> - No more than 5 balls per square inch allowed > - Solder balls cannot be greater than 5 mil (0.005in) > - Solder balls cannot be less than 5 mil from the nearest land or trace This sounds a bit arbitrary so if you want a neat metric rule why not: - No more than 1 ball per 100mm^2 - Solder balls cannot be greater than 100um - Solder balls cannot be less than 100um from the nearest land or trace David Whalley