As a recognised leader in its field, Weymouth based Tecan Stencils Limited (TSL) has again provided the industry with an innovative stencil technology solution.

TSL manufactures multi-level stencils which deliver the distinct paste volumes required by the diversity of components used on today’s electronic assemblies in a single printing action.

“The ability of single thickness stencils to deposit the correct volumes for all component types is somewhat limited,” said TSL Product Manager Tony Weldon. “We all appreciate that continued miniaturisation, with ever-finer aperture and pitch requirements, has resulted in the need for proportionally thinner stencils - to avoid bridging and achieve improved paste release for these devices. This can, however, also lead to inadequate paste deposits and resultant solder fillets on non-fine pitch components.”

For example, PLCC and J leg devices, as used in larger numbers on PCB”s today, need larger solder fillets, both for electrical connectivity and mechanical security. Similarly, fillets for surface-mount connectors, which may contain coplanarity errors, generally require more than 125Fµm to150Fµm of paste. Compromising on a single thickness stencil solution, tailored only to the finest pitch device produces insufficient solder fillets that result in a range of associated problems at the test stage.

Significant reductions in rework, test and field failures can be achieved, says TSL, by adopting the multi-level stencil - which facilitates the optimum thickness deposits for all component types in a single pass of the squeegee. Additionally the multi-level stencil allows some traditionally hand-soldered operations to be fully integrated into the stencil printing process - such as power components, screening cans and enclosures.

Use of multi-level technology has increased significantly over the last few years, not only because it reliably and consistently satisfies today’s compact integration needs - it is also suited to Pin in Hole Reflow (PIHR) applications - a major developing technique used to achieve more cost-effective manufacturing.

In many instances, this emerging technology is the only option able to significantly reduce manufacturing and assembly costs, cycle times and defects, says TSL. The yield raising stencils are novel in that they can have both raised and recessed areas on a “standard thickness” stencil - thereby optimising the paste volumes, printed definition and paste release from the stencil apertures.

Using a comprehensive range of manufacturing techniques, the company can supply electroformed, laser and precision-etched multi-level stencil combinations. TLS”s CAD and Applications staff can optimise the stencil design to deliver the printed results required.

Other application areas for multi-level stencil technology include crystal masks, the production of solar cells and effective screening of conductive inks and adhesives.

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