SMD soldering : Clearing flux residue ?

Sylvain Munaut · Mar 16, 2005

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

Robert Baer · Mar 16, 2005

Sylvain Munaut wrote:

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
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.

John Woodgate · Mar 16, 2005

I read in sci.electronics.design that Robert Baer
<robertbaer@earthlink.net> wrote (in <yw0_d.12439$cN6.9180@newsread1.new
s.pas.earthlink.net&gt

about 'SMD soldering : Clearing flux residue ?',
on Wed, 16 Mar 2005:

That being said, i have yet to find a relatively safe solvent for
rosin; isopropyl soak method removes most, but not all of it.

Have you tried air agitation (or ultrasonics)? Air agitation performs a
similar function in PCB etching, after all.
--
Regards, John Woodgate, OOO - Own Opinions Only.
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

Brian · Mar 16, 2005

"John Woodgate" <jmw@jmwa.demon.contraspam.yuk> wrote in message
news:LpKHc5GHjKOCFwBt@jmwa.demon.co.uk...

I read in sci.electronics.design that Robert Baer
robertbaer@earthlink.net> wrote (in <yw0_d.12439$cN6.9180@newsread1.new
s.pas.earthlink.net&gt about 'SMD soldering : Clearing flux residue ?',
on Wed, 16 Mar 2005:

That being said, i have yet to find a relatively safe solvent for
rosin; isopropyl soak method removes most, but not all of it.

Have you tried air agitation (or ultrasonics)? Air agitation performs a
similar function in PCB etching, after all.
--
Regards, John Woodgate, OOO - Own Opinions Only.
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

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

Acetone and a toothbrish works, too.

dlharmon · Mar 16, 2005

Sylvain Munaut wrote:

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

Try water soluble solder and flux. I use kester 331 solder and a
2331ZX flux pen. It cleans up easily with hot water. I have some
notes on my webpage at
http://dlharmon.com/smd.html

Darrell Harmon
http://dlharmon.com/sbc.html

Ken Smith · Mar 17, 2005

In article <yw0_d.12439$cN6.9180@newsread1.news.pas.earthlink.net>,
Robert Baer <robertbaer@earthlink.net> wrote:

Sylvain Munaut wrote:

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
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.

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.

That being said, i have yet to find a relatively safe solvent for
rosin; isopropyl soak method removes most, but not all of it.

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.

--
--
kensmith@rahul.net forging knowledge

Ken Smith · Mar 17, 2005

In article <VLudnQsI1v8-XaXfRVn-3A@centurytel.net>,
Brian <brian@w3gate.com> wrote:
[...]

Acetone and a toothbrish works, too.

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

--
--
kensmith@rahul.net forging knowledge

Ken Smith · Mar 17, 2005

In article <1111015686.788705.320930@g14g2000cwa.googlegroups.com>,
dlharmon <mail@dlharmon.com> wrote:
[...]

Try water soluble solder and flux. I use kester 331 solder and a
2331ZX flux pen. It cleans up easily with hot water. I have some
notes on my webpage at
http://dlharmon.com/smd.html

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.

--
--
kensmith@rahul.net forging knowledge

Bob · Mar 17, 2005

"Ken Smith" <kensmith@green.rahul.net> wrote in message
news:d1arsc$svl$1@blue.rahul.net...

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.

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

giorgi · Mar 17, 2005

Sylvain Munaut wrote:

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 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.

Leon Heller · Mar 17, 2005

"Sylvain Munaut" <tnt_at_246tNt_dot_com@reducespam.com> wrote in message
news:42388bba$0$28062$ba620e4c@news.skynet.be...

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 ?

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

Leon

Boris Mohar · Mar 17, 2005

On 16 Mar 2005 15:28:06 -0800, "dlharmon" <mail@dlharmon.com> wrote:

Try water soluble solder and flux. I use kester 331 solder and a
2331ZX flux pen. It cleans up easily with hot water. I have some
notes on my webpage at
http://dlharmon.com/smd.html

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) http://www.viatrack.ca

dalai lamah · Mar 17, 2005

Un bel giorno Sylvain Munaut digitň:

But after soldering there is a lot of flux left, how can I
get rid of it properly ?

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

--
asd

Terry Given · Mar 18, 2005

Sylvain Munaut wrote:

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

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

Cheers
Terry

James T. White · Mar 18, 2005

"Terry Given" <my_name@ieee.org> wrote in message
news:Azq_d.10697$1S4.1124781@news.xtra.co.nz...

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

Is that with or without the optional blow torch igniter?

--
James T. White

Brian · Mar 18, 2005

"Ken Smith" <kensmith@green.rahul.net> wrote in message
news:d1arus$svl$2@blue.rahul.net...

In article <VLudnQsI1v8-XaXfRVn-3A@centurytel.net>,
Brian <brian@w3gate.com> wrote:
[...]
Acetone and a toothbrish works, too.

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

--
--
kensmith@rahul.net forging knowledge

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.

Brian · Mar 18, 2005

"Bob" <nimby1_notspamm_@earthlink.net> wrote in message
news:Og7_d.12846$cN6.1288@newsread1.news.pas.earthlink.net...

"Ken Smith" <kensmith@green.rahul.net> wrote in message
news:d1arsc$svl$1@blue.rahul.net...

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.

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

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.

Ken Smith · Mar 18, 2005

In article <q-6dnTm3vuC-xqffRVn-ig@centurytel.net>,
Brian <brian@w3gate.com> wrote:

"Ken Smith" <kensmith@green.rahul.net> wrote in message
news:d1arus$svl$2@blue.rahul.net...
In article <VLudnQsI1v8-XaXfRVn-3A@centurytel.net>,
Brian <brian@w3gate.com> wrote:
[...]
Acetone and a toothbrish works, too.

With film capacitors, acetone will often change their value slightly.
[...]
But probably not as bad as stuff getting stuck in the residue does

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

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

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

--
--
kensmith@rahul.net forging knowledge

Fred Bartoli · Mar 18, 2005

"Ken Smith" <kensmith@green.rahul.net> a écrit dans le message de
news:d1eqvf$c2k$3@blue.rahul.net...

In article <q-6dnTm3vuC-xqffRVn-ig@centurytel.net>,
Brian <brian@w3gate.com> wrote:

"Ken Smith" <kensmith@green.rahul.net> wrote in message
news:d1arus$svl$2@blue.rahul.net...
In article <VLudnQsI1v8-XaXfRVn-3A@centurytel.net>,
Brian <brian@w3gate.com> wrote:
[...]
Acetone and a toothbrish works, too.

With film capacitors, acetone will often change their value slightly.
[...]
But probably not as bad as stuff getting stuck in the residue does

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

ROFL

--
Thanks,
Fred.

SMD soldering : Clearing flux residue ?

Sylvain Munaut

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