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Is there a standard for FPC connector pin numbers? (ie: which end is pin 1)

I'm trying to design a PCB that uses an LCD display module with pin numbering such that when the cable is contact down and facing the connector opening, pin 1 is on the right (RHS image is showing the contact side of the FPC)

Display module diagram

But, I'm designing the PCB in Fusion 360 and have tried a number of different FPC connector models and they all seem to have pin 1 on the left (indicated by the dot near the part number) so the routing is all back to front.

PCB

Adding to the confusion, I've got this little adapter board that I've been prototyping with and it has different numbers on the top vs bottom.

On the top the numbers match the display module: (pin 1 on the right)

adapter top

On the bottom the numbers match the PCB model: (pin 1 on the left, remembering the board is flipped) and pin 1 becomes pin 40??

adapter bottom


Update: I just realized this adapter board is a dual purpose board for either 0.5mm or 1mm connectors and when using one side the labelling on the other should be ignored. In both cases though pin 1 is on the right and different to the connector models I have in Fusion.


What's going on here? Are there multiple standards for pin numbering of these FPC connectors?

More importantly what's the best way to address this in the PCB design?

  1. Keep looking for a model with the matching pin designation?
  2. Try to modify existing model pin numbers? (is that even possible)
  3. Swap the display module pin numbers in the schematic (ie: remap 40 to 1, 39 to 2 etc...) to match the positions of PCB model?
  4. Something else?

At the moment, option 3 seems the simplest, but feels wrong.

I'm pretty new to all this so any advice appreciated.

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3 Answers 3

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The things are tricky, tricky little pains.

Don't forget that if you take that flex thru a slot on the PCB and connect it on the BACK, then the pin numbering can go to pot another way because you are mounting the connector the other way around.

Your answer is to create a footprint for exactly whatever you need it to be in your particular application, then print the silk out on paper and make sure it will really work for you. I dont recall creating footprints being particularly hard in feeble.

Incidentally there is a lovely trap with those 51 pin VESA flexi cables, they are really nice, but the standard cable has the plug on with what amounts to a twist in the cable, pin 1 at one end is pin 51 at the other! Just caused me a respin did that.

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  • \$\begingroup\$ Thanks Dan, took your advice and created a new Fusion library component with the pin numbering I needed. Was pretty easy since I could import everything from the component I was using and just reassigned the pins in reverse order. \$\endgroup\$ Commented Jun 12, 2023 at 22:39
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There is not standard. There is a convention: pin 1 on the left end as you look at the mating face. When deigning a board, in every case, look at the spec sheet for the given connector.

When looking at a board that someone else designed, go by what the silk screen says. As far as the counter-example you saw, it's likely to be because the engineer decided to number it in the opposite direction, either out of ignorance of the spec sheet, or because the spec sheet didn't specify pin 1, or because they needed to match the numbering of the other connector on that board.

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    \$\begingroup\$ Hi Davide, thanks for the insight. What's weird is the top side of the adapter board actually matches the display module, but both are against convention. As for the underside of that board I just realized that I think it's dual purpose board where the 1mm FPC connector and 2x20 can be put on the other side, making it the top side - and again with 1 on the right. In any case I'm still not sure how to address this in Fusion - should I just connect to pin 40 when really I want pin 1 on the display (seems like a bad idea). \$\endgroup\$ Commented Jun 12, 2023 at 3:31
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Even if you have two identical connectors and label one pin as the pin 1, it depends on how you connect the cable between the connectors that will pin 1 go to pin 1 or will the cable flip the connections that pin 1 on first connector goes to last pin on the second connector.

The FPC connectors themselves may have a marking or at least some indication in the data sheet for what they think is pin 1 and even in such case you have to take into account that signals may or may not be flipped when connected to another connector.

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