When ordering a stencil it is important to request the appropriate stencil thickness to insure proper paste release from the stencil. The aspect ratio for rectangular apertures should be 1.5, and an area ratio of 0.66. It is best to evaluate the smallest apertures on the stencil to determine the proper stencil thickness.
You can use the following formulas to select an appropriate stencil thickness:
Aspect Ratio = Aperture Width (W) / Stencil Thickness (T) [should be 1,5]
Area Ratio = Area of Pad (LxW) / Area of Aperture Walls (2 x (LxW) x T) [should be 0.66]
(diagram attached)