| I am fairly new to the SMT game and I am getting conflicting answers to the following. Maybe someone can help me! When printing, one person is telling me that the stencil should be wiped completely clean of all paste because the quality of the print will be better. Another person tells me that there should always be a thin layer of paste on the stencil because too much pressure can cause paste to be pushed under the stencil and cause poor print quality. We use stainless squeegees and do an automatic wet/dry wipe every 20 prints. | Thanks in advance! | The paste thickness is determined by the stencil thickness. This means that by wiping the stencil clean you should be getting a paste thickness very near to what your stencil thickness is. This thickness has been determined, together with aperture reduction, to give the optimal solder deposit so you can produce the perfect solder filet. Leaving a thin film on top of the stencil will give a variable solder thickness over the whole board,and this can vary from board to board.This will eventually lead to shorts, solderballing, wrong filet shapes.....and anything else you can think of. Get your downstop and squeegee pressure in order,(everything should be parallel), the speed should match your paste,(slower speeds wipe cleaner), and you can wipe clean everytime. Joe
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