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Crimping versus soldering, in avionics

I agree with most that has been said.I would like to add just a couple of points (even if some already said one way or another):

-QA: It is obvious that further skill is required to ensure solder joints are properly done, plus it is difficult to verify how far up the wire solder has travelled under the insulation (difficult QA). Crimping with the right parts and tools is fairly fool-proof and ensures consistent results, plus is easy to verify using the pull-test.

-Certification: when you perform a repair or installation in accordance with an aircraft's Maintenance Manual or an STC or other design approval, the approval will typically refer to a specific wiring procedure to be used. Such procedure is normally crimping and rarely soldering for the above QA and associated liability issues. A deviation from the approved procedure typically requires some authority (accepted standard practice or minor change or otherwise).

Antonio
LESB, Spain

I’ve just come across this really great NASA wiring manual – very applicable to avionics wiring

here original URL

Administrator
Shoreham EGKA, United Kingdom

I’m so glad I found this thread!

I’m a solder person but that’s probably because I soldered GaAsFET’s into 1296Mhz pre-amps when I was a kid in the 1980’s. When you are soldering a component that costs you a weeks wages (piece work earned during school holidays) you learn to solder bloody well without overheating components.

Warning off topic
Of course these days kids are probably not allowed to work when at school at all as the would be “exploitation”, never mid piece work. Instead they have a gap year, spend £ 240 going to Glastonbury, allow low paid workers to clear up the trash they threw on the floor and moan “how poor” they are!!

On topic
Anyway, I’m told what you must not do is tin the wire and then crimp as the solder “creeps” and the cable gets loose in the crimp (I used to do that as I thought it was a good idea).

United Kingdom

Another thought. If you solder machined D connector pins, then once you insert them into the shell it’s almost impossible to get an extract tool in to remove a pin if it’s necessary.

Avionics geek.
Fairoaks. EGTF

Yes; very true. One has to keep the solder entirely inside the pin, which is tricky.

Here is a soldered and heatshrink-covered job:

However, the solder has probably crept up in between the wire strands up to roughly where the arrow points

so the joint will not withstand as much vibration as a crimped one would.

With King long finished and most modern avionics using cheap D-type connectors like this one, and good quality solder bucket mating plugs costing say 1 quid (not the above one which is a crappy formed-pin type, costing about 25p) it is a lot cheaper to use high quality solder bucket connectors than the similarly high quality crimped-pin versions from Positronic etc. So, someone who is good at soldering, doesn’t mind the extra time of heatshrinking the joints, and is able to build most of the harness on a bench at home, may as well solder. That is why I usually solder. Like Archer-181 I am very good at it, having been doing it since c. 1963 (age 6).

But one can see why avionics wiremen prefer crimping even on the common D-types – especially when working inside a plane in the (typically) unheated hangar. I was working in one hangar not long ago, avionics shop, and it was -5C there, no heating!

Administrator
Shoreham EGKA, United Kingdom

Soldering equipment in airplanes is a real PITA and just another potential disaster waiting to happen.

That said, I HATE crimped splices, or any splices for that matter, but given a choice, prefer soldered splices with thermo-retractable insulation.

FAA A&P/IA
LFPN

I bought one of these cordless soldering irons from LIDL for 12.99 euros.



It heats well and could be used in awkward spots in an aircraft especially if you don’t have a mains power supply.
Of course crimping doesn’t require electricity.
Simon

Last Edited by simon32 at 12 Jul 08:10

I did solder a lot, but recently went to crimp connectors.
Mainly as soldering thick cables (106mm2) is a bit of pain and you have loads of vibration in vehicles.

EGBE - Coventry, United Kingdom

I think any wiring in confined spaces is a bastard of a job… crimping makes it a lot less of a bastard

The best thing is to prewire a harness back home, but you still need to install a multipole connector in the aircraft. That needs to be a good quality one; I have used the circular milspec ones but again they were soldered…

Overall, I reckon heatshrunk soldering is better in the very long term. It should last for ever. Crimping will always eventually corrode inside the joint, and I saw lots of this trouble in 30+ year old King Airs where I was hangared for 10 years, which had many thousands of crimped joints, mostly ex factory work in circular milspec connectors such as this (this is a KVG350)

and there would be dozens or hundreds of duff joints. I once watched one guy (a former employee of wigglyamp ) re-crimp a few hundred of them… he just kept re-crimping them until the various faults went away. The system (EFIS-40) was complex and impossible to troubleshoot from first principles unless you were a really good electronics engineer, the manuals were not available for all the bits, there was no test equipment for functional testing of the various parts, but with a G1000 retrofit being some way into 6 digits USD the owner just wanted a fix…

Administrator
Shoreham EGKA, United Kingdom

Peter wrote:

Only if you are using an aggressive type of flux

All flux has to be aggressive or it doesn’t do anything.
Solder tends to wick up stranded cables, and the end of the solder forms a weak point for flexing, though your heat shrink helps. Another issue is the tempering of the wire close to the solder joint. Heat alters the structure of metal.

In automotive ECUs we are going away from soldering and crimping where possible towards Compliant Pin connectors. The pins are inserted into the PCB directly, the interference fit and design of the pin forming the connection. They are not soldered. The machinery is expensive though, we are just looking at a new machine which will be in the region of €350,000

Of course the harness end will still be crimped.

Last Edited by Neil at 12 Jul 09:39
Darley Moor, Gamston (UK)
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