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enter image description here

I was looking at the traces of a computer's mother board and noticed that some traces appear excessively long and zig-zaggy(Really couldn't think of a better term). I am wondering why the designer would have added all the extra turns. Is this just a way to fill the empty spaces? Or just this have a purpose such as increasing inductance/capacitance or for EMI? I am aware that there are probably different rules for different things, but is there a semi-generic reason for this? I can't figure out what the little "bumps" in the trace would be necessary for. It should be noted that the traces in the picture connect 2 RAM sticks to the main processor.

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  • \$\begingroup\$ Related \$\endgroup\$ – helloworld922 Dec 28 '16 at 15:56
  • \$\begingroup\$ Speed bumps. Literally. Also, they look cool :) \$\endgroup\$ – Phil Frost Dec 28 '16 at 16:57
  • \$\begingroup\$ RAM, especially DDR3/4 RAM is very sensitive to timing skew between traces, the spec calls for sub-mm length matching on a lot of traces. \$\endgroup\$ – Sam Dec 28 '16 at 20:30
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This is an example of length matching (which can be necessary for both differential pairs and certain interface bus types).

This is done so that a set of signals that are launched together arrive within a short time of each other (how much they can be off depends on the timing error budget available); note that no amount of length matching will guarantee perfect timing across the matched group due to various effects (even manufacturing tolerances have an effect here).

Although the signals in question are highly likely to be impedance controlled that is a separate subject; the length match is specifically for timing; impedance controls are to maintain signal integrity.

It is certainly true that no amount of length matching will be of use if there is a failure to properly implement SI where it may be required.

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This is done to even out the propagation time delays such that signals arrive at their destinations at the same time.

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These traces are part of a bus (look up PCI Express). The signals going into the wires are all synchronized, so the signals are input to the wires (traces) at the same time. If the wires are all the same length, then the signals arrive at the other end of the wires at the same time. If the wires are different lengths, then the signals arrive at different times and the receiver will likely read incorrect data.

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