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GRAPHIC MATERIAL The two most common materials used in the manufacture of labels, overlays and membrane switch graphic layers are lexan polycarbonate and polyester films. These materials are available in a variety of of finishes. These begin as clear materials with the graphics generally printed on the reverse side ("2nd surface") of the product. Selective textures are printed on the front side (1st surface) of the product to allow for clear LED/LCD windows and are also used to create special graphic effects.
CSA, UL, and other specification labels are generally produced using either polycarbonate material, or one of the many materials available for 1st surface printing. Labels which are 1st surface printed are generally more cost effective as they have a background colour and adhesive layer incorporated into the material. POLYESTER Polyester is fast becoming the material of choice in membrane switch overlay applications that require longer switch "life", higher chemical resistance, or tactile feedback from a "poly-domed" graphic layer. Like lexan, this material offers a combination of clarity, dimensional stability, toughness, flexibility, heat resistance, and excellent dielectric performance, however it is somewhat more difficult to process. The full line of polyester films is available in various finishes and thicknesses.
LEXAN (POLYCARBONATE) Lexan polycarbonate has been used in the production of overlays and membrane switches for many years. This material offers a combination of clarity, dimensional stability, toughness, flexibility, heat resistance, and excellent dielectric performance. The full line of Lexan films is available in various finishes and thicknesses. Bayer Polycarbonates
High Chemical Resistance MEMBRANE SWITCH LAYER MATERIALS Membrane Switches are produced by laminating various layers of material together. The circuit layers are produced using heat stabilized polyester. Spacer layers for circuit separation are produced using a polyester layer sandwiched in between two adhesive layers. Note that when specifying an adhesive. It is necessary to specify the adhesive used in the spacer layer, as well as that which adheres the membrane switch to the component housing. Some vendors may quote based on 3M adhesive on the bottom only, and use a different type of adhesive in the spacer layer.
ADHESIVE MATERIALS PadTech Industries Ltd. incorporates 3M materials into the majority of their products. However, competitive materials are used in situations which are highly cost sensitive. When using substitute materials, we make sure they meet all the environmental and functional needs which may be required for the project.
SPACER STOCK
PREMASK Overlays and Membrane Switch Graphic Layers, which have windows for LED/LCD readouts, may be scratched during processing, handling, or assembly. It is wise to specify a premask material, which has a low tack adhesive, be laminated behind all windows. This material will protect windows from being scratched and is easily removed before final lamination to the product housing. Premasks are available in paper and plastic, with various levels of adhesion. TAIL COVER MATERIAL The tail of a membrane switch can be protected by two methods: 1. A .001" thick polyester laminated to the tail before die cutting the switch. This process adds scratch resistance to the printed trace on the tail. Laminated polyester is often used when the tail exits through a slot in metal backing plates. 2. Protective printed dielectric topcoat. This is the most cost effective when used on a matrix circuit as the dielectric is already being printed as jumpers. SWITCH DIMENSIONING
DIMENSIONAL TOLERANCES Standard tolerances for the industry are +/-.010" on all dimensions. With steel rule dies it is possible to hold tolerances of +/-.005" under most conditions. Matched male/female tooling can hold even tighter tolerances; however, tooling and production costs can be much higher using this method. It is advisable that only the most critical dimensions are given tight tolerances in order for products to be efficiently manufactured. CLEAR WINDOWS Overlays and Membrane Switches are often placed over LED Indicator Lights and LED/LCD Displays. The material is left clear in these areas to create "windows" through which LED's and LCD's can be viewed. During production it is necessary to die cut the adhesive away from these areas prior to lamination in order to leave these "windows" clear. When specifying a product, the number and size of all clear windows must be defined so that tooling can be engineered correctly. Note: If a number of round LED holes are placed close together, tooling for the adhesive can consist of several round holes or a rectangle which surrounds all holes (this method is more cost effective). **See Drawing. THROUGH HOLES Any areas in an overlay that are die-cut through all the material layers are called "through holes". When specifying a product, the number and size of all through holes must be defined so that tooling can be engineered correctly. Round Holes Contact PadTech Industries Ltd. for a list of standard punches that exist for die cutting round holes. Using these to standard sizes to specify hole diameters will reduce die cost and ensure better adherance to specs. CORNERS Overlays and Membrane Switch Graphic Layers are produced in virtually any shape imaginable. The parts are die cut from bigger sheet sizes using steel rule dies, lazers, knives, or hard steel tools. Their shapes range from simple rectangles, to triangles, ovals, or even "horseshoe" shapes. Note that if parts have square corners, they can be nested against each other when tooling for production. Parts with round corners or non-rectangular shapes must have .15" - .35" spacing in between them (depending on the thickness of the material being cut). COLORS It is possible to specify colours by providing a reference from either the "PMS" (Pantone Matching System) or any other colour matching system. Samples of colours to match can also be provided in many forms. For example: existing labels, plastic housings, colour chips, or painted metal work. It is important to note that all colour recipes will appear to change when printed onto different materials. If a change is made in texture or base material, always be sure to adjust the colour recipe to match the original. PANTONE MATCHING SYSTEM (PMS COLORS) Pantone, Inc. is the world-renowned authority on color and provider of color systems and leading technology for the selection and accurate communication of color. The PANTONE Name is known worldwide as the standard language for color communication from designer to manufacturer to retailer to customer. Whether you are creating a logo, a product, packaging, an ad, the latest fashion trend or a vision, we have the tools and solutions for keeping your colors accurate and consistent cross-media, around the world. The PANTONE Color language is the most universally understood standard available. TEXTURES For clarity and legibility, materials with smooth finishes are used for overlays that have LED or LCD displays behind them. These materials can be selectively printed on the 1st surface using a UV curable hardcoat texture. The selective texture will help hide fingerprints or smudges, and can be used to create graphic effects on the 1st surface of the product. Matte finishes are the most common texture used; however, many types are available. It is suggested that texture not be printed over switch contact areas. Textures printed over contact areas will break down, become cloudy and crack over time due to the stress of a switch activation. DEADFRONT Deadfront is the printing of a Translucent ink, (usually black but can be achieved with other colors), over a window, allowing the window to be visible only when it is "back lit". Note that all color recipes will appear to change when printed onto different materials. If a change is made in texture or base material, always be sure to adjust the color recipe to match the original. NEMA Seal When designing a membrane switch that will be used in harsh environments, the circuit portion of the membrane switch can be completely sealed within the assembly. EMI/RFI ShieldingAutoShield has been specifically designed to offer a cost effective and reliable method of shielding membrane switches and keyboards from emitting or receiving unwanted airborne electro-magnetic interference (EMI).
