Membrane Switch Design Guide

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DesignWhat is a prototype? Do I need one?Can Pannam assist me with my designneeds?

A prototype is a practical, cost-effective way tocreate and execute your design with a minimuminvestment in tooling and development time. If youare not certain of all final details such as size, colors,shape or hole locations for your switch, a prototypeis for you. Pannam produces prototype parts withoutmost of the “hard tooling” required for production.Pannam’s seasoned Prototype Team can help youdesign your new switch as well as produce the actualprototype.

What about production drawings?

During the design phase, Pannam produces in-house prints to be sent with the job as it movesthrough the shop. These prints can be providedto you for your reference.

How can I send electronic files toPannam and which formats do theyaccept?

Pannam supports files created in AutoCAD®,CorelDRAW® and FreeHand®. If you have filescreated in another package, there is probably aformat you can save to that we can accept. WhilePannam has an extensive library of fonts, it isrecommended that you include the fonts withyour file, particularly if you have edited them insome way. Many packages allow you to converttext to curves or paths, eliminating the need toinclude specific fonts that we may not have. It isalso helpful to send or fax a hard copy of theartwork. You can e-mail your file tographics@pannam.com or send us your CD-ROMor 3-1/2” floppy.

OverlayHow can Pannam assist me in developingan overlay that has the “right” look?

The overlay, the top layer of the membrane switch,is the graphic interface between user and machine.

While other layers make the switch work, it is theoverlay that most directly impresses your customer.To help create the desired look and feel for youroverlay, we offer design assistance from simplecolor and overlay material selection to complexdesign elements incorporating creative function-ality. Pannam offers complete, in-house graphicscapabilities, including computer graphic design,image-setting and scanning. We can incorporatea wide variety of design elements such as logos,selective textures, transparent windows, screentints, dead fronts and embossing.

How can I see what you are designingfor me?

During the design process, you will receive a colorlaser paper proof of your overlay to show colorbreaks. Exact color match swatches, on theselected overlay material, will also be providedfor approval.

What overlay materials are available fromPannam?

Pannam offers polyester and polycarbonatematerials in many gloss levels, textured finishesand thicknesses ranging from .005” - .015.” Mostsubstrate materials used in the construction of aPannam switch are UL approved.

What is important in choosing anoverlay material?

Given that the overlay is what your customer seesin the switch package, the way it looks andfunctions is crucial to a successful switch project.The most important issue after “look” and “function”is overlay durability. It is essential to insure thatthe overlay material chosen will last as long asyour specific application requires. Clearly,polyester is the material of choice for switchesthat require a large number of actuations (>25,000)or if the overlay is to be embossed. Generally,our life cycle tests show polyester keypads canbe actuated over 1,000,000 times before showingany signs of wear. The actual switch, without anoverlay in place, can last over 5,000,000 cycles.Overlays are thus the weakest link in a switch, andthe overall switch must be rated to its weakestlink. While there is more design flexibility withpolycarbonate, you should focus on polyester ifdurability is an issue.

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MembraneSwitchDesignGuide

Pannam Imaging

Pannam Imaging designs and producescustomized membrane switches used inapplications that demand the highest levelof integration, execution and reliability. Weserve many markets including medicalinstrumentation, computers, industrialcontrols, electronics and datacommunications.

Pannam has focused its competitiveexpertise on the high quality, high value-added end of the product-need spectrum.Whether you need one-of-a-kind or a run ofthousands, Pannam provides the highestquality membrane switch to meet yourspecific requirements.

How to Start the Process

Starting the process for designing amembrane switch is easy. Just begin withthe questions and answers in this DesignGuide to help direct you through eachphase. Pannam's full-service PrototypeTeam, including designers and engineers,stands ready to assist you.

Once you've worked through the DesignGuide, our Prototype Team will help youdesign a new switch as well as produce theactual prototype including a complete setof prints and specifications.

No matter what your needs are, ourprofessional designers and engineers arethere to assist you.

Embossing can be a great design enhancementto the function of a switch. For example, rail(perimeter) embossing can be used as a fingerlocator for a switch with many keypads, or aBraille pattern can be added to the overlay forthe visually impaired.

