Hi! Dave, you asked about the reasons for large conductive areas.

>May I ask a dumb question ????

IMO very seldom is a question asked on the technet dumb, that's why 
technet's here and (collectively) we are here to communicate 
requirements, knowledge and experience.

>If the 8 square inch area is unbroken, then what is it used for? It is
>obvious from your statement that there are no isolation clearances, or
>isotherms for holes, so this precludes the use of either leaded or SMD
>components on the surface of the board. Could it be that your 
designers have designed a feature that may be very costly that serves 
>no obvious function??

>I'm curious...

It's the "ultimate" SMT design and assembly, everything is located on 
one-side --- (;-) just think if we could eliminate the dielectric and 
only use "self-supporting" conductive patterns.

Seriously though, some designs are such that all components and 
conductive patterns may form a single-sided board and assembly with all 
components and conductive patterns located on one-side.  This is 
particularly desirable and achievable for some analog/RF designs.  In 
particular, some very high frequency and microwave design can be 
implemented in "single-sided" designs.  Sometimes this is very 
desirable for mixed designs, consisting of analog and digital, or 
analog and analog (where there are some very sensitive (low level) 
analog and "higher" power analog in the same design.  The full 
ground/voltage planes (with no holes) are used as "signal conductor 
reference ground planes" to maximize electrical "E"-field isolation 
from one side of the assembly to the other.  This is particulary true 
in the case of analog/digital, where analog is located on one-side and 
the digital is located on the other, with (ideally) only one through 
connection from one-side-to-the- other.  Most printed board conductive 
patterns provide minimal (like no) "H"-field magnetic  isolation, 
shielding or attenuation due to the characteristics of most printed 
board conductive pattern materials (like copper, tin, lead, etc.).

In some cases, lands are attached to the low impedance "ground" plane 
using "blind" vias, and the supply voltages are very carefully routed 
on the conductive pattern layer.

>Dave Rooke
>Circo Craft - Pointe Claire
>Date: Tue, 10 Sep 1996 20:33:26 -0400 (EDT)
>From: [log in to unmask] (D. Rooke)

Dave, hope this helps in understanding why some printed boards and 
their assemblies are designed as true "single-sided" designs or 
"doubled" single-sided assembly designs.

Ralph Hersey
Ralph Hersey & Associates
[log in to unmask]


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