Sales & Marketing

Membrane Switch - Standard Construction - Membrane Keypad

Figure One

General Considerations

RSPI designs custom membrane switches to your specifications.  Ideally, the membrane switch will be designed simultaneously with the rest of your product.  Too often the membrane switch is the last part designed and does not get built optimally.  Since we want you to have the best membrane switch possible, here are some things to consider during the design phase.

Mechanical

·        What material is the switch laminated to?

·        Will tactile response be required?

·        Is actuation force a factor?

Environmental

·        Will this product be used indoors or outdoors?

·        Is this product exposed to the elements?

·        What temperatures and humidity range will this product experience?

·        What type of solvents and cleaning solutions will come into contact with the switch?

Electrical

·        What type of pinout will be used (common bus, X-Y matrix, other)?

·        How many switches will there be?

·        What closed loop resistance is acceptable?

·        Will EMI or electrostatic shielding be necessary?

Appearance

·        Will edges be exposed?

·        Will embossing be required (for easier user function)?

Design Stage

Artwork

RSPI accepts many different formats of artwork files.  To find out if we can work with your artwork send a file to sales@membrane-switches.biz.  If you do not have artwork or need help, our graphic artists and engineering experts can also design the graphic overlay and circuitry for you.  Common file types accepted by RSPI include:

• Adobe Illustrator - AI or EPS
• CorelDraw-CDR Adobe
• Autocad-DWG or DXF
• PDF

Sample

Providing a sample part (for previously built switches) can be very helpful to our design team when you want us to quote or build a membrane switch.  If drawings are available, a sample can confirm colors and construction in cases where the membrane switch was not built to specifications.  If there are not drawings, in the case of a replacement membrane switch on a machine, a sample may be the only means available to reconstruct the schematics, match colors, and specify the layers.

Color samples provide the best method of color matching.  If an exact match is necessary, please let your sales professional know so that a sample can be provided to you for approval.

·        Pantone Matching System (PMS # # #)

·        Federal

·        The Munsell Color System

·        Color Samples – Preferred samples are 3” x 3” on polyester or polycarbonate

Production Drawings

During the design process RSPI supplies the customer with the same prints that move with the job through production, whether it is being produced domestically or offshore.  Customers can visually see each layer of the switch including key placement and circuitry.

·        Design support team ready to assist

·        Color printed proofs

Prototyping

A prototype is a cost-effective method for creating and executing your design with a minimum investment in tooling and development time.  Often there are changes in size, colors, cut out locations and shape after a prototype run.  RSPI is able to produce most prototypes with little or no hard tooling which provide significant savings.

• Rapid prototypes
• Precision laser cut prototypes
• Fast implementation of design changes and updates

Overlay Construction

Material

Polyester is the most commonly used switch material because of its durability and functionality.  Polycarbonate is also used on some projects.  Materials come in a variety of gloss levels, textured finishes and thicknesses.  It is important to choose a material that not only looks good but offers the life that you need.  If you are embossing the membrane switch or need more than 100,000 actuations use a polyester material.  Testing has shown that a polyester membrane is good for over 1,000,000 actuations.  The actual circuit can last over 5,000,000 cycles.  Therefore, the overlay is the weakest part of your switch and thus determines the overall switch rating.

Generally, for excellent tactile feel in a switch with stainless steel domes we recommend an overlay material thickness of between .006" and .008".  Thicker overlays will decrease the tactile feedback and thinner material will decrease the life.

One of our most commonly used materials in the construction of the top layer of a membrane switch is AutotexV8 for indoor use and AutotexV8XE for outdoor use.  In testing and field experience, this material has proven itself to be superior.  When comparing other membrane switch quotes, make sure you compare not only the price, but the types of material being used.  RSPI puts the types of material being used right on the bid.

Textured Background

The surface can be printed by us or supplied on the material by our supplier.  Extended use keypads should not have a printed texture since it will show wear relatively quickly in a high use environment.  If a texture is needed consider placing it around the buttons or contact points to avoid degradation.

• Pre-textured material or printed textures
• Sample finishes are available upon request

Window Finishes

Fine Textures, Velvet Textures, Satins, or Glosses

·        Custom designed patterns

·        Sample finishes are available upon request

Color Trapping

Light colors should be trapped behind darker colors in order to avoid a halo effect.

• Minimum thickness for a borderline used for trapping should be .020”
• Without color trapping, the minimum line thickness should be .010”

Embossing

Embossing is capable of greatly enhancing the look of an overlay and improving the user experience.  There are two ways to emboss.  First, you can use a male and female die.  This allows for a clean finish but has height limitations.  The second method is hydro-forming, it allows for greater embossing heights but is more expensive.  Typically, a material is embossed 1 to 1.5 times the thickness of the base material.  It is possible to emboss more than this but the durability of the keypad is sacrificed.

