I recently found myself having to make a footprint for a BGA/CSP-style part with 0.5mm pitch (from the center of one ball to the center of the next) and 0.3mm ball diameter. That doesn’t leave a lot of room, and you need to be extremely careful with your footprint design if you want to have decent yields, which is where good documentation and manufacturing suggestions come in handy. The chip maker behind the chip I was using didn’t see fit to provide any suggestions (shame on them), but I remembered an excellent app note from NXP on designing footprints for their BGA chips and found one with identical pitch and ball dimensions (TFBGA180 in this case). If you’re ever wondering how to properly design a BGA footprint, AN10778 is one of the better starting points out there. (Homework assignment: some of the FPGA vendors also have good app notes on this if you want to do some digging.)
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