I wonder if it is possible to manufacture a 4-layer PCB board with top and bottom layers used as ground planes and two inner layers used for signals/power. I believe this approach is a bit complex but reduces EMI significantly.
Problem is that as many components as surface-mounted, their wires need to be routed down into the inner layers. My understanding is that for that short vias between two layers would be optimal as through-hole vias have their downsides (they act as antennas, etc.).
So I looked at the design rules here and I see the following: “Burried, blind, micro or tented vias are not supported”.
Do I understand it right that only through-hole vias are possible to manufacture at the moment, so low-EMI 4-layer stackup is not really possible?
It is correct, we only support trough-hole vias at the moment. The impact of via stubs only become important with higher frequencies and larger stackups >6L. Can you share a bit more about your application requirements?
I suppose 4 layers should be enough. The board would contain digital IC with some signals running at around 150 MHz.
Most of components would be SMD. Packages of ICs would likely be LGA, LQFP, possibly BGA too. Pitch between contacts will likely be 0.5mm, width of contacts likely around 0.2mm.
There will also be a few through-hole components too, such as connectors.
Also, I may need to put a wireless module on the board. Those modules come as small PCBs, sometimes with castellated mounting holes.
Finally, the device would have a magnetometer, hence the desire to avoid EMIs as much as possible.
That’s the current idea so far.
The LGA, LQFP specification will be no issue, but note that a large BGA with 0.5mm pitch will not work as the vias will not fit in between the pads.
OK. So if I exclude BGAs, at least the ones with a small pitch, and use straight-through vias, the rest looks possible to manufacture and you’d expect that such long vias wont’s be problematic for relatively high-frequency signals?