Crimp *and* solder a crimp connector? Good? Bad? Why?

[coppice]

Run a high current through a solder joint and a 6.3mm spade connection and notice the difference.

What do you use to secure your spade-to-PCB connectors to the PCB side of the connection? Most likely solder.

If soldering was a no-go for high-vibration environments, there wouldn't be a ~300 pages long NASA standard about how to tin wires and soldering in general for aerospace applications.

Soldering is not a no-go for high vibration environments. It is used all the time. It is used in specific ways, though. If the solder is requirement to provide no mechanical strength, and simply provides a conductive infill, it works fine. As soon as you expect any mechanical strength from it you are in trouble. Even the minor mechanical strength required to hold a DIP pin in a plated through hole can be problematic. The holes are made as small as possible, so there is the minimum possible space between the pin and the hole.

[coppice]

If properly done, reliability of crimp and solder joints is equal.

E.g., check this out:

"Solder-style splices produce a smaller, more compact splice
termination, with significant weight reductions over crimp-style splices."

http://www.hq.nasa.gov/office/codeq/doctree/87394.pdf

Would they do that if it was unreliable?

The technique is neither reliable nor unreliable. Context is everything. If the splice is in a position where is will not be flexed frequently or be subject to vibration (e.g. inside a lot of NASA ground equipment) a well executed soldered splice will work fine, even on stranded wire.

[CatalinaWOW]

A refrain that needs to be played over and over again, in every context there is. 

Something that is employed properly and executed well works.  Anything short of that can turn out poorly, though even here you can get lucky.  Sometimes more often than not.

The comments in this thread have been helpful in the proper employment part of the equation.

[eneuro]

Run a high current through a solder joint and a 6.3mm spade connection and notice the difference. There is a good reason why they use anything but solder joints for wiring in equipment which needs to have a long service life.

Makes sense to me that solder joints are less satisfactory for high current applications. 

Myth buster time comes 
I want to compare today two connection types: crimped and filled with solder to glue everything VS crimped only-both of them covered with thermal heatshrink 
Those connectors will be in series on huge welder transformer secondary  and slowly current will be raised until.... we'll  see strand wire insulation disapear and then lets see which connector fails first or pobably wire itself, I bet   

[george graves]

Thanks for all the info!

Regarding wire to wire joints,  I will add, that I think the military (and maybe some aviation?) they might be keen to use crimps as with the right tool, they are more-or-less monkey proof.  Where soldering requires a lot more training/experience.

Second question:  Is there any solder that it's flux is so corrosive that when it wicks into stranded wire it will actually eat up the copper over the course of a few years?  I know someone that says he see it on a regular basis.  He installs car stereos for a living(so take that with a grain of salt) - and I'm assuming he's seeing people use copper pipe solder for electrical work.  Anyone else run into this?

[wraper]

Second question:  Is there any solder that it's flux is so corrosive that when it wicks into stranded wire it will actually eat up the copper over the course of a few years?  I know someone that says he see it on a regular basis.  He installs car stereos for a living(so take that with a grain of salt) - and I'm assuming he's seeing people use copper pipe solder for electrical work.  Anyone else run into this?

Yes it's quiet common to happen.

[DanielS]

Myth buster time comes 
I want to compare today two connection types: crimped and filled with solder to glue everything VS crimped only-both of them covered with thermal heatshrink 
Those connectors will be in series on huge welder transformer secondary  and slowly current will be raised until.... we'll  see strand wire insulation disapear and then lets see which connector fails first or pobably wire itself, I bet   

The solder will melt before the wire fails. Some interesting things might happen once solder starts dripping out of the joint. For high-temperature connections, you want to use spot/fusion welds, crimps or appropriate screw hardware until you get out of the hot zone.

Second question:  Is there any solder that it's flux is so corrosive that when it wicks into stranded wire it will actually eat up the copper over the course of a few years?

Plumbing acid flux. That stuff is intended to clean off most of the junk of the surface of solid copper pipes. It does not really harm the pipes since they are 1/16" thick (over 1mm) but on fine multi-strand wires, the wires might be gone in less than a year.

[nctnico]

Plumbing acid flux. That stuff is intended to clean off most of the junk of the surface of solid copper pipes. It does not really harm the pipes since they are 1/16" thick (over 1mm) but on fine multi-strand wires, the wires might be gone in less than a year.

Actually you are supposed to whipe the pipes clean after soldering!

[eneuro]

Myth buster time comes 
I want to compare today two connection types: crimped and filled with solder to glue everything VS crimped only-both of them covered with thermal heatshrink 
Those connectors will be in series on huge welder transformer secondary  and slowly current will be raised until.... we'll  see strand wire insulation disapear and then lets see which connector fails first or pobably wire itself, I bet   

The solder will melt before the wire fails.

