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June 2014

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From:
Karen Tellefsen <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Karen Tellefsen <[log in to unmask]>
Date:
Tue, 10 Jun 2014 09:00:12 -0400
Content-Type:
text/plain
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text/plain (403 lines)
I would use Kester 186-18 instead for tinning.  Alpha 615-15 is another 
good choice.

Karen Tellefsen - Electrical Testing
Alpha / 109 Corporate Blvd./ S. Plainfield, NJ 07080
[log in to unmask]
908-791-3069




From:   Steve Gregory <[log in to unmask]>
To:     <[log in to unmask]>, 
Date:   06/09/2014 05:43 PM
Subject:        Re: [TN] tinning wires - flux entrapment and long term 
reliability
Sent by:        TechNet <[log in to unmask]>



Hi Richard,

Good information! But can I ask a question about a particular no-clean
flux? It's about Kester 951. In their datasheet they say that it
contains a "corrosion inhibitor" such that no corrosion products are
formed when bare copper surfaces are exposed to humid environments. Do
you have any idea what that might be?

We use it as a touch-up flux for our no-clean soldering and do use it to
tin wires. I know that some of that flux gets somewhere where it doesn't
get cleaned, and probably didn't get exposed to a lot of heat when
you're doing point-to-point touch-up and soldering with a single iron. 

We haven't had an issue with this flux, at least any that I know of. But
it doesn't mean that there isn't one. The operators sometimes complain
when they use it because it evaporates so fast though.

Just curious what the "corrosion inhibiter" might be. The SDS says the
flux contains ethanol (50-65%), isopropanol (20-25%), n-butyl acetate
(5-10%), methanol (2.5-5%), and adipic acid (1-2.5%). Everything listed
is pretty much a solvent except for the adipic acid.

Steve 


-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Stadem, Richard D.
Sent: Monday, June 9, 2014 2:23 PM
To: [log in to unmask]
Subject: Re: [TN] tinning wires - flux entrapment and long term
reliability

I agree with George, and also with many others who feel that cleaning
with IPA is not a very good approach.
I should have mentioned also that through the years that I have seen
wires tinned with RMA flux, then soaked in IPA, then that was followed
by a DI wash. 

The old-time engineers back in the 60s and 70s showed me by using 3
stages of wires cut open to show what the strands looked like under the
insulation. Different oldtimers showed me this trick more than once, and
I have never forgotten it.

First, the operators were trained to insert the wires into the RMA flux
only halfway up the stripped portion (generally 1/8th inch to 1/4"
striplength).
Next, the operator was trained to insert the wire only up to just below
the end of the insulation. Some of the RMA flux would always ride up to
the insulation, and the solder would actually flow just under the
insulation, seldom more than .050" past the end of the insulation. In
other words, if you stop the stranded wire just short of the insulation,
the solder continues to wick up to a point just under the end of the
insulation.
Then, when the wires were not cleaned with IPA at all, the cutaway view
would always show a small amount of flux just under the end of the
insulation.
When cleaned in the IPA only, but not followed with a water wash, when
you cut the insulation away you "sometimes" saw a very small amount of
flux.
But when you did all three, any flux residue under the insulation (if
present) could not be seen. It does not mean it wasn't there; it just
was not visible even at 20X.

And in all cases, the oldtimers were never concerned with RMA flux
residues being left behind under the insulation; they felt it was not a
concern even to leave the RMA flux behind, with no cleaning.

But NOT water soluble (OA) and NOT no-clean fluxes. The no-clean
activators are sometimes even more aggressive than RMA. That is still
true. So I stand by the statement that when tinning wires, only RMA flux
should be used, some type of solvent should be used to at least suspend
the RMA solids, and some type of final rinse or wash process should be
used. If all of those are done, I do not think there is ever a concern
for the wires rotting away under the insulation.

And one more item: If you are just cleaning tinned wires (no connector
bodies, sleeving, circuit boards or components,etc.) I have found that
following the solvent clean with an ultrasonic cleaning process where
the entire wire or wire assembly is immersed in hot DI water with a 6%
saponifier will get all of the flux out from under the end of the
insulation.

