Journey from a glass sheet to a Zytronic touch sensor

Article courtesy of Zytronic

Often, when we think of glass, it is the simple square or rectangular shape that forms the window in almost every building we encounter. However, as a rigid, transparent and scratch resistant substrate, glass has many more uses and is a fundamental element in touchscreen displays. In this technical article, Ian Crosby, Sales and Marketing Director at Zytronic explains how glass can be transformed from a simple sheet to a sophisticated Zytronic touch sensor through the application of specialist processing and machining techniques at its UK manufacturing facility.

To create the best touchscreen solution for challenging environments, it will come as no surprise that different types of glass are used. Standard soda-lime glass contains a small amount of iron, which gives it a greenish hue – this is noticeable when looking at the edge of a piece of glass or through a very thick sheet. Low iron glass (also sometimes called ‘water white’ glass) is made using carefully selected raw materials to minimise the amount of iron and reduce this tinting effect, making it ideal for applications where the true replication of the displayed image colours beneath the touchscreen is critical.

At Zytronic, full sheets of glass, in the required thickness, are cut to any shape or size, up to around 90 inches (2.28 m) on the diagonal. As the touch sensors are all produced in-house, using a uniquely flexible manufacturing process, custom designs are possible with no- to low-tooling fees, and in any quantity from a single prototype to many 1000’s of units.

Journey from a glass sheet to a Zytronic touch sensor 1

Once the glass is cut to shape, CNC machines can cut holes and slots into the screens so that peripheral devices such as credit card readers, ticket printers and NFC detectors can be mounted behind the finished touch sensor when installed in a kiosk. Other surface features, such as dimples and grooves or raised markings may now also be added to the glass, to further customise the screen and help guide the user’s fingertips when not looking at the touch sensor. The on-site CNC machines are also used to grind, profile or polish the glass edges for aesthetics or safety. For more sophisticated designs, Zytronic has dedicated ovens which bend the glass to specific radii, matching the latest curved displays to create an immersive, ‘wraparound’ experience for the touchscreen user.

Once the glass has been machined, features such as graphics and logos may be added. Ceramic inks are highly scratch-resistant and recommended for rugged applications, while polymer-based inks offer a broader range of colours. In applications where the most accurate colour replication is critical, it is usually recommended that the touch sensors are made from low iron glass.

Additionally, many types of special glass coatings and strengthening methods can be used to enhance the touch sensor’s functionality in certain environments.

Once  processed, the glass screens are thoroughly cleaned with de-ionised water, air dried and are then moved into one of Zytronic’s ISO class 5 clean rooms for careful inspection before beginning the final steps in their journey to becoming fully functioning projected capacitive touch sensors. During this phase of manufacture, copper touch detection electrodes are applied directly to an optically clear adhesive film, laminated to the rear of the glass. With a diameter of just 10 microns these electrodes are barely visible to the human eye. In contrast with other types of capacitive, acoustic and optical touch sensors, the active touch detecting components (in this case, copper electrodes) are embedded behind the front glass substrate. Placing them here instead of on or around the surface which will be touched ensures protection from any scratches and impacts, creating stability, reliability and consequently ensuring a long product life.

Once the matrix of copper electrodes have been encapsulated by another laminated film applied to the rear – this time a hard-coated, optically clear polyester film – thin, flexible connectors are fixed to the terminating copper electrodes at the glass panels edge, enabling the touch sensor to be linked to the touch control electronics – one of Zytronic’s proprietary touch controllers, the exact type determined by whether the application requires the touch sensor to be single- dual or multi-touch.

Journey from a glass sheet to a Zytronic touch sensor 2Zytronic’s proprietary touch controllers are suitable for use with operating systems and software supporting complex touches such as pinches, zooms and swipes, delivering functionality and a user experience that is smartphone-like, but on a far larger and significantly more durable scale. All Zytronic controllers are designed for compliance with the Human Interface Device (HID) protocol, allowing USB plug-and-play operation with all current MS Windows operating systems and suitable versions of Linux and Android.

In addition, a range of other interface protocols are available including, serial, SPI and I2C, giving touchscreen system designers the flexibility to choose the most appropriate for a given application.

The completed touch sensor is finally and rigorously inspected for function and appearance to ensure the highest levels of quality before being carefully bagged and packed ready for shipment anywhere in the world.  As all of Zytronic’s projected capacitive technology (PCT™ and MPCT™) touchscreens are made entirely at its ISO9001:2015 accredited UK facility, the company is able confidently take full ownership of the products performance and provide consistent and repeatable quality. All Zytronic’s touch sensors are bar coded and scanned throughout their manufacture, from incoming raw materials to final product dispatch, ensuring traceability.

The manufacturing set-up is highly flexible allowing Zytronic to offer the highest levels of support to its customers. For example, there is an entire clean room dedicated to rapid prototyping. Here, skilled technicians can fabricate samples and prototype touch sensor designs within a few days or weeks, supporting customers’ increasingly rapid product development timescales.

Over 40 years, Zytronic has invested heavily in developing these processes and technologies allowing them to turn sheets of glass into highly sophisticated and reliable projected capacitive touch sensors designed for the most demanding commercial, self-service and industrial applications. The design options available are almost limitless and the inherent flexibility of the technology means that often there is little or no investment in special tooling to produce a one-off design. This benefit is passed along to the customer through low tooling fees (in many cases, no tooling fee) and no minimum order quantity, making the design of new touchscreen enabled systems quicker and easier to develop than ever before.

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