Since IPC-7351 is only following the same convention as EVERY reel of parts
I have ever seen (always horizontal to the tape and polarity to the left),
I don't
know how anyone could be unhappy with it. Unless they would prefer changing
all the component reels in existence? Yeah, right...

Anyone who isn't happy about it wasn't paying attention to the
manufacturing
world in the first place.

Jack C. Olson
10G Circuit Board Designer
(630) 754-2431






             JaMi Smith
             <jamismith@SBCGLO
             BAL.NET>
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             10/26/2004 01:32
             PM

                                                                   Subject
             Please respond to         Re: [DC] Pin Numbering Question
                "(Designers
              Council Forum)"
             <DesignerCouncil@
             IPC.ORG>; Please
                respond to
                JaMi Smith
             <jamismith@SBCGLO
                 BAL.NET>





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In IPC-7351, all two terminal components are identified with the Polarity
Indicator
at Pin 1 which is always to the left.

The Polarity Indicator on a capacitor is the "plus" or "notch" or "band"
which
identifies the Positive Terminal or Polarity (and yes there are exceptions
to the
rule such as some radial capacitors which have a stripe which is labeled
"-"), and
thus the "rule" for a capacitor is always "Positive Terminal or Polarity"
to the
left.

The Polarity Indicator on a Diode is the "band" (or occasionally some other
feature)
which identifies the Cathode (by industry convention), and thus the "rule"
for a
diode is always "Cathode" to the left.

Yes, the IPC-7351 figures and language need to be cleaned up to avoid any
ambiguity.

The problem is that everyone in the industry orients diodes differently,
with their
own specific preferences, with some wanting Pin 1 as Anode, some wanting
Pin 1 as
Cathode, and some wanting vertical orientation and some wanting horizontal
orientation, some wanting Pin 1 up or to the left, and some wanting Pin 1
down or to
the right.

IPC-7351 has chosen to adopt an orientation as the standard "zero degrees
of
rotation" or "zero rotation" in which all two terminal components are
oriented
horizontally (which complies with the way that almost all existing
libraries orient
the majority of their two terminal components (which itself is primarily
due to the
height / width aspect ratio and display area of the standard computer
monitor)), and
further to specify that Pin 1 will always be to the left, and further to
specify
that the "Polarity Indicator" will always be Pin 1 which again is always to
the
left. The "Polarity Indicator" is always the "Positive Terminal" for a
Capacitor
(notwithstanding the above mentioned exception) and the "Cathode" for a
Diode (due
to the industry wide standard of identifying the Cathode with a "band").

Some will be happy with this orientation, and others will be not.

Once again, the problem is that everybody currently does it differently,
which
causes major problems for assembly houses, and results in numerous errors.

IPC-7351 has adopted a "standard orientation" for these components as "zero
rotation" which is designed to eliminate these problems in the design and
manufacture of printed circuit boards.

It is not, and was not, designed from the results of a survey, and
certainty not
designed to make everybody happy, which it obviously will not do.

All else said, IPC-7351 does fix the problem, whether or not it you are
happy with
the way it does it.

JaMi Smith

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