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### Aperture Area Ratio, and Determining Stencil Thickness

PostPosted: **Mon May 14, 2012 9:30 am**

by **Al Secchi**

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)

### Re: Aperture Area Ratio, and Determining Stencil Thickness

PostPosted: **Tue Dec 03, 2013 11:36 pm**

by **meli117**

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)

Hello,

thanks , this was really helpful, but do these formulas go in any circumstances ? There are no exceptions ?

thanks

### Re: Aperture Area Ratio, and Determining Stencil Thickness

PostPosted: **Mon Dec 09, 2013 6:56 am**

by **Sal Hernandez**

This is a general formula for stencil thickness. Is there a particular exception you would like to discuss?

### Re: Aperture Area Ratio, and Determining Stencil Thickness

PostPosted: **Sun Apr 19, 2015 10:47 pm**

by **nevertalk00**

Have your board fab house plug the via and then plate copper over it. They can plug with metal or a thermally and electrically conductive epoxy before the final plating steps."