Re: gEDA-user: Centroid data and BGA footprints

[David Kuehling <dvdkhlng@xxxxxx>]

>>>>> "Dan" == Dan McMahill <dan@xxxxxxxxxxxx> writes:

> David Kuehling wrote:
>> Hi,
>> 
>> I'm just wondering, how do I get sensible rotation information in the
>> centroid data for footprints that don't have a pin numbered '1', but
>> only a pin numbered '1B'.  In my case that's a BGA footprint, where I
>> chose pin numbers 1B..7E in accordance to the part's data sheet.
>> 
>> Do I have to rename the pins (and update the symbol), or can I add a
>> kind of rotation hint, or a pseudo-pin #1 to my m4 footprint?

> hmm.  Ultimately I think we'll need to modify how pcb stores
> footprints to actually keep track of rotation.  Until then we can
> probably improve whats currently implemented.

> The BGA's I've seen use numbers like 'A1' 'A2' ... 'B1' 'B2' ... where
> A1 is the top left and the letters give the row and the numbers give
> the column.  Does anyone know of a controlling standard for BGA's and
> PGA's with regards to how pins are numbered?  Besides that does anyone
> have a wide enough experience with either of these to comment on how
> they are numbered in practice?

Not that I have wide experience, but I think numbering '1A' vs 'A1' are
both seen in practice (althouh I only used parts with the '1A'
convention so far).  For all parts I used, letters denoted rows
(top-down), numbers denoted columns (left-right).

> David, are you saying your top left pin (when viewed from above with 0
> degrees rotation) is '1B' and there is no '1A'?

Well, it looks like a 7x7 BGA footprint, where solder balls (pins) at
the edges and in the center are missing, see eg:

http://www.analog.com/static/imported-files/data_sheets/ADXRS150.pdf

Thus no '1A' pin.  Determining the rotation would require determining
the pin closest to the '1A' coordinate.

cheers,

David
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