3.3.2 Implementation Example

In the following figure, capacitors are the green rectangles.

The SAM9X75 had some of its balls strategically depopulated in order to fit 0201 decoupling capacitors on the bottom layer, right next to the power balls, under the BGA array.

Whenever possible, the power is supplied through solid copper polygons placed on the inner layer (power layer). These polygons are formed in such a way that the signals on the bottom layer have their return path through them. However, some of the power rails can be connected with traces if the current drawn is low and they do not serve as reference rails for high speed signals. Such power rails are VDDBU and VDD-2V5.