James,
I think I found your silver bullet... :-) I just looked up the Contact defining section in IPC-7351 and found this: (Since I can't attach in plane text, I'll copy the text)
Section: 14.2.5 Defining Contact Assignment Array contact identification is assigned by the column and Row location. For Example, A1 contact position is always at an outside corner position with alpha characters arranged in a vertical (row) pattern from top to bottom. Numeric characters are assigned in a horizontal (column) axis (I, O, Q, S, X and Z are omitted) (see Figure 14-10).
So there you go, you got a standard that gives you a reason... :-) Hope this helps.
Later...
PS. Sorry for the history thing, I didn't know... :-)
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
[log in to unmask] www.collinsaerospace.com [collinsaerospace.com]
KE7MWT
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-----Original Message-----
From: James Jackson, CID [mailto:[log in to unmask]]
Sent: Wednesday, November 4, 2020 3:56 PM
To: Decker, Scott Collins <[log in to unmask]>
Cc: TechNet E-Mail Forum <[log in to unmask]>
Subject: RE: [External] [TN] BGA Pin Numbering
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
> [log in to unmask] www.collinsaerospace.com
> [collinsaerospace.com] KE7MWT CONFIDENTIALITY WARNING: This message
> may contain proprietary and/or privileged information of Collins
> Aerospace Systems and its affiliated companies. If you are not the
> intended recipient please 1) do not disclose, copy, distribute or use
> this message or its contents, 2) advise the sender by return e-mail,
> and 3) delete all copies (including all
> attachments) from your computer. Your cooperation is greatly
> appreciated.
>
> -----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
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