Check www.ti.com and enter microstar in the text search box.  There are several papers on small pitch BGA devices and the PCB designs to make them usuable.  The thermal issues may also be important in a CSP.
Good luck,
Kim

________________________________

From: TechNet on behalf of Bob Perkins
Sent: Thu 3/1/2007 6:36 PM
To: [log in to unmask]
Subject: [TN] BGA footprint



Hi

I am working on a new board with a 0.5mm pitch BGA and I am wonder if
someone can advise me on the footprint.

1) the datasheet says the solder ball is 0.3mm +/-0.05mm
2) IPC recommends to use 80% of ball diameter for the pad which would be
0.24mm
3) Would it be OK to use a 0.2mm pad? I am hesitant to go against
recommended
size without some corroborating documentation. The reason I would want to
use 0.2mm pad is to avoid using via-in-pad.

I am curious if IPC defines footprints based on what is good for
manufacturing or is it simply theoretical?

Thanks
Bob

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