I am making a PCB where the goal is to keep BOM as low as possible and also the cost to the lowers. It has proven to be quite a difficult task but I am at a final stage now.

My PCB needs to be programmed or interfaced depending on the situation and I do not want to add connectors or get the end user to solder extra wires on so i thought the edge connector would be the perfect option.

I have been looking around and there are thousands of options and I am not sure what the best design would be. My final PCB is 0.8mm thick and 4cm(W)x4cm(H) but could make it larger for this purpose and needs at least 8 pins but more would be great.

First thing that comes to mind is using the old floppy connectors or an ISA slot or even PCI. What should I keep in mind when designing this on my PCB and what would the cheapest connector be?

  • \$\begingroup\$ Does the connector go to a PCB or a cable? \$\endgroup\$ – stevenvh Aug 15 '12 at 13:27
  • \$\begingroup\$ Either - I don't mind I only need to make a few of those. \$\endgroup\$ – Piotr Kula Aug 15 '12 at 13:29
  • \$\begingroup\$ I was thinking of putting them in like a normal pci card - programme it and next one. but I suppose for interface it needs to sit tightly.. \$\endgroup\$ – Piotr Kula Aug 15 '12 at 13:45
  • \$\begingroup\$ In that case note that the connector WillyWonka refers to is specified for only 50(!) mating cycles (which for typical use in a PC should be enough, though). \$\endgroup\$ – stevenvh Aug 15 '12 at 13:48
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    \$\begingroup\$ Mating cycles, not matching. Connector on + connector off = 1 mating cycle. The number of times you can put it on the PCB's edge connector. \$\endgroup\$ – stevenvh Aug 15 '12 at 13:54

Since you're not happy with the 50 mating cycles of the PCI connector I thought what you really need is connector which goes on and off easy. Have a look at this one:

enter image description here enter image description here

warning: not cheap! USD 5.82 at Digikey, and at Farnell even GBP 7.91, that's 12.40 dollar! (I've always known Farnell is expensive, but they keep surprising me.) The good news is that you only need one.

I've used those in a few projects at work, as a board-to-board connector. The contacts are spring contacts, they don't fix the top PCB mechanically. (In my project the top PCB was fixed with snaps in the enclosure.)

You would have to make a small tool which aligns your PCB with the connector, and you simply push your board onto the tool and push the "program" button.

And more good news (possibly): all your contacts are on the same (bottom) side of your PCB. This type has a 2.54 mm pitch, and is available with 2 to 30 contacts, but there's also a version with a 1.27 mm pitch (if you can make your programming tool to that precision). The 2.54 mm pitch will give you a length of less than 2 cm though.

edit re the snaps I mentioned
Snaps in the enclosure are a cheap way of mounting a PCB, since you don't need mounting holes or screws. The operator just has to push in the PCB, and that's that. Takes less than a second, far less than mounting 4 screws.

enter image description here

I don't have such an enclosure here, but this quick sketch should make clear how it works. Underneath the bottom PCB there are also stops like the one shown for the top PCB. So to mount the bottom PCB you just push it down the two levels of snaps until it hits its stops. Then push in the top PCB. This of course doesn't have the recesses to pass by the first level of stops so it's fixed at the level higher than the bottom PCB. If you use the Samtec SIB connector to connect the two PCBs the distance H between them is 3.8 mm, enough for most SMT components.

All very nice, but not for you. First, it's damn hard to remove the PCBs once they're snapped in place. Second, this is a custom injection mold, which will only cost you 10 000 to 15 000 dollar for an entry level mold, for a limited series.

What you need is just two walls at right angles so you can align the board to be programmed by placing it in the corner. Have a ledge in one wall you put the PCB underneath and push the other side down to make contact with the connector.

  • \$\begingroup\$ Thanks Steven! That does look good. The PDF does not seem to work. The other tag-connect looks good too though.. both great answers... \$\endgroup\$ – Piotr Kula Aug 15 '12 at 14:47
  • \$\begingroup\$ @ppumkin - the link works for me, but I found another one. Can you try that one? \$\endgroup\$ – stevenvh Aug 15 '12 at 14:54
  • \$\begingroup\$ Your answer is the best one based on my question. I asked about edge connector and I think I will use that one this time. Thanks for your time. \$\endgroup\$ – Piotr Kula Aug 15 '12 at 17:28
  • \$\begingroup\$ So looking more closer at this now. I will need to make a housing with a slot matched to my PCB thickness. You mentioned something about snaps in the enclose you made. Could you expand on that- I cannot visualise what you mean. I can use 1.27mm pitch no problem. \$\endgroup\$ – Piotr Kula Aug 29 '12 at 21:47
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    \$\begingroup\$ @ppumkin - I added something about the snaps to my answer, but also noted why this isn't for you. Just FYI. \$\endgroup\$ – stevenvh Aug 30 '12 at 8:10

It's not an edge connector, but it sounds like what you need is a Tag Connect cable:

Tag-Connect cable

They're cables with alignment and spring-loaded pins in the end. On your PCB, you just need an extremely small footprint -- no BOM parts. There are versions with "no legs" (very small), and versions with "legs" (which clip into the board to hold it securely in place). The TC-2050 version has 10 pins. I use them for programming all of my boards these days.

