I recently posted a note about fiducials but I didn’t have any images. Here’s a couple of examples:
This first example shows what IPC would like to see. If this is an individual board, this would be it. If it were part of a panel, you would follow the same pattern on the panel rails and also put it on each individual board in the panel.
As I wrote in the earlier post, we don’t require these, but it’s always a good idea. You’ll need them once you go into volume manufacturing anyway.
The next example won’t make IPC happy, but it will make Screaming Circuits happy:
It only uses two fiducial dots, but it isn’t reversible. Reversibility is okay for jackets, but not for circuit boards. Since one of the dots is offset, it can’t be placed on the machine and recognized as correct in any way except in the proper orientation.
The important aspect of both of these examples is that they remove ambiguity. There can’t be any uncertainty, which is good because uncertainty is your enemy. It’s a subtle enemy. It might not bother you 99.9 times out of a hundred, but then, when you’re not looking, it can strike. So, give a hoot and stomp out ambiguity.
Duane Benson
False data can act only as a distraction. Therefore, I shall refuse to perceive.
I tend to put three SEMA standard fids in opposing corners matching IPC-7351 but add a fourth in the other corner that’s not aligned with the others, with an exaggerated offset, and a diamond rather then a 1mm round pad. Totally removes ambiguilty.
I used to use 4 fiducials, one per corner.
This was so that if one was damaged then I still had three others to use.
There was no problems with getting the panel the wrong way around because I also put direction of flow arrows in the borders to indicate the direction in all assembly machines.
Worked extremely well.
You can also add other features that are programmed in so that the panel can be detected as the wrong way around. Never seen it happen though.
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