Quick Question About Circuit Boards

[peter.ell]

I am very curious as to why the etched lines running between components on a printed circuit board run the indirect paths they do.

Looking at one now, I notice that many of the etched lines connecting components make all sorts of turns as if they were navigating around something...but nothing is there. Why aren't they just going in more direct paths, only turning to navigate around other components?

The pattern of etched lines in circuit boards are basically an iconic image of electronics technology, but I'd love to know why these patterns are the way they are.

Thank you.

 

[bob1182006]

Could you link a picture or attach one showing what you mean?

If you mean how most of the traces (copper left after etching out the surrounding) make a lot of angled turns, no curvatures, then that's done to try to keep the impedance of the line constant at the turns.

Also the traces can't be too close together or there will be an inductive effect between them which could lead to problems.

 

[AlephZero]

Without a picture, it's hard to know exactly what you mean.

But laying out the tracks on PCBs isn't as simple as it might seem if you haven't actually tried laying out a simple circuit board yourself.

The biggest constraint on a single-sided board is of course that the tracks can never cross each other, unless you use loops of wire to "jump over" other tracks, or the track passes "underneath" a component on the board.

The power supply tracks are usually connected to a several different components, so they tend to "block" the possible routes of many other tracks.

There are also some practical constraints that mean certain tracks have to be kept as far apart as possible. For example tracks carrying low-level signals need to be kept away from sources of electrical noise (which might be other tracks on the board, and'or some of the components in the circuit). Tracks carrying high voltages may need to be kept away from everything else for safety reasons. In high-frequency circuits, as much of the board area as possible is left covered with a continuous "plane" of conductor connected to ground, to minimize problems with electrical noise.

Given all those factors, connecting components with a track "going in a straight line" is often impossible.