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.

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

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