repairing?

I bought the flux as I've had trouble getting the rosin cored solder I normally use to wet on older PCB tracks which I've carefully cleaned up with 800 grit carborundum paper and isopropyl alcohol.

The flux I've bought is an aromatic solvent based one containing rosin, from Cutter Electronics:

Anyway, do you let it dry, or try to solder while it's still wet, or doesn't it matter?


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Old 23rd March 2007, 02:27 PM   #2
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Join Date: Mar 2007
Location: Canandaigua, NY USA
Not familiar with that one, but it's usually rosin and alcohol. You just brush it on with a small brush and start working. No need to let it dry. IMO, for the best quality work, all flux, including RMA (rosin, mildly activated), should be cleaned off when the board is complete. Use alcohol or a spray solvent made for the purpose- outdoors! FWIW, I once watched a NASA certified solderer come into our plant to do some work on board that were to be launched in a satellite. The person used brush-on rosin flux for all their work, and they did some of the best joints I've seen.
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Old 23rd March 2007, 06:59 PM   #3
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I use “No Clean” solder flux as an extra flux for SMD components and rework. You must dry it thoroughly because otherwise it will “sputter”, giving unreliable joints and very small solder spats around the PCB board. With small SMD components these spats gives a risk of shorts.

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Old 23rd March 2007, 11:46 PM   #4
Stuey is offline Stuey  Australia
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Join Date: Mar 2006
Location: Perth, Western Australia
Hi there,

Thanks for the replies. Yes, I think this one is meant to be a no-clean flux, but I clean my board with isopropyl anyway because of the cored flux I'm using.

Now to get stuck in!


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