Re: [SI-LIST] : why .062?

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From: rbishop (ron_bishop@mentorg.com)
Date: Thu Mar 09 2000 - 07:32:44 PST


    Tony makes a good point.... we tend to get wrapped up in the "electrical" concerns of current designs, but there are still some definite mechanical issues to be aware of out there in the physical
world.

    I know I put my various personal electronic units (everything from cellphone to handhelp pc to laptop) through enough "unplanned" shock tests...!
RonB

"Cusanelli, Tony" wrote:

> A few people asked for the "old guys" to comment on why boards are .062.
> Back in the dark ages (30 yrs ago) the boards I first designed were merely
> mechanical devices that supported parts. Connectivity was accomplished via
> wire-wrap. Parts were heavy and boards had to be thick enough to prevent
> breakage, but thin enough to carry. 1/16 inch became the right compromise
> and card guides, standard socket boards and chassis were all designed to fit
> that thickness.
>
> Even with today's lighter parts, tracks are thin and need some support.
> .032 boards are okay if they are small. Flexing and the pressure from
> connector insertion/extraction will fracture thin traces.
>
> PS - for you young guys - wire wrap was accomplished with a device similar
> to a hollow drill bit that would wrap 6-8 turns of 30 awg wire around a
> square or rectangular post. The edges would bite into the wire and make a
> gas-tight connection that was tested with a pull device (strain gauge). We
> had some PC boards, but they were mostly 2 and four layer. Draftsmen just
> could not lay out a board as fast as I could write a wirelist for the wiring
> machine.
>
> Yes now I feel like a dinosaur.
>
> Tony
>
>
> -----Original Message-----
> From: Alex Li [mailto:alexl@ati.com]
> Sent: Monday, March 06, 2000 9:36 PM
> To: 'si-list@silab.eng.sun.com'
> Subject: [SI-LIST] : different 4-layer board Stack up (S-P-G-S) ?
>
> Recently I saw a 4-layer mother board with 100 Mhz 128-bit memory bus.
> This board has unusual signal-power-ground-signal stack up. I talked to
> one of their engineer for this kind of arrangement. They said since most PC
> motherboard has several power plane split and on the top level there are a
> lot of components with pads. they think if they route all the 128-bit memory
> bus on the back and put it close to ground plane, they have much routing
> area and this will help to keep the signals clean.
>
> This is kind of new idea to me, does anyone see any drawback by this
> arrangement ? Will this decrease the decoupling caps performance ?
>
> Alex
>
>
>
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--
*********************************************
Ron Bishop-High Speed/SI Tech. Mktg. Eng.
Mentor Graphics Corporation                     | Email:  ron_bishop@mentor.com
Board Systems Division                             | Phone: (503) 685-1992
8005 S.W. Boeckman Road;Bld.E-3164    | Fax:   (503) 685-4897
Wilsonville, OR 97070-7777
http://www.mentor.com
*********************************************
"If you think you're a man of influence,
   try ordering another man's dog around..."

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