I know Scott D mentioned to clean the circuit boards really well to remove
the flux because over time it can absorb moisture and cause problems.
(Scott, correcting me if I'm wrong I'm sure you will. Sincerely, Yoda)

So is it only a problem with circuits that handle very low/sensitive
voltages or is it also of concern for other circuits, like mic pres? What
about power amps etc?

Thanks!

--
John L Rice

John L Rice wrote:
I know Scott D mentioned to clean the circuit boards really well to remove
the flux because over time it can absorb moisture and cause problems.
(Scott, correcting me if I'm wrong I'm sure you will. Sincerely, Yoda)

So is it only a problem with circuits that handle very low/sensitive
voltages or is it also of concern for other circuits, like mic pres? What
about power amps etc?

It's always a good idea to remove excessive flux. That doesn't mean you
have to vapor-clean every repair job that you do, but just use your
head. Look at the joint and if you can see flux, clean it off. Then
look closer to make sure that it's really soldered. If you don't have
the joint heated adequately, you might have things glued together with
nothing but flux. This is called a "flux joint."

Of course if you're dealing with high impedance circuitry such as is
found in the impedance converter in a condenser mic, or even tube grid
circuits, you want to be particularly careful about not leaving gobs of
flux. Flux gets sticky, and when it does, collects crud, which, when it
gets damp, conducts electricity in directions that it's not supposed to
go.

Just be neat. That's not asking too much.

"Mike Rivers" wrote in message
oups.com...

John L Rice wrote:
I know Scott D mentioned to clean the circuit boards really well to
remove
the flux because over time it can absorb moisture and cause problems.
(Scott, correcting me if I'm wrong I'm sure you will. Sincerely, Yoda)

So is it only a problem with circuits that handle very low/sensitive
voltages or is it also of concern for other circuits, like mic pres? What
about power amps etc?

It's always a good idea to remove excessive flux. That doesn't mean you
have to vapor-clean every repair job that you do, but just use your
head. Look at the joint and if you can see flux, clean it off. Then
look closer to make sure that it's really soldered. If you don't have
the joint heated adequately, you might have things glued together with
nothing but flux. This is called a "flux joint."

Of course if you're dealing with high impedance circuitry such as is
found in the impedance converter in a condenser mic, or even tube grid
circuits, you want to be particularly careful about not leaving gobs of
flux. Flux gets sticky, and when it does, collects crud, which, when it
gets damp, conducts electricity in directions that it's not supposed to
go.

Just be neat. That's not asking too much.

Hi Mike,

Yes, I like neatness and I especially expect it when I'm paying a lot of
money for gear that is considered 'pro' level.

This came up from a discussion on another forum. Someone commented that
they thought the workmanship of a particular piece of audio gear was not as
good as they thought it should be. It was defended that there were problems
in the past but the model I purchased a couple months ago struck me as not
being 'top notch' in my humble opinion. (excessive solder, excessive flux
residue, some joints look like they needed to be heated more, etc) So I
agreed with the original poster and posted a couple pictures. Another
manufacturer jumped in and said that the flux isn't a problem, which
surprised me. I've long felt that removing the flux is a good idea. Here
are a couple pics of the work I'm referring to (small pics, 70 kb or less) :

www.imjohn.com/misc/SolderDetail1.jpg

www.imjohn.com/misc/SolderDetail2.jpg

Now, I'm not saying that there are operational problems or even that its
'crap' or 'bad', just that I think it could be done better.

John L Rice

John L Rice wrote:
I know Scott D mentioned to clean the circuit boards really well to remove
the flux because over time it can absorb moisture and cause problems.
(Scott, correcting me if I'm wrong I'm sure you will. Sincerely, Yoda)

So is it only a problem with circuits that handle very low/sensitive
voltages or is it also of concern for other circuits, like mic pres? What
about power amps etc?

It's an issue with anything that has very high impedances. If you see
1M resistors on the board, a 10M leakage path is going to be a substantial
percentage of that. If the highest value you see on the board is 1K ohm,
a 10M leakage path is a non-issue.

I often work on mikes with 1000M to 5000M input impedances. You can believe
that a 10M leakage path renders it completely inoperative.

Even so, you should deflux just because it looks nicer.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

John L Rice wrote:
"Mike Rivers" wrote in message

www.imjohn.com/misc/SolderDetail2.jpg

I couldn't tell much about your #1, but #2 definitely looks like a
sloppy repair job and should have been cleaned up just as a matter of
good workmanship.

Fluxes have changed several times over the years. Since I'm still using
flux core solders that I bought perhaps 40 years ago, I use what was
good practice back then. Today's fluxes, to be compliant with
environmental regulations, are mostly water-soluable and
machine-soldered boards all get a good bath before they're installed.

Where you see flux accumulation like in your photo is when there's been
some hand rework or repair, which happens even on new equipment,
particularly if it comes from a small company. A large company would
probably just replace the board rather than rework it.

I suppose that there may be fluxes that provide some sealing as Chel
suggests, but I've never heard of them intentionally used as such. They
have special coating lacquers for that purpose, and the purpose is
almost always to seal against moisutre, not corrosion. There are some
fungs-resistant coatings, too, but they're generally over the entire
board, not just on joints and components that are subject to changing
circuit parameters when they get damp.

