we have been using the IPC-7351 calculator from www.pcblibraries.com. They have a free calculator and a pay calculator. I have been doing boards for a long time and this thing has worked great for us and saved us hundreds of hours. So far the footprints have performed very well.
When I purchased it was less then 200 bucks and has paid for itself many times over.


-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Mark Larson
Sent: Tuesday, August 26, 2008 7:06 AM
To: [log in to unmask]
Subject: [TN] LGA footprint


Hi, 

been lurking for a few months after not having posted for a couple years. I
am wondering if anyone can give a rule of thumb for designing land patterns
for an LGA, specifically for a 5mm square x 1.2mm high with rectangular
metalization pads ( MEMSic MMC302xM to be exact) 

Shouldn't this be treated like any BGA, the pad size on the pcb the same
size as the metalization on the bottom of the part? LGA do not have "solder
balls" like a BGA, so the rule of thumb making the pad 80% of ball size does
not apply, and besides this part has .65mm x .35mm rectangular contact, not
round.

thanks in advance
Mark

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