Tutorial/strategy: layout a 2-layer PCB in KiCad EDA

This gives a high level overview or strategy for laying out a simple PCB in KiCad or other EDA tool.  This is for beginners.  It doesn’t give details, exactly how to use the user interface.  This is not polished.  It tries to teach something which is obvious only to experienced users, that might save beginners some learning time.

This is for a ‘simple’ design where:

  • most of the components are surface mount (SMD) on the front
  • the board is a 2-layer board (copper on the front and back, and not in a middle layer.  Such a board is the cheapest to buy, design, and assemble.)
  • there are few components, and few busses (bundles of signal lines routed together.)

The strategy is:

  • read the netlist
  • auto spread or place your components
  • add a board outline larger than you think the board will take
  • move and rotate the components into the board outline, to minimize crossing of rats nest lines
  • add a front zone for the ground net
  • add a zone on the back for the power net
  • run the DRC tool

Now many of the rats nest lines will be gone, since the ground and power nets are usually the largest nets, and the DRC tool will connect the front and back zones to many of the pads on those nets.  Most of the remaining rats nest lines are for “signal” nets.

Now add tracks and vias to any power pads (that are not through holes) to the power plane (zone) on the back.

Now iterate:

  • move and rotate components to reduce crossing of rats nest lines and to shrink the board area
  • run the DRC tool

When you have in some sense done all you can do to minimize crossing rats nest lines:

  • switch to the OpenGL view (push-and-shove only works in that view)
  • choose “Do not show filled areas in zones” (fill obscures tracks)
  • manually route the remaining rats nest lines, using push-and-shove instead of clicking at many places along the track’s route to make it go exactly where you want it.

If you need to move some components to get room for a signal track, use Grab instead of Move, since that will keep the tracks you have already connected to the component.

Now you might tweak by moving components and nodes of tracks, running the DRC often to check you haven’t violated design rules.  Generally you might tweak to reduce the size of the board, but it is better if you did that before you did manual routing.

Finally:

  • redraw your board outline
  • run DRC again and insure your zones are still contiguous, connected planes (if you reduce the outline too much, it might island your ground and power planes.  Generally a ring of copper around the board edge connects islands of the zone together.  The ground and power planes can have some enclosed island, but one point of a ground plane is to let the signals go where they want in short paths.)

 

 

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