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Selective Photoheating for Silicone Optical Bonding on Displays ABSTRACT IonoQure Limited has developed innovative optical bonding processes that address the challenge of cost-optimized manufacturing of complex optical devices and large display modules. Selective Photoheating is a new photonic technique resulting from collaboration with technology partners to precisely and effectively cure optical (and structural) adhesives in display applications, suitable for bonding all types of glass/ plastic lenses and substrates. With this contribution, IonoQure presents a completely new process concept specifically for the optical bonding of displays. The approach enables a slim line design and shows a high degree of flexibility with regard to the mix of component dimensions. 1. OBJECTIVE AND BACKGROUND Cost pressures, particularly in automotive manufacturing, drive opportunities to refine on new, more efficient processing methods that reduce cycle time and increase throughput and yield. Working with technology partners from the printing and photonics industries, IonoQure have developed a flexible and efficient process and equipment specifically for the optical bonding of displays, aiming to meet the cost and efficiency requirements of the consumer and automotive industry. 2. APPROACH AND PROCESS DESIGN METHOD Main driver of an optical bonding process are flexibility, speed, cost, and overall equipment effectiveness. Resin properties, curing method and the interaction of all material-process-equipment parameters have a great influence on the line design. For maximum flexibility and a lean system design, we have primarily focused on the material application and curing. The approach enabled us to conceptualize a sleek line design with high flexibility in terms of speed and adaptability to component design and dimensions. In addition, we overcome cure issues in shadowed areas and avoid using an oven or autoclave. 3. RESIN, PROCESS AND EQUIPMENT DESIGN DETAILS For the process development we have selected a catalytic cure UV-Activated Silicone OCR (Figure 1.). Viscosity of the OCR is selected so that a layer thickness of 50-300µm can be achieved in one pass. In order to achieve higher yields, we recommend designing a vacuum stage lamination for both processes and types of resin. For a controlled cure, short name Photoheating (Figure 2.), we have used an apparatus that emits electromagnetic radiation to rapidly increase the temperature to a specified target value and maintain the achieved state within high/ low limits for a specified period of time. Photoheating causes the Silicone OCR to self-heat by absorbing certain electromagnetic wavelengths. Usually, the heating time is kept within 10 to 20 seconds, and the temperature in the resin is automatically controlled by optical sensors. During the resin heating, there is little or no heating of the surrounding areas and components (measured by ambient temperature sensor).  In Figure 3 below, the temperature developments in the Silicone OCR (blue line) are plotted against the temperature in the gap between EMW-LEDs and cover glass (yellow line). The set target temperature was 70°C (red dotted line). The EMW-LED driver unit works independently and regulates the LED intensity in closed loop via pulse width modulation (PWM) to keep the temperature as close as possible to the target. The Selective Photoheating will make a significant contribution to increasing throughput and minimizing the footprint and power consumption of a production line. 4. MEASURING METHOD To demonstrate the effectiveness of the Photoheating process, we used an UV-Rheometer for the process simulation (Figure 4.). The OCR is enclosed within a glass and POL + OCA (mimicking a typical display module with a cover glass and a LCD). – Rheometer test setup: Glass/ OCR/ POL – OCR layer thickness: 500µm – UV activation: 365nm UV-LED, 4.500mJ/cm², 300mW/cm² – Target Photoheating-Temperature: 70°C – Frequency: 1Hz, oscillation mode 5. RESULTS AND CONCLUSION Photoheating radiation and measurement starts 60 seconds following the activation with 365nm UV LED. At room temperature, the silicone OCR (black lines in Figure 5.) reaches the gel point after a total of 300 seconds and achieves a storage modulus G’~3.0 kPa. By using the Photoheating (red lines in Figure 5.) the cure speed is significantly increased compared to RT curing, the gel point time drops from 300 seconds to under 20 seconds and a storage modulus G’~15.0 kPa (5x higher vs RT -Cure). By conducting pull tests with the same profile as shown above, Photoheating vs. RT pull force values are ~2.5 times higher. The Photoheating can highly influence the cure profile (speed) and the Silicone OCR bulk material performance. 6. IMPACT IonoQure Selective Photoheating technique, will significantly influence the development of flexible and efficient processes and manufacturing lines dedicated to optical (and structural) bonding.  Therefore, we will continue the development of suitable processes and materials and intensify cooperation with technology partners. 7. ACKNOWLEDGEMENT Many of our developments are supported by specialized equipment and technology partner. 8. REFERENCES AND PRIOR PUBLICATIONS This paper may contain certain forward-looking statements, which are based on internal reports and technical information believed to be reliable. This content has been previously published.

Selective Photoheating EXECUTIVE SUMMARY IonoQure has developed innovative bonding processes that address the challenge of cost-optimized manufacturing of complex optical devices and large displays. The Selective Photoheating is a new photonic technique resulting from collaboration with technology partners to precisely and effectively cure optical and structural adhesives (or coatings) in different applications, suitable for bonding all types of glass and plastic substrates. 1. PRINCIPLE AND INTRODUCTION IonoQure Selective Photoheating and general Photonic Curing are innovative photonic techniques for precise and effective curing of adhesives and coatings.The principle works by using photon energy to generate the heat needed to cure or accelerate the curing of materials. IonoQure Photoheating uses LEDs to emit a specific electromagnetic spectrum (EMS), while built-in IR sensors monitor the temperature. 2. MODES OF OPERATION Selective Photoheating operates in two ways: By direct exposure of adhesives/coatings he adhesive is heated indirectly by irradiating the substrate in direct contact with the adhesive (e.g. under the substrate). The schematic below illustrates the photo-heating principle in an optical display bonding application using silicone OCR.          Further we also show examples of equipment used to cure adhesives in display applications: The LEDs used for these devices will follow certain contours and as such we can accurately define the areas where (and how much) heat is generated or not. It quickly raises the temperature to a specific target and maintains it within set upper and lower limits for a predetermined time. The above example shows a thermoset adhesive, which reached a set temperature of 150°C in 12 seconds and maintained it for 10 seconds. 3. FEATURES AND DESIGN OPTIONS Device design can conform to specific shapes, and we can precisely determine which areas are heated and which are not. Precise monitoring and control of substrate and adhesive temperature is accomplished through the use of integrated temperature and optical IR sensors. The temperature range is dependent of the adhesive used and substrates.   Typically, will be between 70°C to 150°C But we can achieve temperatures as high as 200°C. This technique is suitable for glass, plastics and especially heat sensitive materials. 4. ACKNOWLEDGEMENT Many of our developments are supported by specialized equipment and technology partner. 5. REFERENCES AND PRIOR PUBLICATIONS This paper may contain certain forward-looking statements, which are based on internal reports and technical information believed to be reliable. This content or excerpts of this have been previously published.