How is a cover glass laminated on a touch sensor glass?

Projected capacitive (PCAP) touch screen with glass-on-glass construction is an ideal multi touch solution for touch displays widely used for commercial, smart-home, medical and industrial devices. The cover glass is a front protective layer, but how is the cover glass laminated on the touch sensor glass?

Layers of Glass Solution Touch Screen

Before explaining this question, let’s first look at the three layers of glass solution touch screen in the below picture.

Cover glass is usually strengthened chemically or physically and its surface hardness is 6H. The common thickness is 0.7mm, 1.1mm, 2mm, 3mm, and up to 10mm. Normally, the thicker it is, the more rugged it is.

Optical adhesive is the material used for laminating a touch sensor glass on a cover glass. It is optically clear and UV curable. The thickness is usually 0.2mm.

Touch sensor glass is the layer realizing the touch function, which is bonded with FPC (flexible printed circuit) cable to connect the touch sensor to the controller board or motherboard. The ordinary thickness is 0.55mm, 0.7mm, and 1.1mm.

Laminating Process

1. Dust Removal

Cleanliness is critical for laminating touch sensor to front glass. Laminating process is done in a clean room. All materials need dust removal and all people have to wear dust-free clothes before entering the clean rooms.

2.Laminating the Optical Adhesive to the Sensor Glass

At this stage, the optical adhesive is flexible solid-state glue sheet. We use a laminating machine to bond it to the sensor glass.

3. Laminating the Sensor Glass with Adhesive onto the Cover Glass

Make sure to center the viewing area of sensor glass with the painted opening of cover glass. On the cover glass, there are positioning lines and if necessary, we will use a positioning tool.

4. Making the Sensor Glass Laminated Firmly with the Cover Glass

Put assembled touch screen in the vacuum-laminating machine in the vacuum environment at high temperature for some time. High temperature is for half-melting the optical adhesive, as it is thermoplastic. The vacuum environment is for combining them together firmly.

5. Removing Air Bubbles

Usually, there are a few small air bubbles around sensor glass borders or edge of viewing area, due to the silver layout on the sensor glass. Air-bubble removing process is to eliminate the air bubbles at some temperature and air-pressure for a period of time in the air-bubble-removing machine.

6. UV Curing

After bonding a touch sensor glass on a cover glass completely, UV curing is the last process. Certainly, before UV curing, function test and visual test are 100% executed, as UV-cured touch screens cannot be delaminated.

Above are the major processes for optically bonding a projected capacitive touch sensor glass on a cover glass. We are a PCAP touch screen manufacturer with custom service and technical support. Any questions or inquiries, feel free to discuss with us.

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