Are there any embossing limitations Ineed to be aware of?

There are certain limitations to be aware of:

Height -Typically, emboss height on a polyesteroverlay should range from 1 to 2-1/2 times thethickness of the base material. It is possible toemboss beyond 2-1/2 times material thickness,but only at a cost to durability. Heavily usedkeypads that have been embossed will mostcertainly degrade more rapidly due to a thinnerwall thickness at the point of stress.

Width - Recommended minimum emboss widthis 8 times the base material thickness. This willmaintain strength and form of the overlay.

Radius - The recommended minimum cornerradius is .032”. Completely square corners arenot possible because they will crack the overlaymaterial.

Overlay & CircuitTolerancesWhat are the tolerances for the overlayand circuit layers?

Imaging: ± .015” copy to edgeDie-cutting (Hole & Perimeter Size): ± .010” holeto edge

CircuitsHow is the circuit layer manufacturedon a membrane switch?

There are a number of methods for producingcircuit layers depending on durability, power andsystem integration requirements. Pannam offersscreen printed silver conductive ink circuits as itsstandard construction. We can also supplycopper-etched and PCB circuits depending onyour design requirements.

The silver conductive ink circuit layer is printedon .003” - .005” thick polyester and is designedto minimize overall resistance. After printing, thecircuit layer is die-cut to the proper shape to fitin the switch sandwich.

Do I have to supply Pannam with anelectrical schematic for the circuit layer?

No, not unless you have done this beforespecifically for membrane switches. It is morecost-effective to allow Pannam to do the circuitdesign. Depending on the size and shape of thepart, complexity of the electrical schematic andkeypad configuration, it is sometimes more difficultto fit all of the circuitry on a single layer. It issometimes necessary to use bridging or multiplecircuit layers to accommodate the functionalityrequired. Pannam’s Prototype Team with its yearsof experience, can make electrical schematicsuggestions to limit the number of printed circuitpasses, which will reduce the cost of the switchwith no loss of performance.

How long can the circuit tail beon the membrane switch?

The circuit tail is part of the circuit layer. Thelength of the circuit tail can be as long as requiredto terminate to other functioning parts of thesystem. The longer the circuit tail, the more basematerial and conductive ink used, which willincrease the cost of the switch and the resistance.

Pannam can also supply extension cables with orwithout connectors.

What type of circuit tail connectors doesPannam offer?

• Berg® (Standard)• CrimpFlex® (Standard)• Amp®• Molex®• Various “crimp” pins

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What overlay thickness should I choose?

For excellent tactile feedback (“feel”) in a switchwith stainless steel dome construction, choosean overlay thickness between .006” and .008.”This thickness range will be durable enough tohold up to numerous switch cycles. A thickeroverlay will significantly decrease tactile feedback(give a heavier feel).

How are the colors printed?

All the colors on the overlay are printed on therear or back surface (second surface) of the overlaymaterial using a screen printing process. Thethickness of the overlay material protects thegraphics from damage or wear by the operatoror environment. Selective textures and windowclearing agents are the only inks printed on theoutside or top surface (first surface) of the overlayand are UV cured to produce a hard, very durablefinish.

What colors are available for the overlay?

Pannam uses a computer color matching systemto help formulate any color as well as archiverecipes of colors already matched for specificcustomer applications. We can match colors fromthe Pantone® Color Selection Guide, FederalStandard Guide, European Standard Guide or acustomer-supplied swatch (minimum size - 2”square).

How can I match the background colorof my overlay to a bezel color?

The best way to do this is to have Pannam use itscomputer color matching system to take a colorreading of the customer-supplied bezel. We canthen match the switch background coloraccordingly. Note that molding process colorcan vary, and acceptable standards and rangesmust be established between you and yourmolder. Switch backgrounds will not vary asmuch and to avoid disappointment, acceptablevariations need to be agreed upon up front.

I have seen membrane switches with avelvet finish on the keypads that woreaway. How can my overlay be designedto eliminate this problem?

