For info on this refer to following book
Application-Specific Integrated Circuits
(ASICs... the book)
Michael John Sebastian Smith
Addison-Wesley
VLSI Systems Series
1,040 pages
ISBN: 0-201-50022-1
June 1997
AND
Principles of CMOS VLSI Design by Weste and Eshraghian
though i didn't know much. these two types of IO pad are used in
different design types. If your design are pad limited, the staggered
IO pad are decrease the whole chip area. While inline pad have more
area than stagger pad. But not all the library
vendor supply the two pad type.