IME benefits

Since the advent of touchscreen smartphones, users have become accustomed to touching and sliding their fingers across planar and flat surfaces. Originally invented to offer larger and larger screens and more intuitive use, touch technology is on the verge of becoming an essential standard in human-machine interactions (HMI).

In addition to generational habituation, touch technology offers considerable advantages over traditional mechanical buttons. Mechanical buttons are expensive, cumbersome and relatively aging over time.

The absence of mechanical movements and the simplicity of design and manufacturing make touch technology, especially capacitive technology, more durable, less bulky and less expensive compared to conventional technologies.

The progressive abundance of touch screens and buttons to the detriment of mechanical buttons is a consequence of human and industrial factors.

Capacitive technology

As a low-cost solution, PCB-FR4 or PCB-Flex are often used to create capacitive touch surfaces or buttons for HMIs with low aesthetic and ergonomic requirements. Because neither PCB-FR4 nor PCB-Flex are transparent, it is very often difficult to backlight symbols or pictograms evenly. Usually, only LEDs are used to indicate the status of the nearby button. A coverlay with printed or engraved symbols is glued onto the PCB to form the user interface.

When perceived quality and ergonomics are important factors in an HMI, PCB substrates are replaced by a transparent or translucent film, often PET, on which both transparent capacitive electrodes and conductive tracks are printed to form a set of sensors connected to control electronics. This solution offers the possibility of having a high-quality backlight compared to conventional PCBs. This film is then glued onto a graphic coverlay (usually plastic or glass) that is only transparent or translucent in the areas to be backlit on the HMI.

Our solution :

Our skills with the IME technology allow us to offer a new way of creating modern, intuitive and elegant HMIs.

Our solution consists in screen-printing two distinct films: the aspect film and the technical film. The first contains aspect elements, a logo, pictograms, etc., while the second contains capacitive (tactile) sensors and incidentally LEDs for backlighting. These two films are then thermoformed if necessary, to perfectly fit the 3D shape of the plastic part to be produced. During the plastic injection phase, the two films are placed on either side of the injection mold. The first one is placed on the front user side and the second one on the back side. The plastic material is then injected between the two films to form the final plastic part or HMI.

This solution benefits both from touch (capacitive) technology and film overmolding technology:

  • Freedom of design: homogeneous 3D surface without relief.
  • Manufacturing/production process: drastic reduction of processes and assembly operations.
  • Volume/weight reduction: very few assembly parts, drastically reduced thickness.
  • Robustness and durability: no sticking and no mechanical movements, watertight.
  • Quality/price ratio: very cost-effective perceived quality.

Examples of products

SOMFY

Technical film of an HMI with 19 capacitive buttons and an NFC antenna. The latter allows to unlock the HMI while the buttons form a numeric keypad and access to different functions.

The technical film is transparent with antenna, track and transparent electrode prints. These allow light to pass through from LEDs positioned on the PCB to backlight symbols on the user side.

INLIGHT

The InLight concept is a combination of light and decor in a compact and integrated solution to offer functionality to often inert looking parts (e.g., passenger side dashboard of a vehicle) and instant personalization for the user.

The InLight technology consists in using a portion of the part structure (transparent PC) as a light guide combined with two films acting as mirrors and light diffusers. This technique enables to illuminate nearly 95% of the surface of the part, reduce space requirement and lower the total cost of the part by drastically reducing assembly operations (bi-material injection).

The color, material, appearance and shape diversity offered by this technology gives greater freedom for designers to express their creativity, which is often hampered by technological limitations. In addition, the ability to illuminate homogeneously almost the entire part with the InLight technology allows for decor diversification on the same product basis, resulting in more segmentation flexibility according to the series and/or product range at a lower cost.

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This project has received funding from the European Union’s Horizon 2020 research and innovation program