As a librarian whom builds footprints, there isn't a wealth of infromation out
there about "recommended" pad sizes for bga's. I've gathered most of my data
from trial and error (thankfully no error's on a bga yet). Unless mfg. gets back
to us w/ a problem, we don't here about it.

I've used solder-mask defined and non-soldermask defined pads. Both have worked.
The problem I face constantly is getting a via in-between these pads, make the
engineer happy and stay in the PCB mfg. guidelines.

Michael Kuczynski       Librarian/Sr. Designer
L3 Communications       201-393-2122 (Phone)
Space & Navigation      201-393-6681 (Fax)
699 Rt46E PL1/H13       Mail Stop PL1/J8
Teterboro NJ 07608
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>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

  I don't think it's only Texas Instruments that makes such heavy BGA's. I'm
having bridging underneath some Altera BGA652's (EP20K400) that have a heavy
metal coolingplate. According to Altera the part has no history of bridging
problems, so (until the present discussion) I thought I was all alone with this
nasty phenomenon of balls collapsing more than usual.
  I think the explanation for the fact that some assemblers have a problem with
these heavy BGA's and others don't, is strongly related to the footprint-design
(given the fact that these BGA's are more critical than the normal PBGA's).
  If - as a subcontractor - you have to assemble designs with a footprint that
"just happened to be in the footprint-library", it's all to easy to end up with
defective boards. By the time you realize that you should have used "shims",
you'll probably already have an unsatisfied customer.
  To my opinion the real challenge is to have your customers make their
BGA-designs more robust, so that these heavy BGA's result in defect levels
comparable to normal PBGA's.

> Daan Terstegge
> Unclassified mail
> Personal website: http://surf.to/smtinfo

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