Physically robust edge-to-edge PCB connector design

[lynaghk]

I'm designing a modular prototyping system consisting of daisy-chained PCBs connected edge-to-edge. The PCBs will be roughly the size of a bookmark (2 x 5 cm) and connected so their long ends butt together (e.g., 3 connected boards would measure 6 x 5 cm).

My objectives are:

• rigid physical connection so that a connected set of PCBs can be picked up together, thrown in a storage box, mounted to something, etc. (I.e., not a bunch of boards and cables flopping around.)
• "snap together" (dis)assembly (soldering iron, screwdriver, etc. not required)
• 4 conductors (data, clock, power, ground)
• ~10 A current capacity (sufficient for the system to prototype, e.g., a desktop cartesian motion system with with three NEMA 17 steppers peaking at 2A)
• ideally components can be assembled by the usual quick-turn folks (JLCPCB, etc.) so I wouldn't need to do any soldering at all =D

The two ideas I have are either:

• The venerable common 0.1" (2.54mm) pin headers with power pins duplicated for additional physical rigidity and carrying capacity.  These headers don't seem particularly robust, but perhaps there's a clever way to route flexures in the PCB substrates so they snap together? Or 3d print a carrier / rail?
• Use terminal blocks. JLCPCB seems to have plenty of right angle sockets, but no through-hole PCB-plugs. It seems like the latter exist (e.g. http://www.xinyaelectronic.com/product/xy2500a-50-xy2500a-508) but most usages are wire-to-board rather than board-to-board. There's also supply chain risk/hassle with terminal blocks, since I'm not sure how easy they'll be for collaborators to get in different parts of the world.

Does anyone have any alternative suggestions? Thanks!

[spostma]

AVX has 1mm and 2mm pitch card-edge linking connectors with 2,5 - 3A per contact that seem to be robust:
https://www.kyocera-avx.com/products/connectors/board-to-board/coplanarlinear/9159-7x0/
https://www.kyocera-avx.com/products/connectors/board-to-board/open-ended-card-edge-00-9159/

[tszaboo]

First off, stop stealing my idea. 
I've considered using those AVX connectors when JLCPCB didn't have any connectors in their portfolio. It's not 10A of course. You might find some LED strip connectors with higher current. Or there are reverse polarity pluggable PCB terminal blocks, that will do quite high currents.

[lynaghk]

Thanks spostma! These look pretty cool.

However I can only find the tin-plated version on distributors ($0.60 each in quantity at mouser). Price is OK, but datasheet says only 10 mating cycles.

I'd worry about people being able to source these. It does seem like 2mm bent pin headers are easily available (on Amazon UK, anyway), so maybe I could use a combined footprint so one can fallback to pin headers as a backup. Though 2mm pitch rather than 2.54mm will almost certainly cause trouble...

The LED lighting strip connector market is a great suggestion though, I'll keep digging around there.

[SpacedCowboy]

Depending on how many connections you want, using a pcie connector might be viable, just have the PCB edge routed to (say) a pcie x1 form, and use an edge-facing (rather than vertical) socket. I’ve done this before

You do have the fact that the pcb’s aren’t on the same level, but you could alternate under/over if that bothers you (I didn’t bother

[ywara]

• Use terminal blocks. JLCPCB seems to have plenty of right angle sockets, but no through-hole PCB-plugs. It seems like the latter exist (e.g. http://www.xinyaelectronic.com/product/xy2500a-50-xy2500a-508) but most usages are wire-to-board rather than board-to-board. There's also supply chain risk/hassle with terminal blocks, since I'm not sure how easy they'll be for collaborators to get in different parts of the world.

Does anyone have any alternative suggestions? Thanks!

I don't know if these are the best option for your application, but I wouldn't worry too much about sourcing these. This Phoenix Contact 5 and 5.08mm connector style has been duplicated the world over and should not be difficult to find. Take a look at catalog #8 - "PCB terminal block and PCB connectors"  for options, and you can probably find an equivalent from 20 different manufacturers.

You may also want to consider the venerable D-sub connector. More pins than you need, but signals can be duplicated or pins left unconnected. RA connector both male and female are cheap and readily available, and screw coupling (possibly with thumbscrews to avoid needing tools) can make a very rigid connection.

[Neepa]

You may also want to consider the venerable D-sub connector. More pins than you need, but signals can be duplicated or pins left unconnected. RA connector both male and female are cheap and readily available, and screw coupling (possibly with thumbscrews to avoid needing tools) can make a very rigid connection.

This. Using alternating male to female will give these quite small boards plenty of rigidity.

The only problem is their size relative to the actual board. Using proper right angle ones with a solderable bracket will eat quite a lot of real estate on the surface. Also the high quality ones can be quite expensive if you want gold plated high current contacts. Although there are configureable D-Sub connectors with two or more high current barrel contacts in them.

As extra reinforcement one could design and 3dprint an U-Shaped clip that engages on the metal fronts of the connectors instead of using screws to press them together.


I'm afraid pin headers will be the best solution. Anything too specialized will be harder to get. Staying under 1$ will be a challenge as anything with something resembling a moulded case on it might be more expensive when not bought in the thousands.

Card edge has the fundamental problem of leverage. Any amount of PCB width plugged in anywhere will have to contend with the rest acting as a lever against the connector. Those able to deal with flexing will not be very tight and those very tight ones have the PCB acting as a spring which might cause other issues regarding longevity. And also in them being a bitch to take apart.


My last idea would be card edge contact onto card edge contacts. Simply put a thin blob of sodler on them and use small thumb screws with standoff barrel nuts to squish the contacts together. Small thumb screws can be had from the PC case market.

[EPAIII]

Generally speaking, connectors are not designed to provide mechanical strength. The D sub-miniature variety are particularly bad in that regard. Without actually screwing them together, they can barely hold up a cable, much less a PCB.

I would sooner use the double row header pins and sockets. But they aren't particularly good either.

Frankly, I would separate the electrical and mechanical connection requirements. Some 2 cm lengths of card guides glued to the 2 cm edges with half their length sticking out would provide good mechanical strength and some type of connector that snaps together on the 5 cm edges could provide the electronic connection and a small holding force to keep them from sliding apart.

https://www.mouser.com/datasheet/2/50/DC_XXX_XXX-3001824.pdf

[thermistor-guy]

I'm designing a modular prototyping system consisting of daisy-chained PCBs connected edge-to-edge. The PCBs will be roughly the size of a bookmark (2 x 5 cm) and connected so their long ends butt together (e.g., 3 connected boards would measure 6 x 5 cm).
...
Does anyone have any alternative suggestions? Thanks!

I would separate the mechanical and electrical aspects, as EPAIII posted.

Since it is for prototyping, and not production, one approach I want to try for myself, in a future project:

  * make base plates (thin metal sheet) of various lengths, that accommodate 2, 3, 4, ... boards;
  * have room on each board to screw it into a base plate, using screws (thumb screws in your case), and short spacers for insulation;
  * on the base plate, form threaded mounting points for the boards:
    * use a punch  to draw extruded holes in the base sheet, then roll threads in the extrusions using duo-taptite fasteners
      https://taptite.com/assets/files/duo-taptite.pdf

Your boards are small. So this would be a cheap design with good mechanical stability. The extruded holes themselves will help stiffen
the base plate.

I have scavenged some 2.5 mm dia. steel rods from old CD-ROM and floppy disk drives, to try as punches, for this future project of mine
I'm hoping to use them with M3 taptite fasteners.