I’m using KiCad 8.0.9 and designing an HDI PCB for an FBGA device. This is my first time working on a multilayer board, and I need to create staggered vias across internal layers to build a signal path from L1 to L8, like this:
L1 to L2 (microvia)
L2 to L3 (buried via)
L3 to L4 (buried via)
L4 to L5 (buried via)
L5 to L6 (buried via)
L6 to L7 (buried via)
L7 to L8 (microvia)
I’m trying to fan out signals from top to bottom while maintaining HDI-compatible structures (sequential lamination, no through-hole via blocking). Is there a supported method in KiCad to:
Define and place these staggered microvias and buried vias correctly?
Ensure layer pairs are respected during via placement?
Generate correct manufacturing files with sequential lamination via types?
If not, ask your pcb manufacturer for their capabilities before starting routing. Many manufacturers don’t allow buried vias from even to odd layers, only from odd to even. I mean, they allow a via from layer 3 to 4 but don’t allow from layer 4 to 5.
HDI (High Density Interconnect) is a specific PCB manufacturing technique, in which the PCB is manufactured one layer at a time. “Through hole” via’s don’t really exist in this technique, the result will be stacked micro via’s though all the layers, and this is discouraged because it reduces the reliability of the PCB.
Usage of micro via’s must be enabled before they can be used. There is not much info in the manual:
If microvias or blind/buried vias are enabled in the Constraints section of the Board Setup dialog, these vias can be placed while routing. Use the hotkey Ctrl+V to place a microvia and Alt+Shift+V to place a blind/buried via. Microvias may only be placed such that they connect one of the outer copper layers to an adjacent layer. Blind/buried vias may be placed on any layer.
I once experimented a bit with this myself, but even with the description above I can’t find where the setting is. Too many hours staring at the screen probably.
Apparently micro via’s don’t have to be enabled separately anymore, but this is a guess.
Setting up and working with “layer pairs” may also be of help.
KiCad has been greatly improved in the last handful of years, and the development pace is mostly set by the amount of time that the developers have available. There are options for priority development through https://www.kipro-pcb.com/ but it’s not free. I’m waiting for the day that several big companies realize they can stop with paying for 20 seats of some commercial software (Assume EUR5000/year each) and recoup their investment in 2 years if they invest in KiCad to implement the few extra features that are essential to them. KiCad can do a lot with EUR 200k and some time.
