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Date: 08/30/02 at 2:06 PM
Posted by: John W. Childers
E-mail: jwchilders@goldengategraphics.com

In Reply to: Footprints of Orcad Layout posted by Truong Quoc Hung on 08/29/02 at 11:05 PM:

Try going to this page
http://www.goldengategraphics.com/pcblinks.htm
and then scroll down to PCB Design.

Follow those links there for information and training. Please let us all know what helps the most.

On just the subject of matching footprints to actual parts:

Since I am not using Orcad layout currently, I can only give general guidelines.

Become familiar with the generic names of footprints from IPC (a link to IPC is also on the above page.) In a library of footprints, these generic names will usually show up as part of the footprint name. (Examples: 0805, DIP-14, SO-14, etc.)

To verify your footprints, you should have a Bill of Materials, or "BOM" (follow glossary link in the left margin of this page for definitions), and a specification sheet ("spec sheet") for every device listed in this BOM. Those spec sheets will include the generic names of the footprints if applicable, the mechanical dimensions of the parts and sometimes the suggested PCB layout of footprints with pad sizes and dimensions. You check this data against each different footprint which you have selected from your library as a possible match for the devices on your PC board.

WARNING: Libraries from software vendors are generally untested on actual manufactured PCBs and therefore unreliable. DO NOT TRUST THESE LIBRARIES TO BE CORRECT. Once you match the correct footprint from the library to its corresponding device on your board, you then check its pin numbering and dimensions against that device's spec sheet.

Include a check of the body size of the part. If the silkscreen outline in your footprint is smaller than the specification, edit it to match the spec of its MAXIMUM, not average, size. This will prevent you from putting parts too close together on the PCB.

The software vendor's library of parts is very useful as a place to start from. It is much easier to start with the library, check the footprint against your spec sheet and edit it if necessary, than it is to build the part from scratch.

When you have checked these dimensions for the parts you use, save those parts in your own personal library with any other parts you have built or altered. When your board is built and stuffed, use any problems found to correct your footprints in your personal library. (Believe me, you'll hear about any problems.) Your personal library begins to build, then, into something that is dead-solid perfect.

This sounds like a lot of work, I know. But it will go faster as you gain experience. Still, based on time studies, this portion of a PCB layout job (cross-referencing the BOM to your parts library and building any needed parts) is a good 20% of the entire job.

Good luck,
John W. Childers

Follow Ups:

  Re: Footprints of Orcad Layout nguyen   Posted at: 10/08/03 (0)

  Re: Footprints of Orcad Layout arash yeganeh   Posted at: 09/15/02 (0)

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