Component Footprint Rotation

Before we (or any old assembly house) go about putting surface mount parts on a 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. The illustrations below show 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

Package origins

Passives orientation r2

Chip rotation

Quad and BGA

Three-pin parts

3 thoughts on “Component Footprint Rotation

  1. When is a standard, not a standard? When someone makes their own up.

    “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.”

    Hmm, let me explain my situation. Our pick and place machine, an i-PULSE M2 has its origin at the lower right-hand corner. My CAD package Vutrax has its origin at the upper left-hand corner. Looking at your 14 pin chip, my CAD package would give 0=U, 90=T, 180=H, 270=Q. Not only do I get letters the rotation is clockwise.
    (U= Un-rotated, Q= Quarter, H= Half, T= Three quarter)
    Our Paste machine a DEK Horizon 03i does have its origin at the lower left-hand corner, but it only needs Gerber files to get its paste screen made which fortunately the CAD package manages to get right.

    Thank heavens for ASCII files and Excel as I wrote a macro in visual basic to convert the -x&y’s to + and the letters to numbers, oh and it also converts the imperial co-ordinates to metric, so the only thing that needs patching is the lack of stock codes in the placement file.
    To achieve that I had to call in the big guns (my step son actually who has a masters degree in software engineering), as it needed some C# code to produce what the placement machine needed.

    Are we all just frigging in the rigging?

  2. Alan;

    In my experience, some machines follow IPC standards and some don’t. The same goes for people who make the footprints. It’s pretty crazy and adds a lot of quality risk to the whole process. I really wish companies would follow the same “standard.”

    Don’t get me started on standards in LED polarity markings…


  3. Duane;

    As I said in the opening line, in our line of work you have to have your wits about you!
    Curiously this blog has different comments to that on your Screaming Circuits site, I guess we will all have to come round to your place, to catch all the threads.


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