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terminal numbering convention for diodes

terminal numbering convention for diodes

(OP)
I'm having a disagreement with another engineer on the convention for numbering the anode and cathode of a diode. We both use ORCAD for schematic designs. I always use diode parts with pins numbered 1 for cathode and 2 for anode. His designs only name the terminal, with no numbering. We were collaborating on a design and somehow the PCB layout design shows the diodes reversed. We know the problem is that the pin numbers in the layout are reversed from my convention of 1 for cathode and 2 for anode. So we made changes to fix the problem, but now we are both wondering what the convention acutally is? I saw online a document IPC-7351 that recommends pin 1 as cathode, but this is the only document that I could find. Is this relevant? Does anyone else have this problem?

Thanks,

B

RE: terminal numbering convention for diodes

"K" for cathode.

Numbering 1 / 2 is obviously subject to arbitrary randomness.

RE: terminal numbering convention for diodes

When creating a pcb library as long as you assign the proper pin (be it a number/name or whatever) to match the schematics icon it should never be an issue. If the schematic is right then the layout will be too..always

RE: terminal numbering convention for diodes

I use 7351 as a reference too so all my diodes have the cathode on the left as pin #1. Their guideline that "Pin 1 is always the Cathode" is pretty easy to follow. I'll typically name the pins K and A, respectively so that you can verify the numbering matches within the part definition (I use PADS).

Z

RE: terminal numbering convention for diodes

I haven't done board for a while but know that was an issue. I seem to recall changing the diodes to use A and K to avoid the problem.

RE: terminal numbering convention for diodes

(OP)
Re: mcgyvr,
"When creating a pcb library as long as you assign the proper pin (be it a number/name or whatever) to match the schematics icon it should never be an issue. If the schematic is right then the layout will be too..always"

That is true if you do assign pin numbers, but not true if schematic does not use pin numbers for these parts. The number field is blank, and the pins only have names. This causes some confusion when sent to the layout software. I think the layout software just assigns pin numbers in this case by some criteria that I am not familiar with.

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