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May 2007

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Subject:
From:
Bev Christian <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Bev Christian <[log in to unmask]>
Date:
Wed, 23 May 2007 08:47:15 -0400
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I would be careful with the latter use of a soldering iron!  A well
known gastro-intestinal specialist came to the medical school at the
University of Toronto and gave a very enlightening presentation on
farts.  (He generally called them anal emissions.)  He said there was
one case where they had been doing surgery in that general area and the
anesthetised patient passed gas as they went to cauterize and the
resulting explosion blew the surgeons back against the wall and tore a 5
inch gash in the poor fellow's large intestine.  They had to do
emergency surgery and the guy woke up a tad sorer than he expected.

I read this in the Canadian edition of Time Magazine and it made such an
impression on me I have never forgotten it.
Bev 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Stadem, Richard D.
Sent: Wednesday, May 23, 2007 8:38 AM
To: [log in to unmask]
Subject: Re: [TN] Flux residue, burnt flux

Quite often, the small amounts of burnt flux or other particulates are
from using the solder irons to perform operations they were not intended
to do, such as shrinking tubing on wires, conformal coat removal, epoxy
removal, performing artistic designs in wood while the boss is not
looking, hemmorhoid removal........ 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Brian Ellis
Sent: Wednesday, May 23, 2007 2:38 AM
To: [log in to unmask]
Subject: Re: [TN] Flux residue, burnt flux

I'm sure that an eminent co-contributor to this forum will tell you, "it
depends". If the flux is truly burnt, i.e., black, this indicates
pyrolysis, which is a fancy word meaning decomposed by heat. Pyrolysis
indicates that the residues have split apart into numerous compounds,
leaving carbon-rich stuff. Elemental carbon can be an electrical
conductor; do you want conducting particles in your assembly? They may
appear fixed in place now, but will they remain so during the life of
the equipment?

More important, WHY are they there? It may be because the operators
don't keep the bits of their irons clean. Do they wipe them on a wet
sponge before each joint is made? It may be that the time/temperature
conditions of the joint being made are far from optimal. It may be lack
of adequate training of the operators. I can't tell. Whatever,
prevention is better than cure; a lttle research into the causes may
give you the answer.

As to flux flow, maybe your solder wire simply has too much flux. Some
manufacturers allow you to choose the percentage. Yes, it is easier to
solder with an excess. It's a compromise.

What you have not told us is the essential information: what kind of
assemblies are you making. You can obviously be more tolerant of
imperfections if you are making toys than if you are making inertial
guidance or satellite systems. Probably you are somewhere between thes
extremes. "It depends"!

Brian

Sue Powers-hartman wrote:
> We fight a constant battle with operators leaving burnt flux in 
> joints. Maybe only a small speck, but drives the inspectors nuts.  The

> way I read JStd-001D, if they can not see it at referee inspection
power, they have to accept it.
> How dangerous is this burnt flux to the PWB?  If it's not seen at 
> inspection power and left on the board, what happens.  Also, what
about no clean flux?
> Our solder training video says that if no clean flux runs out to far 
> and is not heat activated, it can cause problems. Operators watch this

> video, but somehow do not get this. They say that it's no clean, they
can leave it all on.
> I keep saying that this can be a problem, and then they ask me, how 
> far out can the flux be away from the joint before it's unacceptable.
> 
> Wow, I'm glad I found this forum, I have so many questions to ask you
guys.  
> Anyway, thanks for the help on this subject.
> 
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