Next generation optical bonding
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In tape-bonded solutions, incidental light is reflected at the surface of the TFT display and cover glass. With increasing light intensity, this results in reduced contrast and limited readability of the information appearing on the display.
In addition, the emerging light from the TFT’s backlight is scattered by the polarizer and reflected on the glass of each component depending on its surface texture and transparency, which causes additional readability issues for the display.
By eliminating air gaps with optical bonding, these reflections are reduced to 1% and the result is optimum contrast and exceptional color brilliance even when the TFT display is used outdoors and under intense ambient light. The readability is improved significantly without increasing the brightness or power consumption.
Optical Bonding allows robust TFT-Displays with optimized readability. Image source/Copyright: Distec GmbH
Under certain environmental conditions, dirt can accumulate in the air gap between the polarizer and the protective glass of the tape-bonded solution. Weather conditions with rapid and significant temperature changes may cause condensation fogging between tape-bonded layers, additionally affecting operation and readability.
Optical bonding not only prevents these circumstances from affecting the display, but also improves heat dissipation. The heat generated by the operation of the TFT display is dissipated through optical material and is not blocked by insulating air layers. Additionally, as proved by ball-drop test, optical bonding increases the strength and resiliency of the display. Shaking, shock, and vibrations are absorbed and reduced by the optical material, enabling use in industrial applications that require higher resistance to vibration, shock and direct impact.
Bonding technologies
Two different bonding technologies are available for TFT display enhancement. The most common one is the “wet bonding”, which uses liquid adhesives and requires a time consuming curing process. The related material shrinkage can result in degradation of optical quality due to bubbles or moiré effects.
These effects are avoided with the “dry” vacuum bonding process, which uses a non liquid optical bonding material. In addition, due to the consistent mechanical conditions when vacuum bonding, so-called ‘yellow spots’ are eliminated and the production process is much faster.
Direct conglutination of the glass plates reduces light refraction and improves contrast. Image source /Copyright: Distec GmbH
Vacuum optical bonding
With VacuBond technology, Distec currently uses the world’s most advanced optical vacuum bonding technology and processes the high performance silicone optoGel from the Japanese Taica company, a global leader in optical bonding materials, with a vacuum-pressing device. Clean room conditions ensure that no dust or dirt particles affect the result. The technology offers enormous advantages compared to traditional bonding methods.
In particular, small TFT displays with an extremely compact design in sizes from 2.4" to 7" can be bonded reliably, precisely and cost-effectively with this new vacuum process. High-precision serial production is guaranteed by the automated process and the homogeneous silicone material. The manufacturing equipment is capable of directly bonding TFT displays in custom bezels and front housings with integrated protective glass. Additionally, Vacubond technology allows for quick-turn prototyping.
12,1‟ TFT display bonded with touch screen and PMMA (Plexiglass). Image source /Copyright: Distec GmbH
VacuBond technology is also suitable for environments that require explosion protection. Free air spaces within the display itself, which lead to restrictions in protection certifications, can be avoided or eliminated by "free air exclusion" bonding. This is an alternative to the very expensive and often irreversible conventional methods such as filling the space with glass beads or injecting silicone into the gap between layers.
Production is streamlined through automated processes and the use of production jigs. These are durable molding tools which guarantee the correct position of the individual components during the bonding process and provide consistent quality when producing large quantities.
The basis for any new combination of TFT display and glass is an exact measurement of the contact angles and the physical adhesion forces. This measurement is made with a modern instrument and software that decodes surface energy in polar and dispersion components by using special liquids. Such a measurement protocol is the basis for every new project. Moreover, the VacuBond process is reversible: individual components can be recovered, simplifying repairs and reducing repair costs.
TFT display bonded in a front bezel. Image source /Copyright: Distec GmbH
Distec provides the optical bonding service for every display up to a size of 24" in combination with touch screens of all technologies and/or protective glasses. In March, an identical VacuBond manufacturing cell will be installed at Distec’s U.S. facility in Ronkonkoma, NY, improving risk management by redundancy.
About the author:
Bernhard Staller, Managing Director of Distec GmbH www.distec.com
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