Insulation shrinkage when soldering wire

[AlfBaz]

Every time I have to solder insulated wire to connectors (D9's usually) I'm reminded of how much this task shits me
You bare back enough copper to solder onto the terminal but inevitably the heat causes the insulation to shrink back exposing more copper wire and usually leaving behind a thin layer of melted insulation. I don't like it as it looks very untidy any tips?

[IanB]

No easy answers. You can either use different wire with heat resistant insulation, or you can improve your soldering technique.

[AlfBaz]

...or you can improve your soldering technique

which leads me to this post

[AKM]

Use heat shrink tubing to cover it up.

[mariush]

Proper soldering iron tip.
Proper soldering iron temperature
Flux & tinning
Speed

This guy doesn't melt the insulation:

[IanB]

This guy doesn't melt the insulation:

Oh my word. He just turned soldering a wire to a pin into the most time consuming and labor intensive process conceivable.

[GreyWoolfe]

I have a friend who is an ISO-9000 certified solderer.  The company he worked for at the time does military contracts.  That is basically how he soldered.  That is why military gear is so expensive.  It take forever to solder all the components in.  Add in that they could only keep the Metcals so long before they needed to replace them.  This was in the contract also.  The employees would get a chance to get the equipment cheap when it was replaced.

[SeanB]

Yes, but if you are aiming at aerospace you will do it.  Helps as well that the wire is not PVC insulated wire either but is likely a high temperature insulation wire like PTFE or polyamide sheathed.

[IanB]

I doubt there is any evidence to prove that such a laborious process produces a statistically significant improvement in reliability.

[babysitter]

I also suggest working fast and hot, sub-second solder time is possible.
Also, if you have a lot of D-SUB to do, get either wires coated with heat-resistant isolation (PTFE, PVDF) or consider crimping which needs a additional tool but is a completely cold process.

[robrenz]

This thread may be of interest. Commercial versions are mentioned later in the thread.

[ejeffrey]

Make sure your soldering iron is hot enough.  Too cold a tip is probably the number one cause of overheating.  Apply flux, tin the wire and the contact, apply more flux, and solder the joint.  Practice.   You can do fancy things like heat sinking the wire if you want, but just getting this basic technique down will improve things dramatically, and should be all that is required for soldering a wire to a pin.

[FrankenPC]

Proper soldering iron tip.
Proper soldering iron temperature
Flux & tinning
Speed

This guy doesn't melt the insulation:

I love that small spade iron tip.  The tip makes all the difference when it comes to applying just enough heat and solder.

[David_AVD]

You can strip less of the insulation to take the shrinkage into account.  Typical ribbon cable shrinks a reasonable amount.

Using a hot iron (700°F or about 350°C) and not lingering on the joint is also important.

Obviously use a decent solder, like 63/37 leaded type.

[AmmoJammo]

This guy doesn't melt the insulation:

Oh my word. He just turned soldering a wire to a pin into the most time consuming and labor intensive process conceivable.

kill me now 

[mikeselectricstuff]

Easiest way for D types etc. is to put solder in the contact, tin the wire, put some flux on, then flow them together. Saves needing to hold wire, solder, connector and iron. 
Also quicker for multi-pin cons as you can fill all the contacts, then tin all the wires (maybe using a solder pot if you have a LOT to do) , flux across all then just dab each into place. 

[Shock]

That guys video was crap and I'd like to see him do that with a multi-strand cable.

This is going to be a breakthrough in your technique as it's really the same principle for all joints.
The trick is to start with more wire than you need when tinning and don't tin right up into the insulation.

1. Flux the wire strands and use an iron with a chisel tip in a stand or a solder pot to tin the wire.
2. Trim to size and arrange every strand while checking for a good fit first.
3. Then add flux and a "solder preform" to the cup.
4. Use the iron to melt the preform as you insert the wire.
5. It will tin and take up a little solder into the wire at the same time.
If done efficiently the heat is localized to the joint.

