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Ratsnest

The thin straight lines on the PCB that show which pads still have to be connected. They come from the schematic and disappear as you route.

What it is#

After Update PCB the footprints arrive on the board with no copper between them. For every net the app draws the shortest set of straight lines that would connect its pads: the ratsnest. Each line is a connection still to make. When a track (or a pour) joins two pads, their line disappears.

Example circuit: After Update PCB this schematic gives ratsnest lines from R1 to D1, R2 to D2, and from J1 to R2 and to the LED cathodes (GND).
After Update PCB this schematic gives ratsnest lines from R1 to D1, R2 to D2, and from J1 to R2 and to the LED cathodes (GND). Open the led_gpio example from this page in PCB Canvas: “Insert into my schematic”.

Using it#

  • Place first. Move parts so ratsnest lines are short and do not cross much; good placement is most of the routing.
  • Route by net. Start with power and the critical signals, then the rest. The autorouter routes what is left.
  • Zero lines = done. The DRC reports unrouted connections, so nothing is forgotten before you order.

Pitfalls#

  • A ratsnest line that should not exist means the schematic connects two things you did not intend; fix the schematic, then Update PCB again.
  • A line to a GND pad stays until the pour is filled; it is not an error.