Carbon fiber thermoplastic composites could make better smartphones

When you first get your hands on the Carbon I MK II (Mark Two) smartphone from Carbon Mobile GmbH, three things are obvious: it is light (125 grams compared to 182 grams for a normal smartphone), thin (6.3 mm) , compared to 8.3mm for regular smartphones), with a visible woven carbon fiber-reinforced composite on the back. Why would a computer engineer-turned-entrepreneur adopt an innovative composite technology on a mobile phone?

Carbon Mobile founder and CEO Firas Khalifeh recalls: “What we wanted was something tangible that, as soon as you got your hands on it, you could really see and feel the difference. Also, from a technical point of view, Look, making a smartphone is one of the most complex consumer products ever made. It has a high density of components and sensors, it's designed to extremely tight tolerances, it has to be as reliable as possible, and it can be used for hours a day in a variety of conditions, with the ability to For several years. We think that if we can make a game-changing smartphone, we can do almost anything - whether it's a tablet, AR (augmented reality), VR (virtual reality), a watch or a headset. "

Carbon Mobile's accomplishments aren't just about launching a smartly styled carbon fiber reinforced thermoplastic (CFRTP) body smartphone that runs the Android operating system and sets a new standard for thinness and lightness. With this phone, the company achieved several milestones: it solved the long-standing problem of carbon fiber blocking RF signals; it also developed isotropic grounding and electrostatic discharge (ESD) solutions; it also pioneered the technology that makes smartphones more A greener, more humane approach.

Integral Housing Design

The strength and stiffness of CFRTP is combined with a clever design that encapsulates all functional components in a single unit/housing located on the back of the smartphone and closes the front by directly gluing the chemically strengthened glass screen to it. This allows the company to eliminate the internal metal frame and external plastic cover typical of such devices, reducing mass, packaging space and materials used in the final product, not to mention the extra protective case that consumers often add.

The same architecture also makes it easier to disassemble and recycle end-of-life (EOL) phones and their structural parts. CFRTP not only provides external aesthetics and forms a protective structural enclosure for the device, but also functions as an isotropic ground plane and dissipates heat, a key feature for proper device function.

Late Changes

Not surprisingly, given its innovative nature, a key aspect of the phone's design was finding the right materials and processes to produce it. At first, the company used carbon fiber/epoxy prepreg. The early challenge was to find the necessary electrical and RF data on the materials they considered, however, their biggest challenge was to launch their first products in early 2020.

Khalifeh said, “The thermoset carbon fiber composite almost destroyed our company at a critical point as we approached commercialization, early in the pandemic, with all the lockdowns and subsequent supply chain issues. We just couldn’t get it. Materials. While we knew we would eventually move from thermosets to thermoplastics, the pandemic has given us time to rethink our options.”

When designing a carbon fiber smartphone, the original plan was to use carbon fiber/epoxy prepreg to make the phone's monolithic housing structure, but the scheme was later adjusted.

Since then, the team started looking for a supplier of automotive-grade CFRTP materials and found Lanxess AG (LANXESS, Cologne, Germany). Soon, LANXESS' Tepex continuous fiber-reinforced thermoplastic polyurethane (TPU) organic sheet (carbon fiber fabric layer with 3K/3K/1K twill weave) was specified for the back of the monocoque fuselage. This was compression moulded and then back injection moulded individually using a short fibre/polyamide 6 (PA6) composite to form glass-faced bonded sides with additional geometry added to encapsulate the antenna, which Carbon Mobile achieved part of the transmittance method.

It takes three hours to make each shell with the originally specified thermoset material/process. Carbon Mobile's current thermoplastic cycle time is 3 minutes; the company aims to achieve a one-minute cycle through increased automation and a hybrid (compression/injection) molding process, rather than the current two-step/two-machine process.

Transmittance

Perhaps the most innovative aspect of Carbon Mobile from a technology standpoint is that the company has found a way to use a carbon fiber composite housing that neither blocks RF signals but provides grounding and static dissipation . They call the patented technology HyRECM, which stands for "Hybrid Radio Composite Technology."

First, the antenna is created using multi-laser direct structuring (LDS) modules encapsulated on the top and bottom of the phone, which are themselves radiolucent under a back-injected glass/nylon 6 composite. Second, the body of the unit uses conductive ink that is selectively printed on the inner surface of the carbon fiber composite shell. This conductive ink changes the anisotropic conductivity of carbon fibers (in the fiber direction only) to isotropic (in all three axes), and is said to have the potential to connect circuit boards, antennas, carbon fiber composite bodies and even metal hardware to Effects of a single isotropic ground plane and ESD solution.

Greener and cleaner

Carbon Mobile places great emphasis on minimising its impact on the environment and participating in the circular economy. "Our ultimate goal is to achieve sustainability in the wider context," explains Khalifeh. “By using composite materials to reduce material usage and make end-of-life mobile phones easier to disassemble for recycling components, we can help reduce the 59 tons of e-waste generated each year. Combined with the longer life and higher value recovered during the recycling process materials, our connected devices embody less energy and have a lower carbon footprint.”

A major focus for Carbon Mobile during 2022 will be dealing with other device and electric vehicle (EV) manufacturers looking to license HyRECM technology. The company also plans to launch the MK III (Mark Three) model, which will feature bio-based polymers - polylactic acid (PLA) and polyamide 11 (PA11), as well as recycled carbon fiber in a back injection compound. The team is also exploring the use of graphene in the matrix to improve the Z-axis heat dissipation value.