RE: [SI-LIST] : multiwire experience?

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From: Thomas Jackson (tjackson@fmi.fujitsu.com)
Date: Mon Jan 15 2001 - 14:41:23 PST


Multiwire is a proprietary technology. There is a very short list of places
to get it done, so I don't think it is very cheap.

It was favored when making PCBs with more than two layers was prohibitively
expensive.

It has fallen from favor for a number of reasons. First, the technology
assumes that an insulated wire can be accurately placed in a layer of liquid
epoxy such that, later on, after the epoxy hardens, a CNC drill can drill
through that wire and make a through hole in the substrate. Next
assumption: Plating that hole will form a good electrical contact with both
of the sheared ends of that wire.

Second, electrically, I have some reservations about its signal performance.
I don't see how each wire can be a uniform distance from a power or ground
plane over its entire length, so there must be impedance variations. The
Multiwire boards I have seen have had only one pair of power and ground
planes. Therefore, everything is microstrip at various heights above the
plane.

At my previous employer, a defense contractor, they were redesigning
Multiwire boards for old systems into PCBs because they were more
supportable.

While Multiwire had its day in the sun, I don't think I would go that way
today with the current cost and performance of PCBs.

Tom

Thomas L. Jackson, P.E.
Staff VLSI Design Engineer
Network Access Development
Systems Solutions Group
FUJITSU MICROELECTRONICS, INC.
3545 North First Street
San Jose, CA 95134-1804
telephone: (408) 922-9574
facsimile: (408) 922-9618
http://www.fujitsumicro.com

-----Original Message-----
From: Zabinski, Patrick J. [mailto:zabinski.patrick@mayo.edu]
Sent: Monday, January 15, 2001 1:57 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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