Q: Why curvy PCB traces?


  • curvy-pcb-traces.jpg
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At first I thought the width of the trace varied smoothly. This is to prevent signal reflections from changes in impedance.

But what I see here looks like you have high-speed digital signals going down these traces, and they all need to arrive at the same time. So, if some paths would be shorter than others, you curve them around so they all line up in the end.
Skew control, have a look at the requirements for DDR memory, one of the more critical interfaces on a PCB. It requires a router that can handle high speed designs, you have to enter the max skew as either a time or a length. It cannot usually be done manually as quite often you are matching signals within one group to signals within other groups and then to clocks. To make matters worse, when this is on a board the board quite often has to be impedance matched, so each signal layer has to be closely tied to a ground plane for return currents.
Its most noticable on mother boards between the CPU, interface chips and the DDR sockets.


Paid Member
2005-12-04 11:46 pm
Not being overly familiar with modern PCB-design (to put it mildly), the pic above got me into asking myself , whether the curvy sections of the traces in post #1 would (also ?) be used as on-PCB inductors.
I found a more revealing sample of this there:
So could this also be the case with the Oppo-PCB ?

Greez & Thanks

No is the short answer, its more prone to artifacts such as mutual crosstalk, the general rule being use 3 tiems the track to track spacing between the consatinas where possible. If you want to create inductors on a PCB look up "planar transformers", you can do all sorts of funky things.
I'd say the pattern on that PCB would create more capacitive coupling between the planes than inductive.
Rememeber it is signal rise times that cause signal integrity problems, use the slowest possible rise time for any signals to minimise problems.
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