RE: [SI-LIST] :PCB Bd thkness'

About this list Date view Thread view Subject view Author view

From: Killoy Richard-P29744 (Richard.Killoy@motorola.com)
Date: Wed Mar 08 2000 - 07:32:19 PST


So our nominal board thickness of 0.062" comes from old plywood laminating
machines...ha!.

I am always amused at how some of the dimensions or specifications we
eventually use come about.
Here is a story someone sent me awhile back, for engineers, it is quite
amusing....

enjoy....

Subject: Barriers To Innovation

The US Standard railroad gauge (distance between the rails) is 4 feet,
8.5 inches. That's an odd number. Why was that gauge used? Because,
that's the way they built them in England, and the US railroads were
built by English expatriates. Why did the English people build them
like that? Because the first rail lines were built by the same people
who built the pre railroad tramways, and that's the gauge they used.
Why did "they" use that gauge then? Because the people who built the
tramways used the same jigs and tools that they used for building
wagons, which used that wheel spacing. Okay! Why did the wagons use
that odd wheel spacing? Well, if they tried to use any other spacing,
the wagons would break on some of the old long distance roads, because
that's the spacing of the old wheel ruts. So who built these old
rutted roads? The first long distance roads in Europe were built by
Imperial Rome for the benefit of their legions. The roads have been
used ever since.
And the ruts? The initial ruts, which everyone else had to match for
fear of destroying their wagons, were first made by Roman war
chariots. Since the chariots were made for or by Imperial Rome, they
were alike in the matter of wheel spacing. Thus, we have the answer to
the original questions. The United States standard railroad gauge of 4
feet, 8.5 inches derived from the original specification for an
Imperial Roman army war chariot. Specs and bureaucracies live forever.
So, the next time you're handed a specification and wonder what
horse's ass came up with it, you may be exactly right. As it turns
out, the Imperial Roman chariots were made to be just wide enough to
accommodate the back ends of two war horses.

There's a very interesting extension of the railroad gauge story and
horses' behinds. When we see a Space Shuttle sitting on the launch
pad, there are two big booster rockets attached to the sides of the
main fuel tank, well known as the solid rocket boosters, or SRBs. The
SRBs are made by Thiokol at a factory in Utah. The engineers who
designed the SRBs might have preferred to make them a bit fatter but
the SRBs had to be shipped by train from the factory to the launch
site. The railroad line to the factory runs through a tunnel in the
mountains. The SRBs had to fit through that tunnel.
The tunnel is only slightly wider than a railroad track and the
railroad track is about as wide as two horses' behinds. So as it
stands, a major design feature of what is arguably the world's most
advanced transportation and rocket system, conceivably was determined
by the width of a horse's backside, or two.
As an astronaut, how would you like to be saddled with that?

------------

Richard Killoy, RF Engineer
Motorola -- Fixed Wireless Systems Group
Broadband Solutions Division
 
richard.killoy@motorola.com
work:  (480) 456-2487     pager:  7174988@skytel.com
cell:    (480) 799-9739

-----Original Message-----
From: Scott Brenneman [mailto:sbrenneman@ideo.com]
Sent: Tuesday, March 07, 2000 4:10 PM
To: si-list@silab.eng.sun.com
Subject: RE: [SI-LIST] :PCB Bd thkness'

My understanding is that 1/16" was the thickness of one ply of plywood, and
that the original PCB lamination machines were based on plywood laminators.

Scott

-----Original Message-----
From: owner-si-list@silab.eng.sun.com
[mailto:owner-si-list@silab.eng.sun.com]On Behalf Of Scott McMorrow
Sent: Tuesday, March 07, 2000 2:35 PM
To: si-list@silab.eng.sun.com
Subject: Re: [SI-LIST] :PCB Bd thkness'

I believe that these numbers were written by the
"Ancient Ones" on stone tablets. Unfortunately, an
irate member of the "Manufacturing Clan" was a bit peeved
at the members of the "Design Clan" and shattered those tablets
in pieces after a fit of disgust. The original intentions of the
"Ancient Ones" have been lost to history and mythology, however,
ever since that day an eternal clan war has raged.

regards,

scott

--
Scott McMorrow
Principal Engineer
SiQual, Signal Quality Engineering
18735 SW Boones Ferry Road
Tualatin, OR  97062-3090
(503) 885-1231
http://www.siqual.com

Dave Hoover wrote:

> I always thought the .062", .093", .125" was for through hole leads, > press fit connector length, and edge card connectors. Standardize > for consistancy and repeatability. That's what I was taught..... > > Dave > -----Original Message----- > From: Abd ul-Rahman Lomax [mailto:marjan@vom.com] > Sent: Tuesday, March 07, 2000 12:59 PM > To: si-list@silab.eng.sun.com > Subject: Re: [SI-LIST] : different 4-layer board Stack up (S-P-G-S) ? > > At 11:14 AM 3/7/00 -0700, ajmani@us.ibm.com wrote: > > >By the way, can someone enlighten me on how 0.062" came to be the standard > >board thickness. > > I haven't seen any documentation, but the reason is fairly obvious. 1/8 > inch was thicker than necessary for most applications and 1/32 inch was too > thin, so 1/16 was chosen. .031 and .125 are still standard core > thicknesses, along with 3/32, 0.093. We see the same history in 1/2 ounce, > 1 ounce, and 2 ounce copper foil. > > marjan@vom.com > Abdulrahman Lomax > P.O. Box 690 > El Verano, CA 95433 > > **** To unsubscribe from si-list or si-list-digest: send e-mail to > majordomo@silab.eng.sun.com. In the BODY of message put: UNSUBSCRIBE si-list > or UNSUBSCRIBE si-list-digest, for more help, put HELP. > si-list archives are accessible at http://www.qsl.net/wb6tpu > **** > > **** To unsubscribe from si-list or si-list-digest: send e-mail to majordomo@silab.eng.sun.com. In the BODY of message put: UNSUBSCRIBE si-list or UNSUBSCRIBE si-list-digest, for more help, put HELP. > si-list archives are accessible at http://www.qsl.net/wb6tpu > ****

**** To unsubscribe from si-list or si-list-digest: send e-mail to majordomo@silab.eng.sun.com. In the BODY of message put: UNSUBSCRIBE si-list or UNSUBSCRIBE si-list-digest, for more help, put HELP. si-list archives are accessible at http://www.qsl.net/wb6tpu ****

**** To unsubscribe from si-list or si-list-digest: send e-mail to majordomo@silab.eng.sun.com. In the BODY of message put: UNSUBSCRIBE si-list or UNSUBSCRIBE si-list-digest, for more help, put HELP. si-list archives are accessible at http://www.qsl.net/wb6tpu ****

**** To unsubscribe from si-list or si-list-digest: send e-mail to majordomo@silab.eng.sun.com. In the BODY of message put: UNSUBSCRIBE si-list or UNSUBSCRIBE si-list-digest, for more help, put HELP. si-list archives are accessible at http://www.qsl.net/wb6tpu ****


About this list Date view Thread view Subject view Author view

This archive was generated by hypermail 2b29 : Thu Apr 20 2000 - 11:35:26 PDT