Hi James,

  I don't know of, (OK, I don't remember which) the IPC spec, although I'll bet there is several documents that cover this, but long story short. The use of I, O, Q, S, V, and Z, (I may have missed one or two) or rather the lack of their use is to prevent misinterpretation of the letters to numbers, etc. An "I" could be seen as "1", "O" the letter as "0" zero the number, S for 5, V for U, Q for O, S for 5, and Z for 2. I think you can get the jest of that. I'm not a historian on this, but back in the day, both copy/blueprint machines and silkscreen on PCB assemblies didn't create such perfect text as they are today, (OK they are MUCH better for sure) and thus, skipping letters listed, was a safe way to ensure the correct character(s) was/were read and understood. I believe there are ANSI drawing documents that also call out this list and perhaps other things, but I'm hoping this answers your question or at least helps. If your tools are helping you out by not allowing the use of these letters and such, let them help you, it's better than making an error and having to fix it later... :-) Stay safe and healthy!

Later...



Scott Decker | Senior Engineer, PCB Design Services CID+ | Electronic Systems Center

COLLINS AEROSPACE

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-----Original Message-----

From: TechNet [mailto:[log in to unmask]] On Behalf Of James Jackson, CID

Sent: Wednesday, November 4, 2020 3:02 PM

To: [log in to unmask]

Subject: [External] [TN] BGA Pin Numbering



I am in the process of creating a BGA footprint.



This BGA is a 17x17 ball package - for this discussion, the particular dimensions are irrelevant.



My question... the IPC footprint generator (Altium) starts the alpha section of numbering with the letter 'A' and then goes sequentially to B, C, D, E, F, G, H - and skips I. The next one is J, etc.



Is this by some 'standard' or arbitrary. I have seen this done through the years with the skipping of the letters 'I', 'O', and... I don't remember the others, but think that there are a few others.



I'm looking for some sort of 'reference' or published IPC statement (JEDEC perhaps?) that says, 'skip the following letters when creating BGA footprints'.



(I hope my ramblings make sense...)



--

Regards,



James Jackson, CID

Oztronics