Author Topic: Leaving flux on the pcboard  (Read 3695 times)

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Offline smbaker

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Leaving flux on the pcboard
« on: April 22, 2017, 04:46:31 am »
I have a computer that I soldered up using Kester 44 solder. According to the distributor, "Rosin "44"® is a high activity RA core flux designed for excellent instant wetting action, even on nickel surfaces. Although "44"® is a RA-based material, the residues are non-corrosive if not cleaned."

I usually don't bother to clean this stuff off my boards, and to my knowledge it hasn't caused me problems before. However, the computer has recently started to act up, and I'm wondering if not cleaning the flux could be causing any issue? The clock rate is 4.77 Mhz. It's been about two months since the soldering was performed.

Thanks,
Scott
 

Offline Pitrsek

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Re: Leaving flux on the pcboard
« Reply #1 on: April 22, 2017, 07:02:44 am »
On several occasion I'v discovered problems that were caused by flux(offsets/leakage - analog stuff ). So since then, I clean my boards regularly. Looks nicer too.
 

Offline David Hess

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Re: Leaving flux on the pcboard
« Reply #2 on: April 23, 2017, 04:13:09 pm »
Kester 44 is my favorite flux for rework or assembling with old parts and boards which may have tarnished in storage.  New production can get by with a less aggressive "no-clean" flux.

With a digital board it should not matter except maybe for an oscillator which uses an external crystal.  Most analog circuits are not that sensitive but for the ones that are, the flux needs to be cleaned off no matter what kind is used.
 

Offline dimkasta

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Re: Leaving flux on the pcboard
« Reply #3 on: April 23, 2017, 05:08:46 pm »
Just make cleaning part of your process. It just takes a few minutes and it will eliminate a potential source of issues that can keep you wondering. Do it just for the peace of mind.
Plus a clean pcb looks far better, so satisfaction and pride increases too :)
 

Online BBBbbb

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Re: Leaving flux on the pcboard
« Reply #4 on: April 23, 2017, 05:34:54 pm »
Does anyone here have any experience with those specialized can sprays for flux cleaning?
I'm thinking of giving a Kontakt PCC a go (spray from Kontakt Chemie), but my PCB work is not so frequent so I'm not sure when I'll get my lazy ass to the shop to buy it.
 

Offline dimkasta

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Re: Leaving flux on the pcboard
« Reply #5 on: April 23, 2017, 06:04:03 pm »
Does anyone here have any experience with those specialized can sprays for flux cleaning?
I'm thinking of giving a Kontakt PCC a go (spray from Kontakt Chemie), but my PCB work is not so frequent so I'm not sure when I'll get my lazy ass to the shop to buy it.

I do not like sprays because the tend to be messy. And you never know what component might not like it.
Whatever you use, try to control its quantity and application with a comfortable brush.

I use isopropyl alcohol applied locally with an antistatic brush, and wipe it off with lint-free wipes (carefully not to get any on coils and such)
You should be able to get it easily from a local drug store.
 

Online BBBbbb

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Re: Leaving flux on the pcboard
« Reply #6 on: April 23, 2017, 06:17:26 pm »
I already use IPA or ethanol, and for something more stubborn acetone, I just thought that these sprays might be good.
They come with a brush attached and it seems that that might absorb the pressure from the can, but if not, than that does not look like a smart idea to use on a pcb.
 

Offline boffin

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Re: Leaving flux on the pcboard
« Reply #7 on: April 23, 2017, 06:20:32 pm »
I use a 50/50 mix of isopropyl & acetone.
 

Offline tooki

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Re: Leaving flux on the pcboard
« Reply #8 on: April 24, 2017, 07:23:43 pm »
Does anyone here have any experience with those specialized can sprays for flux cleaning?
I'm thinking of giving a Kontakt PCC a go (spray from Kontakt Chemie), but my PCB work is not so frequent so I'm not sure when I'll get my lazy ass to the shop to buy it.
I use Kontakt PCC ("Kontakt LR" in German) myself, and find that it works quite a bit better than pure IPA. (It's a blend of IPA and hydrocarbon solvent.) I would just add a can or two of it to your next order from a big electronics supplier.

That said, because of its cost, I tend to do a first cleaning using a cheap IPA/ethanol blend (which has bittering agent that could potentially cause problems), then a final cleaning with Kontakt PCC.

With the can's included brush attached, it's no messier than using alcohol in a squirt bottle.
 
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Online BBBbbb

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Leaving flux on the pcboard
« Reply #9 on: April 24, 2017, 07:32:32 pm »
@tooki
What about the spray pressure, does it get absorbed by the attached brush?

hmmm, but on the other hand, I guess we put more stress on the components via brush while cleaning, than moderate spray application might do.
« Last Edit: April 24, 2017, 07:34:32 pm by BBBbbb »
 

Offline tooki

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Re: Leaving flux on the pcboard
« Reply #10 on: April 24, 2017, 07:48:23 pm »
Yeah, the brush nozzle turns it into sort of a drizzle. It doesn't hit the board with any meaningful pressure.

