Frequently Asked Questions
Below you will find some frequently asked questions that come up from time to time in conversation with our customers. If you need any clarification please feel free to contact us.
- Tactile Metal Domes
- Dome Retaining Tape
- Printed Circuit Board
- Surface Mount Device (SMD) LEDS
- LCD Display
- Graphic Overlay
- Spacer Layer
Tactile Metal Domes
Q: What are the typical metal dome sizes?
A: Typical dome sizes are 8mm, 10mm, 12mm, and 14mm.
Q: What are the typical metal dome actuations (tactile feel)?
A: Typical dome forces range from 85 grams to 700 grams.
Q: What are the different force specs for domes used in user interfaces?
A: There are three different force specs.
- Critical Buttons: These would have critical functions and should provide a higher tactile feel. These keys typically have a high actuation force, usually around 400g and a high snap. With these types of keys the web life is limited due to the snap and high force of the domes.
- High Frequency Buttons: These would be pressed often and should provide a lower tactile feel for easy, quick pressing. These keys typically have a low actuation force around 125g.
- Typical Buttons: These are in between critical and high frequency buttons which relates to most user interfaces. These keys typically have a medium actuation force somewhere between 150g and 250g with a medium snap.
Q: How many actuations can domes withstand?
A: Normally domes can withstand 100,000 presses or less. Some applications require one million or more presses. Epec can design and assemble user interfaces with most available actuation requirements.
Q: What type of dome works better in higher temperatures?
A: Stainless steel domes preform the best in higher temperature applications.
Dome Retaining Tape
Q: What are dome retaining tapes used for?
A: Dome retaining tape is used during the manufacturing process to secure the domes switches to ensure proper placement is maintained throughout the process of building up the layers that make up the user interface.
Q: Do dome retaining tapes impact the height of the final assembly?
A: Typically dome tape is a very thin (0.001”) polyester material to have minimal impact on the overall thickness of the user interface.
Printed Circuit Board
Q: How is a printed circuit board used in HMI applications?
A: Rigid printed circuit boards are used in human-machine interface applications when a high circuit density is required.
Q: What is the advantage of using rigid circuit boards instead of a flexible conductive layer?
A: Flexible user interface assemblies are constructed using polyester sheets and cannot tolerate soldering temperatures. Replacing the polyester layer with a rigid PCB allows components to be soldered directly onto the circuit board.
Additional advantages include:
- Electronic components can be incorporated into the keypad assembly, these include LEDs, resistors, capacitors, diodes, and even integrated circuits can also be mounted to the rear side of the printed circuit.
- Electronic components can be directly soldered to the printed circuit board, thereby eliminating potential intermitted or open circuits caused by external stresses.
- Keypad interconnections to the application's electronics are greatly expanded as a wide variety of connectors can be soldered on the rear surface of the printed circuit board through cutouts in the metal support plate.
- A lot of connector styles can be selected to include high density, through-hole, surface mounted, polarized, latching, or shielded.
Surface Mount Device (SMD) LEDS
Q: What are the different types of LED's available?
A: There are various types of LED’s available.
- Miniature LED's: Used in mobile phones, television sets, and a range of digital devices. They are usually available in market on a predefined, standard size, and shape. This is to ensure its compatibility with different circuit boards. Different companies manufacture these LED’s in 5V and 12V ranges. They come in a “ready to fit” mode which can mount on circuit boards directly. Usually they don’t need support of any additional cooling systems like a heat sink.
- High Power LED: Capable of producing light output with higher luminous intensity. High power LED’s come in different shapes and sizes. A common example of a high power LED in daily use is "LED strips" that are used in light walls and room interiors.
- Application Specific LED (AS-LED): These are LED’s which are manufactured for a particular application in mind. Some examples are digital billboards, public displays, bi-color and tri -color LED’s.
* Note: A tri-color LED is similar to bi-color LED. It is 2 diodes mounted on a single frame with 3 pins. Another type of LED in practical use is RGB (Red, Green, and Blue) LED’s.
Q: What different types of termination connectors are commonly used?
A: There are various types of connectors used. Below are some of the most common.