As far as corrosion is concerned, the tin-lead-copper alloy that's
formed when you make a good solder joint is highly inert. It'll get
dull over the years, but unless bare copper is showing (which it
shouldn't be) there is no corrosion problem in normal service.

Any circuit can be affected. Leakage across a dirty circuit board can
affect bias voltages, not just signals.

I should add that there are several kinds of flux.

Kester makes at least three. Their ordinary flux is similar to other
companies' rosin flux and should be removed if there's a lot of it. In
small amounts, such as after a repair, it's generally OK to leave on.

They make a "no-clean" flux that is transparent and supposedly does not need
to be removed.

They also make a water-washable flux that absolutely must be removed, since
it will attract moisture from the air and become electrically leaky.

On Tue, 21 Feb 2006 19:36:39 +0100, Chel van Gennip
wrote:

I bought my Ersin Multicore solder (7LB) in the late 60's I think. On the
label it reads (rather faint) 362 FLUX DTD599 BS441. Although maybe the
activators might have been modified slightly, I think todays 60/40
Multicore 362 basicly is the same.

I think the big change recently is that the flux no longer contains
colophony - a substance responsible for a lot of serious respiratory
tract problems. You would be well advised to use some sort of fume
extraction - even just a fan - while you solder with this stuff.

d

Pearce Consulting
http://www.pearce.uk.com

On Tue, 21 Feb 2006 19:50:11 +0100, Don Pearce wrote:
On Tue, 21 Feb 2006 19:36:39 +0100, Chel van Gennip
wrote:

I bought my Ersin Multicore solder (7LB) in the late 60's I think. On
the label it reads (rather faint) 362 FLUX DTD599 BS441. Although maybe
the activators might have been modified slightly, I think todays 60/40
Multicore 362 basicly is the same.

I think the big change recently is that the flux no longer contains
colophony - a substance responsible for a lot of serious respiratory
tract problems. You would be well advised to use some sort of fume
extraction - even just a fan - while you solder with this stuff.

Conventional "rosin core" solder still contains colophony. It's good
stuff... it smells just wonderful. Reminds you of soldering, violins,
and baseball. It's bad for you if you breathe too much of it.

Most of the newer flux types don't have it. The newer fluxes basically
came about because of the difficulty of defluxing in an industrial
environment and meeting EPA regulations. These fluxes either form a
hard barrier or can be removed in a dishwasher with soap and water.

None of the new fluxes flow as well as the old rosin stuff. The military
solder specs won't allow them. I recommend avoiding them unless you are
working in a facility where they are required, or unless you're having
to do largescale defluxing. I've never used them on very-high-Z circuits
so I don't know what sort of leakage issues they have.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

Bob Quintal wrote:

Picture Number 1 evidences the following problems:

You should get a job as an inspector. I was looking for the "excess
flux" problem.

"Mike Rivers" wrote in
oups.com:


Bob Quintal wrote:

Picture Number 1 evidences the following problems:

You should get a job as an inspector. I was looking for the
"excess flux" problem.

I used to have a job as an inspector, and Certification to NASA
Soldering Standards. Flux is but one of many issues that affect the
quality and reliability of electronic circuits. One of the problems
with flux left on solder joints is that it can hide other, more
serious problems.


--
Bob Quintal

PA is y I've altered my email address.

Bob Quintal wrote:

I used to have a job as an inspector, and Certification to NASA
Soldering Standards.

Yes, it sounded like you had the course.

Mike Rivers wrote:
Bob Quintal wrote:

I used to have a job as an inspector, and Certification to NASA
Soldering Standards.

Yes, it sounded like you had the course.

I wasn't allowed to take the course. They don't let engineers solder. They
even sent a supervisor over to make sure I didn't have a scope or a soldering
iron at my desk, because that would be taking work away from the technicians.
Resentful? Me?
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

(Scott Dorsey) wrote in
:

Mike Rivers wrote:
Bob Quintal wrote:

I used to have a job as an inspector, and Certification to
NASA Soldering Standards.

Yes, it sounded like you had the course.

I wasn't allowed to take the course. They don't let engineers
solder. They even sent a supervisor over to make sure I
didn't have a scope or a soldering iron at my desk, because
that would be taking work away from the technicians.
Resentful? Me? --scott

The would not let me solder either. Or even inspect work done in-
house. I was doing source inspection at supplier facilities. The
last several years I've spent disassembling ICs and transistors,
and reviewing manufacturer's screening data on everything we buy.

--
Bob Quintal

PA is y I've altered my email address.

I. Care wrote in
.net:

In article ,
says...
Mike Rivers wrote:
Bob Quintal wrote:

I used to have a job as an inspector, and Certification to
NASA Soldering Standards.

Yes, it sounded like you had the course.

I wasn't allowed to take the course. They don't let
engineers solder. They even sent a supervisor over to make
sure I didn't have a scope or a soldering iron at my desk,
because that would be taking work away from the technicians.
Resentful? Me?
--scott

Based on my experience, good for them ;-).

The technicians at my workplace used to joke that engineers'
labcoats should have sleeves long enough to be buckled together
behind the engineer's back. But it is true that a lot of young
engineers are graduating today with no practical knowledge, only
the theoretical, and assume that they know everything.

We used to assign new engineers to an older tech, in order to
tame them a little before letting them loose.

--
Bob Quintal

PA is y I've altered my email address.