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SMT electronics assembly manufacturing forum.


Ficiduals, Best Practice

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#64973

Ficiduals, Best Practice | 6 September, 2011

Just wondering what the best practice for ficiduals, size and shape, or is it depending on the vision system.

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#64976

Ficiduals, Best Practice | 6 September, 2011

We use a 40mil circle with the solder mask backed off another 40 mils (120mil circle) beyond that. Works good for us but not sure if that is an industry standard or not.

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#64977

Ficiduals, Best Practice | 6 September, 2011

There are several shapes that are standard - circle, triangle, two rectangles, cross... I personally have the impression that most people use circle. Anyway, all systems on the market should be able to recognize the standard shapes. Most imprtant is where you put your fiducials - pannel or circuit? Depending on what you use accuracy of the machines may vary.

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#64978

Ficiduals, Best Practice | 6 September, 2011

According to IPC-7351A, the optimum fiducial is a solid circle with a minimum of 1mm diameter, but can be up to 3mm. There should be a solder mask clearance a minimum of 2x the radius of the copper circle. So the minimum fiducial size is 0.040" with a 0.080" mask opening. Also the background under all fiducials should be the same with no traces running under them or differences in ground plane to provide consistent contrast. Be sure to add local fiducials on opposite corners of all fine pitch IC's. I find that our equipment picks up a 0.060" fiducial more reliably than 0.040", but you have to weigh this against available board space.

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#64979

Ficiduals, Best Practice | 6 September, 2011

Thanks all of you for this information.

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#64985

Ficiduals, Best Practice | 8 September, 2011

Are you working with flex? If so, it's a new can of worms.

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#64986

Ficiduals, Best Practice | 8 September, 2011

WHat do you mean, whats "flex"?

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#65015

Ficiduals, Best Practice | 13 September, 2011

Flex circuits are assemblies that can be bent or twisted into shapes after assembly (flexible). When heald in panels for SMT assembly, it's difficult to get repeated x/y offsets so you need to consider fiducal placement in your design for placment machines. Also, flex panels tend not to be flat so the finish on fiducials is not always even which creates problems on SMT machine vision systems. Design consideration can by made as to locate fids that will minimize pad finish flatness problems.

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#65017

Ficiduals, Best Practice | 13 September, 2011

Yeah, Ok, I know what you mean

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