I can't wait to test this, while I do not believe in that 

What about connect this 2.5mm2 strand wire to... 2.5kW spot welder secondary with hundreds of amps of short circuit current? 

Yep, I like this idea-I will start from 1 mains period pulses (20ms) util wire insulation disapears and series connection fails 

[calzap]

I think the main reason solder is not allowed to be the mechanical connector for building wiring is because it may melt in a high or over current situation, especially in a warm environment (junction box on a roof-top or in an attic, for example).  In an over-current situation, this might occur before an inverse time breaker (the usual kind) trips.  Think of a solder joint as a fusible link.  In addition to the circuit going dead,  dripping solder and wires springing apart can cause all sorts of mischief.

Acid flux (plumbing flux) can indeed corrode stranded wire rapidly; I've seen examples.  The main reason copper or brass pipes survive acid flux is their mass.  Wiping the joint after soldering is mostly for cosmetic reasons and to allow the inspector to see the joint better.  Many plumbing fluxes are in a petroleum jelly matrix, and wiping just spreads the residual flux further down the pipe and onto the outer surface of the fitting.  Besides you can't wipe the inside of the pipe or fitting in most situations.  Water flow  may wash away some of the acid  inside, but many pipes have little or no water moving through them (vents, compressed air distribution, etc.).  The  only disastrous corrosion I've seen in copper pipes is when they are used as drain pipes and subjected to all sorts of chemicals over the years or at sharp bends (causes turbulence) in systems that run continuously, like hot water re-circulation systems.

Mike in California

[penfold]

The only problem with solder in those environments is because of the safety factors and already the conductors are already designed to get pretty warm at peak current so a lot of thermal cycling will not be doing it any favors.

In high reliability environments the use of solder in multi-strand wires is discouraged because it limits the natural flex of the cable strands which requires bit more strain relief in the cable. It is not necessarily true that it will always do this, but it is practically impossible to prove that the solder has not wicked up the center of the wire whereas a crimp is pretty easy to test. The additional strain relief in soldered junctions means additional weight which for the aerospace industry is a big deal and it just so happens that they are some of the key players who influence the design of high reliability interconnects.

The big deal is with inspectability, some solder joints can be very misleading and the solder itself hides a multitude of sins whereas with a crimp you can quite quickly determine that the wire was of the correct gauge, the correct crimp die has been used and that the correct depth of the wire in the junction has been reached.

[MK]

In a crimped joint done properly, the uncrimped portion of the ferrule in conjunction with the insulation provides a region of steadily decreasing stiffness from the crimp proper all the way out to the unsupported wire, this region where the stiffness steadily decreases is what will make that connection more resistant to vibration than a soldered joint where the solder backfills the wire out to the unsupported region thus concentrating all the vibration to that single mm of wire, thus it will fail quicker unless there is never any vibration at all.

[tooki]

Look at it this way, the wire connections in a spacecraft (which is probably the highest vibration environment you will find) are crimped and not soldered. Crimping works if you use the right tools and is ultra reliable, soldering will decrease this reliability.

The military does indeed use a lot of soldering and a lot of crimping. They are, however, very particular about where each is used. You would, for example, never be allowed to solder to a multi-strand wire.

Umm, maybe I'm not understanding your comment, because they certainly do allow soldering of stranded wire. Here's a video series of soldering training to NASA standards, and it begins with soldering stranded wire.

[IanJ]

In my experience, tinned strands which are then crimped can have a tendency to work loose.......not just because of the rigidity factor of the wire leaving the crimp but due to the compressibility of the solder and flux residue.
Over time this can deteriorate and the crimp ends up loose.

Soldering after crimping is a different thing and has it own set of issues/benefits depending on where you solder.

Nothing beats or improves on a properly crimped connection......IMHO.

Ian.

[John Coloccia]

I don't see how solder could improve a crimped joint. A properly crimped joint is already gas tight, and often there are even cold welds that develop, like wire wrap.

[VK5RC]

I read on this forum a comment that resonated with me, a good crimp is often better than a good solder joint BUT a really good crimp joint needs a specific wire,  a specific crimp, a specific tool and a trained crimper operator, you can get pretty close to  that quality solder joint with far less bother. I.E much easier to make a bad crimp than a bad solder joint, but both are possible!

[DanielS]

BUT a really good crimp joint needs a specific wire,  a specific crimp, a specific tool and a trained crimper operator

How much training does a "crimper operator" need to operate a $600 ratcheting or powered crimper and die set? The main reason connector manufacturers produce manual crimpers and die sets tailored to specific connectors and wire gauges is to take as much of the human factor out of the equation as possible so field technicians and engineers can achieve connections comparable to factory crimps with minimal training.

(That and vendor lock-in: the connector manufacturer won't guarantee performance of their parts unless you use their specific dies and the specific crimp tools they were designed for even when you have functionally identical tools or die models in every way which should physically matter.)

