> > I bumped the ball size down from the Xilinx recomended 0.4mm to 0.34mm, > > and everything worked out fine.
In our experience, bumping down pad size can be a dangerous thing. I'd be carefull and test a few before I had that many made. The issue is not whether you can attach a bga device to down sized pads, but if it will stay attached through time. In essence, I am suggesting that down sizing the pad can emulate bad printing, device warpage and/or PCB warpage. Printing is talked about here: http://www.aimsolder.com/techarticles/tech sheet BGA voiding- reducing through process optimization.pdf The rest is talked about here: http://www.akrometrix.com/pdf/Tech_Papers/CSP Board Level Reliability.pdf Best regards Marvin
