This is the fourth in a series of articles on BGA routing methods. My objective is to reveal the routing problems often associated with large pin-count BGAs, and provide the PCB designer with effective tech-rnniques that enable higher route density and reduction of layer count.rnThere are not many fanout options, due to the large via pad relative to the 1-mm ball pitch. Either a "Quadrant Dog-Bone" or "Via-in-Pad" method is appropriate.rnOne method proposed to increase route channels on inner layers is not to use fanout vias where possible, for power, ground and unused pins. When using through-vias, there is very little benefit in not adding fanout vias for the 30% to 50% of the BGA pins that will likely be assigned to power, ground or unused. The power and ground pins will be assigned to the center of the device and distributed among the other pins. It is highly unlikely that they, or any unused pins will be distributed in columns and rows.
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