Choosing the PCB stack-up should be aligned with the end product's PCB requirements.
For nRF9151, the following targets should be considered:
- For a best practice design, each signal layer should have an adjacent metal layer, that is, ground plane, which is dedicated to signal return currents.
- Consider the need for 50 Ω RF routings. Sometimes, to achieve 50 Ω routing requires opening the adjacent metal layer, which increases the risk of exposing RF routing to noisy routings.
- Avoid crossing 50 Ω RF routings on the application board. If it cannot be avoided, ensure that their ground planes remain continuous.
- Avoid using through vias in RF routings if they cause a parallel stub to the routing or are not 50 Ω.
- Consider good thermal design and aim to use metal filled vias due to their better thermal conductivity, especially when they are near nRF9151.