TYPE OF CIRCUIT COMMON BUS Mapping the traces for this layout uses one common lead (ground) for all switch locations. Each switch has a single isolated trace that completes the circuit with the common trace. The advantage of this is that only one print is required for a complete trace. The disadvantage is the need for a larger number of leads, connectors and switch size.
MATRIX Mapping the traces for this layout uses leads that run in both the "X" (rows) and "Y" (columns) directions. The advantage of this is that less leads are required to produce a greater number of connections. The disadvantage is the need for multiple prints to produce the trace.
CONNECTORS
RUBBER KEYPADS
EMBOSSING Embossing is used to:
The graphic layer can also be embossed using a doming technique. Polydomes® can also be used. 
LEDs ABSOLUTE MAXIMUM RATINGS FOR LEDs CURRENTLY AVAILABLE
SWITCH EMBEDDED LED CROSS SECTION
TACTILE FEEDBACK Feedback Feedback, in the case of a membrane switch, refers to the response directed back to the operator once a switch has been engaged. Non-tactile vs. Tactile The advantages and disadvantages are:
Shorting Pads Silver or Carbon/Silver Conductive Pads can to printed on the second surface of an overlay in order to create a membrane switch type shorting pad above a printed circuit board. Contact Force Also known as the Trip Force, Actuation Force and Activation Force, refers to the amount of pressure needed to activate the switch. Various trip forces can be achieved by, in the case of a non-tactile switch, using a thicker spacer material or printed dielectric or with a tactile switch the use of metal domes at various "trip forces", 10oz, 12oz, and 14oz for example. The graphic layer can also be embossed using a doming technique. Polydomes® can also be used.
TYPICAL SWITCH SPECIFICATIONS
TYPICAL SWITCH SPECIFICATIONS
LABEL MATERIAL (1st SURFACE PRINT) Following is a list of the most commonly used material for 1st surface printed labels. Both UL and CSA approve PadTech Industries Ltd. to produce specification labels on the following materials.
UL REQUIREMENTS: View More Details Serializing Labels and overlays can be pre-serialized if desired. 3M 7980 and 3M 7983 are 1st surface serialized, polycarbonates and polyesters are 2nd surface serialized. Be sure to provide for a light background in the area to be serialized. BACKLIGHTING Electroluminescent LampsRecent major advances in materials and electronics technology, as well as new demands on lighting technology from the marketplace have provided the opportunity for a fundamental shift in the role of electroluminescent (EL) technology. The main characteristics of EL are:
ELECTROLUMINESCENT LAMP SPECIFICATIONS COLORS
ELECTRONIC DRIVERS
Fiber Optic Backlighting
THRU CUT Thru cut labels are die cut into individual pieces. KISS CUT ON SHEETS A "kiss" cut is a cut that goes through the material and adhesive, but does not cut through the adhesive backing paper. This process is especially advantageous with smaller labels as it leaves the labels in full sheets that can be easier to inventory. It is also easier to remove smaller labels from the adhesive backing paper if supplied in sheets. PRECISION DIECUT MATERIALS Precision diecut materials, those that are cut to fit a specific size and shape, are often required for insulation, shielding, gasket, or spacing purposes. The types of materials used in vary depending on the function that they must perform. Following are some of the materials often used in this process: NOMEX-ARAMID PAPER TYPE 410: A calandered insulation paper which offers high inherent dielectric strength, mechanical toughness, flexibility and resilience. Type 410 is used in almost every known electrical sheet insulation application. PORON-SILICONE FOAMS: Ideal for fire and heat resistant pads and seals, high temperature gaskets and cushions, as well as radiant heat shields. This material is available in a variety of combinations (with and without adhesive) to handle high radiant temperatures, fireblock performance and other requirements. PORON-URETHANE FOAMS: Used in a broad range of design solutions for gasketing, sealing, and energy absorption. Outstanding compression set resistance, lower outgassing to minimize trace volatiles, low fogging And flame retardance that meets Motor Vehicle Safety Standard MVSS 302, and UL 94 HBF. FORMEX GK: Flame retarded polypropylene sheet is used in many demanding barrier applications. Is non-hygroscopic, therefore problems related to moisture are eliminated. KAPTON-POLYMIDE FILM: Is used for a variety of applications where excellent physical, electrical, and mechanical properties over a wide temperature range are required. Kapton films are available in a number of formulations, depending on the projects requirements. Other common die cut materials are polycarbonate, polyester, adhesive and spacer sheets (see specifications). Formats to Send Specifications In TYPES OF ELECTRONICS FILES Padtech Industries Ltd can utilize many of the vector drawing program formats:
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