panel - the main usage is for allowing one PCB to be soldered to another in a stack - thus acting both as a fastener and also as a connector. Three major kinds of vias are shown in right figure. The basic steps of making a PCB are: making the substrate material and stacking it in layers; through-drilling of plating the vias; and copper trace patterning using photolithography and etching. 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. (Laser drills can also be used for smaller and more precisely positioned holes than mechanical drills produce.) 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. If two more layers are consecutively stacked from bottom of core, you can have a 1-2 via, a 1-3 via and a through hole. 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. For cheaper boards, only through holes are made and antipad (or clearance) is placed on layers which are supposed not to be contacted to vias. IPC 4761 IPC 4761 defines the following via types: Type I: Tented via Type II: Tented & covered via Type III-a: Plugged via, sealed with non-conductive material on one side Type III-b: Plugged via, sealed with non-conductive material on both sides Type IV-a: Plugged & covered via, sealed with non-conductive material and covered with wet solder mask on one side Type IV-b: Plugged & covered via, sealed with non-conductive material and covered with wet solder mask on both sides Type V: Filled via, filled with non-conductive paste Type VI-a: Filled & covered via, covered with dry film or wet solder mask on one side Type VI-b: Filled & covered via, covered with dry film or wet solder mask on both sides Type VII: Filled & capped via, filled with non-conductive paste and overplated on both sides Failure behavior If well made, PCB vias will primarily fail due to differential expansion and contraction between the copper plating and the PCB in