Designing pcbs was at one time a sequential process. But the growth in popularity of fpgas has seen that process become more of a parallel operation. Where fpgas once provided 'glue logic' and similar functionality, the devices are now central to the operation of many board level products. Because of this, the fpgas being developed are complex, high pin count devices. This level of complexity brings design iterations and each iteration may require the board on which the fpga sits to be redesigned; even seemingly small changes to an fpga's pin out could have dramatic effects on the pcb's layout and even the number of layers.