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My design has a number of boards stacked on top of each other. I would like to connect signals across the boards. The boards all need the same 10 signals running through them (all boards from top to bottom), so that simplifies it a bit.

What could be a possible solution (or type of part) that is simple but also inexpensive for this type of design?

I am OK with any type of connector (vertical, parallel, right-angle, press-to-fit, contact-based, etc.) or architecture really, because if it would allow this type of multi-board passage of the signals, it would bring significant convenience to my design.

Relevant points:

  • MOST important: I would like the spacing between the boards less than 5 mm. Otherwise, it would make my overall design prohibitively tall.

  • My standard go-to for just two boards would have been a male-female header-socket combo. But, in the multiple-board case, if I were to have female sockets/receptacles on the top of each board and male header pins on the bottom of each board, then overlap creates an issue with the soldering/placement.

  • I also considered female sockets/receptacles which have lengthy/extended male ends (so that the same socket could be used as female and male), but these are rather expensive.

  • The stacked-board count varies for each of several slight variations of my basic design, so I would ideally like a method that works for a variable number of stacked boards.

  • The number of layers is currently 2 (two) but if necessary, I am open to making the board 4-layer or greater.

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  • \$\begingroup\$ How many layers are these boards? \$\endgroup\$ – Matt Young Oct 1 '12 at 17:57
  • \$\begingroup\$ @MattYoung: Added it at end of my question now. \$\endgroup\$ – OrCa Oct 1 '12 at 17:58
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    \$\begingroup\$ You could just use the surface mount version of those headers you were talking about. Then you can stack them back to back no problem. Just use vias to connect. samtec.com/ProductInformation/TechnicalSpecifications/… \$\endgroup\$ – Some Hardware Guy Oct 1 '12 at 18:10
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    \$\begingroup\$ Yes, Samtec has a huge variety of surface-mount board-to-board connectors. I particularly like the SFM/TFM series of 1.27-mm (0.05") dual-row connectors. If you want to go even tinier, try the CLM (1.00mm) series. \$\endgroup\$ – Dave Tweed Oct 1 '12 at 18:22
  • \$\begingroup\$ Perhaps you could glean some ideas from pre-existing stacking modular connector boards. The list at Wikibooks currently includes PC/104, PlugaPodS, R-Dev-Ino, Bug Labs, modules from JeeLabs, etc. \$\endgroup\$ – davidcary Oct 2 '12 at 19:33
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Board to board connectors are what you're looking for. SMT of course

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In this answer I discussed using these spring connectors to connect boards:

Available in lengths up to 30 contacts, 1.27 mm or 2.54 mm pitch, so that a 10 contacts version doesn't have to be wider than 12.7 mm. Like I explained in the other answer this doesn't fix the boards mechanically though, and I explained in the other answer how I used snaps in the enclosure to fix them.

If you have a custom enclosure this is the most easy way of mounting: just push the different PCBs down the snaps. No screws, no mounting holes. The spacing between PCBs is 3.81 mm (0.15 inch).

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If you have the space for these on every board, you could try using long male headers to stack multiple boards on the same pins:

enter image description here

https://www.sparkfun.com/products/10158


If you want to be able to seperate the boards again you can use feed through sockets on the top boards.

enter image description here

https://www.samtec.com/products/hle

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    \$\begingroup\$ Can't be undone though, as you won't have access to the solder joints of the middle PCBs... \$\endgroup\$ – Mister Mystère Dec 28 '15 at 13:28
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How about etching edge connectors on your PCB's, turning them into cards? Then construct a little PCB back plane stuffed with connector sockets. Maybe some such sockets can be found that will give rise to a 5mm spacing.

If no suitable thin-profile edge connector sockets can be found, they could perhaps be condensed by staggering, so that your backplane PCB has two runs of 10 lines, and odd-numbered PCB's have the edge connector on the left, even-numbered on the right.

The boards could actually be identical, so that any board can go into any slot. That is to say, each board could have a pair of redundant edge connectors on the backplane edge. Depending on the position in the staggered-socket backplane (odd slot versus even slot), either the left or the right edge connector engages with a socket. The unused edge connector on the opposite side slides in the narrow gap between the sockets of adjacent boards, where there is just enough clearance for the board width.

One nice thing about a backplane is that if board 1 has a bad connection to the backplane, that usually doesn't interfere with the communication between 0 and 2. If you stack many boards serially with board to board connectors, then when the first board sends a signal picked up by the last one, it's going through numerous electrical contacts.

