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[on:]

I designed a 2x2" PCB that will have a 2.5" square component soldered to it, and I plan to have a row of these assemblies mounted to a plexiglass backing.  What's the best way to mount them?   I put some mounting holes in the PCBs, but once assembled, the larger component will cover them.  If I socket the larger component, the whole assembly will be too thick.

I'd like to just put the screws through the mounting holes before soldering the component on, but once I have a spacer around the screw, I won't be able to stop it from turning while I try to tighten the nut.

I even thought about gluing nuts to the component side of the PCB, but if the glue breaks, I have a metal nut bouncing around my delicate electronics and no way to reattach it.

Thanks for any suggestions.

[Reply #1 on:]

There are things called press-fit studs. They have a plain head.  The shaft is splined near the head and the rest is threaded.  You press them into holes (in your case in the PCB) and they work as captive bolts.  You would put spacers on them, stick them through the mounting panel, and put nuts on the other side of the panel.

I did a cursory search and all the ones I found for for mounting wheels so the smallest was 1/4-20 thread.  I'm sure someone makes them in smaller sizes.

[Reply #2 on:]

Thanks for the reply.  Searching for press-fit studs, I just found the wheel ones you mentioned and a whole bunch of body piercings.  Expanding on your idea though, I did find "self-clinching nuts", which sound good except that my holes are 3.2mm and the smallest self-clinching nuts I could find require a 4.2mm hole.

That also gives me the idea of gluing a bolt into the holes, if that glue breaks, the bolt will have nowhere to go.  Maybe a nut directly on the other side of the pcb from the bolt head?

[Reply #3 on:]

Are these too big for in-board sockets for your component so it can sit on the board as if soldered in?
http://www.dipmicro.com/store/index.php?searchStr=pin&act=viewCat

[Reply #4 on:]

Are these too big for in-board sockets for your component so it can sit on the board as if soldered in?
http://www.dipmicro.com/store/index.php?searchStr=pin&act=viewCat

It matches 68 pages of items, I think you mean the pin receptacles that are the first match.  The smaller size is still bigger than my drill hole and probably too big to get a friction hold on my component, and at 25 cents each in quantity, for the number of holes involved, it will double the price of my project.

I'm thinking of using standoffs like http://www.dipmicro.com/store/SPC-M307B which I screw to the board before I solder the module, but if it loosened, I couldn't retighten it so maybe some threadlocker is a good idea (and I've always hated threadlocker).  Also he only has 13 in stock.  I already emailed him since it says restockable.

[Reply #5 on:]

heh velcro

[Reply #6 on:]

Same kinds of parts are available in other sizes. If you're trying to fit them in holes designed to accept pin legs, you might be out of luck.
Have you looked at "low profile" sockets?
http://www.digikey.com/product-detail/en/115-93-628-41-003000/ED5628-ND/81899
or the pins that are used in them?

[Reply #7 on:]

As far as low profile sockets, I did look at http://www.dipmicro.com/store/HDR40X1FM which might be low profile enough, the site says around 5mm, I think I can handle that, but I'm not very familiar with them as far as how tight they'll hold, and I'll definitely have to trim my leads before insertion, though I don't suppose that's really a problem, as long as I can keep my board heights consistent.

[Reply #8 on:]

That's not low profile. The part I linked to sits just 0.095" above the board.
You haven't said what pin configuration is needed, I bet socket strips for widely spaced legs are available also.

[Reply #9 on:]

Sorry, each module has 2 rows of 0.1" pins, 8 pins on each row, 1.8" apart.  The pins are about 1/2" long, but I was assuming I'd trim after soldering.

I know what I linked wasn't low profile but it's a lot better than the normal headers I'm used to (like the arduino uses for shields).   My part's 5mm is longer than I'd like but should be good enough, plus it's cheap and I've had good experience with dipmicro.  Your 0.095 wouldn't be a problem at all, assuming I don't shoot myself in the foot when I try to trim the leads evenly

[Reply #10 on:]

Ok, you know your height requirements, good to see you have some options.

[Reply #11 on:]

That also gives me the idea of gluing a bolt into the holes, if that glue breaks, the bolt will have nowhere to go.  Maybe a nut directly on the other side of the pcb from the bolt head?

Why not a solder pad on board and solder the bolt-head to the board.

[Reply #12 on:]

Why not a solder pad on board and solder the bolt-head to the board.

I should test this before rejecting the idea, but my understanding is solder won't stick to galvanized steel or whatever they make the bolts out of.  Any idea if that's true?  Maybe if I find some brass bolts?

[Reply #13 on:]

Most hardware is zinc plated. At a prior employer,We had to mask screw heads on PC boards before we wave solder them.