Common Membrane Switch Terminology

Common Membrane Switch Terminology

ACTUATION FORCE

The pressure required for actuating the circuit of a membrane switch or rubber keypad.

ADHESION

The strength of the molecular attraction bond of one material to another determined by the surface energy in each material.

BACKERS

Incorporating backers into membrane switch assemblies for mounting or rigidity purposes. The most commonly used material is aluminum which can be supplied with a variety of hardware installed. Other backer options include G10, stainless steel, polycarbonate or acrylic materials.

BACKLIGHTING

Lighting of membrane switches using LEDs, light guide film, fiber optics or EL panels.

BREAKDOWN VOLTAGE

The minimum voltage at which the insulation between two conductors begins to fail.

CARBON OVERCOAT

Ink that consists of prepared suspensions of carbon black and is applied over silver circuitry to mitigate the possibility of silver migration. Typically used on the flex tail contacts which is the area on the flex circuit most susceptible to silver migration.

CIRCUITRY

Electrical circuit used to operate a membrane switch typically either printed silver, copper flex or printed circuit board based.

CONDUCTIVITY

A material’s ability to allow the flow of electrons.

COPPER FLEX

A type of circuitry used in membrane switches produced using polyimide (Kapton) as the base material. Manufactured by laminating a thin sheet of copper to a flexible film substrate, the copper is then chemically etched away, leaving the copper traces. An additional layer of polyimide is laminated to the circuit leaving the gold contacts exposed. Also known as Kapton circuits, they have become the superior choice over printed silver especially for outdoor applications due to their excellent dielectric strength, thermal stability, chemical resistance and flexibility.

CROSS-OVER

A conductor intersection where the traces are kept separated and insulated by dielectric material insulator.

DEAD FRONT

A cosmetic feature of a graphic overlay in which an artwork feature is only visible when backlit.

DIELECTRIC / DIELECTRIC INKS

An insulating or non-conducting medium. The inks are used for printing protective patterns on conductive printing to isolate selected areas from electrical contact with other conductors. Typically used for cross-overs and tail insulation.

DOMES

A tactile metal dome (or a snap dome) is a normally open momentary contact that provides a crisp tactile feel letting the user know the button was pressed/actuated. Polydomes can also be utilized if necessary.

DOME RETAINER

An adhesive layer made to hold metal domes in the key-switch.

EMBOSS

Method of raising an aspect or aspects of the overlay material to accentuate key surfaces through mechanical and thermoforming of graphical features. Typically used for keys and/or LED indicators.

ENVIRONMENTAL SEALING

Utilizing proprietary design features in order to seal a membrane switch or rubber keypad. Such features include frame sealing, the use of copper flex circuitry and rubber gasketing.

GRAPHIC OVERLAY

The decorative front layer of a membrane switch or control panel.

KEY HEIGHT

The distance from the highest point of a key to the base of the keypad.

LIGHT EMITING DIODE (LED)

Assembled to the membrane switch circuitry to illuminate a feature or features on the keypad.

PINOUT

The schematic that describes the circuit output requirements for membrane switches. Also known as a wire diagram.

PRESSURE SENSITIVE ADHESIVE (PSA)

Adhesive materials that bond through the application of pressure without the need for heat or solvents.

REAR PSA

A pressure sensitive adhesive applied to the back of a membrane switch for mounting purposes. Different types of rear PSA can be utilized depending on the application and bonding surface.

SHIELDING

Utilizing methods for incorporating ESD/RFI/EMI shielding within the membrane switch layers.

SECOND SURFACE PRINTING

Practice of printing a graphic overlay from the bottom in reverse, so the outer layers protect the graphic.  This is particularly useful in membrane switch applications where the graphic overlay experiences abrasive wear.

SILVER INKS

Tiny particles of actual silver suspended in various substrates that produce conductive patterns on rigid and flexible substrates.

SPACER LAYER

A membrane switch adhesive layer separating the electronic circuit layers with button/switch openings.

TAIL BREAKOUT

The location of the tail exit on the back of the membrane switch.

VENTING

Membrane switch openings connected to one another to seal the switch from moisture and other contaminants without venting externally. External venting is also an option if the design allows for it.

