RE: [SI-LIST] : multiwire experience?

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From: Haller, Robert (rhaller@cereva.com)
Date: Tue Jan 16 2001 - 13:30:55 PST


Pat,
        At risk of showing my age , I have some experience with Multiwire.
It was a number of years ago, but I performed a thorough evaluation
utilizing a test board and compared it to a similar designed controlled
impedance multiplayer Layer FR4 PC Board. We were doing a high speed
ECL system design and evaluated Impedance, Prop delay, Crosstalk while some
other folks looked at cost and reliability.
  
I don't have my old notes, but can try and summarize from memory.
Overall I didn't see any show stoppers from bare board electrical parameters
and tolerances. DC resistance was not a problem, and they held 50 Ohms +/-
10 %
on the characteristic impedance.
The propagation velocity was fast ~ 150 ps/in (similar to micro strip)
except varied quite a bit more than stripline and was as a function # of
crossovers.
Depending on board density and prop delay tolerance you need to watch this
(especially clocks).
We never got into the chamber so no hard data on emissions, but I suspect
they would be worse. We expected crosstalk problems, but it wasn't that bad
(Kb< 10%)
Forward crosstalk was OK if networks didn't get to long (remember you have
to
worry about Kf).

We were able to get prototype quantities very fast - and they able to react
to
changes quickly (for a price). Eco's were easy because everything was
accessible.
There was a separate layout group for multiwire because the auto-router
couldn't.
There was considerable quality and reliability work done, I can't remember
the
bottom line, although I don't remember any show stoppers.

It seemed kind of 'hair brained' scheme; wire everything up, drill holes
through the wires,
plate them, them voila. But it basically worked.
BUT, Given the High speed design challenges today, the difficulty in
obtaining qualified
resources, tool specialization, and layout expertise. I would recommend
against it. I wouldn't want to do the SI on it today ...

Regards,
Bob Haller
rhaller@cereva.com
508-787-5365
 

-----Original Message-----
From: Zabinski, Patrick J. [mailto:zabinski.patrick@mayo.edu]
Sent: Monday, January 15, 2001 4:57 PM
To: si-list@silab.eng.sun.com
Subject: [SI-LIST] : multiwire experience?

On a particular project I'm working on, it has been proposed
that we use multiwire boards in place of traditional multilayer
printed circuit boards. Does anyone out there have experience,
good or bad, with multiwire you'd care to share? I'm interested
in any/all experience, including performance, crosstalk, design ease,
reliability, cost, etc....

Thanks,
Pat

-----
  Pat Zabinski Ph: 507-538-5499
  Mayo Foundation Fx: 507-284-9171
  200 First St SW Em: zabinski.patrick@mayo.edu
  Rochester, MN 55905 Wb: www.mayo.edu/sppdg/simulation.html

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