we sometimes have problems with solder paste release. we use a manual stencil printer. does anyone have any thoughts on using two passes of solder paste on the stencil? i have found that running the second pass gives me better deposits on the fine pitch component's pads, but it pulls a little off the larger component's pads.
It depends how manual is the printer. you need to control pressure and speed. If you control both by hand, it is difficult to discuss results. If the pressure is controlled by the printer, than you should be able to do it by one deposit. Also is the stencil chemical etched or something better. With a bad stencil even a good automatic printer will show problems.
We hear you talking two main issues: 1 Solder paste release 2 Thoughts on using two passes of solder paste on the stencil
1 Solder paste release * Check your aperture & aspect ratios [Search the fine SMTnet Archives for more] * Do a better job with snap-off [we know it's hard to do a good job with snap-off when manual printing. Just do better.] * Control temperature in the print area. One *C variation produces a substantial change in paste viscosity. * Clean the stencil
2 Thoughts on using two passes of solder paste on the stencil: You have to produce good print. How you go about that varies. [We have people taking vastly different approaches to manual printing. There's something like 36 variables in printing. Just get a good print!!!] It's more important that you get good fine pitch than loosing some paste on larger apertures. [By-the-by, why are you scooping? Your squeegee is metal, correct?]
hi,brettc! Our stencil openings no more than 4mm * 4mm, you have a larger component of the pads is more than a 4*4? At the same time, with the thickness of the stencil, I would like to increase the printing speed can be improved to reduce the thickness of the template that?if the component of the pads is more than a 4*4,it need to open into a grid-like.