Optical bonding is one of the methods of attaching (gluing) a protective cover glass with a touch screen or touch sensor.
Optical bonding has gained popularity due to its advantages over the previous, most popular choice: Air bonding. Before optical came into view, air bonding was the simplest and most economical way of bonding a cover glass with a touch screen or a touch sensor.
Why?
Well, the process is straightforward: adhesive is placed in the perimeter of the frame of the sensor (what we call the bezels). Once adhesive is set, the cover glass is then placed on top of the stackup.
This leaves a small air gap between the front panel material and the rest of the stackup. As we will see later on, this air gap creates various problems.
To eliminate these problems, another optical bonding method has been developed. In optical bonding, liquid optically clear adhesive (LOCA) is spread over one side side of the cover glass. This side is then turned and bonded on the touch panel.