Re: gEDA-user: latest PCB w/gsch2pcb deletes parts?

[Steve Meier <smeier@xxxxxxxxxxxxxxxxxxx>]

The IPC footprints have been critisized for being overly large. I
believe this is true especially for the smaller size components. My
understanding is that the IPC wants to leave some minimum pad space in
front and behind (toe and heal) the devices contact. If you then compare
the IPC recomended foot prints to a device manufacturors recomended foot
print you will see a consierable size difference. I suspect this might
very from manufacturor to manufacturor. This is one cause of multiple
footprints. A second cause is that different assembly techniques may
suggest variations in the width of the pads.

Is this all really necessary? Propably not. But which one to select?

Steve Meier


Matt Ettus wrote:
>I was able to fix this problem by going back to an older PCB CVS.
>
>One question -- why are there multiple 0603 footprints?  Why wouldn't
>you want to use the IPC one?  All these versions makes for a lot of
>confusion.
>
>Matt
>
>On 12/6/05, Stuart Brorson <sdb@xxxxxxxxxx> wrote:
>  
>>>>I recently upgraded to the latest PCB CVS.  Now when I run gsch2pcb on
>>>>an already existing pcb file many of my components get deleted.  Also
>>>>new 0603 caps no longer have silkscreen around them.  Is it possible
>>>>that changes to PCB caused this?  I didn't change gsch2pcb.
>>>>        
>>>Yes, latest pcb from cvs does not have silk around the 0603 footprint.
>>>IPC-7351 seems to indicate no room for silk on 0603.  The newer 0603 (or
>>>preferably the IPC-7351 compliant names for 0603 -- CAPC1608N for
>>>example) in the ~geda  library should be much better from a soldering
>>>point of view too.  The previous one was no good.
>>>      
>>A tangential point to this:  If you use newlib footprints, John
>>Luciani's caps have partial silk at the ends of the parts which help
>>determine the component body size during placement.  And (shameless
>>plug) some time ago I wrote a perl utility called smtgen which
>>generates footprints for two terminal passives if you give it the
>>physical parameters like length, width, pad dimensions, etc.  You give
>>it all parameters on the command line, and it writes footprint to
>>STDOUT.  It draws a full rectangle around the part on the silkscreen
>>layer.  I put it on my website for interested parties to use:
>>
>>http://www.brorson.com/gEDA/
>>
>>The resulting footprints may or may not be IPC standard (I haven't
>>paid attention to recommendations for dealing with the silkscreen),
>>but I have used them and they work.
>>
>>Have fun,
>>
>>Stuart
>>    
>>
>
>