A Few Hints of the Centroid File

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Every now and then, we get questions on the centroid file (aka pick-and-place file or SMT locations file). Most CAD applications will create one for you. If you use Eagle, download our ULP and run it to create a centroid from your board.

If you want to poke around and need some hints on what’s what you can download our guide on the centriod file. Here are a couple of illustrations from the guide. First, the point of origin needs to be centered in the part.

It should be centered in a box that contains the outline of the pins as well as the body of the part. The chips (above, left) are easy. The connector (above, right), is a little more ambiguous, but as you can see, it’s centered around the imaginary box containing the area. Top-side rotation goes counter-clockwise as shown (below, left) and rotation on the bottom side is simply a mirror image, left to right with clockwise rotation.

Diodes and other passives should have their zero rotation vertical, with pin one (if there is one) facing up. That would place the cathode up for diodes and the positive side up for electrolytics and other polarized two lead parts.

Duane Benson
If you get dizzy spinning counter clockwise, go to Australia

http://blog.screamingcircuits.com/

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About Duane

Duane is the Web Marketing Manager for Screaming Circuits, an EMS company based in Canby, Oregon. He blogs regularly on matters ranging from circuit board design and assembly to general industry observations.

4 thoughts on “A Few Hints of the Centroid File”

  1. Duane,

    Your description for the location of the cathode on chip diodes and positive pin on capacitors disagrees with the zero component orientations for chip components in IPC-7351 (Feb 2005), which is what my CAD library is based on. How much of a problem is that for an assembler? Has the IPC standard changed?

    Regards,

    Charlotte Wilson, CID

  2. Duane,
    The first thing I thought when reading this was that it didn’t agree with IPC, & we have been using IPC as the basis for our internal libs. We all know that an assembler will get used to your rotations, but why make a lib different if you don’t need to?

    Dom
    Sydney, Australia.

  3. If in doubt or disagreement, IPC is the right way to go. Some machines, software and systems do disagree with IPC for legacy reasons, but you can’t go wrong with the IPC setup. We (and any other assembler) will make sure that it all ends up in the right direction once it’s on the PCB.

    Duane Benson

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