How do you de-flux a PCB?

abenn

Senior Member
I've read several times that solder flux left on a joint, be it wire-to-wire or wire-to-PCB, can eventually cause corrosion. With that in mind I bought a flux-remover pen, but I'm not really happy with the way it works -- it just can't get into all the nooks and crannies on my boards.

Is there a cheaper way of removing the flux? Or is it not necessary with the "multicore" tin/lead solder I'm using? I'm thinking, for instance, is there a fluid in which I can bathe the boards, using a soft paintbrush to wash them, that won't harm the components?

On the other hand, does lacquering the board after assembly prevent corrosion by removing all access to air and moisture?
 

fernando_g

Senior Member
It all depends on the flux used.

If your flux remover chemical is not compatible with the flux, you can actually create a mess.

I strongly suggest that you use water-soluble flux. Then with warm water (about 45 to 50C) and a clean toothbrush, the flux will be completely removed.

Blow dry with a hair dryer. Then follow up by rinsing the board with de-ionized water to remove any hard mineral deposits left behind from the tap water.

The best PWB conformal coats are two-part urethane based. Although not as though as epoxy based, they can be removed to repair the circuit.
Don't use common RTV, which smells like vinegar, it can actually corrode some metals.
 

edmunds

Senior Member
The poor mans method is lots of dish detergent and warm water. Or window cleaner. Specialized stuff is much better. I use something called KONTAKT PCC made by KONTAKT CHEMIE. It costs around 10 eur and lasts a very long time even if I solder something every day.

Edmunds
 

Goeytex

Senior Member
I typically use isopropyl alcohol and a toothbrush. Denatured alcohol also works. Sometimes a run in hot water or even the dishwasher but only for FR4/Epoxy based boards (not laminated paper boards). Dry with compressed air then in the the oven set on warm. Avoid acetone, it is nasty stuff and can ruin some plastics.

For a cheap conformal coating I use "exterior" clear acrylic or urethane spray. The best conformal coatings are probably silicon based, but expensive.
 

premelec

Senior Member
I use ethanol with rosin / resin solder core fluxes and old tooth brush - sometimes mechanical dental picking before cleaning...
 

lbenson

Senior Member
On the other hand, and for hobby use only (if at all), in 9+ years of picaxe pcbs, and a good many dozens of boards, I've never cleaned off flux and don't know of a failure which could be attributed to that. Not so many of those boards have been running that entire time, but some have come close.

I am sure others have examples of problems.
 

Circuit

Senior Member
PCB at 5 yrs.jpg
This is a photo of a PICAXE board that I just photographed for you; it was constructed about five to six years ago.
As soon as my perf-board arrives I spray the copper surface with SK10 Flux aerosol (CRC Industries Europe, based in Belgium) to form a varnish-like surface. This product is described as a "protector, solder-active". After drying overnight I stack the board away in my stock until I need to use it - often many months later. The copper surface remains bright and there is a clear, hard lacquer layer visible. I just solder to the copper with "Future No Clean Cored Solder Wire" (Warton Metals). And that is it! The solder flows beautifully, no residue is visible and the boards and the solder joints stay clean for...well, perhaps forever; at least all my boards look like this one. I neither clean nor coat the surfaces after soldering and the solder seems to stay bright as well as the copper. I have never had any corrosion either.

Years ago I used cored solder and various fluxes and those boards did, of course, go green around the joints despite attempts at post-soldering cleaning; the copper tarnished and it all looked really amateur. The combination of this spray and this solder has given me countless joints on dozens of boards with minimum effort.
 

rq3

Senior Member
I've read several times that solder flux left on a joint, be it wire-to-wire or wire-to-PCB, can eventually cause corrosion. With that in mind I bought a flux-remover pen, but I'm not really happy with the way it works -- it just can't get into all the nooks and crannies on my boards.

Is there a cheaper way of removing the flux? Or is it not necessary with the "multicore" tin/lead solder I'm using? I'm thinking, for instance, is there a fluid in which I can bathe the boards, using a soft paintbrush to wash them, that won't harm the components?

On the other hand, does lacquering the board after assembly prevent corrosion by removing all access to air and moisture?
Not enough information. What solder? What flux? What components?
Water soluble flux can be removed with warm water. Ultrasonic bath is very effective. Secondary rinse in IPA (iso-propyl alcohol), and blow dry.
Rosin based flux can be removed with IPA. Ultrasonic bath is very effective. Secondary rinse in IPA and blow dry.

Some components are ultrasonic sensitive, and some are solvent sensitive. If you have a mix of both, you need to select a solder system that allows you to remove flux (or not, if appropriate), in a manner that won't harm either. Like all engineering, it's a balancing act.

"Multi-Core" solder was originally maufactured by Ersin, and is considered an RMA (Rosin Mildly Activated), solder flux. It is removed with IPA in critical applications, or the flux residue is ignored in commercial (consumer) applications.