I am talking about the end of the insulation, not 1/2" up the insulation
or anything like that.



-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Wenger, George M.
[Contractor]
Sent: Monday, June 09, 2014 1:21 PM
To: [log in to unmask]
Subject: Re: [TN] tinning wires - flux entrapment and long term
reliability

As someone who sent 33 years working in the "Bell System" were solder
assembly quality/reliability was the primary concern,  I'll throw my two
cents into this discussion.  I've never like the name "No-Clean".  Any
flux used for soldering that doesn't go through a cleaning process would
be a "No-Clean" if the meaning is it wasn't cleaned off.  The old
BellCore (now Telcordia) GR-78 gives criteria for determining if a
soldering flux residue needs to be cleaned off for reliability reasons.
If you make a solder joint with a flux and don't clean it off and it
passes the BellCore reliability testing then we would consider that flux
a reliable "Leave-Behind" flux meaning if the flux residue wasn't
cleaned off there were no reliability risks.  In general most of the old
fluxes classified as R & RMA passed the "leave-Behind" requirement.  In
fact, our experience was that especially for RMA fluxes the reliability
was much better if you did leave them behind rather than tried to clean
them.  If you take an RMA flux and try cleaning it with alcohol (which
isn't a very good solvent) what you wind up doing is dissolving and
removing most of the rosin in the flux residue, which is what was
encapsulating the ionic activators, which in turn allowed any ionic
activators to be mobile and the first time the humidity increased you
had the worse case for corrosion (moisture, activators, and electrical
potential).

I can see that with a low-solids type "No-Clean" flux that the flux
would wick up the braided wires and yes when a soldering iron was placed
on where you wanted to make the solder joint the flux activators would
be heated and reduce oxides and allow a good solder joint to form but
the flux that wicked up the wires may not have gotten to a high enough
temperature to de-activate the activators and then the humidity goes up
in use you could have a problem.  If I were pre-tinning braided wires I
would only us an RMA flux qualified according to BellCore GR-78 to be a
"Leave-Behind".

Regards,
George
George M. Wenger
Failure Signature & Characterization Lab LLC
609 Cokesbury Road, High Bridge, NJ 08829
(908) 638-8771 Home  (732) 309-8964 Mobile E-mail [log in to unmask]
[log in to unmask]


-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Carl VanWormer
Sent: Monday, June 09, 2014 12:59 PM
To: [log in to unmask]
Subject: Re: [TN] tinning wires - flux entrapment and long term
reliability

I've heard stories of no-clean and hand soldering causing problems.  In
an IR-reflow oven, all of the no-clean flux achieves the passivation
temperature, becoming inert.  With hand soldering, the flux melts, runs
away from the heat source, and penetrates any tiny crevice it can find.
There is an area at the perimeter of the heated area that is hot enough
to cause the flux to flow, but not hot enough to cause it to become
active.  If this is true, than this is the problem I'm worried about.
Comments, please?

Thanks,
Carl



Carl B. Van Wormer, P.E., AE7GD
Senior Hardware Engineer
Cipher Engineering LLC
    21195 NW Evergreen Pkwy Ste 209
    Hillsboro, OR  97124-7167
    503-617-7447x303
    [log in to unmask]     http://cipherengineering.com


-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Steve Gregory
Sent: Monday, June 09, 2014 9:49 AM
To: [log in to unmask]
Subject: Re: [TN] tinning wires - flux entrapment and long term
reliability

It's been some years back, but we were building a cabinet along with all
the boards and cables. The cables had silver plated braided shielding
over them and we would have to solder the shield wires to either a lug
or contact. We were using manufacture XXX no-clean flux. It had been a
rainy spring that year, and rained about every other day for at least a
month, so you know the humidity was high. 

