I have found an excellent source of land pattern information, covering 
all surface mount devices, including BGA, to be the SMT Component and Land 
Pattern Book, from SMT Plus, Inc. For about $300, you get all the 
patterns you could ever want, conforming to IPC and designed by the 
industry leader of practical SMT designs, and a free update service for 
new patterns. No formulas, just ready to use info.

I don't know of an on-line address, but their old fashioned telephone 
number is 408-438-6116.

djr

 On Fri, 14 Jun 1996, John Gully wrote:

> I am looking for sound information regarding the land pattern  
> of PBGA and CBGA components, specific to bareboard fabrication.  
> I have contacted several sources (Motorola, IBM, etc.) and looking 
> for more info.  IPC-SM-782 does not cover this type of component 
> geometry.  Has IPC developed or revised -782 to include BGA land
> patterns?  If so, I need a copy. All sources of information are 
> welcomed.  Thank you.
> 
> John Gulley  - PE
> Dallas, TX
> 
>