I've been doing a lot of short-run board assembly lately, prepping the boards for the reflow oven by using a syringe to dot paste on pads, and then doing the pick & place by hand as well. It kind of sucks to do by hand, and I'm about to do a board that's got 5-10x more pads than the ones I've done before. I'm not sure that I'm ready to move to stencils though, since I'm often doing just a single board at a time. (And also, I don't have any stencils at the moment.)
1) Has anyone used pneumatic dispensers like this: http://sra-solder.com/product.php/6066/5
? If you're not using stencils, are pneumatic dispensers like this the bees knees? Any specific things to avoid, or brands/features to look?
2) What do people recommend for prepping boards to accept paste? Strictly chemical: acetone or isopropyl alcohol? (I've never tried acetone: does it attack conformal coatings?) Or mechanical roughing with a scotch-brite pad?
3) I ask about #2 because my paste (still fresh, I think) sometimes pulls away from the pad rather than remaining on it. It's definitely not as fluid as the stuff in this video: http://www.youtube.com/watch?v=tPjFQ15Zdp0