I agree that homplate is a good design, but also this could be caused by the stencil thickness and aperture size, if you are at 7-9 mils thick stencil and a 1:1 ratio on aperture size then 2 things i know of will happen, one a squishing out of past onto the masking, causing solder ball formation during reflow, and with that amount of paste it is possible to get outgasing during reflow, blowing paste onto boards in the masked area and agin creating beads of paste to form. One thing to check is your aspect ratio make sure you are greater than 1.5 and one way to find this out is to take your fine pitch aperture size and divide it by your stencil thickness, if you get 1.5 or higher you will be good, if lower you may want to try a thinner stencil. Say 5 or 6 mils Ex. 25 mil piich parts with a .o12" aperture and a .006" thick stencil would = an aspect ratio of 2.0 which wuold be good or a .005" stencil = 2.4 even better so just going to homeplate or bowtie may not be the best solution if you have other process problems.
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