What is this stuff on this pc board?

[David Farber]

It is NOT conformal coating. Besides you'll probably only ever see that on
high-end industrial or military gear.

Graham

I should mention that the photograph of the circuit board came out of a high
end Proceed amplifier. These amps costs big bucks and fail frequently. The
company offered no support to the independent guy. The authorized service
place in my area wanted $150 an hour plus parts to repair it. No surprise
that Proceed is out of business now.

The other amp I saw this residue in was an a/v receiver, a Marantz SR-8500.

Thanks for your replies.

 

[Eeyore]

It is not of manufacturing origin.

It looks like a (field? post-inspection?) repair -- the replacement of
"Q200". After soldering, the leads of Q200 have been snipped off with a
pair of flush wire cutters -- leaving a clean exposure of the copper of
the leads.

So, the residue is probably dictated by the brand and the quality of the
solder used in the repair.

That looks possible.

Note the difference in solder finish on those 3 pads compared to the 2 others.

Graham

 

[Ross Herbert]

warning.

When I double click the link it is incomplete.

Are you using Agent?

I referred the problem to Agent support and received this reply;

Hello, Ross.

Your problem has been noted to development.

The URL recognition is a RegEx in the agent.ini file, it's the key
"Pattern6". Unfortunately, I don't know RegEx well enough to suggest
a modification myself.

 

[Ross Herbert]

That looks possible.

To anyone who knows anything about electronics soldering and or pcb
populating it is very obvious that this IS what happened.

 

[Ross Herbert]

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

 

[Smitty Two]

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.

 

[Michael A. Terrell]

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, we manufactured both surface mount and through hole boards,
plus some items like connectors were hand soldered on our surface mount
PC boards. We had a VERY high standard of cleaning, because most of our
equipment was sold to the aerospace industry. I've seen probably every
possible defect in a new PC board, including a batch we received with a
missing internal power plane. I have seen this exact type of residue on
boards that just came out of the dryer, after being washed.


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

 

[Ross Herbert]

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.

 

[Ross Herbert]

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.

 

[Eeyore]

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.

I have seen 'cold joint' issues with TO-220 devices.

Graham

 

[Michael A. Terrell]

I have seen 'cold joint' issues with TO-220 devices.

Sure, from crappy board houses.

--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida