I am designing a board based on SP6 FPGA (XC6SLX25-2FGG484I). I have reviewed some reference boards like SP605 and read ug112 document for recommanded pad size.
According to UG112 for this package - FGG484 - I should use a 0.4mm pad size with solder mask of 0.5mm. This method - NSMD - is recommended by Xilinx in UG112 as shown below:
When I look at SP605 which is a Xilinx reference board I see below pad information:
BGA Pad size: 0.51mm
SolderMask & PasteMask both: 0.51mm
The above values imply that Xilinx has used SMD method for their own board insted of NSMD pads!.. Now, I am confused which one I am better to use in my PCB? Can anybody clarify the reason why Xilinx recommands something and uses another thing?