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Membrane Switches

Membrane switches are commonly used to connect signal command devices such as keypads and buttons to the function circuitry of an appliance.

Membrane switches are unique in that once contact pressure is released from the switch, the flexing membrane returns to its original position.

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Membrane switches are commonly used to enter function commands on many equipment such as cellular phones, remote controls, calculators, machine controls, microwave ovens and kitchen appliances...

Introduction

Membrane switches were first introduced in the early 1970’s for use in microwave ovens to provide easier cleaning (compared to mechanical switches and dials).

Today, membrane switches are manufactured globally, and are in use everywhere on a daily basis. Membrane switches are unique because the manufacturing process requires both circuit printing and graphics printing—and some- times printing industrial materials like
adhesives and spacer layers.

Screen printing is dominantly used to print the conductive switch lines and the adhesive layers in the construction of membrane switches. This is because screen printing mesh offers relatively large openings that help to print the viscous conductive, resistive and adhesive materials. In addition, screen printing offers a wide range of wet ink deposit thicknesses from which to create the circuits (from a few microns to several hundreds of microns). The majority of membrane switch graphic overlays are also screen printed.

Screen Printing Process

Membrane switch layers are typically printed using an “off-contact”, flat bed screen printing process, but some can be rotary screen printed. Press runs are usually performed in a clean room environment (substrates are kept free of contaminants), and range in length between a few hundred to tens of thousands of substrates.

The industry uses automatic and semiautomatic printers that are specifically designed for the critical registration accuracy and precise, repeatable thickness printing applications.

After printing, all ink layers must be cured (using heat or UV light-depending on the layer), and additional ink layers are printed as needed. After all ink layers have been applied, switches are assembled, and physical components can be attached and connected to complete the final switch assembly. The final switch assembly will contain electronic and graphic screen printed layers.

Inks used for membrane switches include polymer thick film silver conductive and resistive inks, adhesives, solvent based (vacuum forming) and graphic UV-curing inks. SEFAR PET 1500, and SEFAR PME polyester meshes are recommended for screen printing graphic overlays, conductive layers, and the adhesive and/or spacer layers.

Substrate materials typically used in membrane switch fabrication include PET (polyester) foils for the circuit layers, and polycarbonate for the graphic overlays.