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NPL releases stencil and aperture design report.

The National Physical Laboratory (NPL, Middlesex, UK, has released a new report on the influence that stencil and aperture design has on fine-pitch printing. The report explored the limits of printing at fine pitch for three different solder pastes.

The investigation used stencils manufactured by different routes and explored the difference in paste release between round and square apertures. According to the report, paste release from the stencil walls becomes key with small apertures, and the opening-to-aperture wall ratio appears to be a good guide to printability. According to the report, for printing, thin stencils and Type 6 solder pastes yield the highest performance, depending on other factors in the assembly process. Stencils that provide the best performance are electroformed and with round apertures.

The report also details practical limits for ultra fine-pitch printing and introduces the concept of aperture area to sidewall area ratio (AAR). For Type 5 and 4 solder pastes and electroformed stencils, a ratio of 0.5 and 0.8, respectively, is necessary--regardless of aperture shape.

For more information, contact Dr. Chris Hunt at +44 (0) 20 8943 6065.
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Title Annotation:Industry News
Publication:Circuits Assembly
Article Type:Brief Article
Geographic Code:4EUUK
Date:Nov 1, 2003
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