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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