STENCIL CONSIDERATIONS FOR MINIATURE COMPONENTSAuthors: William E. Coleman, Ph.D.
Company: Photo Stencil
Date Published: 10/4/2009 Conference: SMTA International
This paper is divided into two parts outlining two different approaches to resolve this issue. Part 1 deals with a Two Print Step Stencil Process where small apertures are printed with a thin stencil thus providing acceptable Area Ratios. A second thicker stencil is used for normal SMT devices, RF Shields, and SMT connectors. This stencil has relief pockets formed on the board side of the stencils anywhere paste was printed with the first stencil.
Part 2 deals with different stencil types (technologies) and different aperture wall coatings. Stencil technologies include Laser and Electroform; Aperture Wall coatings include PTFE coatings. Aperture Wall pictures and paste print tests compare the performance of these different configurations and how they influence paste transfer for miniature devices with Area Ratios less than the standard recommended lower limit of .5. In the second case a step stencil is not necessary.
Key Words: Area Ratio, Stencil, Electroform, Laser, Coatings, Step Stencil, Paste Transfer
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