These videos cover tinning the wire and soldering into a cup.

[Alexei.Polkhanov]

Huh?
Why not simply use KYNAR wire wrap if you care so much? It costs more but does not shrink, well almost.

[David_AVD]

Huh?
Why not simply use KYNAR wire wrap if you care so much? It costs more but does not shrink, well almost.

Probably because it's single stranded.  Move it around a few times and snap!

[MLXXXp]

I'll sometimes pre-shrink insulation on wires that do this. Strip off a length of insulation slightly shorter than what you need and then apply a hot soldering iron to the wire close to the insulation, for a few seconds, to shrink back the insulation. Any insulation "gunk" left from shrinking can usually be pulled off with your finger nails. Cut the exposed wire to the correct length. You shouldn't get much more shrinkage.

[woodchips]

The other little secret is to not use a pull type stripper on the insulation. All that does is stretch the insulation and when it is heated up, bingo, it contracts.

Use one of the hot double Vee type strippers to melt the insulation and then pull it off when no longer connected to the rest of the insulation on the wire. A pair of real precision side cutters can do almost as well, but lots of risk in nicking the strands.

[Alexei.Polkhanov]

Another nice solution for same problem that  use rarely is red insulating varnish from MG Chemicals that I picked up at local electronic supply store. They also have connector coating but it is not transparent and that sucks if you are looking for bad solder joints.

Nail varnish/polish works fine too but cheap ones may be brittle and nail polish does not have the poisonous stuff in it that required to kill off the mold in case if you care about the mold.

[AlfBaz]

meh... good enough I guess

Seems like I got better at it by the time I got to the red and black wires

[Monkeh]

That's absolutely fine. Add heatshrink for strain relief if you want a nice job.

Also, see the preform technique from the Pace videos for consistent solder fill of the cups.

[AlfBaz]

Also, see the preform technique from the Pace videos for consistent solder fill of the cups.

I'll look for them as it's difficult to get a nice fillet on the cups when you are trying to get in and out with the iron real quick

[Monkeh]

Also, see the preform technique from the Pace videos for consistent solder fill of the cups.

I'll look for them as it's difficult to get a nice fillet on the cups when you are trying to get in and out with the iron real quick

You make them out of solder wire. Twisted wire, cut to fill the cup.

I really recommend watching those Pace videos, relevant ones to this are a couple posts up.

[David_AVD]

I go around to all the pins first and fill them with solder, then tin the wire ends.  Lastly I reflow the solder cup, sliding the tinned wire into place.

It's very easy once you get the hang of it.  After a while you'll just know how much solder to pre-fill the cups with for a given terminal and wire size.   

I would never waste my time twisting solder together they way they show in the Pace video.

[Psi]

Number one thing is iron temp. Do some tests and figure out how low you can go while still soldering quickly.
Usually i solder wine into small connectors at around 300C

Next is the wire type, some brands of wire have more of a problem with melting than others.
Some insulation types (silicon) don't melt at all when soldering and are really awesome to work with.

You will notice that the insulation melts back on the wire noticeably more the first time you apply heat compared to the 2nd time.
It seems to be a 'heatshrink' style property of PVC insulation, once it shrunk a little it doesn't shink as much when re-heated.
Or it maybe due to the insulation deforming/stretching from your wire stripper. The plastic then tries to return to it's initial shape when heated.

So.. pre-tin the wire longer than you need then cut to length after tinning. This also helps because soldering tinned wires is easier/faster which reduces the time in which the insulation may melt.

Hold the wire with sometime close to the joint. (to at as a heatsink). This will reduce the temp rise in the wire leading away from the joint.

Lastly solder as fast as you can while still getting a good joint.

[Stonent]

Use heat shrink tubing to cover it up.

That was my thought as well.

[aroby]

Use heat shrink tubing to cover it up.

Sounds like the electronics equivalent of caulk ...

Anthony

[Stonent]

The end result would be something like this:

[AmmoJammo]