The Evolution of Membrane Switches in Today's Electronic Markets.
Updated: Feb 4, 2019
It was 1978 and a couple of my siblings and I were watching the four-channeled television with tin-foiled antennae while de-slugging spacers for some new technology called a membrane switch. You see, my dad had owned a successful screen printing company for years but had only recently been introduced to membrane switches by some associates at Rogers Corporation. They approached him and said that they were making these membrane switches, but really a company like his was probably better suited to do them long term. They wanted to know if he was interested in trying to make membrane switches. Just like that, Dad went from printing decals, nameplates and fleet marking to making membrane switches, and the rest of the family got pulled along whether we liked it or not. Who would have guessed that forty years later my career would be defined by membrane switches and touch screens?
I mentioned “de-slugging” above. What that means is the removal of vent channels and spacer holes that keep two conductive screen-printed silver pads and traces apart, so they don’t make contact and create an electrical short. This was the method used in 1978 and is still the primary way of isolating electric circuits. The de-slugging process was tough and takes a lot of time. Many companies have either developed equipment to help expedite this process, or they have moved the labor-intensive assemblies to low country cost centers. Membrane switch production is very labor intensive. To put this in perspective, there are set-ups for every layer of a membrane switch. If a graphic overlay has 5 colors, there are 5 set-ups for the printing processes. If there are two circuit layers, then there are set-ups to print and die cut those layers, as well as the spacers. You can see how this adds up very quickly. To combat those costs and maximize the membrane switch value, VEXOS turned to China in the late 1990’s for production of their membrane switches.
Membrane switches have come a long way since 1978. They were first introduced in 1973, but it took many years before the technology totally caught on. The global Membrane Switch market is expected to reach USD 13.14 billion by 2025, according to a new report by Grand View Research, Inc. In the beginning membrane switches were simple, non-tactile circuits separated by a thin spacer layer. These switches would achieve 1-2million cycles before breaking down. Eventually the market asked for tactile feedback on switches and this was answered by adding stamped metal domes or thermo-forming poly-tactile domes. Initially these technologies were fraught with issues. The metal domes would be placed on top of the circuits and sometimes the circuit would close before the dome clicked, or the dome would click, and the circuit would not actuate. This caused frustration and damage by the customer. Poly-domes weren’t much better. The early poly-domes were mushy and had a very short life cycle of 250,000 cycles before they would break down.
The interface of choice for a multitude of applications
With the large number of user interface options available today, it is easy to forget why the membrane switch is an excellent choice for instrumentation. The basic advantages are still the same as they were two decades ago, when membrane switches became the interface of choice for a multitude of applications, such as consumer products, medical devices, high-end appliances, industrial controllers, and automotive controls. These applications have been enhanced by developments in materials, processes, and design expertise.
Membrane switch applications are well suited for a multitude of electronics, which are limited to a specific or small number of functions, are portable, and require a high degree of visibility. Membrane switches are particularly suitable for handheld applications and portable devices because they are lightweight, low profile, durable, easy to clean, and RoHS-compliant.
Six key features
We focus on the six key features of membrane switches that contribute to the optimal design of any user interface electronic product.
The biggest advantage of a graphic overlay on any device instrument is its ability to be seen in a 180° radius. Warning lights or other functional indicator lights can be viewed from a distance at various angles. As the top layer of the membrane switch, the graphic overlay is the direct interface between the product and the end user. Besides the obvious function of defining the switch locations and functions, it can also serve purposes of product enhancement and differentiation. With an essentially unlimited color palette, the graphic overlay can provide aesthetically pleasing yet highly functional characteristics to the product. Very simple color and artwork adjustments provide low-cost model or functional differentiations even though the lower switch layers remain constant, which can help to keep total program costs down.
Hard coated overlay materials have excellent resistance to adverse environments. Selective applications of texture coatings provide durable and pleasing background and interface areas, while allowing lower layer displays to be highly visible and undistorted. In addition, lower layer displays, and LEDs can be hidden using appropriate dead fronts and transparent colors. Embossing may be used to give the panel a three-dimensional look and feel.
Membrane switches can easily provide protection against electrostatic discharge (ESD). An inner layer of the switch assembly can take such discharges to ground. Innovative uses of double-sided polymer circuitry (D/SPC®) can provide the path to ground as part of the switch circuitry, thus eliminating the need for extra shield tails or tabs. The use of D/SPC can also help to reduce the footprint of the switch circuit, eliminating potential problems with discharges to the edges of the membrane panel. This shield layer can simultaneously provide EMI/RFI protection. Printed shield layers can be tailored to each unique application to provide optimum shielding effects and prevent unwanted interference from incoming or outgoing signals. Shielding can generally be accomplished without compromising the performance or aesthetics of the switch.
