BGA's require careful placement of bypass capacitors and series terminators. Smaller value capacitors are placed closest to pins, clustered near the center of the BGA on a carefully controlled grid. The importance of placing components and routing on a sensible grid cannot be overstated.
A good BGA fanout will preserve a vertical and horizontal routing channel at the BGA center to maximize autorouting efficiency and bypass capacitor placement positions.
On larger BGA's, it is advantageous to stagger the outer two rows away from the pads. Doing this allows the autorouter to have an easier time routing its escapes outward from the device, and frees up some board area for closer placement of bypass capacitors and terminators.
Route metric BGAs on a metric grid
Place bypass capacitors as close to fanout vias as practical to minimize stray inductance.
Larger electrolytic or tantalum capacitors can be placed outside the BGA outline
Fanout outer BGA rows at a distance to improve autorouter efficiency
Place a via keepout in the center channels to increase routing escapes
Copyright (c) 1995-2012 gendreaumicrosystems.com. All rights reserved. Design by CSS Templates.