One of the supervisors came to me after that month and said; "Steve, we
got a problem, all the cables in the cabinets are turning green..." so I
went and looked at them. Sure enough the shield wires were turning
green, and it was down close to the end sections of the cables where
they had been soldered:

http://stevezeva.homestead.com/files/Green_Junk_1.jpg

http://stevezeva.homestead.com/files/Green_Junk_2.jpg

http://stevezeva.homestead.com/files/Green_Junk_3.jpg

http://stevezeva.homestead.com/files/Green_Junk_Close.jpg

I had a hard time figuring out how this was happening, because right at
the ends where the soldered connection it was fine. The connections were
soldered and cleaned with alcohol. Best I could figure was that the
operators had flux on their fingers when they handled the cables and got
the flux up on the cable where it wasn't reacted with heat, and wasn't
cleaned, and with the high humidity that we had that month turned the
shield wire green.

We switched the no-clean flux to manufacture XXX and the problem went
away.

Steve 


-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Nutting, Phil
Sent: Monday, June 9, 2014 8:25 AM
To: [log in to unmask]
Subject: Re: [TN] tinning wires - flux entrapment and long term
reliability

So for many years I have followed the discussion about flux cleaning and
alcohol always get mentioned as a great way of dissolving the flux and
depositing it on a much wider area.  There has to be a better way to
"clean" the wire entrapped flux if it really must be cleaned.  I agree
that OA flux is not a good solution.  My current choice is to use
"no-clean" flux cored solder when tinning wires and then leave it alone.
Soldering the wire into the board can then be done with "no-clean" or
other flux cored solder.  Where we do not make anything that is designed
as mission critical this process seems to work for us.

Phil Nutting

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Stadem, Richard D.
Sent: Monday, June 09, 2014 9:30 AM
To: [log in to unmask]
Subject: Re: [TN] tinning wires - flux entrapment and long term
reliability

You do not tell us what flux you are using.
But as a general rule, one must never tin insulated wires using OA flux.
Only RMA or no-clean should be used, and that followed by dipping the
tinned ends in alcohol.


-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Carl VanWormer
Sent: Friday, June 06, 2014 8:20 AM
To: [log in to unmask]
Subject: [TN] tinning wires - flux entrapment and long term reliability

My understanding:
While tinning wires with conventional soldering methods, the wire is
heated and the flux-cored solder is applied to the wire.  As the flux is
melted, it wicks up between the wires and the solder flows in, wetting
the wires.  The liquefied flux flows up the wires farther than the
solder, and some of the un-passivated flux is trapped inside the
insulation, around the Copper strands where the solder stopped flowing.

My experience:
One of our control modules had failed in an automotive "road splash"
environment.  Our connector terminals had been soldered to the wires
that came out of the "waterproof" strain-relief assembly.
Troubleshooting let me to cable harness with an open circuit between a
wired connector pin and the other end of the wire.  The wire and pin
looked good, but a gentle tug on the pin popped the 5mm length of
soldered wire out of the wire's insulation, revealing a discoloration at
the end of the solder-flow where the Copper wire had been "disappeared".
A few mm inside the wire insulation, there was another discolored blob
at the end of the wire's total length of good Copper wire.  Our
conclusions of "not quite waterproof" and "chemistry experiment" led me
to be concerned about the problem.

Current worry:
We have a product with a "requirement" that some 16-gauge stranded
Copper wires be soldered to our PC board.  The plan is to have the cable
assembly arrive with pre-tinned wires, and then the wires will be
soldered to the board with "no-clean" flux.  The product is not expected
to be in the water, but may be "near" a wet environment, maybe mounted
in a pouch on some motorcycle gear.  I'm worried about the tinning
process forcing un-passivated flux up, inside the insulation, to wait
for a "humid" condition to start another "chemistry experiment."

Questions:

1.       Assuming we must solder wires to my PC board, is there any
guidance on how to keep "chemistry experiments" from happening on my
product?

2.       Are there any other "very small" connection methods for 15 Amp
wires that I should consider that I might be able to fit on my tiny PC
board that would eliminate my worry?

3.       Am I just being overly paranoid?

Thanks,
Carl





Carl B. Van Wormer, P.E., AE7GD
Senior Hardware Engineer
Cipher Engineering LLC
    21195 NW Evergreen Pkwy Ste 209
    Hillsboro, OR  97124-7167
    503-617-7447x303
    [log in to unmask]<mailto:[log in to unmask]>
http://cipherengineering.com<http://cipherengineering.com/>

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