I'm designing a 4-layer PCB for a very small adapter from a BGA on one side to several discrete SMT connectors on the other. Due to space constraints, I cannot use through holes for some of the interior connections; they must be routed through blind vias.
After some discussion with the PCB fab company I'm starting to understand a bit better why blind and buried vias cost so much money and how these complicated boards are constructed. I also appreciate that microvias add cost to the board. Is there any way to route a signal from one side of the board to the other without at least one set of microvias?
My current design has three via styles:
Layer 1-2
----------+ +------+ +--------------------
| | | |
----------| |------+ +------+ +----------
| | | |
----------| |----------------| |----------
| | | |
----------+ +----------------+ +----------
Through Layer 2-4
So the trouble comes with having both blind vias terminating on the same layer from either side of the board. They can't drill those separately before the layers are laminated together, and so the top one must be bored out afterwards and filled in (at high precision and cost, as I understand it). But I need these signals the whole way through the board! Are there any tricks to working around this? Or are my design specs simply too challenging for my modest budget?