Misalignment Brainstorm - Fiducials On Board VS On Breakaway Tab

In regards to your panelized PCB it sounds like your step and repeat in you pnp program is slightly off, by 0.02mm from the sound of it. Are all of the components moving in the same direction as the fine pitched IC?

I don't know what type of machine you are using or if you have access to this but I would say you need to subtract .02mm from your step and repeat in the X direction.

The other possibility is that perhaps your step and repeat on the PCB is not consistent. I would measure the PCB step just to make sure.

I would also recommend using individual PCB fids if you have them or local fids for the fine pitch IC since it is giving you trouble. This should help minimize these problems as your pnp machine should use the step dimension to locate the fids and then the fid information to actually place the parts and .02mm should be within the search area to find the fids.

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Fids ON the PCB will have a reference to the PCB 0,0 point in CAD data generally or can be measured with good accuracy in gerber if CAD is not available.

Panel fiducials are not always referenced from the PCB 0,0 point but many times are referenced from the outer edge of the panel. Trying to reconcile this offset can be a serious chore without gerber artwork or CAD data and your results sound very familiar.

The best thing you can do is to try and find out the true position of the panel fids in relation to the PCB 0,0 point. I'm not talking calipers here but real data. If you don't have access to the PCB artwork and you're lucky you might be able to get in touch with the fab house's CAM dept and see if they can give you this info. If your customer has the data, that's obviously a quicker route.

To piggyback onto KPM's post - While you're at it, confirm the PCB panel pitch (distance from point A to point A on two adjacent PCBs). Although if you're stencil print doesn't have the same offset and your P&P program is using the same pitch, this wouldn't be your problem.

Good Luck.

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Hi,

I have had similar issues. First as the above replies suggest pcb fids are better than panel scrap fids, even if you have to use fids under QFP's just palce those parts last.

If your machine has board skip. Place 1-2 QFP's on pcb # 1 and check it. If they are off on one board your fids are wrong in respect to the parts and may have been added by the PCB shop on the scrap at a later date.

If the placement looks good, place 1-2 QFP's on the board furthest away in X,Y and check them. This would tell you if your step and repeat is wrong.

Clear double sticky tape helps, but may not be esd approved. Wait until no one is looking.

I have had to use round test points or fids under parts instead of incorrect panel fids that did not correspond to the part X,Y. Not the best solution, but if they come from the same X,Y gerber coordinates they will work.

rob

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