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

Smart surface


This product illustrates a perfect example of Symbiose’s know-how and its management of the entire value chain for the development of IME plastronics products. This is an automotive HMI which includes tactile capacitive touch buttons and a slider for function control purposes. All  symbols are backlit.

Symbiose has developed two films. The first one is dedicated to both a decoration and an  indication purpose including the different symbols of each function. The second one is purely functional embedding printed circuits, capacitive sensors as well as electronic components (RLC and controller) and LEDs. To realize this interface we mainly used the following processes and skills :

  • Product and tooling design: design, electronics, optics and plastics
  • Screenprinting of graphic and electronic inks on both films
  • Thermoforming of the decoration film
  • Transfer by Pick’n Place and dispensing of glue on the functional film
  • Overmolding of the two films by plastic injection

With this product, Symbiose has demonstrated once again the interest of the IME technology in reducing cost, complexity and size compared to a conventional architecture. Moreover, thanks to a patented method, Symbiose is able to manage light leakage between adjacent symbols and reach higher than 650cd/m² per symbol luminance.

Our IME technology is mainly characterized by :

  • A high integration density (number of functions per unit area)
  • Meeting the automotive standards in terms of light leakage, homogeneity and luminance.
  • Assembling SMD components with a pad pitch of 0.5mm


Symbiose is currently participating in the European SmartEEs project whose purpose is to fund the promotion of printed electronics through collaborative projects between industrialists and research institutions. We are in charge of the development of a new automotive HMI withour IME technology. The objective is to propose and develop an elegant, qualitative solution respectful of both the automotive and consumer electronics sector specifications.

Symbiose aims to bring new innovations to implement them in the demonstrator which will be made within the framework of this project; more specifically adding a detection force functionality for supports validation.


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.