Selective velvet texture can be provided twoways. The surface can be printed by us or suppliedby our film producer with a velvet texture integralto the material. Clearly, extended-use keypadsshould not have printed texture on them.Alternatively, the switch can be designed to“window” the keypads so the texture ink is printedonly around the actual pad that functions. In thismanner, potentially objectionable keypaddegradation is eliminated and an attractive designelement is introduced that more clearlydifferentiates the keypad from the surroundingswitch area.

How can embossing improve the lookand function of my overlay?

Depending on design creativity, embossing candramatically enhance the look of the overlay. Itcan add to the function of the switch, as well.There are two basic ways to emboss. The first isthe conventional method, metal to metal withmale and female dies. This is fine for mostapplications, but does have height-of-emboss-area limitations that must be understood. Thesecond method, hydro-forming, has much moreflexibility but is more expensive. The choice ofone method over the other is dependent on therequirements of your design. Pannam suppliesboth methods and can help you decide whichwill yield the best results for your application.

What embossing shapes are available?

Pad The entire shape of thekeypad is raised.

Rail (Perimeter) A rim around the perimeterof the keypad is raised.

Dome The entire keypad is raisedto a spherical shape (thistype of emboss is normallyused in poly-domeconstructions).

Depending on size and shape, custom logos andmulti-level shapes can be embossed, as well.

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Pannam stainless steel dome specifications:

Size Force Travel8.5mm 9-11 oz. .015” - .019”12.2mm 11-14 oz. .020” - .024”12.2mm 16-18 oz. .020” - .024”20mm 17-23 oz. .032” - .039”30.2mm 21-28 oz. .047” - .055”

“Force” listed above is for the stainless domeitself. Other aspects of construction design willaffect actuation force or feel.

How do I know which dome to choosefor my application?

Typically, Pannam makes a proper domerecommendation based on the size of the keypad.Nine out of ten times the 12.2 mm dome is chosenand is the most cost-effective.

The overall tactile switch thickness starts at .027”.

ShieldingWhy should I include shielding in mymembrane switch construction?

Shielding is used to protect the switches fromE.S.D. and E.M.I. interference. Pannam can designa switch that incorporates the proper shieldinglayer for your specific application needs.

What type of shielding methodsare available?

Pannam uses three different basic shieldingmethods to protect switches:

1. Foil Laminated aluminum foil andpolyester.

2. Transparent Shielding required over Film windows - very expensive.

3. Printed Screen printed with silverconductive ink in a grid, bus-baror full-coating format. Typically,the grid format is chosen becauseit is very reliable and does not useas much silver conductive ink asdoes the full-coating format (lesscostly).

How do I choose between a printedshield and foil shield layer?

When the complexity of the membrane switchrequires two circuit layers (top and bottom circuit),a printed shield is more cost-effective. In thismethod, the shield is printed directly on top ofthe top circuit layer, eliminating the need for aseparate foil layer.

When only one circuit layer is required, a foilshield is less expensive than a printed shield.

Does adding a shield layer affect thetactile response of the stainless steeldomes?

The shield layer sits directly above the stainlesssteel dome plane. Typically, the shield layerthickness is between .003” and .005”. Since thelayer is so thin, tactile feedback is not significantlyaffected.

Are there various termination methodsavailable for the shield layer?

Tab The preferred method for reliability.The tab can be attached to a studor standoff on a back panel ormetal enclosure.

Connector Shield layer can be terminated intoa pin or pins on the circuit tailconnector.

Wrap-Around Shield layer can wrap completelyaround the membrane on all foursides to ground to a chassis.Although this method is veryreliable, it is more costly than theother two methods due to theadded labor necessary to execute.

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Surface-Mount LEDsPannam supplies “rigid” or “flexible” switches withembedded, surface-mounted LEDs available in avariety of colors.

Why would I choose to have LEDsmounted in the switch itself rather thanin a PCB to which the switch will bemounted?

There are several reasons. You may only haveLEDs and no other components in your switch.The mating printed circuit board may have manyother components and not enough room for LEDs.Or, the PCB may have to be located too far awayfrom the front surface to illuminate LEDs properlyat the overlay plane.

