Printed Circuit Board Assembly & PCB Design SMT Electronics Assembly Manufacturing Forum

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Dome Fiducials

Dane Stokes

#1897

Dome Fiducials | 15 February, 2000

We are currently having problems with running dome shaped fids. on some of our product. Particularly with the screen printer vision system the domes are reflecting the light to a point where the camera has problems seeing the fid. Has any one else encountered dome fid. problems with recognition?

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JAX

#1898

Re: Dome Fiducials | 15 February, 2000

Dane, I'll give you a quick guess before I log off; The reason you are seeing problems with dome shaped fiducials is probably because the machines in question do not use grey scale recognition. They asign either black or white( not 256 shades of grey ) This lets refraction of the light source change from board to board. No matter what type of screen printer you are using you should be able to teach pad sites to avoid this problem. Overall I suggest getting rid of the dome fiducials. That's just my opinion, I could be wrong!

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Dean

#1899

Re: Dome Fiducials | 16 February, 2000

You might try a no HASL spec on your fids...but shelf life may hamper copper quality. Not a pleasant situation...opertors tend to polish the fids with erasers to compensate but this leads to eraser "bits" in your equipment and your solder! Maby open up your fid tolerence...as your vision processor is probably only seeing the "zenith" of the dome rather than the true diameter.

If your fids are troublesome...I wonder how the rest of the fab is holding up? Hope you don't have fine pitch!

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#1900

Re: Dome Fiducials | 16 February, 2000

Hi Dane, if with "dome" is meant the irregularity of a HASL finish than we had a lot of problems especially like Dean mentioned with finepitch parts and circular fids. It ended up with cleaning the fids with erasers before using the boards. Later we used small crosses as fids and a lightbeam option the machines were equiped with. The disadvantage was a sometimes prolonged recognition time. With planar surfaces of the fids there were no problems with vision and circular fids. I still remember the hours tuning the vision files with little success.

Good luck

Wolfgang

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Dane Stokes

#1901

Re: Dome Fiducials | 16 February, 2000

Thanks for all the feed back guys. We are currently using the eraser when running the product in question. Thankfully there are no FP. placements on the product.I'm working with a friend on the matter right now and we are triing to get in touch with the product engineer to get the dome shaped fids change to round fids instead as you all probably know this process can take a while. Thanks for all the information I will take it all into serious consideration.

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