- Berg Connector: A Berg connector is a brand of electrical connector. Berg connectors are manufactured by Berg Electronics Corporation of St. Louis, Missouri, a division of Framatome Connectors International. Berg connectors have a 2.54 mm (=.100 inch) pitch, pins are square (0.64 mm x 0.64 mm = approx.).
- Nicomatic Connector: A Nicomatic connector is a brand of electrical connectors. Specifically a manufacturer of standard and special electrical connectors for harsh environments.
- Amphenol Connector: Is a brand of connector made primarily by Amphenol Corp. Typically used in military and aerospace applications.
- Tyco Connector: Is a brand of connector made primarily by Tyco Electronics. Tyco offers an expansive portfolio of interconnect products across an array of industry applications.
- Zero insertion force (ZIF): Is a type of IC socket or electrical connector that requires very little force for insertion. With a ZIF socket, before the IC is inserted, a lever or slider on the side of the socket is moved, pushing all the spring contacts apart so that the IC can be inserted with very little force. Generally the weight of the IC itself is sufficient and no external downward force is required.
- Molex Connector: A Molex connector is the vernacular term for a two-piece pin and socket interconnection pioneered by Molex Connector Company. The two-piece design became an early electronic standard.
Q: What is the normal spacing (pitch) between each connection?
A: Spacing is normally between .5mm to 1.0mm
Q: What is a LCD display?
A: A liquid-crystal display (LCD) is a flat-panel display or other electronic visual display that uses the light-modulating properties of liquid crystals. Liquid crystals do not emit light directly.
Q: What are some advantages to using an LCD display?
A: Below are some advantages to using an LCD display.
- Very compact and light.
- Low power consumption. Depending on the set display brightness and content being displayed, the older CCFT (Cold Cathode Fluorescent Tubes) backlit models typically use 30–50% of the power a CRT (Cathode Ray Tube) monitor of the same size viewing area would use, and the modern LED backlit models typically use 10–25% of the power a CRT monitor would use.
- Very little heat emitted during operation, due to low power consumption.
Q: What is a graphic overlay?
A: A graphic overlay displays the cosmetic portion of a user interface assembly such as color, text display windows, key functions, etc. They act as intermediary between the user and machine by depicting functions, with no conductive traces or circuitry.
Q: What are typical materials used in graphic overlays?
A: Graphic overlays are available in both polyester and polycarbonate materials. Data regarding the advantages and disadvantages of materials above can be found in our HMI Design Considerations Ebook.
Q: What options are available with graphic overlays?
A: Options and applications for graphic overlays can include textured, smooth, embossed, digital printed, as well as screen printed in various thicknesses.
Q: What adhesives are used in HMI assemblies?
A: Adhesive selection depends on the mounting surface finish.
Q: What are typical materials used for adhesive layer?
A: Both Low and High Surface Energy adhesives available.
Low Surface Energy (LSE) adhesives are designed to bond to hard to stick to surfaces such as plastics, polypropylene, polyethylene, polystyrene, thermoplastic polyolefin, EVA, PTFE, powered coated paints, and oily metal surfaces.
Epec recommends the use of 3M 300LSE and 4952 VHB adhesive for LSE surfaces.
High Surface Energy (HSE) adhesives are designed to bond to substrates such as steel, aluminum, polycarbonate, polyimide, polyester, PVD, acrylic, and rigid polyurethane.
Epec recommends the use of 3M's 467 MP and 468 MP adhesives for all HSE surfaces.
A mounting surface energy material identification table can be found in our HMI Design Considerations Ebook.
Q: What is a spacer layer used for in an HMI application?
A: A spacer layer is an insulated non-conductive material with openings at switch locations to separate the upper and lower circuit layers.
Q: Should the spacer layer be the same size as the overlay?
A: Yes, the spacer layer should be the same size as the overlay in both height and width. However, all spacer layer cutouts and holes should be .030" larger than the overlay, UNLESS SPECIFICALLY USED IN MOUNTING OF HARDWARE. Also, the spacer layer cutouts behind windows should be .060" larger than the window.
The above guidelines ensure the spacer layer in not visible after assembly.
Q: What materials are typically used in spacer layers?
A: Polyester is the most commonly used material for a spacer layer in user interface applications.