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SMT electronics assembly manufacturing forum.


screen printer - vision

Kirk

#28231

screen printer - vision | 25 April, 2004

I have a question about vision in semi automatic screen printer. How is it work? how operator adjust PCB with stencil?

Kirk

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#28234

screen printer - vision | 26 April, 2004

MPM uses a one-print-Mylar system, as do other printer mfrs. In this system there is a Mylar sheet attached to a frame that is secured over the printer table with the board on it. You print onto the Mylar. The table X-Y-theta manual adjustments are used to align the paste formations over the solder lands on the board. Remove the Mylar. Align the two cameras to a fiducial mark or other feature on the board. The next board placed on the table is aligned using the X-Y-theta manual adjuster knobs while viewing the cameras monitors. In short, the human is acting as the X-Y-theta positioning system to align the board to the stencil.

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Kirk

#28242

screen printer - vision | 26 April, 2004

so the first PCB if i want to aligned with stencil is manual the same for screen printer without vision and vision starts work for next boards? or i am wrong? but if i make mistake during aligment process for the first PCB i will repeat it for next PCBs. what is Mylar? what if i don't have Mylar how can i manage with it?

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#28243

screen printer - vision | 26 April, 2004

You are correct in understanding that the vision system comes into play for subsequent boards- to align them. Yes- if you missalign the first board and set the cameras to that board, all subsequet boards will not be aligned. Mylar is a thin polyester film. The best way to align without Mylar is to bomb-site the stencil to the board. You set the board on the table, then position table under the stencil, raise the table to just make contact with the stencil then turn the X-Y-Theta knobs on the table to adjust until solder lands on board are aligned with apertures in stencil. Vision systems on semi-automatic printers are handy when printing boards with fine or ultra-fine pitch. How well you fixture the boards onto the table effects how "repeatable" your prints will be if you have no vision. Many semi-automatic printers support tooling pins and edge locating. PWB edge tolerances are +/- 0.25mm (0.010") as per IPC 600. So, if you have a good edge locating on the printer table, then you can expect your prints to to +/- board edge tolerance. Tooling pins provide for better repeatability, but tooling holes are often not designed into boards today.

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Kirk

#28263

screen printer - vision | 27 April, 2004

Hallo Pete C Few question. If i have fine pitch PCB for example 0.5 or 0.4 mm, it is difficult to adjust manualy without vision (for the first PCB) and accurantly solder land on PCB with stencil -> reduction apertures in stencil and question how find center?. I thought that vision start playing important role at the beginning for the first PCB, help set precisely printing process. You gave tip to work without Mylar. Ok but again how you set stencil and PCB? using magnifying glass?? to catch aperture window in stencil with pad?

Kirk

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pjc

#28320

screen printer - vision | 29 April, 2004

Yes, using an illuminated magnifing glass helps. How well your board fixuring is on the table will effect print alignment on other boards loaded. 0.5mm & 0.4mm will require very good fixuring, like you can get with tooling pins if the board has non-plated through holes on the board, near the edge of course. Semi-Automatic Vision is the best method for 0.4mm printing to align boards fixtured with tooling pins or by the board edge.

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Kirk

#28323

screen printer - vision | 29 April, 2004

Is it possible to put PCB to the screen printer with vision and on the board put sheet of paper then make print on the paper and it is the reference then i teach vision for example fine pitch aperture then remove paper and align PCB?

We have semi-automatic screen printer without vision and i want to eliminate magnifing glass it is very difficult and less accurancy aligment for fine pitch application so we are consider add vision

Kirk

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#28324

screen printer - vision | 29 April, 2004

OK if the paper is transparent and you can adjust the table X-Y-Theta under the paper- without moving the paper - the align with the solder lands on the board. If you have a DEK or MPM machine, the Mylar frame is like $300. I belive other printer mfrs. use the Mylar frame too. What printer make and model do you use?

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Kirk

#28325

screen printer - vision | 29 April, 2004

we have sm-tech benchmark 90 and we think about Microflex with vision. how i teach the vision? I have two images. One is reference image and is it storage in system how can i create it (is it possible simply use paper as i said before then teach vision where is refernce point?) second is current PCB image. Operator manually align two pictures. Am i right? or still miss something?

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#28327

screen printer - vision | 29 April, 2004

You should be able to get a one-print Mylar frame for the SMTech 90 machine from SigmaPrint, http://www.sigmaprint.co.uk Yes, with vision you store images of two features such as solder lands or fidicial marks from opposite corners of the board. With the vision you don't really have to have a Mylar frame to align the board for the first time, it just makes it easier. Without a Mylar frame you do the bomb sighting through the stencil to the board like I described previously. In this process you would clean off the solderpaste from the board until you get it aligned perfect. Then align the cameras to the marks and off you go- you'll be able to align all the other boards to the images you stored. If you buy a new MicroFlex I'm sure you can get them to include a Mylar frame at no charge. The Mylar frame system works becuase the Mylar frame is fixted to the table- does not move- while you adjust the board in X-Y-Theta under the Mylar- the Mylar is clear so you see right through it. You align the paste formations printed in the Mylar over the solder lands on the board. This way not paste is printed onto the board- only the Mylar. The Mylar is in a metal frame that secures to the print table.

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