At 02:04 PM 7/25/01 +1000, John Haddy wrote:
>Under no circumstances should the Protel libraries be copied! They
>are riddled with errors (I'd list them all as "unverified"). For
>instance, any metric pitch component that's been created with the
>footprint wizard is likely to be wrong.

First of all, I doubt that the Protel footprints were created with the 
footprint wizard! If Protel employees had to use the wizard, it would be, 
shall we say, ... improved.

I'd list the Protel footprints as "Protel-supplied." To call them 
"unverified" would be rude, even if, technically, from the user 
perspective, they are unverified.

It is important that they be in the database so that users can verify them.

>The biggest hurdle I forsee is the widely differing requirements
>of any single footprint. For example: a footprint for wave solder
>is different from that for reflow; the IPC "worst-case" design
>methodology generates overly conservative footprints; a designer
>working on high density layouts will want "bleeding edge" land
>pattern designs, not general purpose ones with excessive silkscreen
>clearances (for example). So just with these few variations, we're
>up to at least four variants of every footprint!

Right. But it is a question of standards. The standard to which a footprint 
is designed would be coded into the name of the footprint.

The library would be indexed to manufacturer part numbers. (Schematic 
libraries likewise). I see no other way to cleanly organize the parts. 
Obviously, many different MFR part numbers will point to the same symbol.

>Much as I applaud the sentiment, I can't see a single library ever
>providing a single source set of footprints.

For some of us, the user library (actually it will be a library of 
libraries) will be sufficient for most uses. There will always be a need 
for users to make new footprints or to modify existing ones.


>We're going to need much more sophisticated design rules before I'd
>consider using anybody else's designs (so that I can check, for
>example, paste aperture ratios given a specified screen thickness)

I'd assume that the libraries would not normally contain paste mask 

The libraries will be as good as the rules used to design them, and the 
rules will be as good as we make them.

Abdulrahman Lomax
P.O. Box 690
El Verano, CA 95433

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