On Fri, 17 Aug 2007 21:09:27 -0700, Smitty Two
wrote:

In article ,
Ross Herbert wrote:

On Fri, 17 Aug 2007 11:41:11 -0400, "Michael A. Terrell"
wrote:

David Farber wrote:

I occasionally see this residue where the components are
soldered.
Is this
flux? Something else?

http://www.pbase.com/image/83992679


That is flux residue left after a run through a PC board washer,
and
oven dry cycle.

Not in this case it isn't. This is the result of failing to clean
the
flux away at all after a manual part placement and soldering
procedure. Such instances may occur when an OEM does not trust that
reflow or wave soldering will be ultra reliable where heavy
component
leads are involved. The reflow time has to be adequate to ensure
proper wetting of the heavy leads but where other very small
componets
may be damaged by heat this is not recommended. The reflow time is
always set to ensure the most sensitive components will not be
damaged
by heat and this may require that heavy leaded components are
fitted
manually afterwards.

The result of inadequate cleaning after finished board manufacture
is
usually a much lighter white ring or anulus of residue, nothing as
thick or heavy as in the picture.

This is more like what you are talking about
http://www.residues.com/pdf/white_residue1.pdf

Ross, why do you bring up reflowing? Wave soldering, sure, but this
ain't no SMT board. And, a small transistor like that hardly
qualifies
as "heavy" leads. However, on another look, I agree that it was added
by
hand - but only because it's on the far side of the board.

You are right with regard to reflow - my mistake for mentioning it.
However, with regard to the component and reasons why it would have
been manually fitted, I was just giveing an example. It wasn't meant
to be the ONLY reason why the component might have been added manually
yo this particular board although I admit it would have been wise to
stick to this point.

Still, flux that is "not cleaned away at all" bears little
resemblance
to the picture.

In my experience it is. It is obvious that there has been some
"scratching around" in the residue which has removed some of it
(perhaps by the OP). In its natural state it would have been far more
regular and quite thick as it appears to me. I would wager that after
this component was manually soldered the operator didn't even so much
as wave cleaning fluid over it let alone attack it with a brush. After
adding a single component I doubt too many manufacturers would put the
whole board through a clean and dry cycle since it takes a lot longer
than doing it by hand immediately after soldering.

Again, I agree with those who say it's incompletely cleaned flux
residue
from an automated cleaning system.

Incompletely cleaned flux in my experience has always been more in
keeping with this effect
http://www.residues.com/pdf/white_residue1.pdf but a water soluble
flux applied by hand and which has not been cleaned at all is more
akin to the OP's situation.