6-layer stack up

The 6-layers stack up is formed using 2 core and 2 prepeg. Core and prepeg are as below in the given image:

There is a video in our channel which explains about the construction:

https://www.youtube.com/watch?v=Dkf4RWgWRxQ

6-layer PCB is selected based on the density and routing complexity of the board. For electrical engineers, lower the PCB stack up better to test and evaluate. But to pass all the specifications, it is good have higher stack up with good reference planes. 

PCB Layout Engineer might plan routing in the layers as below:

• Signal Routing - Top, Bottom, Layer 3, Layer 4
• Reference Plane - Layer 2, Layer 5 (POWER,GROUND)