"Olson, Jack" wrote:

> Ok you guys, I need a quick survey here....
>
> I seem to have gotten myself into a big raging discussion here about whether library footprints should be created (and placed) using the nominal dimensions or the maximum dimensions.
> Most companies have some kind of placement standard that says something like "don't place discretes closer than 30mils to each other" and similar guidelines for different types of parts. I would think the 30 mils is for the pick-n-place machine to have a little room to work, save some space in case the part needs to be reworked manually, and take into account any variations in component size.
>
> For example, if I make an 0603 footprint, I make it assuming the part is 60mils by 30mils, which is the nominal size. If a part comes in at 61x31 we have already allowed a 30mil gap to the next part, so it shouldn't matter. We use this 60x30 rectangle for DRC checking, back and forth to mech department, etc.
>
> Now some are saying we should be using the MAXIMUM size, which I don't think buys too much and creates other headaches (different vendors list different tolerances, etc) so I would like to know how YOUR library is created.
> NOMINAL or MAXIMUM?

Jack

It's better to create them at maximum with a 10-20mil gap.  But even if there
is no gap you should still be safe.

David Hill
Mullard Space Science Laboratory
Holmbury St. Mary
Dorking  UK
RH5 6NT