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stencil printing parameters

#19288

stencil printing parameters | 27 March, 2002

hello evryone. I am rleatively new to smt production. Though we have been successfully running pcb assy's and getting very good solder quality we are trying to get some proccess control parameters set up for our printing process. We have a semiauto stencil printer using stainless steel squegees and was wondering about snap off, squegee pressure and any other parameters we should consider when printing. Are these parameters used when using stainless steel squegees and any rules of thumb to keep in mind. any input would be appreciated.

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JAX

#19291

stencil printing parameters | 27 March, 2002

Barry, If you are looking to set up a documented process with set parameters you might think about performing a DOE based on the parameters you can control or change. With any measurement device you should be able to log the info gathered so you can gauge results.

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#19295

stencil printing parameters | 27 March, 2002

STARTING RANGES * Pressure � 1 pound/inch of blade (metal); 1.6-3 pound/inch (plastic) * Speed - 0.5 to 3 inch per sec [for standard pitch]; 0.5 to 1 inch per sec [for fine pitch] Your paste supplier�s recommendation is a good place to start. * Separation speed � Start at 50%. Separation speed that is too fast can leave fine pitch stencil apertures clogged, result in paste tailing, and form high edges around the solder paste �brick�. Separation speed that is too slow is too slow. Solder paste selection and stencil design [ie, aperture wall smoothness, aperture ratios, etc.] drive separation speed.

SETTING UP A PRINTER * Set the down stop to default * Start with pressure of about 1 pound/inch of blade. * Adjust the pressure up/down to leave a very thin film on the stencil. * Speed should match your paste [slower speeds wipe cleaner] and apertures [finer pitch needs slower speed].

YOU�RE PRINTING CORRECTLY WHEN: * Paste at least as big in diameter as your thumb is rolling across the stencil. * Paste is filling the apertures. * Squeegee pressure wipes the top of the stencil of clean. * Paste releases from the stencil. * Paste is on the board in nice bricks.

ADDITIONAL INFORMATION * EMPF published an article on printing in Emphasis, but I couldn�t find it in their listing. Their �search�, ummm, er, leaves room for improvement. Maybe Cal can tell us, or maybe just call EMPF and ask [and report back to us]. * Our old friend Brian wrote an excellent article on printing at http://www.smtinfocus.com/processguide_printing.html

* �The Basics of Fine-Pitch Solder Paste Printing� by Alan Hobby, Manager at DEK Printing http://www.dek.com/comms.nsf/3A52AB46BE9D1DD380256957003BE796/F4E635AE9D305396802569FF0052CCF7?opendocument

* Your printer supplier. They like to help new process types understand their machines to help develop a relationship, preclude a war of words, etc. * Search the fine SMTnet Archives.

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