Board coatings (lacquering) of any kind (urethane, silicone, acrylic) are a great idea IF:
1) The board is absolutely free of flux and other surface ionic contaminates prior to coating
2) You don't have to repair the board afterwards (although some silicones and urethanes are easier in this regard)
3) Your board doesn't have EXTREMELY LOW leakage current needs. At times air is the only acceptable insulator.

So. If your design has no ultrasonic or IPA sensitive components, and is soldered with RMA flux, scrub it with iso-propyl alcohol and a toothbrush, or IPA in an ultrasonic cleaner. Rinse it with fresh IPA, and then blow it dry gently with clean compressed air. If it's that important, wear clean surgeon's gloves to keep your finger oils and salts off the boards during handling, though now we're talking about guard ring layouts and the like.

Dipping or spraying the clean board with something like Krylon acrylic may help, or may hurt, depending on the board and it's final application. As I say, not enough information. Tell us more.
 

mikeyBoo

Senior Member
I use Acetone (finger-nail polish remover). It's free (if you live near females) & works great. Don't know if it damages the boards, my oldest still-used boards are ~30 years old, so need to wait a while for the answer to that question. Do need to avoid breathing the fumes or lighting a cigar as it may catch your head on fire.
If your boards are used outdoors, consider spraying with a clear-coat (although repairs may cause you to use offensive language).
 

abenn

Senior Member
Thanks for all the replies. I already use water-soluble flux when pre-tinning my boards, and wash it off with hot water. It's the flux that's in the solder I'm concerned about.

My solder is RS Components' own brand, and they claim it uses flux which with "a careful balance of resins and activators provides clear residues without the need for cleaning in most applications". So what applications might fall outside their definition of "most"?

I can't tell you any more other than my boards are a mixture of the "usual" components -- transistors, resistors, capacitors, PICAXE and various other integrated circuits -- both through-hole and surface-mounted. To date I usually haven't done any post-construction cleaning or coating, but one of my boards has visible blackening where the components go through the board, which made me wonder if I need to do anything more. From what you say, it sounds like maybe I didn't wash the initial paste flux off that one properly. Sounds like if I do the initial wash thoroughly, I don't need to do anything else after mounting components.
 

SteveDee

Senior Member
I think this issue is probably over-blown.

In the summer of 1972 I staggered back from the pub one evening and spent the next couple of hours building a Texan stereo amplifier: http://www.tempusfugit.ca/techwatch.ca/texan_amplifier.html

Despite multi-core solder flux, cigarette ash, and alcohol fumes from my beer-breath, this brilliant amp was still fully functional the final time that I switched it on, just prior to taking it to the local rubbish tip in December 2016. ...the loss still brings a tear to my eye!

Just how long to you want your hand-soldered circuit boards to last?
 

Jeremy Harris

Senior Member
I typically use isopropyl alcohol and a toothbrush. Denatured alcohol also works. Sometimes a run in hot water or even the dishwasher but only for FR4/Epoxy based boards (not laminated paper boards). Dry with compressed air then in the the oven set on warm. Avoid acetone, it is nasty stuff and can ruin some plastics.

For a cheap conformal coating I use "exterior" clear acrylic or urethane spray. The best conformal coatings are probably silicon based, but expensive.
Exactly my preferred system!

IPA is pretty good at getting even stubborn flux off, when used with a toothbrush, I've found, and doesn't damage components either. My technique is to have a small pot of IPA, just big enough to dip a toothbrush in and no bigger, then to hold the BCB at an angle, reverse side up, with one edge resting on a wad of kitchen roll, to absorb the mess.

IPA is cheap when bought in 5 litre drums, too, and useful for a lot of other cleaning and degreasing jobs, like degreasing copper-clad board before making the PCB.

I use the silicone conformal coatings when I feel there's a need, but they take a long time to air dry and ideally need to be over-baked to cure properly, so for indoor projects I don't bother with any coating.
 

Jeremy Harris

Senior Member
I think this issue is probably over-blown.

In the summer of 1972 I staggered back from the pub one evening and spent the next couple of hours building a Texan stereo amplifier: http://www.tempusfugit.ca/techwatch.ca/texan_amplifier.html

Despite multi-core solder flux, cigarette ash, and alcohol fumes from my beer-breath, this brilliant amp was still fully functional the final time that I switched it on, just prior to taking it to the local rubbish tip in December 2016. ...the loss still brings a tear to my eye!

Just how long to you want your hand-soldered circuit boards to last?
I still have the original Texas Instruments amp, that I built from the application note for the TIP series power transistors that spawned the Texan! It's here under my bench, over 40 years old now. The circuit boards I made were copies of the ones in the Texas App Note, and were made with tracing paper and then a resist felt pen.
 

