The stencil manufacturer uses the solder paste Gerber file. This is what they said about our latest design:
The design rule check determine if the solder paste would have good release through the apertures. When considering the printability of an SMT design, the surface area ratio for optimum paste release should be >0.66 and these apertures don’t pass the DRC with an area ratio of 0.5. That means ratio of the area of the aperture opening to the area of the aperture walls is not enough for proper paste release.
(Area of the aperture walls) = (perimeter of the aperature) X (thickness of the stencil)
So The full formula for the “solder paste release aperture ratio” is:
[(aperture length) X (aperture width)] / [ (perimeter of the aperture) X (thickness of the stencil)] > 0.6
Notice that that ratio does not have pad size in it.
The thickness of the stencil order is 0.05mm.
Here is the file they provided . The pads in red do not pass the design rules.
Where to set this value in Kicad?
Also if KiCAD has a DRC for “solder paste release aperture ratio”? If there is no DRC feature, then I will have to check manually which will not be a big problem because it only applies to very small apertures.
I have no big knowledge about PCB production, but from what you have written my first thought is that they are wrong. You have smaller and bigger rectangles at your PCB. Why some looking as being in the middle should not pass the rule that other passes.
I would expect here the other problem - the distance between those red rectangles seems for me being too small. I would expect - it is not possible to produce such stencil.
So I guess they got that from DRC but sending it to you they Ctrl-C+Ctrl-V wrong text.
I think I would re-formulate the equation thus:
[(aperture length) X (aperture width)] / [[(aperture length) X 2 + (aperture width) X 2] X (thickness of the stencil)] > 0.6
Are you able to make those pads slightly larger to fit the above equation? Maybe make them slightly longer extending further away from the sides of the package (sort of like the methodology for extending pads for hand soldering, just on a smaller scale)?
