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I have two separate circuit boards that each have the same 8 hole row near their edges and I need to make a bridge from one PCB to another. Placed like that, the distance from the first PCB’s first hole to the second PCB’s mirrored one is about 4mm - 4,5mm.

What is the best way to permanently connect these to one another in a neat and compact way? Some sort of staple shaped pins that I don’t know the exact name of yet because I’m new to this?

Usually I can easily find the answers by searching online but somehow the key words in this are involved in far too many rather general topics, so I'm afraid that a mere search engine won't understand the relations of the terms involved here; better ask a human.

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  • \$\begingroup\$ Maybe extended pin headers or ribbon cable. \$\endgroup\$ – H. Puc Jan 30 '18 at 10:12
  • \$\begingroup\$ Are you designing the PCB boards? Because then I would recommend something like an ISA or PCI slot. \$\endgroup\$ – Goswin von Brederlow Jan 30 '18 at 12:39
  • \$\begingroup\$ @GoswinvonBrederlow These were bought as is, almost; The larger PCB is a ready 4x4 switch matrix with housing and all, and the small PCB is an RJ45 socket breakout board. The key matrix (numeric pad) is a part of a much much larger project that I'm designing myself, but I want freedom in the physical placement of the key pad, so this is my plan now. If the key pad's physical distance from the rest of the actual mother device varies by setup, all I need to do is swap the RJ45 cable into one of perfect length. \$\endgroup\$ – user158589 Jan 30 '18 at 15:17
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For staple-shaped connectors you are either looking at:

  • U-Shaped Headers. For example, Farnell sells them as Board-to-Board connectors, such as these here.

  • Solder anchors. Digikey sells these, they are single U-shaped components used on motherboards to hold heatsinks in (typically). Digikey link is here.

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I would consider connecting them with 90° angled male and female header pins, while on each end of those add 2 "spacers" and use small (such as M3) screws to hold in place, as shown on photo below.

Different shade of green shows on 2 different PCBs, while on one side there are female and on the lighter green side they are male pin headers. I've drawn straight instead of 90° angled, but you get the point. On each side, you have those small grey "boxes", which are aluminum parts with 2 drilled holes for your screws (as I've said, such as M2, M2.5 or M3, depends on size of your PCB) and the red are the screw heads. Needles to say, use washers and nuts on the bottom of your PCBs. I think this will be quiet a good, permanent connection between them.

enter image description here

EDIT: 3 new options came to my mind; Both ones start with setting one PCB on top of another, so the holes match. One option is to fully cast both holes together with the solder. I wouldn't recomend this option very much, as other 2 are more stable.

Second one is to stack holes again, one on top of another and push through copper wire, as thick as possible, that goes through the holes, then solder it on both edges (on top of top PCB and bottom of bottom PCB).

The third one is very simmilar to the second one, but use pins for this application, such as these: enter image description here

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  • \$\begingroup\$ Actually the other PCB is only the width of the 8 holes (it's an RJ45 breakout board, widest edge is the one with the holes), so there's no space for additional holes.. I may need to secure things directly to the housing in way or another. (oops, didn't realize that pressing enter posts the comment) But as you suggested, I managed to find 8-pin 90° headers; Looks like the other one has to be male-male and the other one has to be male-female. Of what I find, the female side housing looks quite tall, i.e it might not allow the PCBs to be as close as that but it does make a connection. \$\endgroup\$ – user158589 Jan 30 '18 at 10:50
  • \$\begingroup\$ But if the connector(s) used are not staple shaped but consisting of two L shapes instead, they will detach.. If I won't be able to use screws, I'm thinking if I could join the board edges with epoxy glue that would disallow the angle pins from detaching, but I must say, the holes on the small PCB are very close to the edge: Distance from edge of hole to edge of PCB is shorter than edge of hole to another hole's edge. \$\endgroup\$ – user158589 Jan 30 '18 at 10:58
  • \$\begingroup\$ @user158589, why would they detach? If you use a male header on one side and female on the other, they should stay connected. \$\endgroup\$ – Catsunami Jan 30 '18 at 23:13
  • \$\begingroup\$ @Catsunami Well, if there is no fastening method that secures the actual boards together, then if all you have is a plug-in type connector that detaches by moving the boards away from one another, that can be an issue. Unless the female sockets are really tight, being able to endure some pull and weight. That's why I was thinking of an uninterrupted staple shaped "bridge" because not only can it be fastened to the board by soldering, for it to come off, you'd have to pull it to a direction that's different than one that makes the boards come apart. \$\endgroup\$ – user158589 Jan 31 '18 at 15:18
  • \$\begingroup\$ @user158589, we use female->male 90 degree connectors in manufacturing fixtures and they are really tightly connected. I deal with the manufacturing facilities constantly and they've never reported any issues with connectors coming apart. However, I guess it depends on the stress your boards can encounter. I was thinking in traditional embedded applications you wouldn't apply stress directly to the boards anyway (maybe you would apply it to the enclosure). Continued in next message... \$\endgroup\$ – Catsunami Jan 31 '18 at 15:33
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It depends how many units you intend to produce, if this is a one off, bent zinc-plated paper-clips are cheap, easy to solder and very strong.

just make staples out of paper-clip wire and solder them in. alternate top and bottom for extra rigidity.

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  • \$\begingroup\$ Or just use copper wire to do the same. \$\endgroup\$ – Fredled Jan 30 '18 at 20:49
  • \$\begingroup\$ It's a one off, yes. Is there a significant difference in the metal of paper clips vs. actual staples? As in why staples wouldn't work. I actually only used the term staples to describe the basic shape of a connector, not to really refer to actual paper joining staples. They could of course be wonderful if they work and can be soldered. I have no idea. For now I don't have a tool to agilely bend or cut actual paper clips so I'll only go for that if there's significant benefits to it, as compared to use of dedicated electrical components. \$\endgroup\$ – user158589 Jan 30 '18 at 21:15
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    \$\begingroup\$ Staples: there's lots of different kinds of staples, some with rectangular wire, some with round, some with copper, some with zinc, probably some with aluminium plating. Test solderability. one advantage of paper-clips is you can find a size that nearly fills the hole and get maximun strength, also solerability is good. staples are usually made from softer steel than paperclips and the don't fill the holes as well as paper-clips do. \$\endgroup\$ – Jasen Jan 31 '18 at 5:12
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    \$\begingroup\$ @Jasen Hmm that's true. Although, staples probably exist for various uses as well, for example I'm sure that upholstery staples must be heavier than paper staples. There may also be other industries that use them. Are there any materials that I should avoid? Metal is metal, but if I'm ignorant, what looks good at first could end up being an unreliable conductor or a material that changes over time either due to current flow, materials and heat used at soldering, or just spontaneous wearing out. On the other hand, jeweller's wire twisters and cutters should be easy to get though. \$\endgroup\$ – user158589 Jan 31 '18 at 15:24
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    \$\begingroup\$ alluminium is nearly impossible to solder galvanised steel (which is Common for most hardware staples) is moderately hard to solder stationery staples come in many different finishes some will take solder easily. whatever they use to collate the staples into sticks probalby doesnt help solderability. \$\endgroup\$ – Jasen Feb 1 '18 at 2:21

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