What are the different types of vias used in PCB design?
different types of vias used in PCB design
PCBs contain thousands of traces, pads, and holes to conduct signals and power between components. One of the most important jobs of a circuit board layout designer is organizing these elements to correctly transition between layers without causing signal interference and power dissipation issues. To do this, they must ensure vias have proper clearances to other vias and component edges. This is done by using various via types, including blind, buried, and microvias.
Conventional through-hole vias are the most common type of via used in a pcb. They connect the inner and outer layers and are used for both internal interconnection and as positioning holes for connectors and components. These vias require specialized fabrication techniques because they are plated through the entire copper layer stack. As such, it is recommended to avoid them whenever possible and only use them when necessary for signal integrity reasons.
Blind and buried vias, on the other hand, are not plated through the whole copper layer stack. This makes them much more cost-effective than through-hole vias. They are used for inner signal interconnection but cannot be seen from the outside of the board and are therefore ideal for high-density designs. They also reduce the likelihood of signal interference and save space on a PCB.
What are the different types of vias used in PCB design?
A buried via consists of a hole in the inner layer with an annular ring and a pad at both ends of the hole. The hole is filled with a conductive paste or epoxy and the annular ring is plated over with copper. This structure is known by several different names, such as via in pad plated over (VIPPO), filled and capped via, plugged via, and IPC-4761 class 7 hole. It is important to note that changing a via design at the manufacturer, prior to the actual fabrication of the board, is never a good idea. It is always a better idea to carefully plan your PCB’s layer and via layouts during the layout phase and submit them with correct Gerber files.
Microvias are a type of buried via with a smaller hole and less copper plating. These vias are often used in high-speed applications, as they can allow for more current flow while maintaining a low characteristic impedance. However, there are certain restrictions regarding the size of the hole and its annular ring when using microvias.
Another common use of vias is escape routing. This is when surface mount components need to be connected to a via for routing on the inside layers of a multilayer PCB. Escape routing vias should be placed in a defined pattern and are typically routed before other traces. In addition, they can be used to connect a ground plane or power traces. However, it is important to note that the escape routing vias must be large enough to accommodate the power and current requirements of these traces. Otherwise, they could be a source of overheating and power loss. This is why it is important to follow the high speed pcb rules and guidelines when using these vias.