These are the rules that I use:

If all components are larger than 25mil (or .65mm), I use a 0.008" thick
stencil and I make all of the apertures the same size and shape as the pads
on the board.

If the stencil has components that are smaller than or equal to 25mil, I use
a 0.006" thick stencil.  I make all of the apertures for componets larger
than 25mil the same size and shape as the pads on the board.  For componets
which are 25mil, I use the same size aperture but I change the shape to
oblong.  For components which are 20mil (or .5mm), I reduce the aperture
width to 0.009", leave the length the same, and change the shape to oblong.  

We always use a metal squeege and stainless steel stencils.  If the board
contains 20mil parts, we also have the stencil electroplated.  I confess
that I have not measured the final thickness in years.  I did do it quite a
few times a number of years ago however and I got thicknesses very close to
the thickness of the stencil.  If your process is consistent, you should be
able to achieve your desired paste height by selecting the correct stencil
thickness.  Good luck.

>At 08:30 03/04/1996 -0600, you wrote:
>>Can you be more specific.  What types of components are on the board?
>>
>
>Patrick,
>The type of components are mainly chip components like SOT.
>There are quite a number of QFPs and PLCCs.
>
>Regards,
>Chan Yong Kwee
>E-mail:[log in to unmask]
>Tel    : (65) 746-6617
>Pg     : 9-490-6514
>
>
>

-Pat-

-------------
Patrick McGuine
Nicolet Instrument
[log in to unmask]
(608) 276-6334