You need to brush anyway. The flux doesn't just rinse off, it needs a bit of mechanical agitation.
 

Offline David Hess

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Re: Leaving flux on the pcboard
« Reply #11 on: April 24, 2017, 11:50:44 pm »
When I need a board to be really clean, then I use an ultrasonic cleaner.  Otherwise I like to scrub with a toothbrush or for small areas like when I do rework, I use cotton swabs.

Acetone is pretty hard on some things.  I have some flux thinner which is 50/50 IPA and toluene but toluene is also pretty hard on some things.

Spray flux removers are nice but expensive.
 

Offline rdl

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Re: Leaving flux on the pcboard
« Reply #12 on: April 25, 2017, 01:24:33 am »
In the US the "bittering agent" in ethanol is usually just some other organic solvent and is generally referred to as "denaturant", hence "denatured alcohol". The purpose is simply to render the ethanol undrinkable so that it can be sold cheaply and not taxed as if it was liquor. The amount of denaturant used varies, but 5-10% is common. Isopropanol at 5% was used in the ethanol we bought at one place of employment. Check the label or MSDS of whatever ethanol you buy just to be sure, but most likely the denaturant will not cause any problems.

 

Offline tooki

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Re: Leaving flux on the pcboard
« Reply #13 on: April 25, 2017, 12:01:45 pm »
In the US the "bittering agent" in ethanol is usually just some other organic solvent and is generally referred to as "denaturant", hence "denatured alcohol". The purpose is simply to render the ethanol undrinkable so that it can be sold cheaply and not taxed as if it was liquor. The amount of denaturant used varies, but 5-10% is common. Isopropanol at 5% was used in the ethanol we bought at one place of employment. Check the label or MSDS of whatever ethanol you buy just to be sure, but most likely the denaturant will not cause any problems.
You misunderstand. I'm not using the term "bittering agent" as a generic and inaccurate synonym for "denaturant". I know exactly what denaturing is, its purpose, and various ways it's accomplished. Adding non-drinkable solvents (which may or may not be bitter) is one way. It's not the only way.

I specifically said "bittering agent" because that's specifically what I am talking about. It's not a solvent, it's a chemical additive. (Its name is "denatonium", presumably derived from precisely this use case.) It leaves aggressively bitter-tasting residue on anything - readily noticeable on fingers even after a regular hand washing. (It takes a surgeon-style hand washing to really get it off.) I have no information on the electrical properties of denatonium residues, so for anything permanent (or sensitive, like high impedance areas of multimeter boards) I use proper flux remover.

Yes, using such cheap industrial alcohol is crap, but if you saw how expensive IPA is here, you'd use cheaper alternatives, too, where possible! :p (It's actually sold as decorative fireplace fuel.) IPA costs so much, it's actually only insignificantly cheaper than commercial flux remover like the Kontakt PCC!!!  |O
« Last Edit: April 25, 2017, 12:03:45 pm by tooki »
 

Online BBBbbb

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Re: Leaving flux on the pcboard
« Reply #14 on: April 25, 2017, 02:01:04 pm »
Yes, using such cheap industrial alcohol is crap, but if you saw how expensive IPA is here, you'd use cheaper alternatives, too, where possible! :p (It's actually sold as decorative fireplace fuel.) IPA costs so much, it's actually only insignificantly cheaper than commercial flux remover like the Kontakt PCC!!!  |O
Really?
I get 1l of 99% IPA for about 8.5eur vs around 12eur for a single can of PCC(LR), and I can find it for a few euros less, but this is pharma production, and I'm sure of the purity.
I use IPA and acetone for laser optics cleaning, so any impurities are easily spotted.

How come you can't find it cheaper online from DE, I've noticed that some sellers of those kind of sensitive substances in Germany do ship to CH and A, but not elsewhere.
 

Offline tooki

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Re: Leaving flux on the pcboard
« Reply #15 on: April 25, 2017, 02:19:57 pm »
The pharmacies here charge around €25/l for "technical grade" IPA. I haven't found a cheaper source that sells to consumers.

I also haven't found any places readily willing to ship it from Germany. Moreover, if I understand the law correctly (a dubious assumption!) it appears that one would have to pay a VOC emissions compensation fee, which seems to be CHF3/kg.* Some vendors seem to indicate they ship to CH, but don't know about the VOC fee, or how and when one is to pay it.

So €14 for a 400ml can of Kontakt LR/PCC (or €10 for cheaper competing product I'll try next) isn't that much more, considering it also performs a lot better than straight IPA.

*The law says that VOCs sold for the purposes of burning for fuel are exempt, which is probably part of why the fireplace alcohol I bought is less than half the cost of the pharmacy IPA.
 

