Related to the past point, the impedance of any signals on L4 will likely have more compact deviations in close proximity to power rail splits on L3 The minimum hole diameter of mechanical drilling potential has dropped from 0.4mm to 0.2mm or even lesser. The hole diameter on the PTH https://sethruwwx.glifeblog.com/30474093/6l-8l-10l-12l-layer-second-order-pcb-circuit-board-options