How is the L.E.D. circuit manufactured?

The LEDs are “glued” to the screen-printed silverconductive traces with a heat-cured conductiveepoxy. The LED circuit tail can terminate to itsown dedicated connector or it can terminatethrough the same connector as the keypad circuit.

Are switches with surface-mountedLEDs thicker?

Surface-mounted LEDs increase overall switchthickness by .020” - .030” due to the height of theLEDs.

Electrical SpecificationsSwitch Contact Rating 28V DC/30mA max.

Loop Resistance 100 Ohms max.

Switch Configuration SPST normally open

Surface-Mount LED Available uponSpecifications request

Contact Bounce Less than 20milli-seconds onbreak, less than10 on make

Actuation Force / DesignNON-TACTILE

Non-tactile switches can be designed with abroad range of actuation forces starting at 3 oz.Switch travel, which affects actuation force, canrange from .007” - .011”.

Actuation force is determined by the spacerthickness (layer between the top and bottomcircuit layers – see diagram above) and thediameter of the spacer hole. For example, aswitch with a thin spacer and large diameterspacer hole will have a light actuation force.

Examples of actuation choices for specificapplications:

Light Force (3-6 oz.) High-Speed DataEntry

Medium Force (10-14 oz.) Most Applications(Medical, TestEquipment etc...)

Heavy Force (16-20 oz.) ManufacturingPlant, where amachine operatormight accidentallylean or placesomething on theswitch

The overall non-tactile switch thickness starts at.030”.

TACTILE

Actuation force in a switch designed with tactilefeedback does not have as much feel flexibilityas a non-tactile switch. Using different sizes ofstainless steel domes will vary the force to meetmost requirements.

Non-Tactile Switch Construction

Tactile Switch Construction

OverlayAdhesiveTop CircuitSpacerBottom CircuitRear Adhesive

OverlayDome / Dome RetainerCircuitRear Adhesive

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Actuation Force The maximum force measured prior to or including the point at which keypad contactclosure is achieved.

Alodine A chemical conversion process that oxidizes aluminum to form a non-porous aluminumoxide. Referred to as "poor man's anodizing" because it is less costly and not as durableas anodizing.

Anodize Electro-chemical oxidation of aluminum to form aluminum oxide with a porous nature.The anodized layer can be durably colored and is non-conductive, non-corrosive andresistant to abrasion.

Arcing Discharge of electricity (a spark) that can occur when contacts are opened or closed.Arcing can degrade or burn contacts, reducing useful life.

Backlighting A flexible layer within a membrane switch construction that illuminates select areas of theoverlay, such as text or graphic symbols. Examples of backlighting methods are E.L.(electroluminescent) or fiber optic.

Circuit Functioning component (sub-layer) of a membrane switch. Typically made of a silverconductive ink printed on polyester. Also can be a flexible copper circuit, a PCB orpolyester printed with other conductive materials.

Contact Bounce Intermittent contact opening and contact closure that may occur after switch operation.

Contact Closure (Make) - Point at which specified resistance is achieved.

Contact Force The force at contact closure.

Dead Front Printing translucent ink in an area so that the graphic is visible only when backlit.

Density The degree to which light transmits through a color or transparent window. The higherthe density, the less light will be transmitted.

Dielectric Strength The voltage that an insulating material can withstand before breakdown occurs, usuallyexpressed as a voltage gradient (such as volts per mil).

E.M.I. (also R.F.I.) Electromagnetic Interference (Radio Frequency Interference). Radiated energy fromelectrical devices, lightning and similar sources which interferes with the proper operationof electronic circuitry.

E.S.D. Electrostatic Discharge – transfer of high potential electrical charge between objects bycontact or through the air.

Files Information or documentation created electronically by computer.

Font A set of characters having a unified design.

Gloss Level The degree of shininess of a particular material, usually specified in percentages such as75% gloss, 90% gloss and so forth.

Halftone Image made of a pattern of various size and shape dots (newspaper photograph) ratherthan continuous gray.

