Harald Grumm and Dominique Graupner
Christian Koenen GmbH - HighTech Stencils
Miniaturization, a growing need for more functionality and low production cost are the highest aims for electronic products, especially for mobile devices. The combination of these claims lead to complex substrates and production processes. Highly integrated components help to concentrate functionality on a very small footprint, bringing fine pitches and small connection pads / pins to the substrate (like QFN, MLF, iBGA).
Fine pitch and small pads increase the printing process standards. This can be countered with a thinner stencil thickness. But almost all electronic products also include components with a need for a high amount of solder volume (e.g. connectors, mechanical strained components, power components). This component mix demands a detailed set-up of the printing tool to be able to maintain a high yield at low production costs.
This document introduces stencil technologies, which address these claims and help to increase the first pass yield of your production line: Layout optimization directly addresses production process issues like tombstones, coplanarity, bridging, solder beading and voiding. Also processes like Through Hole Reflow (THR / PiP) or leadless components (OFN / MLF) should be designed regarding a detailed solder volume calculation.
Step Stencil Technology combines different stencil thicknesses into one stencil, allowing the correct solder volume for each component. Also this technology can be used to implement cavities into the substrate side of the stencil to overcome substrate issues like too high solder resist, too high via filling or plugging, labels or overtop clamping.
3-D-Stencils are capable to print simultaneously on different height levels of a substrate and extend the usability of stencils into new areas. PLASMA Stencils are coated with a high tech material to enhance paste release, reduce the need for cleaning and minimize the effect of line down times to volume transfer. By choosing the right combination out of the possible options you will be able to speed up your production, enhance your quality and yield.
Stencil technology is the key to establish a reliable and cost effective printing process. Efficiency and yield will increase together with the correct selection of layout and stencil options to meet the demands of the process. To select the right combination of options a good communication between production and stencil design is essential.
Initially Published in the SMTA Proceedings