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I learned soldering after IPC-J-STD-001 E during my apprenticeship 10 years ago and my instructor told me that you don't use heat shrink tubing on connectors, but recently I've seen a lot of this and some of my colleagues say that you should do it.

Let's say you have a connector like this:

enter image description here

Should I use heat shrink tubing on each pin or not and why?

Darkproduct
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  • There is no one true answer if you should or should not. It likely depends on who you ask and for what the connector is used. Maybe you should ask your colleagues why if they say so. It might be highly dependant on what you do. – Justme Apr 28 '22 at 08:59
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    i like to entomb such close-knit connectors with hotglue to provide electrical isolation, strain relief, and mechanical strength. You can peel it off with a hot air station later if needed, much easier than carving off shrunk shrink tubing... – dandavis Apr 28 '22 at 09:02
  • Let's say it is for a 50 cm cable for an absolute encoder using CAN Open. – Darkproduct Apr 28 '22 at 09:02
  • It still provides no info what would happen differently whether or not heat shrink is present. – Justme Apr 28 '22 at 09:12
  • @Justme It's used in a custom robot built for agricultural purposes. The connector will get the normal d-sub casing. The robot is used in competitions and runs maybe a few hours every month. – Darkproduct Apr 28 '22 at 09:22
  • if run in a moist and/or saline environment, tubing could help prevent corrosion of some of the pins with constant DC voltage. – dandavis Apr 28 '22 at 09:25
  • @dandavis In case corrosion is an issue then something is off though. Wrong currents, botched soldering, wrong materials, problems with the enclosure etc etc. – Lundin Apr 28 '22 at 09:45

3 Answers3

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Generally, when doing things by the book/IPC, then shrink tube should not be necessary on DB9 solder cups, because the need for them implicitly means that the solder job was botched somehow.

Common problems would be: peeled the insulation too far or melted it, used too much solder, placed the wires at bad angles, got solder wetting on the outside of the cup etc etc.

However, these are a classic example of connectors that the majority who haven't gotten professional IPC soldering certification will definitely mess up. And then shrink tubing can be used for damage control purposes. Note: shrink tubing will rarely cause any harm!

This is how you formally solder DB9 and similar solder cup connectors:

  • Use AWG26 wire with multiple strands.
  • Peel the wires in advance at a fixed length equal to the depth of the solder cup.
  • Gather the strands gently with your fingers - don't twist them together with force, they should follow the natural twist they had before you peeled.
  • Pre-solder the wires by covering the exposed wire with solder. Easiest way to do this without melting the insulation is to start with the tip close to it, then move the tip outwards towards the cut.
  • Fixate the DB9 with a vise or similar.
  • Cut off a bit of your ~0.5mm solder and leave it inside each cup.
  • Heat the cups from the outside while inserting the prepared wire. Wire straight along the cup, obviously, with no space in between.
  • There should be no solder leaking out or wetting on the outside of the cup, or touching the iron tip etc.
  • If everything is correct, the plastic insulation of the wire now ends exactly where the cup begins, no part of the peeled wire is exposed, the insulation isn't melted and of course there needs to be proper wetting in the joint itself.

This would be as per the highest IPC requirement for solder certification, military use and the like. Very few people solder DB9 this carefully!

I certainly don't when I just need some quick & dirty lab cable assembly done, rather than spending some 30 minutes on a single DB9. And that's when the shrink tube comes in - to hide away your quick & dirty solder job...

Also these solder cup connectors are a pretty horrible invention in my opinion, since you often get mechanical strain at the solder joints. Shrink tube could help slightly in catching that blow, though if doing things by the book, then some proper external strain relief mechanism should of course be used. I would generally recommend to forget all about solder cup DB9 if possible and use IDC versions instead, they are far more rugged and reliable.

Lundin
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you don't use heat shrink tubing on connectors

This should come with a explanation. Why did he suggested not to use heat shrink tubing?

Should I use heat shrink tubing on each pin or not and why?

You should do whatever fits the application. In my workplace, we do use heatshrink tubing on those connectors when we make a device for a customer, since there is a chance that a piece of stray metal can fall between the connectors and short them out while we test the device or when the customer uses the device.

But when I do prototyping and use these connectors, I dont use heat shrink since it will take me much more time to apply them, and I might have make a wrong connection (since its prototyping) and its easier for me to change the connection without heat shrink.

Christianidis Vasileios
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If you want a durable connection that looks professional and can be relied upon in a moderately safety-critical application then heatshrink is a good idea. For less demanding applications it’s fine not to apply heatshrink, especially if you might need to probe the connections with a meter or oscilloscope.

Frog
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