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Quad Fiducial Types

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#68157

Quad Fiducial Types | 11 February, 2013

I'd like some recommendations on the type / size of quad fiducials to use. I started with a small + on the silkscreen layer, but i think that a via is better, and have been using it. Now i'm considering a round smd pad, but not sure the size. Any suggestions welcome.

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#68158

Quad Fiducial Types | 11 February, 2013

Use a circle 40-50 mils. Via's and silkscreen layer markings are inaccurate.

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#68164

Quad Fiducial Types | 11 February, 2013

You want your machine to spot the fiducials automatically. A 40mil round copper pad is the absolute minimum fiducial to use, but we found in practice that our Quad equipment won't spot them reliably. I am now using a 60mil round fiducial and it picks them up every time. I've not tried 50mil.

Never use silkscreen for a fiducial due to poor registration. You will be forced to use an SMD pad or via if your legacy boards don't have them (manually spot).

Always provide a solder mask clearance of at least 2x the pad radius as a clear area, void of any traces, silkscreen, etc. This means a 60mil fiducial will have at least a 180mil mask clearance.

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