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    \$\begingroup\$ +1 for very neat and fairly-easy-to-implement idea. I have to mention though that this may not be suitable in my case because I have a variable number of boards in the stack. \$\endgroup\$ – OrCa Oct 3 '12 at 20:53
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    \$\begingroup\$ +1 good idea. Freescale seems to think it's a good idea ( freescale.com/tower ), although unfortunately they picked a 21.6 mm board spacing that's too big for the original poster. \$\endgroup\$ – davidcary Oct 17 '12 at 17:07
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    \$\begingroup\$ @Kaz: Can you draw a rough sketch of this? It seems it doesn't work for OP, but I find this idea potentially very useful. Having trouble visualizing your odd-even scheme though. \$\endgroup\$ – Thomas E Oct 19 '12 at 7:27
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I'm a new contributor so I can only post two hyperlinks, I found after writing, please type the part numbers below into the search box on the GCT website!

Two connector solution 2.0mm pitch - dual in line:

Socket: 2.2mm stack height, Newark 67R8237

Header: 2.77mm stack height, Newark 67R7787 (2mm mating pin suitable to mate with BF120

Total stack height = 4.97mm, inexpensive solution.

Two connector solution 1.0mm pitch- single in line:

Socket BC070 2.25mm stack height, Newark 67R7215

Header BC032 2.00mm stack height, Newark 69R6950

Total stack height 4.25mm, inexpensive solution.

For both 1.00mm & 2.00mm pitch board to board connectors we offer stacking headers:

1.00mm pitch thru hole, stacking header: BC025

2.00mm pitch thru hole, stacking header: BF055

or in SMT:

1.00mm pitch SMT, stacking header: BC055

2.00mm pitch SMT, stacking header: BF145

Of course you might choose to to use one SMT stacking header with a pass through SMT socket on a mid PCB and another socket on the top PCB to acheive a three PCB stacking solution.

The other option using socket on top PCB, socket on bottom PCB with a thru hole stacking header to connect two extra central PCB's.

Unfortunately I cannot offer a truly modular solution which will allow you to stack 2, 3, 4 and more PCB's using the same connector set. The other issue is that the stacking headers are not stocked by Newark and would carry a 1,000 piece MOQ, there is no way around that. However, I hope these connectors might give you some ideas.

GCT are working on a board to board connector web stacking guide, but it's not ready yet!

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You should investigate the PC/104 format, it's made for stacking boards on top of each other, and has all the interconnect buses with the header pins lined up correctly for ISA, PCI, and additional power, etc signals. You can buy off the shelf PC-104 cpu boards, display, network, etc.

Also, you can design your own to interconnect to the stack.

There are actually a few different form factors 104 (smallest), EBC and EBX.

https://en.wikipedia.org/wiki/PC/104

The down side: The COTS boards can be on the expensive side, esp. for the 104 format. The EBX and EBC boards are a little cheaper.

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The cheapest and meanest option: Use an old floppy disk or IDE/PATA hard disc cable as a "backplane". Add connector from other cables as needed. Then you only need angle headers on each PCB.

An additional advantage is that the distance between the PCBs is flexible to a certain degree, if you allow the cable to be curved.

enter image description here

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    \$\begingroup\$ Did you mean PATA? SATA cables are a bit limited in number of conductors. Those cute little kapton ribbon cables and tiny connectors one sees inside laptops also come to mind, though I don't know what there is for "generics" of those if you are not custom-ordering a few million for the factory. \$\endgroup\$ – Ecnerwal Dec 28 '15 at 14:58
  • \$\begingroup\$ Thanks Ecnerwal, right, it's "ATA" I believe (long, long time ago...), just edited the answer \$\endgroup\$ – fraber Dec 28 '15 at 15:07
  • \$\begingroup\$ They are both ATA - one is Parallel ATA and the other is Serial ATA (PATA is also IDE) \$\endgroup\$ – Ecnerwal Dec 28 '15 at 15:12
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10 pin 0.1inch spaced pin headers on your boards, mount 'smd' style , flat on your board, (or get SIP right angle pin headers). Let the pins hang over the edge of the board, parallel to it.

Build a 'veroboard' backplane with 0.1inch spaced female sockets into which the headers plug. sockets at right angles to the backplane.

Cheap and nasty.

You can do the same thing with 'box headers' and pin sockets. This gives mechanical stability. I sometimes put dual row pin headers mounted SMD style with the board between the rows.

@fraber's solution works well with this for testing since you can 'unstack' everything.

At Control Data we used to have an eviscerated PC and motherboard for testing. We also used board extenders so we could get to components.

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