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Screen Stencils with Improved Release Properties

IP.com Disclosure Number: IPCOM000112730D
Original Publication Date: 1994-Jun-01
Included in the Prior Art Database: 2005-Mar-27
Document File: 2 page(s) / 68K

Publishing Venue

IBM

Related People

Lawson, IA: AUTHOR [+4]

Abstract

Disclosed is a method of improving the release properties of a screening stencil used for the pattern deposit of solder paste (or other screen printing material) onto Printed Circuit (PC) cards prior to surface mounting assemblies. A bonded lubricant on the stencil apertures is employed. Benefits are a more efficient and accurate release of solder paste images onto PCs than conventional processes.

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Screen Stencils with Improved Release Properties

      Disclosed is a method of improving the release properties of a
screening stencil used for the pattern deposit of solder paste (or
other screen printing material) onto Printed Circuit (PC) cards prior
to surface mounting assemblies.   A bonded lubricant on the stencil
apertures is employed.   Benefits are a more efficient and accurate
release of solder paste images onto PCs than conventional processes.

      As SMT is driven to finer pitches, the challenges presented in
the screen printing operations become greater.   Stencils with higher
tolerances, solder pastes with smaller particles and stencil
apertures with smoother walls are demanded.   Currently stencils
manufactured to the highest tolerances are laser-cut.   The walls of
laser-cut stencils are not as smooth as brass stencil walls
previously used.   As smaller particle size pastes come on stream for
fine pitch printing, there is a tendency for the particles to lodge
in the apertures, leading to insufficient paste deposits through
paste hanging up in the stencil.  By applying a 'bonded lubricant' to
the laser cut stencil apertures, the paste release will be
significantly improved, since the coefficient of friction of the
aperture walls will be reduced.   The improvements combines the
higher tolerances achieved of a laser cut stencil with a much
improved paste release via the bonded lubricant.

      Application requires the bonded lubricant to be simply spray
coated onto the metal mask (stencil) on its bottom (board touching)
surface.  The spray will also coat the apertures which is the desired
resul...