zig-zag PCB tracks, what are they for?

[ErikBaluba]

Hi,

I sometimes see zig-zag copper patterns on some PCBs. What is the purpose of
these?

Example, I have a PCI I/O card where there is a copper-track that make nice
symmetric and repetitive half turns from the I/O chip to the CLK signal on
the PCI slot.

erik

 

[Don Bruder]

Hi,

I sometimes see zig-zag copper patterns on some PCBs. What is the purpose of
these?

Example, I have a PCI I/O card where there is a copper-track that make nice
symmetric and repetitive half turns from the I/O chip to the CLK signal on
the PCI slot.

Even though signal propagation is faster than you and I will ever see
with our own eyes (since they're too slow) it isn't instantaneous. Add
length to a trace, and you add to the time it takes for a signal to get
from one end of that trace to the other. The amount of time added per
unit of length can be calculated accurately, even though it can't be
directly observed easily.

What would this suggest to you in relation to a CLK signal?

 

[Ben Jackson]

I sometimes see zig-zag copper patterns on some PCBs. What is the purpose of
these?

It's called "tromboning" and it's to extend IO lines (usually to length
match).

Example, I have a PCI I/O card where there is a copper-track that make nice
symmetric and repetitive half turns from the I/O chip to the CLK signal on
the PCI slot.

The "PCI Local Bus Specification" (not freely available, unless, of course,
you google for that exact phrase) says (v2.1, section 4.4.3.1, "Trace
Length Limits"):

The trace length for the PCI CLK signal is 2.5 inches +/-0.1
inches for 32-bit and 64-bit cards and must be routed to only
one load.

If you're making an experimental PCI card you can get away without
meeting those specs while you play around in your home pc...

 

[[email protected]]

The trace length for the PCI CLK signal is 2.5 inches +/-0.1
inches for 32-bit and 64-bit cards and must be routed to only
one load.

If you're making an experimental PCI card you can get away without
meeting those specs while you play around in your home pc...

Having recently done some PCI designs, I would highly recommend that if
anyone is building a PCI card, they adhere strictly to the layout
specifications, or you may find that your project doesn't work.


YMMV

Mark

 

[John Fields]

Hi,

I sometimes see zig-zag copper patterns on some PCBs. What is the purpose of
these?

 

[Deefoo]

The original post is from November 2005. Did it take you six months to come
up with this lame joke?

--DF

 

[John Fields]

The original post is from November 2005. Did it take you six months to come
up with this lame joke?