SteveDee

Senior Member
...The circuit boards I made were copies of the ones in the Texas App Note, and were made with tracing paper and then a resist felt pen.
Oh I cheated. I sent Henry's Radio a cheque for £28 and they sent me back a complete kit. I was in a real hurry to wake up our neighbours with the sounds of Deep Purple!
 

techElder

Well-known member
Wow! You guys are old! :D

The only time I didn't use isopropyl alcohol, was when a customer auditor for my QA program was coming around. Then I put cans labeled "flux cleaner" out on the shop workbenches. :D
 

MartinM57

Moderator
...spent the next couple of hours building a Texan stereo amplifier: http://www.tempusfugit.ca/techwatch.ca/texan_amplifier.html
Well I never - I built one as well (*) at the time, complete with the slide-in wooden case :D. Can't recall where it is now though - I have an inkling that I deconstructed it, but I suppose I may come across it in the loft one day. Thanks for the memories...

(*) - replaced by a Quad 33 pre-amp (which I do still have) and a homemade power amp, that I can't recall the provenance of

(sorry for the OT)
 

fernando_g

Senior Member
Actually the words are: experienced veteran.

Speaking of coats, as I mentioned, Hard-epoxy ones are the very best, protection-wise. By a long shot.

But they are definitive coats....no way you can repair or modify these coated units.

BTW, I also listened to Deep Purple, from the Mark I lineup until Ritchie Blackmore left the group.
 

SteveDee

Senior Member
Actually the words are: experienced veteran...
I agree with texasclodhopper: "[very] old" is about right. Maybe "old-timer" is a good polite America expression that also works.

...BTW, I also listened to Deep Purple, from the Mark I lineup until Ritchie Blackmore left the group.
One night in the early 70's I stood behind the net curtain, backstage at the Rainbow, looking out at the audience over the shoulder of the drummer, Ian Paice. When they came off stage and waited to go back on for the encore, Ian Gillan stood one side of the stage, the others on the other side. Relationships were very bad by that time, but you would not have guessed it from their on-stage performance. Ian Gillan left the band a few months later.

...sorry, what's this got to do with Picaxe?


I haven't really noticed any flux deposits on vero-boards or pcbs that I've used a soldering iron on for a long time. In my experience (industrial and domestic) dark visible flux deposits often come down to; materials, equipment and/or technique.

Both the soldering iron and the type of solder/flux must be appropriate for the task. I use Ersin 309, 0.5mm diameter 60EN Multicore solder. 60EN means its 60% tin and the rest is mostly lead (I know, I should be using a non-lead alternative). The small diameter means you can heat it up quickly, and the small amount of flux generally just "steams" off. (I feel it is my responsibility to inhale in order to save the planet, but for the rest of you, that want to live a long and health life: DO NOT DO THIS!).

This type of solder becomes liquid above 180'C. But for any youngsters reading this, DON'T think of soldering as simply sticking components to boards using liquid solder. A proper joint results in molecular changes at the interface between solder and metal; a process known as wetting. Hence a bad joint is often known as a dry joint. You should apply heat to the joint long enough for the solder to flow successfully over component wire and copper track. And you must remove your length of solder wire before you remove the soldering iron.

Many modern flux compounds are not corrosive. Take a look at this for Multicore 309 which mentions cleaning and also describes the soldering process: http://www.farnell.com/datasheets/319742.pdf

Like I said in an earlier post, how long to you want your electronic assembly to last? Most of the stuff you build these days will be irrelevant in 10 or 20 years from now. And if you are making your own PCBs, it is the etching fluid you should be worrying about.
 

techElder

Well-known member
When I say "old", the word is certainly used in a self-deprecating manner! :D

As regards to cleaning off flux residues, I always told those that worked for me that it is much easier to find soldering defects when you are staring at a shiny clean board. I believe that to be the most compelling reason to "de-flux" with today's soldering materials and tools.
 

stan74

Senior Member
SteveDee:- "In the summer of 1972 I staggered back from the pub one evening and spent the next couple of hours building a Texan stereo amplifier"
I did that to :) epitaxial transistors..wow! It was a good amp. I still got the toroid, which was new then. Henry's Radio,Edgeware Rd.
In the uk you can't by isopropyl alcohol. Methanol is dearer than vodka and has blue piridine in it to stop us drinking it :)
I used white spirit paint thinner. It works and it's easily available.
 

Jeremy Harris

Senior Member
In the uk you can't by isopropyl alcohol. Methanol is dearer than vodka and has blue piridine in it to stop us drinking it :)
Yes you can, I buy it in 5 litre containers all the time. You can even buy it on ebay: http://www.ebay.co.uk/sch/i.html?_from=R40&_trksid=p2050601.m570.l1313.TR12.TRC2.A0.H0.Xisopropyl+alcohol.TRS0&_nkw=isopropyl+alcohol&_sacat=0 from loads of sellers. I usually buy it from a cheaper source, at under a tenner for 5 litres.

