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Rework using flux pens

mregalia

#18584

Rework using flux pens | 7 January, 2002

My company has been doing its hand soldering using drip bottles for application of no-clean flux. This has created quite a few problems, especially on our microwave boards. I want to convert us over to flux pens. Does anyone have any suggestions or caveats? Any shared experiences would be greatly appreciated.

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#18592

Rework using flux pens | 7 January, 2002

Using a flux pen sounds like a good idea. Comments are: * I assume you�re talking aqueous flux. If not, some NC flux pens leave white residues. Nearly all of 15 samples suffered to varying degrees with white residues. * Use the same flux that you are using in your automated soldering processes. * Sometimes, the fibrous material that holds the flux is cotton, which may be bleached to be white. [She be lookin preeetee, ummm] Bleach is chloride and can contaminate the flux as it flows out of the container.

Oooo, just re-read your post. NC flux in a microwave shop, mmmm. Tell us about that [ie, flux manufacturer, apllication control in wave soldering, etc.]

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mregalia

#18595

Rework using flux pens | 8 January, 2002

We use NC flux exclusively for SMT and wave soldering. And it is a fairly old formula from Multicore, though we are currently qualifying a new formula. The automated soldering does not appear to be a problem. It is only the hand soldering that causes performance issues. This seems to be due to much of the flux not being activated by heat when hand soldering. It may also be due to less of it being evaporated. With the automated soldering all of the flux gets heated. At first we assumed it was due to the flux having a different dielectric constant than air. My research into the subject makes me suspect it is more due to the electrical conductivity of the flux and the moisture the unactivated flux absorbs. I've done some simple tests to show that most of unheated flux stays on the board. One of our outside board assembly houses has tested the newer low residue NC fluxes up to 18 GHz and found no significant problems when using reflow ovens. We have not pushed past 9 GHz yet.

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#18603

Rework using flux pens | 8 January, 2002

Your research is on track. NC flux needs to reach activation temperature. Also, do not depend on the corrosion characteristics associated with the flux classification (ie, L1, L0, M1, M0, etc.), until the flux is activated by exposure to soldering temperatures. These are the same issues as applying too much NC flux.

It�s interesting to learn about the frequency characteristic of your nc flux.

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