die size pad limited
Core Limited design is where the size of the core is relatively high when compared to the number of I/O cells, thus leaving ample space for the I/O cells and sometimes even free space after their placements. This results in the die size being decided as a function of the core size.
In the case of a pad-limited design, the core size is small, but the I/O count is proportionally high and hence the size of the die is limited by the number Pads and not the core.
In order to reduce the die size to a minimum, the arrangement of the I/O's is in a staggered fashion where the bond pads are placed in a staggered way thus enabling more number of I/O's in the same die size.
Whereas in the Core limited design, having ample space for I/O's enables the desiners to place them in an inline fashion.
The things will be much clearer looking at the pics attached.