Fiducial Shapes---

recognition and computation methods plus commonality.

Thanks

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I'm no math wizard, but this is my understanding

Did you ever have a spirograph as a kid? Took you about 5 minutes and endless number of lines to create one circle ( and some pretty cool patterns too ). To create a square ( or diamond ) you only need 4 straight lines, so the vision system only has 4 lines ( so to speak ) as a reference to ensure your fiducial is correct. A circle or donut, using straight lines to create it, has hundreds of lines, which gives the system more to work with.

Maybe a confusing analogy, but then again it took me days to figure out my spirograph as a kid.

Any one know of a consulant who offers spirograph lessons???

Phil

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One thing I have found when using square or diamond etc... Fiducials is, if it is a HASL finish board, the finish may be thick and the fid camera will see them having rounded edges different sizes etc.. and will cause quality failures.

Russ (My spirograph won't make squares either)

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Hi

I hope more post on this one. Since it interests me and I haven't read enough on this topic in recent years.

Donoughts with a dot in the middle I have seen.

The dot in my opinion could be over or under etched or plated with the center of the dot always staying in the same place. Also the dot could be a single flash with the artwork generation machine. The dot should also give a nice reflection or transmission to optics and then simple algorithims can easily find the center compared to other shapes.

The above could also hold true for some other shapes and there might be more reasons that are more historical so I am interested in reading more inputs.

Also interested in internal shapes.

YiE, MA/NY DDave

This message was posted the Electronics Forum @

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Since you asked for more here is my $ .02. There are many different vision systems, camera and software combinations that will make each make and model machine work differently. For instance a 1999 Siplace machine might work best with a 1.5mm round FID but a 2000 circa machine might be more accurate with a double diamond. Most of the better equipment manufactures will tell you what is best for your machine. Phil�s analogy is correct, the better systems will work better with more lines or surface edges to look at I also believe they will also do better with more right angles such as the double diamond shape. Consistency is the key to success no matter how good your vision system is. Make sure that you have as few different fiducial shapes as possible.

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Thank you friends for your discussion Regarding the reason behind using Solid disk or donut fiducials.Still I am understanding clearly the reson behind using Solid disk or donut fiducial shape. In all the above discussions we had we did not discuss about the manufacturing of fiducial shapes on the board.I doubt whether any manufacturing intricacy makes solid or donut fiducial to be used more commonly...Please throw some insight about the problems in manufacturing of Fiducials on the circuit board.Is there any advantage from manufacturing point of view to use the soild disk or donut fiducial rather than square or diamond or double square. Thank you Mani

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