One of the biggest threats to any type of user interface is the risk of water or chemical ingress into the switch cavity. A membrane switch can be sealed against various types of environments typically used in a portable handheld environment. This can be achieved with a full perimeter seal or gasket within which the circuit tail exit is routed. With the proper design and material choices, not only can the switch array be sealed against the environment, but it can also seal the enclosure to which it is mounted. The sealed membrane switch can also provide highly visible status indication through the use of low profile surface mounted LEDs.
There are two common and proven methods of illuminating a membrane switch: LEDs and electroluminescent panels. The LED is a very effective way of communicating — either close or at a distance — a device status, even at oblique angles and differing light conditions. Advances in polymer surface mounted technologies, as well as commercially available low-profile LED packages, offer a reliable and effective way to incorporate status indicators into a membrane switch. The combination of chip bonder and conductive epoxies provide the strength and conductivity necessary to attach .010"-tall LEDs to flexible polymer circuits. LEDs are best suited for status indicators but can be adapted to provide backlighting. This becomes a design challenge as the overall height of the switch is increased when using LED backlighting.
Electroluminescent (EL) lamps are not interchangeable with LEDs for lighting purposes. The EL lamp is most appropriate for backlighting in low light situations. It is not suitable as an indicator light or in daytime or bright light conditions. The advantage for backlighting is an even light source (no point source of light is evident) and can be provided in a very thin layer. Typical EL thickness is approximately 0.010".
5. Tactile Feedback
Tactile feedback enhances error-free data entry and can be achieved with two different materials. Metal dome constructions are used for high reliability applications where a high number of actuations and extreme temperature cycling is anticipated. Metal domes are offered in a variety of sizes, shapes, and actuation forces. A second option is a formed polyester dome. Actuation force is highly customizable with this approach because there are numerous combinations of dome heights, sizes, and shapes. With either material, the user confirms switch closure by “feeling” the switch dome collapse, which acts as a shorting patch to close the switch loop.
6. RoHS Compliance
As RoHS compliance is a requirement for most electronic devices built today across multiple industries. Typically, there are no banned substances in the basic building blocks of membrane switches if screen printed conductive inks are used. Pressure-sensitive adhesives, the polyester film used for the substrate, and the inks used for graphics are generally free of restricted substances as well.
Choosing Vexos as your Membrane Switch partner
The membrane switch industry has come a long way since those early days. At VEXOS, we now have flat non-tactile switches that will exceed 10,000,000 actuations. Our metal domes come in an array of actuation forces and are formed to be placed directly on the circuit ensuring a consistent make/break of the switch and dome. VEXOS and our supply partners have developed a unique poly-tactile graphic layer that provides outstanding tactile response, reduced material usage and a life expectancy of 2 million cycles. We have also developed proprietary epoxies to place LED’s and 7 segment displays directly on the membrane circuits. Our switches can be terminated with open tails coated in carbon or with male or female clincher connectors.
I can assure you that in 1978 I never dreamed that my career would revolve around the membrane switch and touch screen industries. With that said, I am thrilled to have been a part of the technologies evolution and the growth of the industry.
VEXOS’ engineers are capable in helping take a concept to a finished product and are ready to help. By designing the switch and tooling in house, manufacturing all hard tools, steel rule dies and embossing tools in house we can provide the most reliable parts at a competitive cost with industry leading delivery times. Touch the Future with VEXOS.
For more information on Membrane Switches Contact VEXOS today!
or Call 855-711-3227
Vexos, is a mid-size global Electronics Manufacturing Services (EMS) and Custom Material Solutions (CMS) company, providing complete end-to-end supply chain management solutions in electronic and mechanical products for Original Equipment Manufacturers (OEMs) and new emerging technology companies.
Vexos services extend over the entire electronic product life cycle, from value engineering services for product development to prototyping and New Product Introduction (NPI) through to the growth, maturity and end-of-life phases with a strong focus and commitment to quality and customer service satisfaction.
With manufacturing facilities in LaGrange Ohio United States, Markham Ontario Canada and 2 locations China. Vexos can efficiently compete in today’s marketplace, primarily focus within automotive, industrial, networking, communication, medical and security market segments. Vexos enables their customers to focus on their core business, reduce your cost, speed your time-to-market and gain a competitive advantage.