I am not quite sure of what the context of this statement is, since the
thread took a rather twisting road to get to this point, and I could not
quite follow it, so I will just comment on the statements below just as they
stand, and hope that it is not too far out of context.

According to IPC, the top side of the PCB is the is the "Primary Side" of
the PCB, which generally corresponds to what we used to call the "Component
Side", and the bottom side of the PCB is the "Secondary Side" of the PCB,
which generally corresponds to what we used to call the "Circuit Side".

The "Primary Side" of the PCB us usually chosen or selected by the Designer
for some distinctive reason, such as being the side with the most
components, or most complex features, etc., but this is not necessarily so,
and there may be no other reason beyond the Designers preference for this
side being chosen as the "Primary Side" of the board..

Physical Layers of the PCB are numbered beginning from the "Primary Side"
(top layer) being numbered as Layer 1, and counting down sequentially thru
the board to the "Secondary Side" (bottom layer), and then continuing with
Solder Mask (Top, then Bottom), and then Silkscreen (or "overlay") (also Top
then Bottom), etc., etc..

The PCB also is usually demensionally defined as having three mutually
perpendicular datum planes. The first of these is called the "Primary
Datum", and is defined as being the "Bottom Side" (or "Back Side"), of the
PCB, or I suppose one could say that it is the theoretical plane upon which
the PCB is said to rest.

This sometimes leads to confusion, because the "Top Side" of the PCB is the
"Primary Side" of the PCB, but the "Botton Side" (or "Back Side") of the PCB
is the "Primary Datum Plane" of the PCB.

For further confusion on the subject, see IPC-2221 Generic Standard on
Printed Board Design, Sections 5.4.3 Datum Features, and 11.2.1 Viewing
(which will refer you to IPC-D-310).


----- Original Message -----
From: "Michael Reagan (EDSI)" <[EMAIL PROTECTED]>
To: "Protel EDA Forum" <[EMAIL PROTECTED]>
Sent: Thursday, October 10, 2002 12:22 PM
Subject: Re: [PEDA] flipping board

> The only thing left now is Jun is now producing a design counter to IPC
> guidelines for documentation,   Primary side is on the bottom.

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