What is Optical Bonding? 

Optical bonding is a process that eliminates the air gap between two layers: the glass or touchscreen and the TFT LCD panel of a monitor. The purpose of removing this air gap is that different mediums, such as air, glass, and the LC panel, have different refractive indices. For example, the refractive index of air is about 1 but that of glass is around 1.5. This difference in refractive indices causes light to bend as it passes through these mediums, leading to readability issues. In optical bonding, a resin or adhesive film is used to fill the air gap, adjusting the refractive index to closely match that of glass and LCD panel. This adjustment allows light to pass through a single refractive index, reducing unnecessary refraction and distortion. As a result, optical bonding improves both light transmission and readability. 

OCA bonding and OCR bonding

Optical bonding consists of two types based on the bonding materials: OCA (Optically Clear Adhesive) bonding and OCR (Optically Clear Resin) bonding. OCA bonding, also known as dry bonding, involves bonding a touchscreen or cover glass to the surface of the display using an optically clear adhesive film. OCR bonding, or wet bonding, uses a thin layer of clear silicone-based resin to attach the display to the cover glass or touchscreen. Both OCA and OCR bonding utilize materials with refractive indices similar to that of glass and the LCD panel. This removes the air gap and reduces light reflection, enhancing contrast and readability. The result is the optical bonding display with better contrast, less ambient light interference, and improved light transmission.

Why is Optical Bonding Needed?

Optical bonding offers several benefits, including improved readability and durability. By eliminating the air gap and bonding the glass or touchscreen directly to the display panel, optical bonding enhances contrast and color accuracy while reducing light reflection and eye strain caused by reflections. Optical bonding also minimizes parallax error, resulting in a more accurate touch experience. The brighter screen and enhanced contrast provide a wider viewing angle. Additionally, optical bonding protects against dust, moisture, and scratches, which increases the overall durability of the display.

Benefits of Optical Bonding:

• Increase optical clarity by removing light reflection and interference.
• Enhance contrast and color accuracy.
• Improve the touch experience and enhance viewing angles.
• Protect against dust, moisture, and scratches: The bonding strengthens the glass, acting as a protective layer. 

Applications:

CES LG TOLED

At CES 2025, LG Display showcased its Transparent OLED technology, which requires optical bonding.

Image source: LG Newsroom, January 13, 2025. "A Technological Journey Through Affectionate Intelligence at CES 2025”

Casino curved LED

In the gaming industry, including casino displays, picture quality is crucial for attracting customers. Therefore, optical bonding is an excellent option for enhancing the picture quality of curved LED displays in casinos.

E-ink

The thickness of E-ink is less than 1mm, so glass bonding is necessary to strengthen its cover and enhance durability. Additionally, as the size of E-ink has increased, the importance of optical bonding has also grown.

Image source: Eink website, 25.3" E Ink Kaleido 3 Outdoor Color ePaper Display

BSI Optical Bonding

BSI has necessary optical bonding equipment to provide optical bonding service upon request. We offer OCA bonding for sizes ranging from 2” to 65”, with various film thicknesses available. OCR bonding is available for sizes ranging from 2” to 105”.

BSI optical bonding page: https://bisearch.com/capabilities/optical-bonding

BSI clean rooms for optical bonding