SMD soldering : Clearing flux residue ?

Alcohol in an ultrasonic cleaner works good, in fact, excellent.

Acetone and a toothbrish works, too.

One could use solder with the more modern "no-wash" fluxes, and use a flux pen for additional purposes, like fluxing the IC leads and pads first. If one does that, use isopropyl alcohol ~75% (balance is water) for wash as follows:

1) Soak for 0.5 hr, rinse and soak again, then final rinse. Air or oven dry. 2) Rinse and use artist short-hair brush to remove flux; repeat at least 3 times, then two final rinses. Air or oven dry. ** That being said, i have yet to find a relatively safe solvent for rosin; isopropyl soak method removes most, but not all of it. Using a toothbrush can be of great help, but places that are not too accessible tend to have some residue left behind - giving a whitish cast around the offending joint. Using a small pin point to scratch off that whitish residue helps, then repeat the cleaning as above may get all visible rosin off. Good luck.

Hi,

I'm hand soldering my first SMD board. Since it has soldermask, soldering the SMDs is pretty easy, even the 0603. To do so I use additionnal solder flux. I bought it at farnell, a Multifix 425 flux, rosin based. But after soldering there is a lot of flux left, how can I get rid of it properly ?

Sylvain

I read in sci.electronics.design that Robert Baer wrote (in ) about 'SMD soldering : Clearing flux residue ?', on Wed, 16 Mar 2005:

Have you tried air agitation (or ultrasonics)? Air agitation performs a similar function in PCB etching, after all.

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The good news is that nothing is compulsory.
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WARNING! WARNING! DANGER! DANGER!

I have learned the hard way: never use a "no-wash" flux and then expose the PCB to any kind of solvent. "no-wash" fluxes contain basically a plastic that is supposed to trap the ionic stuf that is in the flux. If you expose the board to a solvent, the plastic stuff partly loses its grip on the ions and they head straight for the most sensitive circuit on the PCB. The remaining plasic stuff then serves to hold the ions exactly where they cause the most trouble.

The company that I use to do coating and potting strongly recomends that easily washed fluxes be used. Next on their list is the stuff that takes fair amounts of non-polar solvent. For the "no-wash" stuff they suggest you send it somewhere else to be cleaned.

There is evil smelling stuff called "ensolve" that works but you can't buy it in the hardware store.

Some people claim to have luck with switching back and forth between mineral spirits and water based cleaners. The mineral spirits lifts the non-polar stuff to let the water at the ionic stuff. The water gets the ionic stuff away so the mineral spirits can get to the next bit of non-polar.

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kensmith@rahul.net   forging knowledge

In article , Brian wrote: [...]

With film capacitors, acetone will often change their value slightly.

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kensmith@rahul.net   forging knowledge

In article , dlharmon wrote: [...]

Depending on your local water supply, finish up the washing with distilled water. After the PCB is clean, leave it in a hot dry environment over night before you apply power.

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kensmith@rahul.net   forging knowledge

YESSSSS!!!!! Heed this warning!!!!

I, too, found out the hard way.

If you use no-clean flux then either do nothing else (after soldering) or clean the entire board. If you wash part of the board, after soldering, then ions will form nasty little electrically-conductive things called dendrites. Dendrites will short-out your electronics.

No-clean flux leaves an ugly looking residue, but it is non-conductive.

If you use other types of flux (other than no-clean) then clean the entire board after soldering.

Bob

I switched to all water soluble flux. Flux pen is great chips. Just saturate the pins and drag the iron tip over them. With plenty of flux solder snaps in place without smearing. You must wash off the water soluble flux thoroughly and shortly afterwards. It is very conductive and any residue will play havoc wit high impedance circuitry. Does that answer why the 32kHz clock does not start? If you have to interrupt the work, store it along with some desiccant in a airtight container. Humidity in air reacts with the flux residue and forms white crud that is difficult to remove. I use electric toothbrush for cleaning the boards.

Regards,

Boris Mohar

Got Knock? - see: Viatrack Printed Circuit Designs (among other things)

I use an old toothbrush and IPA, a few seconds of brushing removes all the flux.

Leon

i clean my pcb as follows:

1) clean with normal fuel car (in Italy we call it "benzina" ) with aid of a short-hair brush

2) after, clean with water and liquid soap (and brush)

3) be shure of removing all soap. It happens when disappears bubbles during brushing.

let warm for humidity removal. Sunlight is good. The aid of compressed air during 1) and 2) is useful.

bye - S.

Un bel giorno Sylvain Munaut digitò:

Someone says that a dish cleaner works pretty well. I haven't tried it though.

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asd

Is that with or without the optional blow torch igniter?

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James T. White

But probably not as bad as stuff getting stuck in the residue does :)

I have had RF board completely go nuts when flux residue remained after the wash process.

No clean means that though, no clean. It also means don't coat with any conformal coatings that use a solvent. Use a water-based coating instead.

The thread 'OT: Check out this idiot' on ABSE shows one technique.

Cheers Terry

[...]

Yes, the goal *IS* to remove the flux without removing the circuit in the process.

Me too + low noise amplifiers weren't + 5V regulator wasn't + high impedance input wasn't.

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kensmith@rahul.net   forging knowledge

"Ken Smith" a écrit dans le message de news:d1eqvf$c2k$ snipped-for-privacy@blue.rahul.net...

ROFL

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Thanks,
Fred.