A look at cover glass construction

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By Jim Badders | Mar 16, 2016
Cover glass construction front panel integration

As a front panel integrator, one of the layers that GMN adheres to a display is a piece of cover glass. When designing the integration of a display, it is very important to consider the different aspects of cover glass construction including material type, glass strengthening, glass thickness, and surface finishes.

There are many different types of glass used in the display bonding market including soda-lime, alumina-silicate, borosilicate, ceramic, and fused silica/quartz glass. These types of glass are used in various formulations to create cover glass and each combination has its benefits and challenges depending on the particular application.

When combined with raw glass, any of the common glass types can come in both strengthened and non-strengthened forms depending on the intended application and environment. Strengthening is conducted by chemical or heat tempering and is normally determined based upon the thickness of the glass and shatter requirements.

Another major aspect of cover glass construction is the material thickness because it affects impact resistance. While numerous thickness levels are available, the standard levels that are typically stocked from most glass suppliers include 0.7 mm, 1.1 mm, 2.0 mm and 3.0 mm.

Because surface finishes have a big impact on the perceived and quantified display image, they are another major aspect of cover glass design. A few of the most commonly used surface finishes include gloss, anti-glare (AG), and anti-reflective (AR) finishes. An anti-glare etch on the surface of the glass is perhaps the most widely used surface finish after plain gloss finishes.  An anti-reflective finish is used alone or on top of an anti-glare to provide the best optical performance for high brightness, or direct sunlight, usage. Surface finishes can also affect the display image contrast and luminance. In order to ensure the correct cover glass combination, specialized equipment can be used to ensure that the design is sound and that precise measurements can be made to characterize the results for duplication.

Other types of finishes, also known as specialty coatings, include infrared (IR) blocking, anti-smudge or anti-fingerprint/oleophobic, and anti-fog. Because of cost, these are not as widely used.

A growing trend in cover glass construction is printing on the backside of the glass. This is done for many reasons including printing a border to hide mounting hardware or including a logo or other backlit icons. Printing on the backside of the glass is predominately done in black, but can be done in custom colors as well. For white or light colored borders, the glass will need to be a low iron type so that it doesn’t tint the color. For example, the soda-lime glass has a green tint that will show on lighter colored borders. While there are many different types of ink and processing methods available, UV cured and epoxy inks are common. For demanding applications, a frit type process (during which batch material is fused with other materials and ground into powder) is best because the ink is fused onto the glass surface making it almost indestructible. 

Additional features including holes, or slots and notches in the glass can be done to provide a unique and custom look and feel.

The glass offerings used in mobile and fixed displays have evolved recently and play a big part in the overall appearance and performance of cover glass.  In order to achieve the optimum cover glass design, it is important to work with a display solution provider to determine the best fit for product design.