Originally published at: https://www.protoexpress.com/blog/how-to-breakout-a-4mm-bga/
One thing PCB designers will all agree on is that to breakout a BGA, you need precision and discipline. When you break out a BGA, you basically apply a fanout solution. You route traces from those fanouts to the perimeter of the device prior to the general routing of the PCB. Here are two examples of a .4mm BGA breakout.
Watch our demo here: How to Fanout a 0.4 mm Pitch BGA