nRF52840 Reference Layout vs PDK Layout

[Fabian Frei]

I have a question about the nRF52840 QIAA Reference Layout v1.0 which can be found in the infocenter /nRF52 Series/Reference Layout. I saw that it has keepout areas on mid-layer 1 and mid-layer 2 between antenna and the  nRF52 SoC. On the other side, the layout of the nRF52840 PDK does not have these keepout areas. 

What are these keepout areas for? Is it recommended to add these to a design or not? 

Thanks in advance!

[Andreas]

Hi,

 

I think the internal keepout has stayed in the design from an internal characterization board somewhere along the line to be consistent with other RF52 devices and this is the design which the RF performance has been characterized for. The PDK HW is older, now that the (regular, non-preview) DK arrives it will have the same layout as the reference layout v1.0.

 

Keepout on internal layers is not as critical on nRF52 series as nRF51 series. We generally see little difference, and if any at all it usually vanishes if tuning C3/L1(/C4). It he substrate is very thin though (<<0.8 mm) you might want to add the keepout as a safety margin to avoid a big hit on performance, if not it can be handy to omit the keepout so that you can route things underneath the RF path by keeping L2 as a solid ground layer.

 

Best regards,

Andreas

[Fabian Frei]

Thanks for your detailed answer! :)