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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