mairomaster , 06-03-2016, 03:07 AM
As I said, I don't think you can use micro vias between layer 1 and 2 with this particular stack up, since the core between 1 and 2 is 0.254 mm thick. For a micro via with standard aspect ration of 1:1, that would mean the via hole diameter would need to be about 0.254 mm, which is not a convention micro via (I don't even know if they can manufacturer such a big micro via). Micro vias normally have a hole diameter about 0.1 mm, which requires the separation between the two particular layers to be about 0.1 mm (+/- 0.05 lets say).
So the only option I can see is either to use Blind vias (it is blind, not buried) from layer 1 to layer 3 (Mid_Layer_1), or TH vias. I don't know what is the pitch of your devices, but both the blind vias and TH vias will occupy quite of bit of space, because they can't be that small.