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Differences between screen and stencil printing



Differences between screen and stencil printing | 16 December, 2004

Sould anyone explain me pros and cons of stencil and screen printing and the advantages of using a screen printing over stencil printing

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Differences between screen and stencil printing | 16 December, 2004

Simple differences.

Both processes require a very similar machine platform, controlled motion, vision fiducial recognition and alignment of a substrate (PCB or hybrid ceramic) to the "image", the image being either a stencil (hence stencil printing) or a mesh screen (screen printing).

In general, stencil printing has become the defacto standard process for applying a film of solder paste to SMT bare boards (pads only image of the SMT layout is laser cut, etched thru a metal foil)to allow parts to be placed and reflowed further down the line. Stencil printing process may also apply adhesive dots for wave solder dual sided proceses. An entire tribology of succesful stencil, solder and squeegee blade exists for success with this process.

Screen printing (which started earlier than the stencil printing process) involves a metal mesh screen which has an emulsion to expose a pattern to be deposited, generally on a ceramic substrate. An entire tribology of techniques exists to be succesful with this process.

Both processes may deposit solder paste, but in general stencils do this, and screens are used for conductive epoxy materials for hybrid ceramic parts.

Stencil printing generally involves the use of "trailing edge" metal squeegee blades with "on-contact" print (the SMT board and stencil come together during the squeegee deposition of solder paste).

Screen printing is generally off-contact with a gap between the mesh and substrate, the squeegee blades are generally poly materials (not metal). In some cased due to material viscosity, screen printing may employ a "flood-print, print-flood" cycle, meaning the material to be printed is spread thickly over the mesh by a squeegee "flood" blade, and allowed to penetrate the metal mesh before a final print stroke generates the image/material deposit.

EKRA, MPM-Speedline, DEK, AMI and Fuji all produce capable products for either process, although AMI has focused on hybrid screen printers.

Hope this covers your question. Neither better or worse, just depends on what you are doing.

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