Optical bonding of the touch sensor, cover glass and the display are made possible by means of different bonding technologies. At our site in Weikersheim, the bonding process was continuously developed along with the production of PCAP touch sensors and the possibility to bond these with custom-made cover glass. The bonding process takes place in a cleanroom where the air gap between the touch sensor and the cover glass is replaced with a transparent adhesive to guarantee error-free touch functionality. Touch front assembly of the display unit also takes place in a cleanroom and varies between air bonding or full bonding, depending on customer requirements.
During the process of air bonding, the components are bonded to the display by means of a double-sided industrial adhesive. In the full bonding process, the air gap between the components is bonded with transparent adhesive. Full bonding technology requires a high degree of expertise in order to improve optical display characteristics and minimize reflection.
A new bonding technology that combines the advantages LOCA and OCA bonding is enabling DATA MODUL to manufacture touch display solutions in a cost effective manner for high volume demands. This technology is suitable for bonding touch sensors to glass, as well as for glass or touch to displays. The bonding process starts with dispensing a liquid adhesive on the surface to be bonded, in exactly the right amount, followed by pre-curing. The components are subsequently positioned and attached to each other under vacuum, and finally the adhesive layer is fully cured using UV light. The technology is implemented in a fully automated process with high productivity.
DATA MODUL most commonly implements the bonding technology called liquid optical clear adhesive (LOCA) as a bonding agent. By means of a special detent, the liquid adhesive is spread over the cover glass, turned at a 180° angle and then bonded to the touch panel or TFT panel. The adhesive is spread evenly and bubble-free between the components. The adhesive is cured without heat using UV light. This prevents material stress caused by heat or mechanical effects. This technology is specifically suited for the adhesion of hard materials like glass, plastic and TFT panels. Various types of display production are available – from certified protection classes to explosion protection.
The optical clear adhesive (OCA) lamination process coupled with liquid adhesion round out the technology spectrum of optical bonding at DATA MODUL. The adhesive layer on touch films is used to laminate the sensor to the cover glass. Autoclaves are used to help remove air bubbles after this process is complete. In order to improve the optical or electrical function, EMC or UV filters and protective films are applied to the cover glass or the sensor.
Air bonding is the simplest and most economical way to bond displays to cover glass or touch sensors. This process takes place in a cleanroom where industrial adhesive tapes are relied upon to bond the metal frame of the TFTs by means of a special positioning aid. Assembly using single adhesive strips or a closed stick-on frame takes place depending on the application.
At gel bonding, display and touch unit are glued using gel pads. In doing so the pads are tailored individually according to display size and construction in width, height and thickness. The cut is applied to the touch unit (glass pane incl. touch sensor) via roll lamination. Finally, the touch unit in the vacuum - prevalent in the bonding machine - is then placed on the display. This method is particularly suitable for bonding displays with thin or no frame, since no more sealing is necessary.