[mikerj]

Run a high current through a solder joint and a 6.3mm spade connection and notice the difference.

What do you use to secure your spade-to-PCB connectors to the PCB side of the connection? Most likely solder.

If soldering was a no-go for high-vibration environments, there wouldn't be a ~300 pages long NASA standard about how to tin wires and soldering in general for aerospace applications.

Does that NASA document permit stranded cables to be tinned and soldered when used in high vibration environments?  I suspect not.

[eneuro]

I don't see how solder could improve a crimped joint.

I've some theory behind it-higher conductivity area ~ lower connection resistance 

Preparing welder transformer secondary connector on 6mm in diameter copper strand wire and for testing purposes I've used classic (old) vice , and patent pending  screw cut into two pieces, so when copper pipe was pressed by screw forming  copper connector into circular shape and prewenting flat pressing, I've got decent results:



However (it is not cleary visible) I've made also ~1.5mm hole in front of connector, to be able fill empty space from connector hole side by solder inserted throuught this small hole, while connector is heated from hole side.

I expect, strand small wires soldered to connector from front and not too much penetration to wire after connector since there will be lower temperature, so solder will rather be kept in front of connector.
Additional connection area made with solder this way, I hope, it  will lower down total connector resistance even more and while this wire will not work in high vibration environment I do not expect any flexibility issues-of course thermal heatshrink will improove rigidiity w few centimeters around connector.

I will have a chance test this connection during test welding tomorow and meantime I will make this experiment with 2.5mm2 connectors in crimped vs crimped and soldered version 

[CatalinaWOW]

If any of you have a late 90s Chevy or GMC 4WD vehicle you have probably experienced a failure of the drive selection system.  The problem in every case that I have found is failure of the press fit connections between two circuit boards in the switch.  Presumably these had all of the benefits at assembly, new materials, proper sizes of both sides of the joint, carefully designed pressures and proper tools.  While this is not a crimp joint, it is one form of the same joining concept.  They are touted to be gas tight and occasionally forming cold welds.  They can and do fail if everything is not perfect.

While my solution is not perfect, it has lasted longer than the original connection.  I soldered them.

[TopLoser]

"Presumably"

At that point your argument becomes very much less convincing...

[DanielS]

While my solution is not perfect, it has lasted longer than the original connection.  I soldered them.

When you do not know what the proper connector, die and other specs are, do not have the necessary tools and parts, cannot be bothered to look them up and order, or did but the price is out of the acceptable range for the small quantity you need, soldering is usually better than improvising crimps with whatever you have on-hands.

And every now and then you have cases where mechanical connections fail, like one microwave oven I repaired last year which had a burnt switch. After breaking off the melted and charred connector plastic from the intermittent switch because the connector wouldn't come off, I found that the contacts had also spot-welded themselves to the switch, indicating that they were once loose enough to start an arc.

[ConKbot]

Run a high current through a solder joint and a 6.3mm spade connection and notice the difference.

What do you use to secure your spade-to-PCB connectors to the PCB side of the connection? Most likely solder.

If soldering was a no-go for high-vibration environments, there wouldn't be a ~300 pages long NASA standard about how to tin wires and soldering in general for aerospace applications.

Does that NASA document permit stranded cables to be tinned and soldered when used in high vibration environments?  I suspect not.

Your joint shouldn't be providing mechanical support for the wire that's what the lacing on the harness, back shell clamps and padded p clips are for. And for larger gauge stuff, stranded would hold up better than solid everywhere else anyway.

[Psi]

I don't see how solder could improve a crimped joint. A properly crimped joint is already gas tight, and often there are even cold welds that develop, like wire wrap.

It improves your confidence that it's not going to pull out.

Personally, if your quick about soldering and use a high temp I don't think the solder will wick up the wire fast enough to get past the insulation retention crimp.  Might be a good experiment to try. Tin some wire and time how quickly the solder wicks up the wire. Then crimp the same wire and see how fast you can solder it.

[John Coloccia]

I don't see how solder could improve a crimped joint. A properly crimped joint is already gas tight, and often there are even cold welds that develop, like wire wrap.

It improves your confidence that it's not going to pull out.

If you're worried about the wire pulling out, your crimps are no good. If you don't have complete confidence in your crimps, there's no point crimping. You should switch to some sort of solder cup style connector instead because that will be designed for soldering. The whole point of crimping is to make a gas tight, solid connection. If you only manage to make a crappy connection that "pulls out", or whatever, and you feel it needs to be soldered, isn't it better to use a connector that's designed to be soldered?

But that said, it's absolutely trivial to make a proper crimp with a crimper and the correct dies. None of this is particularly expensive, and you would have to be completely brain dead to mess it up. Just make a couple of test crimps and then yank on them to see what it really takes to compromise it. That should give you a bit of confidence in the technique.