You can also buy clear methanol very easily, like this: http://www.ebay.co.uk/itm/25-LITRE-PURE-99-85-METHANOL-ACS-25L-BIODIESEL-VIRGIN-/201610278890?hash=item2ef0e8b7ea:g:wU8AAOSwPhdVN-HU , again I have a 5 litre drum of it sat here by my bench.
 

stan74

Senior Member
I meant in shops. Solvent abuse or as Americans say "get off on zoff" whatever that is..zoff medicine?
" again I have a 5 litre drum of it sat here by my bench."...and a pub cross the road :)
 

fernando_g

Senior Member
In the US, if one refers to something that is measured in Metric units, he/she is usually referring to some mood-ameliorating substances.

For everything else, there are Imperial units.
 

tmfkam

Senior Member
In general, I use standard 60/40 multicore solder and don't (normally) feel the need to clean the flux off.

If I've been de-soldering, whether I've used Chip-Quik or de-solder braid to remove the faulty component, I go over the area with a Stannol flux cleaning pen and then dry with a tissue before soldering the replacement in.

For new PCBs we assemble at work, I would normally not feel the need to clean them myself, other engineers possibly use a different soldering technique to me and those boards can be left with some unsightly flux residue. For those, we assess the components fitted and assemble the majority of the board, then clean them in an ultrasonic tank, first with some flux cleaner, rinse under the tap, place them in the ultrasonic tank filled with de-ionised water then dry with a heat gun. We then fit any components judged to be unsuitable for 'dunking' in the ultrasonic bath.

Both processes are really only to make the job look neat and tidy rather than for electrical stability, I've never had a problem where the flux in multicore solder has damaged a joint or PCB track over time.

When I was young and got my first soldering iron, my Dad, who was a welder/metalworker/forge hand by trade, got me some flux which was liquid. This all but allowed me to solder rusty nails to stainless steel! Trouble was, on PCBs it would eventually eat through any area that it had been in touch with. Eventually I realised and bought some 'real' electronics suitable solder. Still, the liquid flux did keep repair work coming in. It would take about 6-9 months to corrode a track so the customer was none the wiser, and I kept quiet.
 

abenn

Senior Member
OK guys, my first real electronics project was building a valve mono amplifier and pre-amplifier from a plan in Practical Electronics magazine -- got it finished just before stereo and transistors and copper-clad board became the thing :rolleyes:

Anyway, judging from the many responses to this post, many people seem to feel that post-soldering cleaning is not vital when using modern multicore solder, so I think I'll continue the way I have been for 60 years or so. The one blackened board I've had recently must have been, I think, from inadequate cleaning after initial tinning, for which I used a flux paste.

As for isopropyl alcohol, it seems to be available from many sources, including RS Online, Maplin, Amazon, etc. if I do decide I need it.

Thank you everyone.
 

Jeremy Harris

Senior Member
I meant in shops. Solvent abuse or as Americans say "get off on zoff" whatever that is..zoff medicine?
" again I have a 5 litre drum of it sat here by my bench."...and a pub cross the road :)
Also available in shops. I bought some methanol over the counter a year or so ago. My local chemist sells bottles of IPA, as does a model shop in town, but they are both expensive compared to buying it mail order.

There are no UK restrictions I'm aware of on selling either methanol or isopropyl alcohol at lab grade (i.e. not adulterated with a dye or other bittering agent) to anyone.
 

rq3

Senior Member
Also available in shops. I bought some methanol over the counter a year or so ago. My local chemist sells bottles of IPA, as does a model shop in town, but they are both expensive compared to buying it mail order.

There are no UK restrictions I'm aware of on selling either methanol or isopropyl alcohol at lab grade (i.e. not adulterated with a dye or other bittering agent) to anyone.
In the US, isopropanol (iso-propyl alcohol) is commonly referred to as "rubbing alcohol". It's what your personal trainer uses for your muscle rub-down after a tough day of soldering. It's easily available at any drug store (chemist?) in both 70% and 90% concentrations, diluted with water.

Methyl alcohol (methanol) is sold generally as "denatured" in hardware stores (mixed with nasty stuff so it's not pleasant to drink). Usually used for chaffing dish fuel, paint brush cleaning, and similar chores.

95% ethyl alcohol (190 proof ethanol, the drinkable stuff) is available in some liquor stores as Graves grain alcohol, or EverClear; both are brand names, and it's availability varies from state to state.

For de-fluxing, I stick to iso-propyl, since that's the solvent for the RMA rosin flux I prefer, and doesn't hurt metals or plastics. The other two alcohols don't work anywhere near as well, and dissimilar metals in methanol can electrolytically corrode VERY quickly!
 
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