  • \$\begingroup\$ Very nice! So where can I buy them like in EU (where do you buy them from?) \$\endgroup\$ – Piotr Kula Aug 15 '12 at 14:43
  • \$\begingroup\$ FindChips might help. The 6-pin version (TC2030) is in stock in a bunch of places, but the 10-pin version only seems available at DigiKey, which does ship to Europe. \$\endgroup\$ – Jim Paris Aug 15 '12 at 14:51
  • \$\begingroup\$ Not cheap eh? :-) Thanks! \$\endgroup\$ – Piotr Kula Aug 15 '12 at 14:54
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    \$\begingroup\$ Wow, 35 dollar! "Not cheap" may well be the Understatement of the Year :) \$\endgroup\$ – Federico Russo Aug 15 '12 at 15:01
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    \$\begingroup\$ Depends on your point of view. How much did your development and programming hardware cost? What's your time worth? For any serious project, a NRE like this is trivial. \$\endgroup\$ – Jim Paris Aug 15 '12 at 15:59

Pogo pin test points

For programming, many people design boards with traces running to round metal pads or rectangular metal pads (a, b) or through-holes as "test points", and then use pogo pins on the programming fixture that hit those points. (see What is a good way to in-circuit update the program on a SyncMOS 5964? ; also "Pogobeds at Sparkfun").

Sometimes these designers put the pads or holes in a pattern that allows some more permanent connector to be soldered on -- but they don't actually spend money on that connector. They do not stuff that component, so the cost of this pattern is close to zero, much like the cost of the edge pattern on a board that plugs into an edge connector is close to zero. They continue use pogo pins on a test jig that hits the holes where that connector might, in the distant future, be someday soldered in."Making a test jig w/pogo pins". "ICSP touch connectors"

Often that pattern is a standard 0.1" pin pitch "programming header", such as the standard Atmel AVR ISP connector or the standard Microchip PIC ICSP connector. a b c d Or one of the other common ICSP connector arrangements.

Alas, often that pattern has more or less the same pins, but in some one-of-a-kind semi-random arrangement."Build a ICSP Jig"

  • \$\begingroup\$ I like the ICSP jig.. but I really need something more like plug in, programme, take out and next. I can see some people bending the pins and not holding it correctly and all sorts. Great answer +1 \$\endgroup\$ – Piotr Kula Aug 15 '12 at 19:59

I would say that the PCI connector will give you good density and seems like the cheapest board connector

enter image description here

You should be able to design the PCB pretty easily as its one of the most common connectors used. Here is the design with a PCB footprint advice too.

This particular connector is 39mm (edge to edge) wide so it seems like it should work well with your design. But if your fabrication house will allow you to cut out a connector or slot then just make a connector for either the right or left side out of your pcb. It total this one gives you 64 connections. The PCB trace is 1mm wide and 3.2mm

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    \$\begingroup\$ I'm not sure if they work for 0.8 mm PCBs. \$\endgroup\$ – stevenvh Aug 15 '12 at 13:27
  • \$\begingroup\$ Yea I thought of that also- just was not sure about 0.8mm like stevenh suggests... \$\endgroup\$ – Piotr Kula Aug 15 '12 at 13:28
  • \$\begingroup\$ @ppumkin - They might make contact (probably will), but the mechanical force may be too low and especially an attached cable may pull to connector from the PCB. \$\endgroup\$ – stevenvh Aug 15 '12 at 13:33
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    \$\begingroup\$ @ppumkin - that's not going to help you: you place it on the PCB's edge connector, and you end up with exactly the same edge connector. It's a "riser" to place your PCI board a bit higher, mostly for mechanical reasons, like big components on the motherboard in the way. Let me see if I can find something else. \$\endgroup\$ – stevenvh Aug 15 '12 at 14:01
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    \$\begingroup\$ @ppumkin - Moisture Sensitivity Level. Class 1 means it will withstand the specified moisture level indefinitely. Other classes have shorter times. \$\endgroup\$ – stevenvh Aug 15 '12 at 14:17

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