WINDOWS

Utilizing the base clear overlay to incorporate windows in a membrane switch typically for displays. Can utilize hardcoats or textures depending on the application. Incorporating a reinforced opti-bond window is also a common technique for windows susceptible to excessive abuse.

WIRE DIAGRAM

A diagram showing the desired connections to the pinout connector.

Membrane Switch Copper Flex Circuitry
Membrane Switch Copper Flex
Backlit Rubber Keypads
Membrane Switch Silver Circuit
Sealed Rubber Keypad

Emulating Seven Segment Displays in Membrane Switches

Emulating Seven Segment Displays in Your Membrane Switch or HMI

Are you looking to integrate a seven segment display or displays into your interface but are encountering space constraints and/or trying to keep costs down? 

CSI has years of experience emulating seven segment displays using LEDs, light guide film and light blocking features. We also utilize additional methods including light “piping” features within the layers of the membrane switch. We can integrate LEDs of any color and any window color to give you the exact aesthetic you are looking for in your product. The result is a thinner membrane switch package size at a much more cost effective price.

Advantages:

 

1. Thinner membrane switch package size.

2. More cost effective than using actual seven segment displays.

3. Can integrate into a flexible circuit (versus printed circuit board).

Of course, if you want to use actual seven segment displays that is also an option but will most likely require a printed circuit board design (versus a thinner flexible circuit) and an overall thicker membrane switch package. The CSI engineering team can assist you in this process in order to ensure you get exactly what you are seeking for your interface.

Seven Segment Displays in Membrane Switches

A Heartfelt Thank You to All Visitors at the MDM Tradeshow

A Heartfelt Thank You to All Visitors at the MDM BIOMEDevice Show

CSI Keyboards would like to extend our gratitude to all of the visitors that stopped by our booth last month in Boston. It truly was a pleasure meeting each and every one of you and cannot thank you enough for your support.

The MDM BIOMEDevice Tradeshow has become a beacon in the medical industry allowing companies like CSI to showcase our products and designs enabling individuals to explore innovations, source products, and make vital connections that help grow the industry as a whole.

Thank you again and hope to see you next year!

 

CSI Keyboards to Exhibit at the MDM BIOMEDevice Show

CSI Keyboards to Exhibit at the MDM BIOMEDevice Show

CSI Keyboards will be exhibiting at the MDM BIOMEDevice trade show at the Boston Convention & Exhibition Center on September 20th-21st. 

Come visit us at Booth 1031.

BIOMEDevice focuses on the medtech research, development and products that matter to you, get continuing education experience to keep you current in the industry and on the job. Then explore innovations, source products, and make important connections. 

Design & Manufacturing (D&M) New England is your entryway to the most advanced technologies on the market, from design software and biotech solutions, to contract manufacturing, automation, and robotics. Walk the entire expo floor and meet face to face with thousands of peers while gaining valuable insights from industry pros across the medtech, design and manufacturing, and embedded systems spectrum.

Spanning the embedded systems spectrum, the Embedded Systems Conference brings together engineers searching for solutions with leading suppliers whose products can reduce cost and efficiency.

Most Suitable Graphic Overlay Material for UV Resistance

Most Suitable Graphic Overlay Material for UV Exposure

A very common question many customers ask us: is there a graphic overlay material that is better suited for a product that will live outside with constant UV exposure?

The answer to this question is really dependent on the membrane switch design.

If the membrane switch doesn’t have a window, then the polyester Autotex XE would be ideal.

If the membrane switch does have a window, then we have found that the best UV resistant graphic overlay material is actually polycarbonate as there is no available UV polyester (including Autotex XE) that is non-textured which would be required for any part with a window. 

When it comes to UV resistant polycarbonates, these are really the best available material options:

HP92W: UV resistant gloss hard coat – non-texturable

HP92X: UV resistant – texturable

Thicknesses:

.007 (7mil) is needed for anything that requires an emboss

.010 (10mil) can be used for parts that don’t require an emboss or standalone windows.

Hot Tub Keypad

Utilizing Epoxy Keys in Membrane Switches

Utilizing Epoxy Keys in Membrane Switches

Often times, membrane switches are simply embossed which is the process of raising the key area using magnesium membrane switch overlay embossing dies. A popular alternative to embossing the overlay material is using epoxy keys.

