Re: Utility of copper pours on four-layer boards

On Mon, 07 Apr 2008 16:37:45 -0700, Joerg
<notthisjoergsch@xxxxxxxxxxxxxxxxxxxxx> wrote:

Joel Koltner wrote:
"John Larkin" <jjlarkin@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote in message
news:s16lv3tmf5nge0aljddeii2do85k2b8fre@xxxxxxxxxx
Crazy... a professor who can't compute a wavelength.

In academia I think what happens is that if you haven't actually sat down and
thoroughly analyzed the situation and published a paper about it, you often
tend to err on the side of cuation and assume that any small change may have
some huge impact even if some quick "thought experiments" like calculating the
wavelength don't immediately suggest otherwise. (I once worked at a place
where we had an Asian software engineer -- English as a second language for
him -- who couldn't quite describe the problem with some code he was looking
at, but turned to me and another guy and told us it was, "some kind of
dangerous." It's become a popular phrase since then... hence I think the
professor felt that moving the SMA connector was some kind of dangerous. :-) )

Of course there are plenty of "hands-on" professors in academia too, although
their numbers seem to be dwindling as electronics becomes a "deeper" field and
people specialize early on and many end up having never built a circuit
outside of a simulator.

I just did a 4-layer FR4 board, and included a test trace: thru-hole
SMA, 50 ohm traces on layers 1, 3, and 4 (2 is ground), then another
SMA. I included a couple of sharp right angles and a beveled corner.
All the bends are invisible on 20 GHz TDR. The vias do show up, but
not real bad.

Good information. I think the beveled corners are meant to tell others that
you're an Official Microwave Designer and not just a PCB layout hacker. :-)


Hmm, for some reason John's post didn't make it onto the Pacific Bell
news server. Strange. So if I don't respond to some stuff my apologies,
I might not be able to see all the posts.

WRT beveled or rounded traces it depends on the effective number of bits
of the TDR scope. Minute reflections may go under in the noise but they
sure can matter in some hot pulse-echo applications.


On FR4, at 20 GHz, the fiberglass weave makes more impedance bumps
than a right-angle trace bend. An 11801 will zoom, smooth, and signal
average enough to show stuff like this.

John


.

Relevant Pages

  • Re: Utility of copper pours on four-layer boards
    ... In academia I think what happens is that if you haven't actually sat down and thoroughly analyzed the situation and published a paper about it, you often tend to err on the side of cuation and assume that any small change may have some huge impact even if some quick "thought experiments" like calculating the wavelength don't immediately suggest otherwise. ... I included a couple of sharp right angles and a beveled corner. ... than a right-angle trace bend. ... in the field I was thinking of they don't use FR4 and cost isn't really an issue. ...
    (sci.electronics.design)
  • Re: Utility of copper pours on four-layer boards
    ... In academia I think what happens is that if you haven't actually sat down and thoroughly analyzed the situation and published a paper about it, you often tend to err on the side of cuation and assume that any small change may have some huge impact even if some quick "thought experiments" like calculating the wavelength don't immediately suggest otherwise. ... I included a couple of sharp right angles and a beveled corner. ... All the bends are invisible on 20 GHz TDR. ... Rounded traces have the additional advantage of better ruggedness if the circuit board is exposed to lots of flexing. ...
    (sci.electronics.design)
  • Re: Utility of copper pours on four-layer boards
    ... In academia I think what happens is that if you haven't actually sat down and thoroughly analyzed the situation and published a paper about it, you often tend to err on the side of cuation and assume that any small change may have some huge impact even if some quick "thought experiments" like calculating the wavelength don't immediately suggest otherwise. ... hence I think the professor felt that moving the SMA connector was some kind of dangerous. ... I included a couple of sharp right angles and a beveled corner. ... I think the beveled corners are meant to tell others that you're an Official Microwave Designer and not just a PCB layout hacker. ...
    (sci.electronics.design)
  • Re: Utility of copper pours on four-layer boards
    ... where we had an Asian software engineer -- English as a second language for ... professor felt that moving the SMA connector was some kind of dangerous. ... Of course there are plenty of "hands-on" professors in academia too, ... I included a couple of sharp right angles and a beveled corner. ...
    (sci.electronics.design)