A via connecting the lowest layer of metal to diffusion or poly is typically called a “contact”. The types of pcb pdf and green layers are non-conducting, while the thin orange layers and vias are conductive.
Resistance vs Diameter on a 1. PCB to be soldered to another in a stack. Three major kinds of vias are shown in right figure. With this standard procedure, possible via configurations are limited to through-holes. Depth-controlled drilling techniques such as using lasers can allow for more varied via types. PCB manufacturing typically starts with a so-called core, a basic double-sided PCB. Layers beyond the first two are stacked from this basic building block.
Each type of via is made by drilling at each stacking stage. If one layer is stacked on top of the core and other is stacked from the bottom, the possible via configurations are 1-3, 2-3 and through hole. The user must gather information about the PCB manufacturer’s allowed methods of stacking and possible vias. This differential expansion and contraction will induce cyclic fatigue in the copper plating, eventually resulting in crack propagation and an electrical open.