A Few Hints of The Centroid File
NOTE: I've recently (8/18/2010) updated this post and the downloadable PDF to match the IPC 7351. We will properly assemble both ways, but this now matched industry standard.
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 Understanding the Centroid file r2. Here are a couple of illustrations from the guide. Fist, 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 on the left are easy. The connector, to the right, is a little more ambiguous, but as you can see, it's centered around the imaginary box containing the area.
That would place the cathode left for diodes and the positive side left for electrolytics and other polarized two lead parts.
If you get dizzy spinning counter clockwise, go to Australia