Wow, that is a lot of steps. So is this for aerospace or general assembly?
Phil
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Let me correct that sentence:
For very large quantities of wires, there are machines that will cut the wires to length, strip to length, and then dip the stranded ends first into IPA or some other solution simply to clean the wires prior to tinning, then dip them into the RMA/NC flux, dip and hold in the solder for 2 seconds, and then drop them into a container of IPA or a solvent compatible with the NC/RMA flux.
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OA is organic acid flux, typically much more corrosive and should not be used with stranded wires. No clean and RMA fluxes are typically very similar to each other, and only mildly corrosive at best.
I am a VERY old dog, and worked in my father's shop tinning wires back in the 60s. We would use the methods I described.
When I started working for Honeywell in 1978 they did it exactly the same way, but for wire cups used on connectors as well as many other types of gold-electroplated terminals.
When I worked for various other companies, they also did it the same way. Tyco, Benchmark, ADC, you name it.
That is how we do it today at Analog Technologies Corp., Kongsberg Defence AS, and at General Dynamics, and have done so for more than 20 years.
Never use water-soluble or OA fluxes with stranded wires. As Dr. Kondner pointed out, it will wick up the wires as the solder wets up the strands.
RMA or no-clean flux residues are mostly removed if you simply let the wires soak in a pan of IPA or a similar solvent intended for those types of flux, immediately after tinning. Then wash in DI water with a good saponifier. What works really well is to do the final cleaning step in an Ultrasonic cleaner with a saponifier, provided you are only cleaning mechanical terminals/wires, no electronics, at least not without fully qualifying the process for the electronics.
As I stated, any minor flux residues left after this process is followed, is typically so negligible as to present little or no risk.
As for the solder going too far up under the insulation, that is controlled by operator training. IPC is very clear on this, stating that the solder should not wick up under the insulation more than 1 or 2 wire diameters, but it must wick up somewhat to prevent birdcaging. For very large quantities of wires, there are machines that will cut the wires to length, strip to length, and then dip the stranded ends first into IPA or some other solution simply to clean the wires prior to tinning, then dip them into the RMA/NC flux, and then drop them into a container of IPA or a solvent compatible with the NC/RMA flux.
A relatively simple process, but it must be done right.
Odin
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From: Robert Kondner <[log in to unmask]>
Sent: Friday, March 8, 2024 2:44 PM
To: 'TechNet E-Mail Forum' <[log in to unmask]>; Stadem, Richard D <[log in to unmask]>
Subject: RE: [TN] Metallurgical Inquiry
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Hi,
I recall that with stranded wire it is not a good idea to solder. Flux wicks up into the wire and it just cannot be washed away. Most no clean fluxes are type OA (correct me here) which is corrosive and needs to be cleaned. RMA is better.
Solder also wicks up into the stranded wire making the wire very stiff. This concentrates any flexing to the solder point which can fail. Crimping stranded wire give some level of strain relief and this is why the soldering of stranded wire in crimp terminals is not recommended.
But, I am an old dog and my memory could be failing. Please let me know.
Bob K.
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Sent: Friday, March 8, 2024 1:19 PM
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Subject: Re: [TN] Metallurgical Inquiry
It is not recommended. I would first tin the terminals using RMA flux to remove the gold. Tin the stranded wire with either RMA or no-clean and soak in IPA, then blow off thoroughly and wash with a good saponifier, bake dry, and then solder the tinned wires to the tinned terminals with the same NC/RMA flux and clean again the same way. Do not use DI water first. Clean off (or at least dilute) as much of the flux as you can with IPA, then clean with water.
Otherwise you will have a reaction between the DI water and the no-clean/RMA flux (white conductive residue).
Any flux residues that might remain after cleaning will be negligible.
Dean
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From: TechNet <[log in to unmask]> On Behalf Of Hernandez, Victor G
Sent: Friday, March 8, 2024 11:19 AM
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Subject: [TN] Metallurgical Inquiry
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Fellow TechNetters:
Is it permissible to solder a stranded wire to a gold finger pads with either Sn Pb or Pb-free solder?
Typically, gold fingers are electroplated, hard gold.
Any chance of galvanic corrosion?
Victor,
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