nRF52840 Layout for 10-layer PCB

Question

Hello Nordic team, 
 I am designing a 10-layer PCB with nRF52840. 
 Should I place a ground plane under the chip in each layer, connected through the vias in the middle ground pad? Or using few of the layers is enough? 
 Thanks, 
 Avihay

Bendik Heiskel · Accepted Answer

AvihayZ said: Can you share a rule of thumb for calculating the width of the transmission line? 
 A tool like AppCAD or Saturn PCB Toolkit can be used to calculate the impedance of the transmission line, which is directly dependent on the width of the trace. When using these tools its important to select the correct dielectric constant for the PCB substrate you are using, you can get this information from the PCB manufacturer you are using. 
 AvihayZ said: And regarding your remark of the VDD layer under the SoC - do you see any problem with having a VDD layer in the 5th layer, assuming:
 
 there is a GND fill under the SoC on the 2nd layer? 
 there is a GND fill under the SoC on the 9th layer? 
 This shouldn't be a problem. 
 If you are using the 9th layer as the reference ground for the transmission line you will need a keep-out area under the transmission line on layers 2-8 like we have on the internal layers in the reference layout:

Best regards, 
 Bendik

nRF52840 Layout for 10-layer PCB

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