Image-Setting The process by which electronic files are transferred to film or paper directly from thecomputer (computer onto film technology).

L.E.D. Light Emitting Diode.

Membrane Switch A momentary switching device in which at least one contact is made of a flexiblesubstrate.

Glossary

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Switch BackingWhat are my backing material options?

Switches that are not mounted on PCBs or copper-etched circuits are adhesive or aluminum backed.

Pannam can provide a wide variety of adhesivebackings on switches. Primarily, it is important tounderstand the nature of the surface to which theswitch will be applied. For instance, a smoothsurface will readily accept an adhesive while apowder or rough surface will require a thicker,more aggressive adhesive. Additionally, it isimportant to understand the durability andenvironmental requirements of the switch after itwill be applied in a system to insure the properadhesive choice.

Pannam has full, in-house capabilities for shearing,bending, milling, punching and installing PEMinserts in aluminum back panels. They typicallyrange in thickness from .032” to .125”. They canbe alodined to create a non-corrosive surface, orif required, they can be anodized to create a non-conductive, non-corrosive surface that can becolored. Although alodining is usually lessexpensive, anodizing is more durable.

Notes

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Moisture Resistance Ability of a material to repel moisture either from air or when subjected to water.

Non-Tactile Switch A switch assembly that has a tactile ratio equal to zero.

Overlay Top layer of a membrane switch (the graphic interface between device and user) generallymade of polyester or polycarbonate.

Pad Emboss A raised area on an overlay, which defines an entire graphic. (i.e., a full keypad or L.E.D.window).

Proof A paper simulation of what a screen-printed overlay will look like, submitted to a customerfor approval.

Polyester Dome A keypad on a membrane that has been dome-embossed on the overlay or top circuitlayer to add tactile feedback when the switch is activated. The dome shape, which isusually formed by a hydro-forming process, can vary in size and shape to achieve adesired “force” and “tactile feedback” of the keypad.

Prototype Tooling Method of fabricating prototype components without using steel rule dies (hard tooling)allowing changes before production runs without expensive tooling charges.

Rail Emboss A raised area on an overlay which defines the perimeter of a graphic. (i.e., perimeter ofa keypad or a border).

Schematic A drawing showing electrical interconnections and functions of a specific circuitarrangement.

Screen Printing Method of printing by forcing ink through a mesh selectively. This is done by closing partsof the mesh with a stencil.

Screen Tint Area of image printed with dots so ink coverage is less than 100%, simulating shading ora lighter color.

Selective Texture A transparent velvet finish printed on specified areas on an overlay to accentuate designelements such as windows, keypads or graphics.

Shield A layer of polyester material that is either laminated with aluminum or printed withconductive ink to protect a switch from E.S.D. or E.M.I. interference.

S.M.D. Surface Mount Device.

S.M.T. Surface Mount Technology.

Specified Resistance Maximum allowable resistance measured between two terminations whose internal switchcontacts, when held closed, complete a circuit.

Sub-Surface Printing Imaging on the back (second surface) of an overlay so the printed graphic is protectedfrom wear by the actual material.

Tactile Ratio A measure of tactile response.

Tactile Response A sudden collapse or snapback of a membrane switch prior to contact closure or aftercontact opening.

Tactile Switch A switch assembly that provides a tactile ratio greater than zero. Tactile switches give theuser immediate physical feedback that the switch has been activated. Tactile feedbackon a membrane switch can be achieved by using a stainless steel dome or a polydomeconstruction.

Termination How a switch is connected to the device it activates.

Translucent Partially transparent. Having the property of diffusing light.

Transparent Having the property of transmitting light without appreciable scattering so that objectsbeneath are entirely visible.

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Hard-working. Creative. Full-service.The "easy-to-do-business-with" membrane switch supplier.

From preliminary idea to custom membrane switch,it's a team effort at Pannam.

18531 South Miles RoadCleveland, Ohio 44128

1.800.482.7758 • FAX 216.587.0358e-mail: sales@pannam.com

PANNAM IMAGING