Scott,

I understand the history, and fully agree. That's not my issue - at the 
moment.

My issue is that I am tasked with creating a BGA footprint that has a 
17x17 grid.
The drawing I was handed to use as a datasheet has a BGA on it - and it 
is 'lettered' A - Q - with no 'skips'.

Now, I can look at this two ways. I can shrug and ignore it, and create 
my BGA footprint using the Footprint generator - which skips the letters 
'I', 'O' and 'Q' - which means that I will have to manually renumber 
those rows to comply with the companies' mis-numbered BGA. (Lots of 
work.)

My other option is to raise my hand and ask why we are not following 
XYZ spec which states to skip these letters. I just need to know what 
that XYZ spec is, cause I may be in for a discussion which will most 
likely begin with 'we've always done it that way'.

The ANSI spec (as previously mentioned) may be the way to go.

Thanks for the feedback.

Regards,

James Jackson, CID


On 2020-11-04 16:34, Decker, Scott             Collins wrote:
> 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
> 3445 S. 5th Street, Suite 170, Phoenix, AZ 85040 U.S.A.
> Tel: 602 308 5957  FAX: 602 243 2347
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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

-- 
Regards,

James Jackson, CID
Oztronics