Carl,
I also have heard about these "Heat to xxx to De-Activate No Clean Flux"
stories, that sounds like the "Passivation Temperature" word you mentioned.
Has anyone see a no clean flux with a "Passivation Temperature" rating or
anything that might even be close?
Thanks,
Bob K.
-----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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