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Design Guide

Design Guide

1. Introduction

Today's marketplace sets high demands for fast, accurate, and reliable human-machine interface solutions. It is critical to provide your customers with ease of use, satisfactory tactile response, and rapid functionality when developing your specific application.

Membrane switches are designed to meet a very specific set of criteria depending on the application. Effective membrane switch design requires a good understanding of the application and the ability to communicate what is required for a successful and efficient design.

The purpose of this design guide is to outline the requirements and their role in the membrane switch design process. Using these guidelines will help maximize the quality, reliability, and efficiency of the membrane switch. Cubbison Company is capable of providing custom membrane switch design assistance to meet all of your requirements.

2. Types of Switches

In general terms there are two types of membrane switches, tactile and non-tactile, and both of these can be constructed with or without a graphic overlay. Tactile switches use a metal dome or poly dome to provide a physical “snap” feedback response to the user’s finger, letting him/her know that the button has been depressed. Non-tactile switches do not incorporate a metal or poly dome into the construction and therefore do not provide feedback to the user’s finger when a pushbutton is depressed.

3. Construction

A typical membrane switch construction consists of the following layers:

Membrane Construction

Graphic Overlay
Graphic Adhesive
Dome Retainer (or a Top Circuit for Matrix Circuit Configuration)
Dome Spacer (for use with metal domes)
Bottom Circuit
Rear Adhesive

Other design constructions are available. For further information, contact the Cubbison Company.

4. The Graphic Overlay

Graphic Overlays are a critical component in membrane switches and touchscreens. They provide both protection and a surface for printing to generate a functional and user-friendly interface.

Prepress

Cubbison employs a full service art department. If you do not have artwork, Cubbison offers complete membrane switch design services. One of our design engineers will work with you on designing and building a membrane switch custom for your application. Cubbison can also help you select the best printing option available for your intended printed electronics application. Our printing technologies include: screen printing, digital printing, or a combination of screen and digital printing.

Customer Supplied Artwork Requirements:

Artwork Requirements:

  • Native (original program) Editable Vector image file (i.e. Illustrator .ai file)
  • Fonts supplied or outlined
  • Legible blueprint or layout (i.e. .dwg or a .dxf file; hardcopy or physical sample)

Customer must supply:

  • Dimensions (Overall size and if applicable, the Round Corner Radius)
  • Dimensions of the copy and graphic location within the layout if critical, as well as text point size
  • PMS colors (Graphics, Lines, Background)
  • Clearly identify and provide sizes, location, and dimensions of thru cuts and clear windows

Acceptable Software Files:

  • .AI – Adobe Illustrator CS6 (or previous versions)
  • .EPS
  • .PDF – (from native PDF conversion such as via Adobe, AutoDesk, etc.)
  • .DXF or .DWG (via CAD, SolidWorks or MicroStation)
  • .TIFF – Raster files set to 300 dpi (used for digital printing only)

Material selection

Cubbison offers a range of hard coated and textured polyester and polycarbonate films. These substrates have been designed specifically for the graphic overlay film on membrane switches, and range in finish from high gloss to velvet matte. Both product ranges are screen printable on the second surface; they are solvent, chemical and scratch resistant on the first surface. Polyester is the most popular choice as it is more robust, providing superior chemical resistance and allowing for up to 5 million actuations over its lifetime, as opposed to polycarbonate, which is only rated for up to 100,000 actuations. ***For further information on this please contact the Cubbison Company.

Color matching

The Pantone Matching System (www.pantone.com) is the most popular for graphic art applications.Cubbisonhas the ability to match Pantone, custom, and transparent colors with our digital presses. There are separate matching criteria for both opaque and transparent colors.

It is important to remember that matchingscreen printed overlay colors to surrounding components is difficult. For this reason,we are using state-of-the-art color matching equipment in the X-rite Ci7600 spectrophotometer. As long as we have a control color to match against, we can achieve a color match under 1.0 delta in the CIE Lab color space. We are capable of matching Pantonecolors, custom colors, as well as transparent colors for windows. We also have the capabilities to do transmission and density readings.

Embossing

Cubbison can provide either pillow (pad) or rim (perimeter) key tactile designs into polyester or polycarbonate overlays. This process requires a male/ female die set. Overlay embossing dies are manufactured with sophisticated tolerances to allow for material flow.
Our Cubbison design staff will precision-calculate a die for your application.

Windows

Display windows are typically transparent and they can be either clear or color tinted. LED windows can be either transparent(with or without color added) or translucent. A transparent color is optically clear and used to filter backlight displays. The transparent color reduces the "blooming effect" of the display. A translucent color is normally used for diffusing an indicator light or backlighting for printed graphics, such as an instrument cluster that is backlit.

Selective surface texture/hard coat

Cubbison offers hard coat films that are ideal for membrane switch overlay applications. These films are polycarbonate and polyester substrates that have been specially treated so that their surfaces can be selectively textured, embossed or printed with UV inks. Available in finishes ranging from glossy clear to textured matte black; hard coat films offer a range of display options.

