Screaming Circuits: And Another Footprint Thing


And Another Footprint Thing

Footprint wrong zero When you are creating a footprint in your favorite CAD program, or reusing someone else's footprint, double check the zero orientation. This post discusses the IPC-7351 specified zero rotation orientation.

This picture on the left shows a library component with the improper zero rotation orientation. Your centroid file will never be correct if you start from the wrong point.

IPC-7351 states that the LED should be oriented horizontally and the cathode (pin 1) should be to the left. Obviously, vertical and cathode up is not the same thing as horizontal and cathode left. If it's obvious, why do I feel the need to state it? I don't know. I just do.

Duane Benson
Red is gray and Yellow white
But IPC decides which is right

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Comments

And which is an illusion

Pads Layout allows multiple decals for one part type. (eg Parttype RES with 0402, 0603, 0805 decals options)
If the zero orientations are not the same , it gets really messy changing size if already routed. In addition to the size change, the new part is dropped in with a different orientation!

Hi Charles; We (and probably most companies like us) always do double check each component in the centroid file and correct any orientation errors. The challenge is that doing so is a mostly manual process, and manual processes always increase the possibility of error. LEDs seem to be the most problematic in this regard due to the wide variability in markings from different manufacturers.

How do you handle it if you get X/Y data generated from parts with the wrong orientation? Do you manually edit it in pick-and-place CAM program? Is there incrased risk of the part getting stuffed backwards?

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