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June 2014

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From:
Robert Kondner <[log in to unmask]>
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Date:
Mon, 9 Jun 2014 15:26:06 -0400
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George,

 

I agree with 95% of what you wrote but you did write:

 

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.  

 

But yet you describe how RMA is better to use, does it not have "Activators"
remaining up in the wires?

 

I just cannot find anything in the literature that describes required heat
processing of No Clean Flux to render that flux appropriate for any specific
application.

 

Thanks,

Bob K.

 

 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Wenger, George M.
[Contractor]
Sent: Monday, June 09, 2014 2:21 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
<mailto:[log in to unmask]> [log in to unmask]
<mailto:[log in to unmask]> [log in to unmask]

 

 

-----Original Message-----

From: TechNet [ <mailto:[log in to unmask]> mailto:[log in to unmask]] On Behalf
Of Carl VanWormer

Sent: Monday, June 09, 2014 12:59 PM

To:  <mailto:[log in to unmask]> [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

     <mailto:[log in to unmask]> [log in to unmask]
<http://cipherengineering.com> http://cipherengineering.com

 

 

-----Original Message-----

From: TechNet [ <mailto:[log in to unmask]> mailto:[log in to unmask]] On Behalf
Of Steve Gregory

Sent: Monday, June 09, 2014 9:49 AM

To:  <mailto:[log in to unmask]> [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_1.jpg

 

 <http://stevezeva.homestead.com/files/Green_Junk_2.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_3.jpg

 

 <http://stevezeva.homestead.com/files/Green_Junk_Close.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]> mailto:[log in to unmask]] On Behalf
Of Nutting, Phil

Sent: Monday, June 9, 2014 8:25 AM

To:  <mailto:[log in to unmask]> [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]> mailto:[log in to unmask]] On Behalf
Of Stadem, Richard D.

Sent: Monday, June 09, 2014 9:30 AM

To:  <mailto:[log in to unmask]> [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]> mailto:[log in to unmask]] On Behalf
Of Carl VanWormer

Sent: Friday, June 06, 2014 8:20 AM

To:  <mailto:[log in to unmask]> [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

     <mailto:[log in to unmask]:[log in to unmask]>
[log in to unmask]<mailto:[log in to unmask]>

 <http://cipherengineering.com%3chttp:/cipherengineering.com/>
http://cipherengineering.com<http://cipherengineering.com/>

 

This message may contain confidential and/or proprietary information, and is
intended for the person/entity to whom it was originally addressed. Any use
by others is strictly prohibited.  If I sent this to you by mistake, please
be nice and delete it, and then tell me of my mistake so I can send it to
the right person.

 

 

 

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