Electronic – Purpose of “wave shaped” PCB traces


On some PCB designs, specific traces are routed in curious ways. This probably has to do with high frequency design considerations and general signal behavior that I am not familiar with.

Let's take this PCB (somewhere from the web) as an example. It shows part of a PCIe card with SATA routing and DDR2 RAM:

Example PCB

I highlighted 4 areas that qualify as unusual trace layout (from my perspective).

  1. What are those shapes supposed to achieve? How do designers come up with what pattern is required?
  2. Another example of wave shaped, antenna like routing.
  3. This is fairly rare. But obviously the designer deliberately avoided 45° traces. Why?
  4. Curves again and a single "pulse" within the trace. How can this have any significant effect?

So what are the use cases and benefits of this techniques?

I want to be able to take those into consideration when doing future PCB designs.

Best Answer

1) Equalisation of length of pairs of traces

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From Board Design Resource Center

2) Delay (e.g. of clock for timing purposes)?

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See also Adding delay intentionally

3) Reduce signal reflections due to discontinuities in trace width?

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from Circuit Board Layout Techniques

See also How should I lay out timing matched traces?