What's important when matching PCB traces?

Printed circuit board traces are often required to be very closely matched in delay. This is accomplished by making the trace routes the same length and the via spans cover the same number of layers. But there are other impairments lurking in the vias that can change the actual time it takes a signal to propagate from transmitter to receiver. In this paper, we will explore aspects of a via that can change the total delay of a trace.

When driving along a road, we care more about how fast we get to our destination than about how far we must travel. Two routes may be the same distance, but various factors along the way can affect the time we arrive. The same can be said for traces on a printed circuit board (PCB). While two traces may be the exact same length, the time it takes a digital signal propagating on those traces to make it from the driver to the receiver and be recognized as a “one” or “zero” can vary significantly.

In this paper we will explore how signal propagation delay is affected by the characteristics of vias on PCB traces.

If you’re working on high-speed designs, this one is a very worthwhile read.