Hard coat films resist scratching and staining from a broad spectrum of foods, household cleaners and aggressive chemicals. For special applications, such as medical equipment, our hard coat films may be embossed or otherwise thermoformed without sacrificing performance characteristics.

Cubbison can print inks specifically designed to give a decorative texture effect on first surface polyester or polycarbonate used for membrane overlay applications. Cubbison offers many, state of the art forms of texture coats from very fine to course. We can custom match your texture. With the new technologies in UV inks we can provide a texture coat that is very durable and will withstand marring.

5. Circuit Design

Circuit

Circuitry is designed using either a common bus or matrix configuration, or a combination of the two. The connection from the membrane switch to the PCB is made via a cable interconnect, or “tail” that is terminated with either bare contacts or a plastic connector housing (solder tabs can also be used). The tail termination pitch can be 2.54mm, 1.27mm, 1.00mm or 0.5mm. The tail can exit from either an edge or inset location of the part, but not from the button area.Cubbison can supply a range of heat stabilized polyester films which offer high stability specification and are designed to be screen printed with conductive silver and/or carbon, graphite and dielectric inks.

Backlighting Design Options

Cubbison provides 3 types of backlighting:

  • LED – Surface mount LED’s can be embedded into the membrane switch. LED’s are mounted onto the circuit layer using our pick and place unit. This is the least expensive backlighting option, and it is used primarily for indication and single point illumination.
  • Fiber Optic – A fiber optic layer can be incorporated into the membrane switch when even, uniform lighting is required.
  • Light Guide Film – This option also provides even, uniform lighting.

Shielding Options

  • ESD, RFI/EMI Our most common types of shielding are printed using either carbon ink or silver ink or by using solid aluminum foil. Carbon is the least expensive printed option. Aluminum foil has certain advantages if a printed top circuit is not specified. The shield can be terminated by either a conductive trace routed to the connector, or by a ground strap cut from the polyester material. Our design engineers will help to determine your best shielding solution.

6. Other Considerations Metal Domes (For Tactile Switches)

Cubbison offers 4 legged and oblong style domes, see below for the typical characteristics of each:

4-Legged Domes

    • Sizes range from 11.2mm up to 25.0mm in diameter
    • Activation forces available from 85g to 2000g
    • Available with life expectancy of up to 3 million activations

Oblong Domes

    • Sizes range from 11.2mm up to 50.8mm in diameter
    • Activation forces available from 230g to 450g
    • Available with life expectancy of up to 3 million activations

Connectors

Cubbison is tooled for Nicomatic and Amphenol FCI (Berg) plastic connector housings.

Venting

When a switch is deflected there needs to be a small track designed into the switch for the displaced air to move. The tract will connect all of the switch keys so that air can be displaced. Venting is done internally, and using this design technique allows the switch to remain sealed. External venting is not recommended.

Backer/Subpanel

Cubbison can offer aluminum, polycarbonate and acrylic material options for a rigid subpanel. Cubbison can laser fabricate a subpanel to your specifications. It is usually advisable for the subpanel to be slightly smaller than the membrane switch. Conversely the holes and cutouts should be slightly larger than those on the membrane in order to conceal the sub panel.

NEMA 4 Gasket

This design feature can be used for added protection of the membrane switch against environmental factors such as dirt and moisture.

Membrane Switch Operational Characteristics

Mechanical:

Life Expectancy
Force Range
Switch Travel
Contact Bounce

Greater than 1,000,000 Actuations
6 oz. to 18 oz.
0.010" to 0.030"
1 to 10 milliseconds

Electrical:

Contact Rating
Circuit Resistance (On)
Circuit Resistance (Off)
Current
Voltage
Power
Configuration

20mA at 30 Volts DC
100 Ohms or Less
10M Ohms
100mA (max.)
50 Volts DC (max.)
1.5 Watts (max.)
SPST Normally Open

Environmental:

Storage Temperature
Operating Temperature

-40 to +80 Degrees Celsius
-30 to +70 Degrees Celsius

Glossary

  • Voltage: The difference of electrical potential between two points of an electrical or electronic circuit, expressed in volts. It measures the potential energy of an electric field to cause an electric current in an electrical conductor. A measure of the pressure under which electricity flows.
  • Dielectric: non-conducting substance, i.e. an insulator. Although "dielectric" and "insulator" are generally considered synonymous, the term "dielectric" is more often used when considering the effect of alternating electric fields on the substance while "insulator" is more often used when the material is being used to withstand a high electric field.
  • Optical fiber: A thin glass strand designed for light transmission. A single hair-thin fiber is capable of transmitting trillions of bits per second.
  • ESD (Electrostatic discharge): The rapid, sudden transfer of electrostatic charge between two electrically charged surfaces.
  • RFI(radiofrequency interference): Interference or “noise” that adversely affects the operation of an electrical circuit.Limited to the radio frequency spectrum.
  • EMI (electromagnetic interference): Interference or “noise” that adversely affects the operation of an electrical circuit. Encompasses all frequencies of electrical noise.
  • Light Guide Film (LGF): A film that is patterned and uses LED’s to guide light along the patterned surface.
  • Emboss: A raised surface on the graphic overlay, typically applied to a pushbutton. Embossing is also used for a poly dome layer.