fiducials

In past PCB designs I have cleared all traces from all layers (except pwr/gnd) from fiducial area. It has come to my attention that this is only necessary on the side where fud is placed. Which is the correct method of design using a fidicial?

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| In past PCB designs I have cleared all traces from all layers | (except pwr/gnd) from fiducial area. It has come to my attention that this is only necessary on the side where fud is placed. Which is the correct method of design using a fidicial? | You only have to clear the area that the assembly machines are going to look at. It would be wise to keep layers above the power/ground layers out of the way to prevent any variation of contrast in the fiducial keepout area. Generally, design standards require a fiducial (0.04" round or whatever size and shape your machines require) to be surrounded by a keepout area twice the size of the fiducial. This area would have no features, silk screening or solder mask. Of course, some machines or processes have unique requirements. You would usually strive for the cleanest and greatest contrast between the fiducial and the surrounding keepout area of bare board. John Thorup.

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| In past PCB designs I have cleared all traces from all layers | (except pwr/gnd) from fiducial area. It has come to my attention that this is only necessary on the side where fud is placed. Which is the correct method of design using a fidicial? | John said it all very well. It's all about contrast. The more the better as a dark PCB surface against a bright fiducial surface. Depending on the camera resolution/recogintion system capability, grey scale is the reason.

Often, HASL boards cause some difficulty with any image capture system. It's uneven and can cause recognition problems.

I'm currently having problems with our SmartSonic cleaner removing the black epoxy from the circle and aperture fiducials on our stencils. I'd like to go to a more permanent oxide or nitride treatment. Any comments would be welcom here as well. Also, how many folks are using "through etched" apertures as holes all the way through the stencil foil?

Earl Moon

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| In past PCB designs I have cleared all traces from all layers | (except pwr/gnd) from fiducial area. It has come to my attention that this is only necessary on the side where fud is placed. Which is the correct method of design using a fidicial? | Hi Roseanne,

I agree with John Thorup's response. A 1mm round unmasked pad (or other shape, but round is more symetrical to a camera) w/ a 2mm free area.

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