Integrated electronics make for sleek, smart surfaces

That's a lot to pack into a compact device, and polymer materials will play a key, enabling role.

A number of firms are working to advance this technology, which is gaining in popularity for a number of reasons. One estimate suggests that in-mold electronics can be up to 70 percent lighter in weight and 90 percent thinner than conventional constructions. This in turn offers significant design freedom to those creating new products. And one cannot underestimate the current demand for surfaces that eliminate cracks and crevices that can harbor germs and bacteria.

A report last fall by research firm IDTechEx noted that in-mold electronics (IME) "is most applicable to use cases that require a decorative touch-sensitive surface, such as control panels in automotive interiors and on kitchen appliances. It enables a 3D, smooth, wipeable, decorative surface with integrated capacitive touch, lighting and even haptic feedback and antennas."

A couple companies active at the forefront of ongoing development in these areas include custom graphics manufacturer DuraTech Industries of La Crosse, Wis., and pressure former and tool maker Niebling GmbH of Penzberg, Germany.

For 44 years, DuraTech has provided decorative and functional identification products to OEMs worldwide. About a dozen years ago it began combining printed electronics and the in-mold decorating process to create new interface products that can incorporate capacitive touch buttons, integrated light displays and the like, said Paul Hatlem, the firm's sales manager, in a recent phone interview. Home appliances and medical devices represent the biggest markets for DuraTech, which says the automotive sector currently accounts for about 10 percent of its business.

Niebling, meanwhile, is at the other end of the spectrum, market-wise, with automotive accounting for some 90 percent of its business. Founded in 1984, the firm is known for its toolmaking and high-pressure forming (HPF) process. Douglas Gray, a Scotland-based sales executive focused on developing the Asia Pacific market for Niebling, notes that its IME interface products are in many major automakers’ vehicles on the road today.

"Electrification and autonomous driving have rewritten many of the design rules" in vehicles, Gray said in a Feb. 16 phone interview. "They still have four wheels, but the cockpit has changed dramatically. IME will address some of these needs."

Gray's Niebling colleague, Sales and Marketing Director Udo Weustenhagen, noted that the pandemic has accelerated the development of certain types of components. Automakers, for example, now are keen to incorporate parts with closed surfaces that are easy to clean and disinfect. One leading German OEM, he noted, is pushing ahead aggressively now with integrated molded electronics on its steering wheels. The aim increasingly is to use IME to replace mechanical switches for applications such as for volume and cruise-control buttons and climate-control panels.

With its large production volumes, the automotive sector often forges the way with adoption of emerging technologies. That sector also appreciates the opportunity to reduce weight and add distinctive design features.

But, at the same time, Gray said Niebling recognizes the growth potential of other sectors, particularly appliances and consumer electronics. Certainly, the explosive growth of smartphones has helped to make users much more familiar with technologies such as capacitive touch.

An attractive appliance market

DuraTech, meanwhile, produces about 5 million parts a year for the appliance market. The firm took its first IME interface project into commercial production last year. When it comes to appliances such as washers and dryers, Hatlem said, the use of such technology allows the product designers to move the printed circuit board (PCB) away from the user interface. The resulting IME component is about a tenth of the size of the traditional, flat PCB and enables the use of three-dimensional surfaces.

Many OEMs in such sectors are reluctant to be early adopters of emerging technologies such as the capacitive touch used with IME parts. "We're pushing appliance makers to adopt IME," Hatlem said. "But few want to be first." 

To that end, DuraTech is building a full-size demonstrator in the shape of an appliance part that measures roughly 27 by 7 inches. The aim is to provide a device that can help to familiarize engineers with all the technology has to offer.

Medical device makers also see the potential advantages of IME but have been slow to adopt due to liability concerns. Such equipment needs to have fail-safe buttons that cannot be turned on or off inadvertently by accidentally bumping or touching them. So, Hatlem explains, for such applications they often need instead to create a system of press and hold, pressing a combination of buttons or using pressure-sensing technology.

One of the newest, most advanced demonstrator devices was unveiled recently at the CES show by German materials giant Covestro AG. Dubbed the Nighthawk Demonstrator, it showcases in a single device ­­many of the features made possible with this technology.

Developed via Covestro's ongoing partnership with Finland's TactoTek®, the Nighthawk is meant to show how such capabilities can be achieved using polycarbonate (PC) resin and PC film to produce smart, interactive and eco-friendly surfaces. TactoTek is well known for its pioneering work creating in-mold structural electronics (IMSE®).

IMSE manufacturing consists of four primary processes—printing, surface mounting, thermoforming and film-insert molding. Decoration, circuitry, touch controls, antennas and proximity sensors are printed onto a film insert material, and then electronic components are mounted to the substrate using conductive and structural adhesives. The flat electronics film is given a 3D shape via thermoforming, and that formed structure is then insert molded. 

John Skabardonis, who heads Covestro's technical marketing for electronics in North America, describes the Nighthawk Demonstrator as being "like an Oreo" cookie. That's because the firm's Makrofol® PC film forms both a top and bottom layer on the device, sandwiching a layer of its Makrolon® PC resin in the middle that bonds everything together. The top layer is decorative, while also providing resistance to scratches, water and harsh chemicals. The bottom layer serves as the electronics carrier. The middle resin layer, meanwhile, provides structure, as well as optical qualities (transmitting light from LEDs within the structure) and encapsulates the sensitive electronics, protecting them from the environment.

