Reliability of potted spring loaded connector - Page 1
Forum section: electronics / projects

author: webgiorgio
author_rank: Regular Contributor
timestamp: May 03, 2017, 09:35:44 am
content: I have to resin pot a PCB which is connected to only a network cable. The 8 pin RJ45 connector goes into the plug, which is soldered onto the PCB.What happens to the contacts "spring" loading when potted?The potting compound is, when poured, as liquid as water, so I am afraid that wetting the spring loaded contacts will isolate them, causing reliability issues.Has anyone heard of potted wire-to-board connectors failing?Here I've found that potting connectors is a bad idea, and solder the wire directly on the board is much more reliable. Even though it is time consuming.https://electronics.stackexchange.com/questions/96002/potting-connectors

author: DTJ
author_rank: Super Contributor
timestamp: May 03, 2017, 09:50:09 am
content: Do you want to plug the cable into the RJ45 and then pot the lot immersing the plug & connector?My experience is that if the potting compound can get between contacts it will and you'll end up junking the entire assembly. To save time soldering the wires to the PCB just use surface mount pads and don't bother with placing them through a hole. If you want strain relief run the insulated cable through a 2 or 3mm hole in the PCB adjacent to the solder pad.Or do you want to pot the board leaving the aperture for the RJ45 still accessible?

author: webgiorgio
author_rank: Regular Contributor
timestamp: May 03, 2017, 11:14:07 am
content: The idea is to use a network cable with pre-moulded plugs, and to resin the plugs as well as the connector.In that case the plastic container will have a rectangular hole on the side, through which I will insert the plug into the connector. I will then seal the plug to the plastic wall with hot glue (to avoid the resin to flow out).See attached drawing

author: BrianHG
author_rank: Super Contributor
timestamp: May 03, 2017, 11:29:14 am
content: Due to potting compound entering the connector and locking the location of the contact springs, the moment you move or bend the cable externally, or, there is a change in temperature, the stresses will eventually disconnect the springs in the jack from your plug. I tried it before with simpler sip connectors, it was a disaster.

author: Ian.M
author_rank: Super Contributor
timestamp: May 03, 2017, 01:16:38 pm
content: On-board IDC connectors, terminate a bare cable end with a punchdown tool, secure the cable then pot.

author: webgiorgio
author_rank: Regular Contributor
timestamp: May 04, 2017, 08:20:34 am
content: Mhh, after hearing your experience, I will solder.My issue with soldering was also the wiring mistakes that might occur (which are avoidable with the pre-made cable and PCB RJ45 socket).So far I soldered the cable on the footprint of the RJ45 socket, which is quite small and very uncomfortable to solder (two rows of 4 pads).Next PCB will have 8 large pads in a single row, and silkscreen the cable colours. So hopefully no mistakes (anyway I test every unit just before potting).I tried with a 10 pin IDC connector (like the black one in figure attached), but being it made for flat ribbon cables, the cat5 wires are very hard to push into the connector.Maybe with a real punch down PCB connector is better (second attachment), but I could not find the part number. Anyway, also the punch down solution is spring loaded, so, as others said, it will end up having problems after potting.

author: rs20
author_rank: Super Contributor
timestamp: May 04, 2017, 08:26:30 am
content: Can't you just prevent ingress of the resin into the connector?

author: AndyC_772
author_rank: Super Contributor
timestamp: May 04, 2017, 08:55:24 am
content: An IDC connector should be much better than an RJ45 in this case.With a properly made IDC connection, the wire ends up cold welded to the sharp corners of the IDC terminal. It's not relying on spring pressure, and there's no gap between contacts into which potting compound might flow.AVX do a range of surface mount IDC contacts which could be ideal.