Component Datum and Insertion Origin

[OlekSz]

Hi everyone,

When creating a component I deal with datum and insertion origin.
As far as I know the best position for the insertion origin is at a component centre and it is used to define position of the component in the insertion repot (for pick & place machine).

What about component datum.
I suspect that it defines component position when moving a component. When moving a component, datum is placed on placement grid.
Where a datum should be placed?
Orcad libraries have it placed at the centre of pin 1.
Other libraries have it placed in the centre of the component (exectly where insertion origin is.
Summarizing.
What a component datum is used for and where it should be placed?

Aleksander

[randychase]

Insertion origin as you note should be the center of the part, and some libraries will build a part with a different point of origin, such as pin 1.

I disagree with that practice. I think that the center of the part should always be the origin AND insertion point, with a few exceptions. One reason is so that when you are moving and rotating the part, it stays centered, which is a lot cleaner for design. The center of the part is what should be on your grid for surface mount parts.

There are some parts like certain connectors that I will use a different point. A D-Sub for example, I like to use the center mating face (where it contacts the panel) because that matches what most of the mechanical data I use for a constraint.


Anyway, I would suggest just using the center as the insertion and part origin/datum.

[Jackie Oh!]

Hi Aleksander,

I agree with Randy. It's much easier to deal with the part on the board when the insertion origin and the datum are at the center of the part. It's also much easier to build the part in the library.

Jackie Oh!

[OlekSz]

Thanks for the responses.

Aleksander

[Colorado-PC-Dude]

I have to agree with Randy, to a point. We build all of our parts with the origin at the center of mass for the part, unless there is a mechanical feature that prevents that. Of course, on most parts, the center of mass coincides with the dimensional center.

We had some trouble a year or so back where a pick and place machine at a sister company was having trouble with a +12V regulator. Because the mass was off center, even though the origin was at the dimensional center, the vacuum nozzle would occasionally drop the part.

Ben