Termination of shield on ribbon cable - Page 1
Forum section: electronics / projects

author: ahbushnell
author_rank: Frequent Contributor
timestamp: November 18, 2018, 01:35:25 am
content: I have a application with a ribbon cable that is shielded. I would like suggestions on bringing out a wire to terminate the shield. The shield is a copper wire mesh. I was thinking about soldering a wire to the shield and covering with heat shrink. I have looked on line and I have not seen any examples.ThanksAndy

author: coppercone2
author_rank: Super Contributor
timestamp: November 18, 2018, 01:58:59 am
content: Since its a ribbon cable you can also use a braid of the same dimension I guess.With normal cables you leave the wire in contact with the braid exposed a bit, then do a solder joint and fold it back over the insulation and then put heat shrink on top of it, I don't think you typically solder to the braid itself because its thin wire and it can break from deformation, unless your really careful and have good strain relief.If you do the above method then the insulation of the cable is pressed into the soldered joint and the heatshrink is firm so you have good strain relief around the soldered area, unless you have a real connector that uses a collet.Not sure but you can maybe put a harder backing plate out of plastic in between the cable and the joint to firm it up and offer strain relief, perhaps with some double sided tape.Make sure the solder does not flow under the insulation where it can crack, leave enough braid exposed so there is a non-soldered fold to the junction.What I can't answer is how to use heat shrink in this application without a backing plate, since it will fold the ribbon cable. I think you need one. Or maybe two to make a sandwich.I would ask for a vibration test to be conducted since its pretty weird.

author: ahbushnell
author_rank: Frequent Contributor
timestamp: November 18, 2018, 02:44:15 am
content: Thanks,Since they sell the cables I would think there would be products for termination.

author: wraper
author_rank: Unknown
timestamp: November 18, 2018, 03:09:30 am
content: The only things with shielding I've seen were for round ribbon cable like DB-25(LPT) and connectors for external use on panel, basically usual IDC connector placed into metal shell. For internal use I would suggest simple IDC connector + additional fast-on connector for shield.

author: coppercone2
author_rank: Super Contributor
timestamp: November 18, 2018, 03:31:09 am
content: I got stuck its a junction in the middle of a cable i.e. to terminate it to some random place on the chassis thats convenient for assembly. Otherwise I would recommend a connector too. Unless its some weird high reliability stuffBut not a IDC. Those suck. Try to find some kind of connector like aDINDBx connector that has a ribbon cable acceptance and solder or crimps. I find quite a bit of failed IDC, especially MTA in things like lab PSU, particularly on the front panel where the potentiometers are. Sorensen seems notorious for this. I hate IDC. I would recommend soldering over IDC. I think all 3 of my broken soresen power suppies had issues with the IDC MTA style connectors.My backup battery had a soldered ribbon cable with strain relief and that failed too, but to be fair the ribbon cable they used was complete garbage and it was stiff as hell for some reason. It was one of those plastic sandwich ribbon PCB cables not real ribbon cable IIRC.

author: wraper
author_rank: Unknown
timestamp: November 18, 2018, 04:18:26 am
content: Quote from: coppercone2 on November 18, 2018, 03:31:09 amIME I've seen way more crimps failing compared to IDC. I mean usual IDC with a fixing clip on top. IDC MTA like on the picture below have horrible reliability.

author: ahbushnell
author_rank: Frequent Contributor
timestamp: November 18, 2018, 10:55:32 am
content: Quote from: wraper on November 18, 2018, 03:09:30 amI'm not familiar with fast-on connector? Where do I find that?ThanksAndy

author: SeanB
author_rank: Super Contributor
timestamp: November 18, 2018, 11:56:02 am
content: Fast-on connector, that spade terminal found on small lead acid batteries, on your car and pretty much every electric part used in airconditioners. A way to make assembly faster, but still capable of low resistance, decent resistance to corrosion and does not come loose easily.

author: coppercone2
author_rank: Super Contributor
timestamp: November 18, 2018, 03:49:20 pm
content: Be sure to have a look at the fast on catalog to see the various sub-configurations for something as simple as a 0.250 fast on and check out the lubricants used with them that increase reliability and ease of installation.

