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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