Mechanically mounting connectors to PCB - Page 1
Forum section: electronics / general

author: dkonigs
author_rank: Regular Contributor
timestamp: August 26, 2024, 06:04:24 pm
content: So I'm not entirely sure if this is the right forum section for this, but here goes...I have a PCB that has a bunch of right-angle IEC connectors along one edge. These connectors have mounting holes on both the PCB side and the enclosure side, and I want both to be secure.On the PCB side, my current solution involves a stack-up of screws, washers, and locknuts. Here are a bunch of pictures showing this, from CAD renderings. (since its easier to do it from renderings than photos at the moment)Assembling this is a little on the fiddly and annoying side. I have some jigs that hold the connectors in proper alignment, but I then need to feed the screws in through holes in these jigs. On my last prototype, I made the bottom a tad easier by making a jig to also hold the nuts in place, but it won't stand up to tightening without some changes.I keep wondering if there's a better way to mount these. I once saw another device that used what appear to be pop rivets to solve a similar problem:Though its unclear if this is actually a good solution, whether there are mechanical stress concerns on the PCB or connector side that might make it a bad approach, or even exactly what type of rivets would work best for this.Its sure tempting, for the likely ease of assembly, but without taking all those other details into account it makes me a tad uncomfortable committing to.Another option is to simply have a really good jig for putting this together. That would involve building something that holds the nuts in socket-wrench-like fittings, so I only have to worry about screws from the top. I'm not making jigs in a machine shop, just using a 3D printer and ordering laser-cut parts where applicable, so I have some ideas for bringing the two together. But not entirely sure yet.So any tips for how to make assembling something like this easier/quicker?

author: Doctorandus_P
author_rank: Super Contributor
timestamp: August 26, 2024, 07:01:38 pm
content: Pop rivets look like a bad solution here, especially when inserted from the underside. It puts a lot of stress into the plastic and pushes the holes "sideways".Why use a jig at all? Is alignment not good enough without a jig? I had a look at right angle C14 connectors and was a bit surprised that these do not have alignment pins. Many smaller connectors do have alignment pins molded into the plastic.

author: themadhippy
author_rank: Super Contributor
timestamp: August 26, 2024, 07:33:00 pm
content: instead of individual nut hows about a plate with threaded holes

author: thm_w
author_rank: Super Contributor
timestamp: August 26, 2024, 07:37:50 pm
content: You can get push in plastic rivets, though they are not terribly strong.Or you can SMD nuts that you solder on to the PCB on the back side, and then screw into those.But, the receptacle is mounted to the case, the PCB is mounted to the case as well right? There should be no need for these lower screws, I don't see how they add any mechanical strength unless its the PCB is loose inside and completely hanging off this receptacle, or you are doing some serious drop tests.

author: dkonigs
author_rank: Regular Contributor
timestamp: August 26, 2024, 09:16:33 pm
content: Quote from: Doctorandus_P on August 26, 2024, 07:01:38 pmYeah, that's my big concern and the reason I'm quite hesitant to take that approach.Quote from: Doctorandus_P on August 26, 2024, 07:01:38 pmYeah, because these connectors don't have alignment pins, its hard to make sure they all form a straight line parallel to the PCB edge without using a jig. Regardless, I still need to hold everything together in a way that makes it easy to actually install the screws/nuts without something falling out during the assembly process.Quote from: themadhippy on August 26, 2024, 07:33:00 pmThat's not a terrible idea in theory, it just that it might be easier said than done.I'd need to get this plate manufactured with holes tapped into it, possibly also with a layer of insulation between it and the PCB, and the cost of all of that could easily add up. Especially when the alternative is using cheap mass-produced off-the-shelf fastener hardware.Quote from: thm_w on August 26, 2024, 07:37:50 pmPush-in plastic rivets are an interesting idea, and the mechanical strength problem may or may not be an issue.SMD nuts would likely require double-sided reflow, which I'd rather avoid.Quote from: thm_w on August 26, 2024, 07:37:50 pmThe PCB is primarily secured to the case through these connectors, since I want them tightly fastened to the rear panel. There are screws on the other side, but the positioning of those is a bit looser on tolerance.

author: thm_w
author_rank: Super Contributor
timestamp: August 26, 2024, 09:57:05 pm
content: Quote from: dkonigs on August 26, 2024, 09:16:33 pmOK so you are using it as support for the board itself on that side, that does make sense now.You can also have plastic self-tap or thread forming screws coming up through the bottom of the PCB and into the connector. But the plastic is so thin that might not be effective.https://engineeringproductdesign.com/knowledge-base/self-tapping-screws-for-plastics/

author: langwadt
author_rank: Super Contributor
timestamp: August 26, 2024, 10:15:53 pm
content: Quote from: dkonigs on August 26, 2024, 09:16:33 pmmake the plate as cheap PCB with just the SMD nuts ...JLCPCB has nuts,https://jlcpcb.com/partdetail/Sinhoo-SMTSO3015CTJ/C2915632

author: dkonigs
author_rank: Regular Contributor
timestamp: August 26, 2024, 10:18:09 pm
content: Quote from: thm_w on August 26, 2024, 09:57:05 pmI actually use those extensively for installing PCBs into plastic enclosures on other projects. In those cases, the hole in the plastic is sized appropriately for them and deep enough to grab well. But yeah, they really wouldn't work very well in this particular case.

author: dkonigs
author_rank: Regular Contributor
timestamp: August 26, 2024, 11:01:53 pm
content: Quote from: langwadt on August 26, 2024, 10:15:53 pmThat's a very interesting idea I hadn't thought of before, and I'm not sure I've seen anyone do it. But it just might work, assuming JLCPCB can crank them out for cheap. May even be worth prototyping the design files, just to see. Would also probably do it as a single-sided PCB just to be safe on scratching and insulation. I'd still likely need to put a tab of threadlocker in each hole, but otherwise it would save most of the "fiddly work".

author: mtwieg
author_rank: Frequent Contributor
timestamp: August 27, 2024, 11:54:00 am
content: I would only use those board-side screws/rivets if they're fastened before the through hole soldering process. Otherwise when you apply the fasteners you're going to put a great deal of stress on those solder joints, even before mounting the PCB in your assembly. Doesn't look like those pins are meant to bend at all.Using threaded inserts or SMT nuts would also make assembling those fasteners a lot simpler, at the cost of an added process to the PCB assembly.

author: dkonigs
author_rank: Regular Contributor
timestamp: August 27, 2024, 02:05:56 pm
content: Quote from: mtwieg on August 27, 2024, 11:54:00 amThe pins on my board look quite similar to the ones in the example board I showed. They're just covered with shrouds on my variant of the connectors. So they should be okay with a little flex in at least one direction.However, I do align and mechanically secure them before soldering for the reason you suggest. Otherwise the same flex concerns would also come up from enclosure mounting.