Epoxy keys are applied using a precise dispensing process. Epoxy keys are typically used for aesthetic purposes giving the membrane switch a clean look and really making the keys pop. Epoxy keys are still raised off of the surface allowing the user to easily locate the keys similar to an emboss.

Epoxy keys are also utilized when there are space constraints around the keys. If the keys are too close together or close to the edge of the part, there often times isn’t enough space to emboss due to adhesion issues. The epoxy keys ensure there is enough adhesion around the keys to prevent delamination.

Epoxy Keys in Membrane Switch

Backlighting Membrane Switches with Fiber Optics

Fiber Optic Backlighting in Membrane Switches

Backlighting membrane switches with fiber optics provides many benefits that cannot be obtained using standard LED backlighting or EL techniques.

Advantages:

1. Fiber optics provides a flexible and customizable back lighting layer (as thin as 0.2 mm) that can easily be incorporated between the graphic overlay and the circuit layer.

2. Can evenly backlight the entire surface area of the membrane switch.

3. Fiber optics allow for a uniform and evenly distributed backlit surface.

4. Low power consumption typically only using one single LED.

 

Fiber Optic Membrane Switch

Integrating Backers into Membrane Switch Assemblies

Integrating Backers into Membrane Switch Assemblies

When a membrane switch is affixed to the enclosure or housing of the end product there are essentially two options: rear pressure sensitive adhesive (PSA) or a backer plate. Many of our membrane switches require backers or support layers for rigidity and structural integrity. The design often dictates whether or not a metal backer is needed. For instance, often times the customer’s enclosure or housing design requires mechanical fastening.

The most commonly used materials are aluminum or stainless steel. Other options include G10, polycarbonate or acrylic backers. Metal backers can also be supplied with a variety of hardware installed such as PEM studs. 

If the keypad is PCB (printed circuit board) based, we can typically utilize the PCB as the backer and install hardware directly into the board.

Membrane Switch Defined

Membrane Switch Defined

What is a Membrane Switch?

A membrane switch is an interface between man and machine, enabling an operator to communicate with equipment, instrumentation, or machinery. A membrane switch is a printed or etched electronic circuit that uses pressure to open and close a circuit. The membrane switch circuitry can be: screen printed using conductive inks which are typically made of silver or carbon, etched copper on Kapton, or can be printed circuit board based. The membrane switch overlay is typically made of polyester, polycarbonate, or molded silicone rubber. Membrane switches are part of a range of devices considered to be user interfaces or human machine interfaces (HMIs) along with touch screens and mechanical switches.

Membrane Switch Construction

A typical membrane switch assembly typically consists of six to seven main layers:

  • Graphic Overlay – Graphic overlays are typically constructed of polyester, the material of choice due to its superior chemical resistance and flex life compared to polycarbonate. CSI can either digitally print, screen-print, or employ a combination of both methods to insure you get the right colors, textures, and finishes your Silver Flex membrane switch design requires.
  • Overlay Adhesive – The overlay adhesive layer bonds the graphic overlay to the top circuit layer. This overlay adhesive is typically an acrylic adhesive, selected for its durability and ability to maintain adherence in atypical environments, such as moist environments.
  • Top Circuit Layer – Typically a .005″ – .007″ heat-stabilized, polyester printed layer with silver-filled, electrically conductive inks and dielectric inks. This layer can also encapsulate metal domes or incorporate polydomes, which are used to achieve tactile feedback, an important design consideration impacting usability.
  • Circuit Spacer – This layer separates the top circuit from the bottom circuit, so the switch remains normally open until the keypad is pressed. The circuit spacer is a polyester spacer with adhesive on both sides.
  • Lower Circuit Layer – The lower circuit layer is typically a .005″ – .007″ heat-stabilized, polyester-printed layer with silver-filled electrically conductive inks and dielectric inks. This layer terminates as a flexible tail that serves as the interconnect to controller PCB’s or other electronics.
  • Rear Adhesive Layer – This adhesive layer bonds the entire membrane switch package to the product enclosure, housing, or to a rigid support panel. CSI can specify the appropriate adhesive type and thickness to bond your membrane keypad to your equipment.
  • Rigid Support Layer – This optional layer can add structural integrity to the membrane switch assembly. Materials can be aluminum, FR-4, steel, etc. Mounting hardware such as studs and standoffs can also be utilized in this layer.
Membrane Switch Guide

Copper Flex Membrane Switches

The Copper Flex Membrane Switch constructions are ideal for smaller designs, where space is at a premium, or where dense circuit patterns or trace routing limitations exist. Copper Flex membrane keypads utilize silver or copper layers which are laminated to a dielectric layer and etched away.

