Bernard and Jim,

Here is my approach to Solder Stencil design.  Feel free to use it if
the results please you too.  You can also have a spreadsheet program
that I've developed to simplify the stencil design process - its in
Microsoft Excel format.  If you are interested, contact me directly and
I'll E-Mail it to you.  BTW, you can get additional information on
stencil design, and many other topics of interest by doing a keyword
search at the IPC E-Mail Forum for DesignerCouncil
http://jefry.ipc.org/archives/designercouncil.html and TechNet
http://jefry.ipc.org/archives/technet.html .   Enjoy !

Solder Volumes:

Toe = average Terminal Width x 0.5 x average Terminal Thickness x (
average Terminal Thickness + 1.5 mils)

Sole = the lesser of ( average Terminal Width and ( Design Pad Width -
Etch Factor )) x average Terminal Length x 1.5 mils

Inner Heel = average Terminal Width x 0.215 x 2 x average Terminal
Thickness x 2 x average Terminal Thickness

Outer Heel = average Terminal Width x 0.5 x 2 x average Terminal
Thickness x ( 2 x average Terminal Thickness + 1.5 mils )

Sides = average Terminal Length x 2 x 0.5 x absolute value of ( average
Terminal Width - Design Pad Width - Etch Factor ) x 1.5 mils

Aperture Dimensions:

Aperture Width = Design Pad Width - ( Etch Factor/2 if Design Pad Width
< = 12 mils, otherwise Etch Factor/1 )

Aperture Length = ( Paste Volume/Solder Volume ) x ( 1/( (Stencil
Thickness + 1 mil ) x Aperture Width )) x ( Toe + Sole + Inner Heel +
Outer Heel + Sides )

Paste Volume/Solder Volume = 2.00 for 90% metal, 2.57 for 85% metal,
3.60 for 80% metal, 4.50 for 75% metal


John Balchunas
IPC Designer Council Member
Southern New England Chapter

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