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December 1998

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From:
Cyrus Ringle <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Wed, 30 Dec 1998 09:34:39 -0700
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text/plain (93 lines)
I agree with the square cathode pin 100% we have been doing it this way for
a LONG time.  Had an interesting problem occur with a SMT diode.  Since the
pads are both square and to make an outline of the part showing the cathode
bar was unfeasible due to limited space we used a K to mark the cathode
side,  Guess what?  The assembly house that was building the board thought
the K was diode symbol.  Well it made some sense why they stuffed it wrong,
a K next to the cathode side meant that pin was the anode to them.  Now we
mark cathodes on SMT diodes with a bar or a dot.  Anyone got a better way
of doing it?


Cyrus Ringle
Sr. CAD Specialist at Inter-Tel ---- http://www.inter-tel.com
7300 West Boston Street
Chandler, AZ 85226
Email [log in to unmask]
Voice (602) 961-9000 x21216 or Direct 961-2263
Fax (602)961-1370

Vice President of the Greater Phoenix Designers Council ----  A part of the
 IPC http://www.ipc.org/html/framesetdestypes.html
PO Box 3805
Scottsdale, AZ 85271





"Wolfe, Robert" <[log in to unmask]> on 12/30/98 08:15:52 AM

Please respond to "TechNet E-Mail Forum." <[log in to unmask]>; Please respond
      to "Wolfe, Robert" <[log in to unmask]>

To:   [log in to unmask]
cc:    (bcc: Cyrus Ringle/Inter-Tel)
Subject:  Re: [TN] Assy: LED Failures, I found out what happened...




I would second the motion for Jeff's input. We have pretty much done the
same thing. Made one shape standard and one symbol standard for all
diode's,led's & transistor's. Pin 1 is always the cathode. , no matter what
the spec sheet etc. calls out. Now we have had some weird looks and
questions from some engineers at times, but when you show them and say does
it match the schematic and do the functions of each pin match usually they
see the light. Also TO-92 transistors is also a similar problem where
different mfg.'s call d, s & g or e, c & b different pin numbers,
physically/electrically they are equivalent but between vendors the pin
numbers are different (why they do this still amazes me). We did the same
here made one shape and made sure all our symbols using this shape reflect
those pin numbers. Now from time to time an engineer will blame the cad
library because the spec sheet that the engineer happen to look at when
they
can't get a circuit to work does not match the board markings, (and that is
not to say the librarian never makes a mistake) but in this case by keeping
it standard this way we have not missed yet on any of these type of parts.
The circuit needed tweaking not the library. From the librarian's viewpoint
I think by standardizing diode,led,transistor, etc. pin #1's makes for more
consistency and less error entering parts. Also once the rest of the
departments using this data become familiar with the standard I believe
they
will embrace it too.

Robert M. Wolfe
[log in to unmask]

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