Changing stack-up layers in designing nRF52832 with CSP package

[Dave]

Hi guys,

I have a question when design the pcb layout stack with nRF52832, CSP package (CHAA). As recommendation from Nordic, using 4 layers will give best performance but is it ok if I change to use just 2 layers intead of 4 layers?

Here is my configuration: Top layer : 12um

Dielectric : 50um, FR4, e = 4.8

Bottom layer : 12um

To maintain the 50ohm impedance of RF signals, I changed the width of the feed line to 3mils (instead of using 8 mils in 4 layers configuration).

Is it ok to keep the performance of RF signal still good as 4 layers? And with the thickness of the dielectric is so small, is it effect on any working principle of nRF52832?

Many thanks

[Ole Bauck]

The recommendation for 4 layers is to be able to route out all pins, not to get better radio performance. In a 4 layer board, the two top and bottom layers are close to each other which allows microvias to be placed, which will make it possible to route out the inner balls. In your case the two layers are close so you will probably be able to do the same. If you are able to make the board with 2 layers, there is no problem with using that.