Gary,

            According to IPC-7351 Generic Requirements for Surface Mount
Design and Land Pattern Standard (which supersedes IPC-SM-782A)
specifies that all 2 pin molded and MELF diode land patterns shall be
drawn horizontally with Pin 1 on the left @ zero rotation. Furthermore,
the Cathode is always on pin 1 according to this standard.

 

This is, however, only half the battle. Let's assume that your physical
land pattern symbol was built properly with respect to IPC-7351. Let's
further assume that a datasheet for this diode device illustrated the
Cathode on pin 2. If the logical or "schematic" symbol was drawn with
pin "2" bearing the Cathode designation and silk markings to match the
datasheet, then the device could in fact be mounted in the incorrect
orientation with respect to the electrical connections associated to it.
This is a common problem that is easily avoided by standardization,
adherence to such standards, and verification to ensure quality.

 

All designs should ideally go through footprint verification during the
design phase before manufacturing - especially designs generated in
environments that lack physical and logical library symbol generation
control standards. Polarized caps and SOT's are the most common mistakes
I find. Those pesky SOT23's have many different possible pin assignments
and their logical and physical symbols are seldom in harmony with each
other in the service bureau world. Hope this helps.

 

Regards, 

Patrick Courtade, CID

Dallas CAD Manager

7Core Inc

214-347-4274

 

www.7core.biz <http://www.7core.biz/> 

 

 

 

 

-----Original Message-----
From: DesignerCouncil [mailto:[log in to unmask]] On Behalf Of Gary
Bremer
Sent: Monday, March 19, 2007 8:25 PM
To: [log in to unmask]
Subject: [DC] Footprint standards for Polarized components (Diodes)

 

Hi,

I have been asked if there is a standard for creation of footprints 

espicially for diodes. One of the designers reversed the cathode and
anode 

causing all the diodes to be placed backwards. The rational was the pin
1 

was the anode for this device for other diodes pin 1 is the cathode.

 

 

Gary Bremer CID

Manufacturing Engineer

 

_________________________________________________________________

Exercise your brain! Try Flexicon. 

http://games.msn.com/en/flexicon/default.htm?icid=flexicon_hmemailtaglin
emarch07

 

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