author: coppercone2
author_rank: Super Contributor
timestamp: November 18, 2018, 03:50:07 pm
content: Quote from: wraper on November 18, 2018, 04:18:26 amFor anything but production with pneumatic calibrated tools I would recommend solder cup types for DB cables.But I have seen DBx connectors fail too, because the pin managed to ream/push its way out of the plastic over enough installs.Keep in mind too with a oversized DB connector you can do weird stuff like use X2Y capacitors to make a distributed decoupling network directly in the connector housing or install one of those ferrite plates with holes in it to improve EMI performance or do both possibly. I don't know how those options effect reliability though. If he already has to use a shielded cable this might help.http://www.x2y.com/appnotes/suggestions/5002.pdf

author: wraper
author_rank: Unknown
timestamp: November 18, 2018, 04:22:10 pm
content: Quote from: coppercone2 on November 18, 2018, 03:50:07 pmActually with usual IDC it's very hard to do anything wrong unlike with crimp connectors. There is a fixed distance how much you can push the clip until connector fully closes and you cannot push any further. I usually simply place IDC connectors in a vice (with flat shims).

author: wraper
author_rank: Unknown
timestamp: November 18, 2018, 04:29:07 pm
content: Quote from: ahbushnell on November 18, 2018, 10:55:32 amgoogle.

author: coppercone2
author_rank: Super Contributor
timestamp: November 18, 2018, 04:32:53 pm
content: https://www.te.com/commerce/DocumentDelivery/DDEController?Action=showdoc&DocId=Catalog+Section%7F82004_FASTIN_FASTON_Product_Line%7F0311%7Fpdf%7FEnglish%7FENG_CS_82004_FASTIN_FASTON_Product_Line_0311.pdf%7F180907

author: coppercone2
author_rank: Super Contributor
timestamp: November 18, 2018, 04:35:37 pm
content: but for a ground you need to use the ring terminal that's tensioned by a screw

author: wraper
author_rank: Unknown
timestamp: November 18, 2018, 04:39:35 pm
content: Quote from: coppercone2 on November 18, 2018, 04:35:37 pmWhy you would do something like this? It's a shield, not Mains earth connection.

author: coppercone2
author_rank: Super Contributor
timestamp: November 18, 2018, 05:10:37 pm
content: I would recommend terminating it to the same stud you use for earth ground with a ground wire on the chassis.

author: wraper
author_rank: Unknown
timestamp: November 18, 2018, 05:27:59 pm
content: Quote from: coppercone2 on November 18, 2018, 05:10:37 pmWhy in would you generally want to do this? It's quite possible that earth point could be tens of centimeters away and do not provide good high frequency path. And it's purpose is safety, not signal ground.

author: coppercone2
author_rank: Super Contributor
timestamp: November 18, 2018, 05:31:48 pm
content: If possible otherwise another thread mount can be used. How do you typically bond shield to chassis if not through a bulkhead mount or thread protrusion? You can't really mount a faston receptacle on the chassis directly, you need to use a screw, you might as well minimize the amount of interconnects since the screw can be unthreaded. If manufactured you would rather insert a threaded rod into the chassis rather then a threaded hole since its more material efficient and you don't need to use very short screws that are not common or hold weird things in your inventory since you can just use a standard nut and star washer.Unless you mount to a internal wall then you can use a threaded hole since it does not really matter the bolt is not flush with the other side of the internal wall so long its not an obstruction. but IMO its generally kinda shit because well its a screw thats half way sticking out of something lol

author: wraper
author_rank: Unknown
timestamp: November 18, 2018, 05:36:32 pm
content: Quote from: coppercone2 on November 18, 2018, 05:31:48 pmWhy would you want to connect cable shield directly to the chassis to begin with?

author: coppercone2
author_rank: Super Contributor
timestamp: November 18, 2018, 05:39:13 pm
content: that's what I saw typically done on harnesses that connected various electromechanical devices and control/power/communication boards in a single chassis, but it was not a point to point connection more like a harness for an entire device with many many systems.I imagined it similar to basically running all the wires through a shielded raceway but cheaper.

author: ahbushnell
author_rank: Frequent Contributor
timestamp: November 18, 2018, 06:36:29 pm
content: Quote from: SeanB on November 18, 2018, 11:56:02 amHow does a fast-on connect to braid on a shield?

author: wraper
author_rank: Unknown
timestamp: November 18, 2018, 06:42:25 pm
content: Quote from: ahbushnell on November 18, 2018, 06:36:29 pmIf a total thickness of the shield wire is not that high, you could simply put a piece of heatshrink on it and then crimp the end as if it was a usual wire. If it is too thick for crimping, then solder a piece of wire to the shield and then crimp the wire.