I'm working on a PCB with 0.4mm WLCSP's and 0201 discretes. It will have components on both sides. The routing is very tight; I can't use a simple plated through hole ("PTH") design.
I'd like to avoid the costs of sequential laminations. It looks like I can get away with six layers with a single-lamination design. This only gives me one set of blind vias and no buried vias. I've figured out fanouts that should allow for a mechanical drill (6-mil drill; 12-mil ring; filled via-in-pad).
Now I have to decide how to use my stackup. The board has RF at 2.4GHz and 3.5GHz. The transceivers will be very close to their respective antennas.
If I place ground and power planes on L2 and L5, I can use the blind vias for power, as shown:
In this case, one of the power connections will be a blind via and the other will be a PTH. All of my signal routing will have to be carried by PTH's. There are decoupling benefits when using blind vias for power connections. This layout gives me a close reference plane to the RF on layer #1. It also shields the signal layers L3 and L4.
Or, if I put ground/power on L3 and L4, I can use the blind vias for signal routing:
In this case, the routing will be much easier. However, I lose any low-inductance decoupling benefits of the blind vias. Also, my RF on layer #1 is now farther from a reference plane (I'd remove copper on L2 to make L3 the reference...)
The first case strikes me as better, but the second case will significantly simplify my routing.
Is there an obvious better choice here? What are the primary considerations?