Question about meandering tracings on computer circuit board

[Ernie Werbel]

On many computer circuit boards, mainly motherboards, traces will fill areas
with "S"-shaped and wavy lines that seem to meander around themselves,
rather than go in a straight path to the destination. In fact, certain (but
not all) tracings will often zig-zag (with smooth corners) while following a
direct path.

I have seen this in the past and thought nothing of it, but since I have
been building some new computer systems these past couple of weeks I have
taken the time to really notice it, but could not understand why they would
do this. Is there a technical reason for it?

 

[Mark Fortune]

Ernie Werbel wrote:

On many computer circuit boards, mainly motherboards, traces will fill areas
with "S"-shaped and wavy lines that seem to meander around themselves,
rather than go in a straight path to the destination. In fact, certain (but
not all) tracings will often zig-zag (with smooth corners) while following a
direct path.

I have seen this in the past and thought nothing of it, but since I have
been building some new computer systems these past couple of weeks I have
taken the time to really notice it, but could not understand why they would
do this. Is there a technical reason for it?

I'm probably just guessing here (and hence wrong) but I imagine it has
something to do with tuning the capacitance of the tracks - or perhaps
cancelling out RF interference, these things do run at pretty high
frequencies after all.

 

[John Fields]

On Fri, 28 Jul 2006 00:07:06 GMT, "Ernie Werbel"
<no_spam_please@fake_email_address.xyz> wrote:

On many computer circuit boards, mainly motherboards, traces will fill areas
with "S"-shaped and wavy lines that seem to meander around themselves,
rather than go in a straight path to the destination. In fact, certain (but
not all) tracings will often zig-zag (with smooth corners) while following a
direct path.

I have seen this in the past and thought nothing of it, but since I have
been building some new computer systems these past couple of weeks I have
taken the time to really notice it, but could not understand why they would
do this. Is there a technical reason for it?

---
Yes. The auto-router software is told, by the netlist, what has to
be connected to what, and it's also told how close the traces can be
to each other, how wide the traces can be, where the components's
footprints are and, perhaps, the maximum length of trace, the
impedance of the trace WRT a plane it rides above (or below) or its
proximity to its neighbors.

With all that information on hand, the autorouter proceeds to
connect everything up according to the schematic and the rules and,
after a while, comes up with an ingenious solution which seems to
meander around unnecessarily.

The solution, if that's a problem, is to route it (or part of it) by
hand.


--
John Fields
Professional Circuit Designer

 

[jasen]

On 2006-07-28, Ernie Werbel <no_spam_please@fake_email_address.xyz> wrote:

On many computer circuit boards, mainly motherboards, traces will fill areas
with "S"-shaped and wavy lines that seem to meander around themselves,
rather than go in a straight path to the destination. In fact, certain (but
not all) tracings will often zig-zag (with smooth corners) while following a
direct path.

I have seen this in the past and thought nothing of it, but since I have
been building some new computer systems these past couple of weeks I have
taken the time to really notice it, but could not understand why they would
do this. Is there a technical reason for it?

Yes, they're doing it to slow the signal on that conductor down.

Bye.
Jasen