# Pad 'Electrical Type' in Altium

When create footprint in Altium, we can set the 'Electrical Type' of the pad, and have three choices: Load, Terminator and source. But what's their meaning and when they will take effect?

When you specify the routing topology of a net, the Electrical Types may be used to decide where the connections go. Here are the choices for topology design rules (Shortest is the default):

Topology– defines the topology to be used for the net(s) targeted by the scope (full query) of the rule. The following topologies can be applied:

Shortest – this topology connects all nodes in the net to give the shortest overall connection length.

Horizontal – this topology connects all the nodes together, preferring horizontal shortness to vertical shortness by a factor of 5:1. Use this method to force routing in the horizontal direction.

Vertical – this topology connects all the nodes together, preferring vertical shortness to horizontal shortness by a factor of 5:1. Use this method to force routing in the vertical direction.

Daisy-Simple – this topology chains all the nodes together, one after the other. The order they are chained is calculated to give the shortest overall length. If a source and terminator pad are specified, then all other pads are chained between them to give the shortest possible length. Edit a pad to set it to be a source or terminator. If multiple sources (or terminators) are specified, they are chained together at each end.

Daisy-MidDriven – this topology places the source node(s) in the center of the daisy chain, divides the loads equally and chains them off either side of the source(s). Two terminators are required, one for each end. Multiple source nodes are chained together in the center. If there are not exactly two terminators the Daisy-Simple topology is used.

Daisy-Balanced – this topology divides all the loads into equal chains, the total number of chains equal to the number of terminators. These chains then connect to the source in a star pattern. Multiple source nodes are chained together.

Starburst – this topology connects each node directly to the source node. If terminators are present, they are connected after each load node. Multiple source nodes are chained together, as in the Daisy-Balanced topology.


Mostly this is important for high-speed designs (where reflections are important). And mostly you'll find pins in libraries just left at the default of "load".