Offline mariush

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Re: Leaving flux on the pcboard
« Reply #16 on: April 25, 2017, 02:23:19 pm »
You can buy 5 liter cans of IPA from TME.eu for 20$ ... add maybe 5-10$ for shipping, and since seller is in Europe, they probably have several shipping options , one which should send  by train or truck to you (if IPA is considered too flammable to ship by air)

Here's link : http://www.tme.eu/en/details/ipa-5000ml/cleaning-maintaining-products/ag-termopasty/kontakt-ipa-_-5000ml/

One liter bottles are less than 5$ : http://www.tme.eu/en/details/ipa-1000ml/cleaning-maintaining-products/ag-termopasty/kontakt-ipa-_-1000ml/

See the whole cleaning and maintaining solutions category as well (including a bunch of Kontakt products) : http://www.tme.eu/en/katalog/#id_category=100098&page=1&s_field=artykul&s_order=ASC
« Last Edit: April 25, 2017, 02:28:11 pm by mariush »
 

Offline tooki

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Re: Leaving flux on the pcboard
« Reply #17 on: April 25, 2017, 02:25:45 pm »
And yes, as an American, the price of (solvent) alcohol here shocks me. In USA, a liter of 91% IPA is about €2.50 in any pharmacy or department store. 99% IPA on Amazon.com is about €5/l when bought by the gallon.
 

Offline tooki

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Re: Leaving flux on the pcboard
« Reply #18 on: April 25, 2017, 02:35:55 pm »
You can buy 5 liter cans of IPA from TME.eu for 20$ ... add maybe 5-10$ for shipping, and since seller is in Europe, they probably have several shipping options , one which should send  by train or truck to you (if IPA is considered too flammable to ship by air)

Here's link : http://www.tme.eu/en/details/ipa-5000ml/cleaning-maintaining-products/ag-termopasty/kontakt-ipa-_-5000ml/

One liter bottles are less than 5$ : http://www.tme.eu/en/details/ipa-1000ml/cleaning-maintaining-products/ag-termopasty/kontakt-ipa-_-1000ml/

See the whole cleaning and maintaining solutions category as well (including a bunch of Kontakt products) : http://www.tme.eu/en/katalog/#id_category=100098&page=1&s_field=artykul&s_order=ASC
I wonder whether they actually ship those items to Switzerland.

And as an EU company, there's also the issue of customs fees... any order over CHF62 value (including shipping) is subject to 8% VAT -- plus a fee of between about CHF15-35 just to calculate how much VAT you owe...  |O |O |O

Amazon handles its own customs clearance, so ordering from them has no surprise fees - but they won't ship chemicals to Switzerland. (Same with ELV, Conrad, and Reichelt, as best I can tell.) It remains unclear to me how Farnell/Mouser/Digikey handle Swiss customs. There are some indications that they handle it, but it's not clear.
 

Offline tooki

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Offline rdl

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Re: Leaving flux on the pcboard
« Reply #20 on: April 25, 2017, 03:15:18 pm »
Interesting. I knew of bittering agents, but was not aware that any were sometimes used as one of the denaturant components in ethanol. I don't recall ever coming across "denatonium" as an ingredient of any industrial grade ethanol that was used in my formulations. At the typical levels I see quoted it would only be considered a trace amount anyway and probably would not appear on a MSDS. There are probably much worse things in 99% pure grade alcohols, and industrial coatings rarely require anything better.

As an fyi, when I left the coatings business in 2008 we were paying about $0.50 per pound for ethanol, purchased in quantities of 5000-10000 US gallons.

 
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Offline macboy

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Re: Leaving flux on the pcboard
« Reply #21 on: April 25, 2017, 03:19:44 pm »
I buy 99% IPA from Costco, for only $10 CAD (~$7.50 USD) for 2 litres (4 of 500 ml bottles). The key to cleaning flux is to remove the dirty solvent from the board before it evaporates. Blotting with paper towel is effective as a first pass. I usually then scrub with more fresh IPA and a clean brush, then use compressed air (real air, not canned duster spray) to blast the residue off the board.

I also use 90% IPA for various things, especially for cleaning the exterior of newly acquired old equipment. The extra water content acts as an effective solvent for many types of 'dirt' that IPA won't even touch. Pure distilled water can also be quite useful. Being completely free of ions, it is a much more aggressive solvent than tap water, as if it's eager to dissolve something.
 
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Offline tooki

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Re: Leaving flux on the pcboard
« Reply #22 on: April 25, 2017, 03:47:21 pm »
If only we had Costco (or anything distantly like it) here... ::sigh::
 

Online BBBbbb

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Re: Leaving flux on the pcboard
« Reply #23 on: April 25, 2017, 04:43:41 pm »
Interesting. I knew of bittering agents, but was not aware that any were sometimes used as one of the denaturant components in ethanol.
When we were kids we were told they put methanol so we would go blind if we tried it.

It would be possible for me to get pure ethanol from specialized producers of such chemicals, but have to go through ordering as a business, and I really don't see why I would go through the hustle when IPA and acetone is easily available.
 

Online 2N3055

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