PCB Structures: Vias, Pads, Lands, Dimensions, Traces, and Planes


This article in the PCB Design Guide is to help define the pcb structures and terms a designer will need to in order to complete their pcb design.

Vias

A via is a physical piece of metal that makes an electrical connections between layers on the printed circuit board. Vias can carry signals or power between layers using plated through holes (PTH Technology). Using this technology a via is formed by drilling a hole through the layers to be connected and then plating the inner surface of the drilled hole. Vias should be sized according to the traces it’s connecting between layers and ultimately how much power it must carry.

Another via technology exists, High Density Interconnects or HDI. This technology forms a connection between layers by deforming the copper with a laser. These ‘microvias’ cannot penetrate more than one or two layers. This means that microvias must be stacked or stair stepped in order to make a connection through the entire pcb.

Pads or Anti-Pads

Pads are small areas of copper in predetermined shapes normally used to make a connection to a component pin. In some cases and anti-pad is needed which means the predetermined shapes are removed from the copper. Generally an anti-pad is used around a via to isolate it from a power plane where a connection is not needed.

Lands

If you took all the pads needed to solder a component to the top or bottom layer of the printed circuit board it may be referred to as a land. Making electrical connections throughout the entire board may require vias. When using the plated through hole technology vias are not included in the land pattern. The general method is to use a small trace to connect the land and via to make the appropriate electrical connection.

Traces or Tracks

A trace is a piece of copper, think of a wire, that makes an electrical connection between 2 or more points on a pcb. Traces carry current between these two points on the printed circuit board. Many times you also see people in the pcb design industry refer to traces as tracks. These are synonymous with each other and may be used interchangeably.

Planes

A plane is an uninterrupted area of copper covering the entire pcb layer. It is common to have cuts in a plane in order to distribute different power forms to the pcb components needed. Its critical that good pcb design practices be followed when making cuts in power or ground planes. Also refer to the Understanding PCB Layers article for more information.