Power Planes Ch 6

A typical 4 Layer Stackup looks as follows

Signal 1
Ground
Power
Signal 2


Notice that the ground and power are interchangeable. If it this PCB has many power islands AND there are controlled impedance traces, then it may be a better idea to keep all the controlled impedance traces on Signal 1 and Ground layer beneath it. If controlled impedance traces refer the power planes it must not either cross the split power plane junctions. If it is unavoidable to pass the split power plane junctions, we should place stitching capacitors.
The four layer trace has one inherent drawback. You can not keep the power and ground traces tightly coupled for a typical 0.063” thick PCB.


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