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Component Footprint Rotation

Before we (or any old assembly house) go about putting surface mount parts on
your board, we need to program our assembly robots. I'm oversimplifying, but
essentially, the machine program needs to know the X / Y coordinates, relative
to the board origin (which is the lower left-hand corner), the part rotation,
and the side of the board.

In years past, we needed a Centroid file (AKA pick-and-place file) containing
all of that information. In some cases, we still need the Centroid, but not
always. Today, we can get the same information from ASCII CAD files, ODB++
CAD files or Eagle .brd files. You only need a Centroid if you send us your
board files in Gerber format.

If you do send us a Centroid file, you no longer need to worry about
rotation. The IPC has defined the zero degree orientation, as well as proper
rotation direction, but too many part footprints set the zero degree at
different angles. We can't rely on the data.

While we have to ignore rotation and figure it out with other means, we still
do strongly recommend that you follow IPC standards when you make your own
footprints. I've got some illustrations below, showing how footprints are
supposed to be oriented.

Duane Benson
There's no earthly way of knowing
which direction we are
going
There's no knowing where we're rowing

Posted on February 13, 2015 in CAD
Parts Libraries , Our
website and Process

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Comments

With those odd shape type parts, the center should be placed in the center of
the entire footprint. We always double check and adjust for the odd ones, just
in case (as I imagine do most other manufacturers). I'll do a follow-up post
with some examples.

Posted by: Duane
Benson | March 05, 2015 at 04:41 PM

Where should the centroid be placed in instances where the physical component
is not centered on the land pattern? Good examples are edge mounted components
such as connectors and switches.

Posted by: mightyohm | February 28, 2015 at 10:40 AM

The comments to this entry are closed.

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