I use a 10% reduction across the board on all NoClean stencils. I use home
plate on all chip resistors and caps ... you have to inspect the silkscreen
to make sure you do not home plate any melf diodes or you will have
trouble. There is also a an aspect ratio formula to ensure no over
reduction on fine pitch and micro bga devices. W/T > 1.5 is for fine pitch
and  LxW/2x(L+W)xT > .66 is for BGA . These work in most cases. The paste
viscosity and print parameters must be set up properly to get a clean
release.






Marcus Wheeler
Sr. Mfg. Engineer
Apsco International
[log in to unmask]
440-352-8961 * 530




                      Carlr Ray
                      <Carlr.Ray@SANMIN        To:       [log in to unmask]
                      A-SCI.COM>               cc:
                      Sent by: TechNet         Subject:  [TN] Stencil Aperture Mod
                      <[log in to unmask]>


                      01/16/2003 02:41
                      PM
                      Please respond to
                      "TechNet E-Mail
                      Forum."; Please
                      respond to Carlr
                      Ray






How many of you guys still run product with 1:1 apertures? How many
commonly use reduced or modified apertures?

I have an issue where I can not convince some other Engineers that
modifying the apertures to correct for solder balling is a good
solution.

The process is a no clean process and the profile meets the solder
paste manufactures recommended parameters.

The solder ball appear on next to the middle of the parts (like solder
escapement) and some are trapped by the flux others or not.

Do you guys know of any standards that address these issues?

Carl Ray
Sr. Manufacturing Engineer
Huntsville, AL 35807
Phone: 256-882-4800 ext. 8845
Cell: 256-990-1990

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