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Isopropyl alcohol + rosin flux residue --> white gunk?

R

Rob

Jan 1, 1970
0
Does anyone have any idea on what the composition of the white residue is
that is left behind on PCBs when IPA is used to remove the flux residue. Is
is inert? / hygroscopic?

I have noticed it seems to be worse when methylated spirits is used in place
of IPA.

TIA
rob

PS -I agree more appropriate reagents exist for flux removal!
 
C

CFoley1064

Jan 1, 1970
0
Does anyone have any idea on what the composition of the white residue is
that is left behind on PCBs when IPA is used to remove the flux residue. Is
is inert? / hygroscopic?

I have noticed it seems to be worse when methylated spirits is used in place
of IPA.

TIA
rob

PS -I agree more appropriate reagents exist for flux removal!

This sounds more like an organic flux you have here. If so, it's not inert --
it can combine with humidity to start etching away circuit board traces or
anything else on the board that gets hot. (particularly high current traces
under SMT IC packages). There can also be conductivity problems..

For a hobbyist/non-production issue, use Palmolive Green or other detergent
with very warm water, followed by an oven dry at, say, 60C. For a production
issue, contact the manufacturer of the flux. That's what they're there for.

Good luck.
Chris
 
R

Rob

Jan 1, 1970
0
This sounds more like an organic flux you have here. If so, it's not inert --
it can combine with humidity to start etching away circuit board traces or
anything else on the board that gets hot. (particularly high current traces
under SMT IC packages). There can also be conductivity problems..

For a hobbyist/non-production issue, use Palmolive Green or other detergent
with very warm water, followed by an oven dry at, say, 60C. For a production
issue, contact the manufacturer of the flux. That's what they're there for.

Good luck.
Chris

I neglected to mention - the solder is Multicore 362 - Rosin activated flux
according to catalog blurb.
rob
 
N

Nico Coesel

Jan 1, 1970
0
Rob said:
Does anyone have any idea on what the composition of the white residue is
that is left behind on PCBs when IPA is used to remove the flux residue. Is
is inert? / hygroscopic?

No idea. I noticed the same problem though. Sometimes I washed boards
with hot water and dried them afterwards using compressed air.
 
T

Tilmann Reh

Jan 1, 1970
0
Rob said:
Does anyone have any idea on what the composition of the white residue is
that is left behind on PCBs when IPA is used to remove the flux residue. Is
is inert? / hygroscopic?

I have noticed it seems to be worse when methylated spirits is used in place
of IPA.

This problem is due to the nature of the flux.
Normally it consists of an alcohol mixture, the flux itself, and
an activator (an acidic salt usually). The alcohols used are
normally ethyl and isopropyl. They have different properties,
with respect to solving polar and nonpolar stuff. The activator
salt must be solved with a polar solvent, while the flux needs
a nonpolar solvent.

After having soldered a board, there are some residues of flux
that also contain small particles of the activator salt. As long
as you leave the board this way, these particles are covered by
the flux and do not cause any harm.

Now if you use ethylic alcohol to wash the flux off, the activator
salt does not get solved (since it needs a polar solvent), so it
stays on the board. That's the white residues you can see after
washing with an improper solvent.

Now these salt grains can catch humidity and start their acidic
work again, causing damage to the board.

To overcome this problem, use a solvent that has polar and
nonpolar components to wash the complete flux and activator
from the board. AFAIK, a 50:50 mixture of ethyl and isopropyl
is commonly used. Alternatively, you could wash in two steps:
remove the flux with alcohol, then wash off the activator with
water.

(Maybe I confused polar/nonpolar for the two alcohols, but
that's the principle.)

--
Dipl.-Ing. Tilmann Reh
Autometer GmbH Siegen - Elektronik nach Maß.
http://www.autometer.de

==================================================================
In a world without walls and fences, who needs Windows and Gates ?
(Sun Microsystems)
 
B

Baphomet

Jan 1, 1970
0
Rob said:
Does anyone have any idea on what the composition of the white residue is
that is left behind on PCBs when IPA is used to remove the flux residue. Is
is inert? / hygroscopic?

I have noticed it seems to be worse when methylated spirits is used in place
of IPA.

TIA
rob

PS -I agree more appropriate reagents exist for flux removal!

For military work, we used to use Ethyl Acetate. It was really effective,
left little residue, evaporated quickly, but was a bit pricey. Acetone works
but not as well.
 
S

Sergey Kubushin

Jan 1, 1970
0
Baphomet said:
For military work, we used to use Ethyl Acetate. It was really effective,
left little residue, evaporated quickly, but was a bit pricey. Acetone works
but not as well.

50:50 mix of Xylene and Ethyl Alcohol is fine for such a job and its darn
cheap.
 
R

Rob

Jan 1, 1970
0
Hello Tilmann, thank you for your reply - it contains the information I was
trying to get. It supports my argument to use a either a flux remover
intended for the purpose or an alternative that works on both elements of
the residue as you stated.

Thanks to others for replies also.

regards
rob
 
W

Walter Harley

Jan 1, 1970
0
Baphomet said:
For military work, we used to use Ethyl Acetate. It was really effective,
left little residue, evaporated quickly, but was a bit pricey. Acetone works
but not as well.

Acetone? Wouldn't want to get it around any of the plastic bits...

On a hobby (dozen boards at a time) basis, I've been using flux remover,
which is not horribly expensive on a small scale. Have also tried washing
first with isopropanol, then distilled water; this works but is slower.

I put the flux remover into an ultrasonic cleaner - it's very fast and
doesn't take much flux remover. Works great. (I still rinse afterwards
with distilled water, though, just for the heck of it.)
 
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