Covestro says the high clarity, low viscosity and process consistency of its Makrolon resins make these devices possible, while its Makrofol PC films lend the demonstrator UV and scratch resistance.

The Nighthawk features electronics for wiring and touch controls that are printed on the electronics carrier film. Electronic components are surface mounted on the same PC film, which, along with a decorative film is inserted into an injection mold for encapsulation in the resin. This process, says Covestro, yields a single-piece, seamless, electronic structure. The last step in the process consists of optically bonding an organic LED (OLED) screen under the sandwich construct – a task which requires specialized know-how.

The result is a thinner, lighter, yet durable device that features integrated electronics, including hidden-until-needed back-lit icons. The design also features a capacitive touch slider and allows for a proximity sensor, which would enable the user to turn the device on or off by simply hovering a finger close to the surface. This would eliminate the need for an on/off switch. The ability to deliver so much functionality while eliminating gaps in the surface is vital, he notes, as it reduces places for germs and bacteria to hide – a factor that is increasingly important for obvious reasons during today’s pandemic-challenged times.

The Nighthawk demonstrator shows how such constructions can reduce the number of component parts of electronic products while also lowering the amount of plastic used by up to 70 percent compared to conventional electronics, resulting in devices that are thinner and 50-70 percent lighter.

The all-PC, monolithic structure, meanwhile, not only bonds together exceedingly well, but it also offers positive end-of-life aspects such as an improved prospect of recycling. And by being all from the same resin family, the materials' coefficient of linear and thermal expansion (CLTE) is consistent, which can be very important, especially if the device in question is to be used outdoors and exposed to various weather elements.

At the same time, notes Niklas Meine, Covestro's marketing segment manager for electronics/electrical and appliances in the EMEA region, the materials used meet all UL specifications related to flame retardancy and optical properties, without the use of bromine, phosphates or chlorine compounds. Meine is based at the firm's headquarters in Leverkusen, Germany.

The controls essentially remain hidden until the user needs them, when the backlighting displays functional "buttons" or commands, Skabardonis said. This can make use of the resulting device more intuitive, as it can indicate to you where you need to touch when to perform a certain task. PC's inherent transparency (even when opaque) makes this possible.

Good connectivity is vital, so the thickness of the enclosure matters, said Meine in a recent telephone interview. The thin-wall design enabled by Makrolon is better for connectivity and touch performance while still exceeding high strength requirements.

Joel Matsco, Covestro's senior marketing manager for polycarbonates in Pittsburgh, Pa., pointed out the value propositions for the various segments of the supply chain:

• The consumer gets a product that is simpler and more intuitive to use.
• The assembler of the device needs much less labor to make the final product.
• The designer gains a lot of space within the architecture of the device, meaning she either can make it smaller and sleeker, or can pack more features into the same form factor; and
• OEMs can leverage these features to build their brand identity, while also benefiting from the sustainability angle offered by a mono-material product with a lower carbon footprint than competitive electro-mechanical assemblies.  

Covestro adds that the technology allows designers to seamlessly blend control surfaces with decor in cars, kitchens, bathrooms and industrial workspaces.

Other resins may be less expensive than polycarbonate, Matsco acknowledges, but they also would need to be thicker to achieve the same structural integrity and are likely to be less stable when it comes to flame retardance, and chemical and water resistance, not to mention adhesion to the films which form the top and bottom surface of the construct. "The balance of properties [with PC] is excellent for an IMSE sandwich," he said.

Devices made in this manner also offer "infinite customization," he added, "and are limited only by what the film can do."

The previously noted Lidar laser sensing will be a desirable feature for certain types of end-use applications (e.g., an autonomous robot that needs to navigate around obstacles). Lidar uses selective wavelengths, and the right PC formulation can be transparent to Lidar while remaining opaque to the naked eye. Some devices also will need to be able to integrate sound features to handle voice recognition. Others will need to include built-in antennas or various types of LED lighting.

And haptics remain important, too. "How does it feel to the touch," asks Skabardonis? The surface finishes can range from cool, high gloss or a warm, leather-like feel, to different textures. While the use of microtexturing doesn't make the surface more scratch-resistant, it can help to hide any marring of the surface. "You can get many different looks just by changing the mold surface," Meine said.

Covestro highlights many of these options in the Circular Design Guidebook for electronics makers that it created with REnato Lab, a Taiwanese sustainable engineering firm. Its aim is to help designers and developers integrate end-of-life disposal and circularity into the design of new products.

Matsco stressed that much materials know-how and processing knowledge is needed to execute this type of complex product. He noted that TactoTek has "torture tested" Covestro's PC resins and films and given them a T3 certification, the highest possible rating. The resulting Nighthawk Demonstrator showcases very effectively many of the technical requirements and key user features that future electronics devices and smart surfaces are likely to incorporate.

Such advances mean that technologies like IME are quickly evolving from being just cool concepts at shows such as CES to real-life manufacturing solutions for an increasing number of industries and applications.