Hi Ioan,
PCB's are poor indicators of Pick and Place machine accuracy since the PCB is not dimensionally stable. In other words, if a land pad on the left end of the board is used as an origin, the land pads on the right side of the board can vary as much as ±5mil. For this reason, the dimensionally stable glass plates must be used.
However, I know your pain! The Fuji's will slowly drift out of calibration. At a former employer, we would constantly battle this until we organized ourselves.
1.)We made sure every program was generated with the fiducial coordinates from the gerbers. No guessing here!
2.) Pick and place offsets were only made as global offsets to the primary fiducials. If a component is off during the proto, then the component center is corrected in the Gerbers and the program regenerated. No guessing here!
3.) All pick and place programs are stored on a networked server and changes to the pick and place program coordinates are not allowed to be uploaded to the server.
4.)Once programs are "known golden", pick and place global offsets on the machine file are only allowed up to a reasonable amount before the machine must be "quick recalibrated". In other words, a full calibration might take an entire shift, but bringing the machine back into reasonable calibration only takes 30 minutes or less. (If I remember correctly, it's a software offset at the machine). Determining the amount of "shift" can be done using live product that is currently on the line, so no special boards are needed. But a full calibration, and the recording of placement performance must use a "calibrated" substrate, or the drift in the pad locations will make the pick and place machine placements appear to be off. While a photo process is accurate, I'm not convinced that the glass/epoxy laminate is stable to the dimensions required for placement equipment calibrations.
By the way, since Fuji charged an arm and a leg for their glass calibration plates, we had custom glass plates manufactured locally for a fraction of the cost.
Thanks,
Ryan
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Tempea, Ioan
Sent: Tuesday, June 26, 2007 7:56 AM
To: [log in to unmask]
Subject: [TN] SMT placement test PCB
Dear colleagues,
I am pondering the necessity of having a custom PCB designed, PCB that would serve for periodical testing of the placement of our machines. We have Fuji CP6 and IP3, just FYI as I don't think the board should be speciffic to a machine in particular.
I am wondering if any of you felt the need of having a special PCB to perform this, or you find the glass board for IP and the regular Fuji test board sufficient?
I have checked the available boards from Practical and Topline and find them unsatisfactory when it gets to 0402 and 0201 landpatterns.
If you would order a special PCB, how would you use it? What components should it be there?
Thanks,
Ioan
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