You are not being paranoid; I have also seen this sort of problem.
It is very hard to clean the flux out from underneath the insulation.
Maybe if a heavy ROL1 or ROL0 flux, such as 615-15 or 615-25 (other
suppliers have similar materials), is used during tinning with a solder
pot, the corrosion problem can be somewhat alleviated. Tin with lots of
rosin and very little other activation, and the little other activation
should be halide rather than organic acid.
Karen Tellefsen - Electrical Testing
Alpha / 109 Corporate Blvd./ S. Plainfield, NJ 07080
[log in to unmask]
908-791-3069
From: Carl VanWormer <[log in to unmask]>
To: <[log in to unmask]>,
Date: 06/06/2014 09:21 AM
Subject: [TN] tinning wires - flux entrapment and long term
reliability
Sent by: TechNet <[log in to unmask]>
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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