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Printed Circuit Board Assembly & PCB Design Forum

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Local fiducials

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Local fiducials | 20 October, 2010

Hi everyone, here a question for the SMT production engineers... is possible today mount the fine pitch and ultrafine pitch devices (BGA, QFP, CSP), without using the local fiducials, but using the three standard fiducials of row card only? The correct placement precision is still assured? what is the maximum distance to put the local fiducials from the devices body allowed in a layout, to assure the placement precision?

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Local fiducials | 20 October, 2010

Circuit and Local Fiducials are all the same. The difference is the amount of "Stretch and Skew" that is accounted for. Local fiducials apply "Stretch and Skew" to a single placement or area of the circuit, depending on Equipment used. Circuit fiducials apply "Stretch and Skew" to the entire ciruit.

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Local fiducials | 20 October, 2010

On our Fuji NXT and AIM machines I never program local fids...we place down to 16 mil fine pitch and BGA, uBGA, multirow QFNs with no placement issues. Most boards are panelized in an array and we have corner fids added to the rails.

Regards, Mike

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Local fiducials | 20 October, 2010

We've done many fine pitch parts using only global board fids with good results. However, if you're working with flex or flex/rigid designs, I would never use global or panel fids for fome pitch placement. We always request addition of local fids upon design review if they are not present on flex/rigid designs. As far a proximity is concerned, I can't give you #'s - I would say in general, as close as possible for local fid sets. We even run some designs that have local fids under parts when real estate becomes an issue.

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Local fiducials | 21 October, 2010

depends on the machine the old amistar machines I used local fids they were needed we got new universal machines now it does'nt seem to need them we place down to 16 mil pitch and small bga with no problems at all using global fids

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Local fiducials | 25 October, 2010

In csae you use 2 fiducial recognition, ensure that board fiducials are oriented across a diagonal and spaced far apart. Also, maintain a prefered dia between 1-2 mm for the fiducial on board to have have a better correction factor recorded during fiducial scan by your SMT equipment, while the prefered fiducial geometry is always a circle. Any fiducial should have a clean finish, to facilitate high quality recognition during scan by your SMT equipment camera.

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Local fiducials | 28 October, 2010


Hope the information in the above thread may help to get You right.

BTW, Local Fiducial Marks are meant for specific devices in the Circuit Cards & typically selected to overcome offset or precision placement issues faced from Global Fiducial Mark Placements. And if Your Placement Program chooses to apply Local Fiducial Marks for CSPs or any other Active Device locations Placement, Processing Time of each card would rise to a few seconds uphill direction accordingly.

However, if Your Placement Machine has a perfect or near perfect vision recognition process in place, running with Global Fiducial Marks is sufficient enough to build SMAs.

Many Thanks, David, India.

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