Browse Prior Art Database

Method for Improving Stencil Performance

IP.com Disclosure Number: IPCOM000103189D
Original Publication Date: 1990-Aug-01
Included in the Prior Art Database: 2005-Mar-17
Document File: 1 page(s) / 35K

Publishing Venue

IBM

Related People

von Voss, WD: AUTHOR

Abstract

Disclosed is a method to improve the performance of etched metal stencils used for printing solder paste for circuit boards assembled using surface mount technology. Standard industry practice is to use the same optical pattern (artwork) to expose the photoresist on both the top and bottom surfaces of the metal foil which, after etching, becomes the stencil. When the metal foil is etched from both sides using the same size images, the walls of the openings will not be straight and vertical but rather scalloped and undercut, the extent depending on the residence time in the etcher. The scalloped shape of the openings in the stencil degrades the quality and accuracy of the prints made with the stencil.

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Method for Improving Stencil Performance

      Disclosed is a method to improve the performance of etched
metal stencils used for printing solder paste for circuit boards
assembled using surface mount technology.  Standard industry practice
is to use the same optical pattern (artwork) to expose the
photoresist on both the top and bottom surfaces of the metal foil
which, after etching, becomes the stencil.  When the metal foil is
etched from both sides using the same size images, the walls of the
openings will not be straight and vertical but rather scalloped and
undercut, the extent depending on the residence time in the etcher.
The scalloped shape of the openings in the stencil degrades the
quality and accuracy of the prints made with the stencil.  The
material being printed with the stencil will release from the stencil
more easily if the openings are slightly larger on the bottom or exit
side of the stencil.  In metal casting, this principal is called
draft and is obtained by building the patterns with a slight taper to
their sides. The same effect can be obtained for etched stencils by
using two separate artworks, the top side image being made .001 inch
narrower than the nominal opening size, and the bottom side made .001
inch wider.

      Disclosed anonymously.