Soldering connectors vs crimping...

SupraGuy

People talk about this a lot in automotive circles too, where we have all kinds of vibration and hostile environments to deal with.

Soldering a wire to a ring or spade terminal does provide a more secure connection, and people like it when they compare it to the crimp that they get when using the cheap tool that comes in their $9.99 terminal kit. I fell prey to that a lot in my younger days too, seeing as how you had to spend what seemed like a lot of money to get a crimping tool that seemed even a little better.

For cars at least, the failure seems to be that any kind of vibration or strain on the wires breaks the strands at the end of the solder blob. The solder to lug joint remains secure, but you start to get a dodgy connection, because the wire is fraying away inside the insulation, even if you have reasonable strain relief, though this process takes several years. This can also happen in wire-to-wire joins where there is strain.

I've heard it postulated that a crimped connection can allow the strands of wire a tiny amount of slide against each other at the end of the crimp which increases the radius of any bend that the vibration takes, thereby reducing the metal fatigue on the wire strands. I don't know if this is really what happens, but it's a certain fact that car manufacturers don't solder their wire connectors. I will still solder wire-to-wire if I'm installing an aftermarket car stereo using a wiring harness adapter so that it can plug into the OEM wire harness, but since some time in the early 90s, I no longer solder terminals onto the wires.

I have tinned leads into screw terminals. Yes, I know it's a bad practice, and I know why it's bad practice. I've never used it as a long-term solution, it's generally for testing purposes where I'm just keeping a wire end from fraying when it will be frequently connected and disconnected until I have a configuration that will be more long term. I could substitute ferrules, which would do the same thing, and maybe one day I will, but I make up test leads fairly often, and a dab of solder is quick and easy, and works extremely well for what I need.

Wyvern

Wire-wire I try to solder when I can, but the joint must be isolated from flex as the solder joint acts like a stress riser- that said I printed 100hrs on a solder joint right in a wire chain with no failures, But I extended the shrink tube far outside of the joint as to isolate the connection. Obviously I have since replaced the whole wire bundle.

Clamped, I twist it tight the wire and crank it down- if the joint is subject to vibration I use shrink tube and tie it down to help isolate the clamped end- The idea is to get the wire crushed, but not spread apart.

If you must use a plug, GET THE CORRECT CRIMPER, I bought a $30 weather-pack crimp tool from a tool truck before my duet build and all the crimps are perfect and were effortless to do, using a standard stripper/crimper is asking for failure.

I work on cars,trucks,trailers, and hydraulic powered aerials and excavators as well as R/C cars and drones- so I have learned over the years what works and what doesn't work.

Catalin_RO

I think you need to look a little bit differently at the problem.

Whenever some wire connection must/may be done outdoors, crimping is the only reasonable solution. Just try to solder some wires at -20deg, with mild wind blowing - you need a very powerful soldering iron. Cars and industrial equipment must be maintainable with relatively simple tools, and as already stated, without requiring much skill. Also, even if not available on the market, it is relatively easy to make custom crimp tool dies - we had a situation when the guys out in the field had to carry 3 crimping tools, or spend time to swap the dies, so we went for custom made dies and they had just one crimping tool covering all their possible needs.
If you go for RF, soldering the central pin of the coaxial connector is the best approach as crimping doesn't really insure proper impedance across the whole frequency range. What happens to the cable shield (crimp, solder or clamp) is a different story because of the relatively large contact surface area. RF cables are almost never repaired in the field, and even when they are, usually it is a highly skilled job that also implies a lot of precautions.
If you need some crimped connection on a copper cable, in wet environments, the wires must usually be corrosion protected. Applying a little bit of solder prevents corrosion in the contact area and it is usually cheaper and, most of the times, easier to apply than other sealing solutions.
Some industrial connectors come with different pins for crimping and soldering. Usually in the those cases the crimping tool is dedicated and crazy expensive.

But that is in a perfect world!

It may happen that you have to crimp some strange connector, for a one time need, and you don't have the tool. Usually a pair of pliers and some soldering cover that in a decent way.

I usually crimp all data connectors but I always solder my coaxial connectors (at least the central pin, depending on the connector type).

chuckb67

When I went to RADAR repair school many years ago (1963) we had a solid week of soldering training and the rule was always to make sure you had a solid mechanical connection before you solder. I have always lived by that rule with good results.

I don't think this was mentioned in the replies, but another big issue with soldering are cold solder joints. This occurs when you don't allow the melted solder to flow completely onto the surfaces, if you move the connection while the solder is still fluid, or you blow on the solder joint to cool it. Cold solder joints are very difficult to troubleshoot and can create real headaches. If a solder joint looks cloudy it is very likely a cold joint that might or might not cause problems.

What I learned was that good soldering technique takes time and practice to become proficient. Don't forget to use a magnifier to inspect your work.

Chuck

dc42

When I owned a light aircraft, I had at least three avionics failures caused by bad solder joints, one of which was made by my avionics engineer while installing an avionics upgrade, and two by the manufacturers of the avionics. By the time I had another avionics upgrade done, crimp connections had become standard. I never had a crimp connection fail.

This was before lead free solder was in general use. With lead free solder now mandatory in most countries for anything that will be sold, the benefits of crimping over soldering for joints under any sort of mechanical stress are even greater.

Danal

Interesting that @dc42 mentioned aviation practices.

There is a BIG thick book in the US that specifies everything about how to work on aircraft. It is "AC 43.13-1D - Acceptable Methods, Techniques, and Practices..." blah blah. Long government title. That book has EVERYTHING that is acceptable in an aircraft. Tubing, Welding, Bolts, Nuts, Washers, Sheet Metal, Rivets, Fabric, Composites, pull-cables, electrical wiring, Rod-ends, bearings, you name it.

Including a whole section on electrical connectors, crimping, etc, etc, etc.

THERE IS NO CHAPTER ON SOLDERING. Because it is not acceptable on an aircraft... ever.

Wyvern

@danal
A good solder job is a quality connection, a poor solder job is a disaster waiting to happen.

There are too many variables and too many ways a solder joint can fail, so I can see why they don't allow it.

That said, you can mess up a crimp too, but with the right crimp connection and the proper tool it more dummy proof.

They have crimp/solder/seal connections, they are awesome as you get the mechanical connection, solder to reduce resistance and increase bond, and heat-shrink to keep out moisture and protect the joint- again you can STILL mess these up.

JuJuDelta

My experience.

I hate lead free solder. I leave that to my PCBA company and their SMT machines.

I use a low temp solder for development work, Tin lead silver 179’C

Generic crimp tools don’t always give a reliable crimp.
The manufacturers crimp tools can run into £100s but do a great job.

Kimberly

just a note..

If you solder on wire going to a screw connector the mechanical pressure will compress the solder overtime. and will eventually get loose..
better go with crimped and then solder (solder the wiren in the crimp) or pure wire

Danal

@danal said in Soldering connectors vs crimping...:

Solder on a twisted wired end placed in a screw terminal is a HUGE no-no. The solder WILL creep over time, thus loosening the connection and starting the heat/loosen/more-heat cycle that leads to burned up connectors.

Screw Terminal? Bare twisted wire or crimp (usually "bootlace"). NOTHING else, period, end of story.

Solder two wires together? Fine. Just no screw terminals.

@kimberly said in Soldering connectors vs crimping...:

just a note..

If you solder on wire going to a screw connector the mechanical pressure will compress the solder overtime. and will eventually get loose..
better go with crimped and then solder (solder the wiren in the crimp) or pure wire

Wise words from @Kimberly