Fiducial replacements?

I hope you are not building for the aviation industry.

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One of our former SMT Technicians used a component we pick and place for this purpose.

The component is a bond pad that is soldered to a ceramic PCB during SMT assembly. The assembly is now obsolete. I tried looking up the manufacturer's part number in our system for you but it's no longer listed there.

I encourage the SMT Techs and operators to reject boards with bad fids as nonconforming materials.

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Hi Paul M, There are no silly questions but silly answers.. and here is maybe a few if I understand you correctly: If you consider place anything less than a 1.27mm (50mil) pitch component down or a chip less than a 1210, hey it maybe don't even work if we are talking about a 2.54mm (100mil)pitch component package and you still need to fulfill the IPC rules and get a good solder paste print and component placement & soldering. Don't even consider this "replacement fiducial" as an option!

As I see it (based on the limitation of detailed info you gave us) you have 4 options: 1. Try to tweak the fiducial camera settings in the program/machine: lighting, threshold, surrounding pattern, search area, inner/outer lighting (depending on what vision system you are using) and make sure that there are no similar surrounding patterns such like a test point that has the very same diameter as the fiducial nearby.

2. If it is HASL surface finish on the board (If Not skip to No.3 below), then an uneven surface will be at the fid's and pads. This will cause the light to reflect a strange pattern back to the fiducial camera and it will see dark spots in the fiducial area. If No.1 above didn't work and if it is only a few board's to be produced, concider rubb the existing HASL (thinned) fid marks with a simple eraser (back end of a pencil or eq.). This will in such case make the surface matt/dull and therefore the image to be even and bright, for the fiducial camera & recognition vision system.

3. If You have tried No. 1 & 2 above, consider contact your pcb manufacturer and tell them that you are Not going to accept this low quality, please make new ones. This only works if you can actually pinpoint that they have made a poor fabrication of your pcb:s.

4. Out of business. Unless...

I think you can make an easy calculation of the time consuming and the costs...

BTW. it could be interesting to hear what type of boards regarding surface finish, typical component packages on it and which type of SMT-equipment you have. And... you have not described exactly (in detail) the actual fiducial problem for us... If You have any questions, please don't hesitate. Best Regards Ps. Sorry for my poor english and grammar. Ds.

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Hi Paul,

It may not be the perfect replacement for a proper fiducial but I have had some success using thru-holes for fiducials. The tightest pitch part we place is 0.8mm however 0.032").

If the thru-holes are drilled accurately and you are able to use "negative" fiducials (black on white) this may work for you.

Regards,

Bert

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I hope this isn't a silly question but... isn't there a way to manually override when a fiducial fails vision? I can't imagine a machine that would be available without this basic feature.

Greg

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Peelable solder mask works well. Hand dispense and peel off after. Paint sticks work OK, but it depends on the mfger of the paint stick. In both methods you hand apply after screen print. Your Dek can be taught pads to get by. You may have to teach board by board depending on how steady a dot you can dispense.

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I don't know how accurately you're going to be able to put a replacement down. You could use BGA replacement pads, but that is a lot of time and the results will be shakey.

On the DEK, make a copy of your program and teach some pads or through holes as fids. For a given lot, the drill offset is often pretty close, so you print a couple, figure out the offset you need for the machine and you ought to be able to get those last 25 or so without too much greif.

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If the machine or machines couldn't recognize the fiducials, you can grind it with a fiberglass eraser. If the fiducial are missing you can use tooling holes, and/or via holes. You can verify the hole size and tolerance on the PCB assembly drawing. Also, this drawings provide the coordinates with respect of the absolute PCB zero.

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I have read all the replies here and have yet to see this one which I know works when our fids are HASL and distorted, thus unable to seem uniform enough for the vision systems on our MPM's or MyDatas to see them clearly.

Using a stainless steel needle pick, scratch the entire surface of the fids which then reflect light more evenly making the dark areas appear brighter.

It really does work....give it a shot.....cheap and easy and no re-programming for you!

Good luck!

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