OEM & Lieferant - Ausgabe 1/2021

71 ARRK Engineering www.arrk-engineering.com Website ARRK Engineering Dipl.-Ing. Sebastian Masi is Senior Engineer Display & Instruments at ARRK Engineering. Among other things, he deals with the integration and testing of displays with touch functions for road traffic. From below, the display is supplemented by a backlight, and protected at the top by a cover glass. The deeper the sensor techno- logy is built into the cell, the more the sur- rounding components offer protection – a slimmer, thinner design becomes possible. Limiting the number of layers in the opti- cal „stack“ results in lower reflection and improved solar radiation without increasing the brightness of the backlight. Initially, the so-called outcell design was com- mon for the development of touch displays. Here, the display was connected to the sensor by a bonding process. The biggest advantage of this design is that any display technology preferred for the application can be used. For example, any commercially available touch sensor that meets the requirements can be combined with the display. However, this means that the sensor technology rests ex- ternally on the polarization filter, which makes the entire component thicker than is desired in consumer electronics. In order to counteract this disadvantage of the Outcell design, the Oncell design was established as the next step. Here, the sen- sors within the display are mounted directly on the cell, which already leads to a thinner construction possibility due to the integra- tion. This trend towards thinner displays is reinforced in the automotive industry today with the complete integration thanks to the Incell variant in combination with TDDI tech- nology (Touch and Display Driver Integration). This allows sensors and even controllers to be moved right into the center of the display - optimally protected. The advantages of this design are a thinner module and improved optical quality. The production process itself is also accelerated by this design, since fewer production steps and suppliers are required for an Incell display. High requirements for road traffic However, with the complete Incell integration of sensor technology and controller, not all challenges for touch displays in vehicles have yet been mastered. This is because many auto- mobilemanufacturers have high demands and special requirements. One of the most com- mon demands is for a water-proof design, for example, in which touching by raindrops or condensation is recognized and ignored by an algorithm in the touch system software. Thanks to this technology, the system can be operated even in moist conditions without an unexpected behavior. Another often re- quested feature is a display that allows touch gestures even when passengers are wearing gloves the details for such features vary from manufacturer to manufacturer and must the- refore be tested and developed for the respec- tive performance requirements. In order to ensure smooth series production, reliable tests that meet the standards of ob- jectivity, reliability and validity are already re- quired during prototype construction. To this end, the respective test procedures should provide the same conditions for each com- ponent. At the automotive service provider ARRK Engineering in Munich, this is made possible by an internal department - the local test department for display and control sys- tems. There, all customer requirements can be checked with the help of the comprehensive know-how of the experts for touch displays and extensive analysis and test equipment. For example, automated endurance and stress tests can be used to check certain points in rapid succession in order to detect possible deviations on the entire touch surface and eliminate sources of error at an early stage. In addition, the use of standardized gloves with different materials makes it possible to test functions for different applications. ARRK can assist with extensive knowledge in the selec- tion of suppliers as well as provide technical and organizational support for the nomination process. : In the outcell design, the display was connected to the sensor using a bonding pro- cess. The biggest advantage of this design is that any LCD preferred for the application can be used. In the oncell design, the sensors within the display are mounted directly on the cell, which already leads to a thinner construction option due to the integration. Today, the automotive industry typically uses Incell design using TDDI technology. This allows sen- sors and even controllers to be moved to the center of the display – optimally protected. Graphics: © ARRK Engineering Image: © ARRK Engineering