gEDA-dev: PCB - XY values of centrioid in BOM/DXF exproter (wasgEDA-user: PCB Element for a Molex 71661-2068?)

[John Griessen]

Gabriel Paubert wrote:
> On Thu, Mar 08, 2007 at 12:39:42PM -0600, John Griessen wrote:
>> OK then, still on the pragmatic tack, why not use silk for a centroid 
>> calculation?  Find the most extreme corners of  (silk OR pins OR pads).
>>
> 
> What does OR mean in that context? The bounding box?
I was thinking of the centerline of the silk layer package outline.

> 
> I strongly suspect that, for example, pick and place machines want the 
> same centroid for SOT23 with 5 or 6 pins, 
[jg]Ideally there's a point defined in the part datasheet that is good for 
picking it up from with a vacuum tip, but in its absence, we can pragmatically
calculate a workable point.  It maybe different from the exact center of the
flat spot on top of a molded package.  It will be close though, so picking the 
part up at its tape and reel centroid will only be off maybe... 5% of the 
distance across a package...

So the first part-placing run will probably place all the parts without a total 
miss and collision with nearby parts.

John Griessen