I’m working on a few boards that have 0.5 QFN’s and lots of 0402’s, very tight work.
I’ve been using a metal laser cut stencil (stencilsunlimited), and its kinda messy, mostly because there always seems to be a slight gap between the stencil and the board and hence every pass with the squeegee deposits quite a lot of solder.
And ofcourse when baking the board, the extra solder sometimes causes the chip to rise on one side, or usually creates large solder balls outside which need to be wicked up etc.
I know this is happening because of my process, because the stencil is really good quality.
I was looking at a couple of stencil printing devices but wanted to get an idea from folks who have used it before. Are they any good? which one would you recommend? Any caveats to watch out for?
use a syringe to apply the solder to your ‘holes’ in the stencil instead of a squeegee, and I recommend using electrical tape or duct tape on the stencil to hold it to something the same height as your board to keep it still.
I’m assuming you have the board on a table with nothing around it, which is likely what’s causing your major problem the tombstoning, since it it’s 100% flat it bends, it’s plastic afterall, leaving gaps.
put boards of the same thickness as the board you’re working on all around it.
I’m about to try a Mylar stencil for the first time. My hope is that because the Mylar is a more flexible material, that it will conform better than a metal stencil and reduce or eliminate this problem. And of course, a Mylar stencil is a whole lot cheaper and does not need a frame.