• Perimeter embossing requires a minimum thickness of .030”
• Key-to-key distance should be a minimum of .050”

Tactile Feel

Most membrane switch keys are built with tactile feedback.  Tactile feedback is the ‘snap’ you feel when pushing a button.  It lets the user know that they have actuated the key.  The embossing type (if any), the material, and part thickness are all important in determining the actuation force needed to activate the switch.  For instance, in a tractor where panels might be bumped, you might want the actuation force to be high.  However, in a health care setting you might want the safety switch to require a low actuation force. 

There are two types of domes that provide tactile feel, stainless steel and mylar.

Stainless steel domes are the most common.  They offer the longest actuation life and a better tactile feel.  RSPI maintains an inventory of domes ranging from 3mm to 20mm in size.

Mylar domes can be formed into the upper switch or a dome layer can be added on top of the upper switch.   

Our engineering staff will provide expert advice on the type of dome best suited for your application.

LED’s (Light Emitting Diodes)

RSPI can provide integrated LEDs on membrane switches.  Overlay base material is usually clear with gloss or matte finish.

Colors are printed on the reverse side of the overlay.  The LED window area is generally clear or translucent allowing LED light transmission. 

LED's can either be surface mounted to the lower switch or be on a separate LED layer.  

RSPI stocks a variety of colors from several manufacturers, please call for particular needs and specifications.

Overlay Adhesive

RSPI typically uses a .002” 3M adhesive on the back of the overlay and throughout the internal membrane switch.  3M adhesive is recognized in the industry for outstanding adhesion and life span.  Make sure when you compare quotes that each supplier is using 3M adhesive for both the internal and rear adhesive layers for the best possible switch.

Most membrane switches are constructed from 3M’s 200MP family of adhesives.  Internally, a .002” adhesive is typically used (3M 467).  For the rear adhesive, a .005” adhesive is typically used (3M 468).

Ask your RSPI professional for recommendations on particular adhesive qualities and uses.

Internal Construction

Upper and Lower Circuit Layer

Typically polyester with thickness ranging from .005” to .015”

EMI/ESD/RFI Shielding

Printed conductive inks, aluminum foil, copper foil or Indium Tin Oxide (ITO) is employed in membrane switch designs to minimize the impact of electromagnet interference (EMI), electric static discharge (ESD), or radio frequency interference (RFI).

Conductive Traces

Conductive Traces are generally Printed Silver or Etched, Plated Copper

• Traces usually have a minimum line thickness of .016”
• Standard line thickness .025”

Spacer / Insulator

Insulators vary in thickness from .002” to .010” and are generally polyester with double-sided acrylic adhesive.

Rear Adhesive

Adhesion qualities are affected by the substrate surface energy (high or low), types of materials used, the required bonding requirements, environmental concerns and a number of other factors.  Your sales associate will help you decide what is best.

Connectors

RSPI recommends the Nicomatic crimp connector. We have found the product to be high quality and long lasting.  We can also supply almost any standard connection method.

Nicomatic

• 0.10” pitch Male, Female, and Solder Tab
• Plating-Tin or Gold 

Berg

• 0.10” pitch Male, Female, and Solder Tab
• Plating-Tin or Gold

Zero Insertion Force (ZIF) Connector

• This connector is designed for installation of ZIF Connectors

Sub-Panel / Back Plate

Aluminum-Anodized, sealed, unsealed, dyed or un dyed.

Cold Roll Steel-Plated with, Chrome, Zinc, or other plating

Stainless Steel-Brushed, Sanded, other finishes.

Plastic Panel

Printed Circuit Board-Single or Multi-Layer

 PCB

The PCB can act as the lower switch layer. 

All other layers can be assembled above the PCB. 

Studs or standoff can be integrated into the PCB with the board acting as a supporting panel.  PCB's can also be assembled directly to housing.

RSPI does not manufacture PCB’s in house but works directly with offshore partners to supply you a complete package.

References

                    A. Die Cutting Tolerances

                    B. Electrical and Mechanical Specifications

                    C. Membrane Switch Blueprints

                    D. Glossary

A. Die Cutting Tolerances

Standard tolerances for the industry are +/- .010”

Laser cutting offers exacting standards.

B. Membrane Switch - Electrical and Mechanical Specifications

Electrical

1. Configuration – momentary SPST normally open

2. Current Rating – 30V – 100MA to 120V – 10MA maximum

3. Breakdown – 220 V RMS

4. Closed – 100 OHMS typical contact resistance

5. Open – 10 MEG OHMS contact resistance minimum

6. Capacitance – 30 Picofarads

7. Life -

a. Flat Switch – approximately 5 million cycles

b. Domed (embossed) layer – approximately 5 million cycles

c. Domed circuit – approximately 1 million cycles

d. Metal Dome – approximately 5 million cycles

8. Contacts – Silver to silver.  RSPI uses only high quality silvers since low quality silver may not last as long and may contribute to silver migration (the tendency of silver to spread or creep especially when exposed to moisture).  

Mechanical & Environmental

D. Glossary