This switching technology combines the ability to accommodate the complex circuit patterns of a FR4 rigid printed circuit board with the flexibility of a membrane switch. Copper Flex keypads also have the advantage of being able to “hard” solder both active and passive components into the assembly, making it a good choice in high-vibration environments.

Copper Flex membrane switch panels can be produced using polyester or polyimide (Kapton) as the base material depending on your interface requirements. A very thin sheet of copper is laminated to the flexible film substrate then chemically etched away, leaving copper traces. 

Copper Flex membrane switches offer you a variety of design options:

  • Single and double sided designs
  • Lower electrical resistance and higher conductivity vs. traditional Silver Flex membrane switches
  • Tight trace routing capabilities
  • Thin profile and flexibility of Silver Flex membrane switch
  • Plating options can be tin-lead, nickel, or gold
  • Tactile and non-tactile with either metal or polyester tactile domes
  • LED’s and other components can be soldered
CSI Keyboards Medical Membrane Switch

PCB Based Membrane Switches

The PCB Membrane Switch construction utilizes a printed circuit board (PCB) which can serve a dual purpose in your membrane switch design. PCB Switches are typically more costly than Silver Flex membrane keypads, but can accommodate dense circuit patterns and more complex circuit patterns compared to Silver Flex membrane keypads.

A PCB membrane switch also allows the electronic components to be “hard-soldered” into the PCB, whereas membrane switch components are placed using a polymer thick film conductive paste. With a PCB membrane switch, the PCB can serve as a rigid backer, and is also a very durable and reliable method to incorporate LED’s, resistors, LCD’s and other components.

CSI Keyboards PCBA Rubber Keypad

PCB membrane keyboards offer you a variety of design options:

  • Tactile and non-tactile with either metal or polyester tactile domes
  • Pillow or rim-embossed graphic overlays
  • Embedded LED’s that are soldered directly into the PCB
  • Fiber Optic backlighting
  • EL – (Electroluminescent backlighting)
  • Rigid backers such as aluminum and FR4
  • EMI/RFI shielding
  • Unlimited choice of connectors, which can be soldered directly into the PCB

Silicone Elastomer Rubber Keypads

Silicone rubber keypads use compression-molded silicone rubber with conductive carbon pills or with non-conductive rubber actuators.  They have exceptional resistance to extreme temperatures and aging, making them an ideal choice if reliability is a prominent concern due to likely environmental influences.

A rubber membrane switch uses compression-molded silicone rubber with conductive carbon pills or with non-conductive rubber actuators. Rubber keypads are relatively inexpensive on a per-piece basis, but require fairly expensive tooling, usually making them a design choice for higher-volume projects.

Silicone rubber keypad switches have numerous features that set this type apart from other traditional membrane switch designs. Some of the main differentiating features of this type make the silicone rubber keypad switch an ideal choice for applications requiring more durability or better resistance to exposure to moisture, chemicals, or other compounds.

Molded rubber keypad: copper flex circuit based with domes and backlit keys

Some of the primary distinctive features of silicone rubber keypad switches include:

  • Work as a conductive shorting device for Silver Flex membrane switches, PCB membrane switches, and Copper Flex membrane switches
  • Can utilize carbon pills, non-conductive rubber actuators, or stainless steel tactile domes
  • Actuation forces and switch travel can be customized
  • Any shape or size can be designed
  • Multiple colors can be achieved by flow molding the color during the compression-molding process
  • Rubber keypad top graphics can be customized by screen-printing
  • Rubber keypad switches can be PU spray-coated for enhanced durability
  • Rubber membrane switches have excellent weatherability for outdoor use
  • Can be designed to seal the keypad assembly from moisture and contaminants
  • Silicone rubber is resistant to chemicals and moisture
  • Laser etching the rubber keypads can allow for backlighting individual keypads
  • Backlighting options