Projection capacitive touch screen structure

- Jun 06, 2019-

Since the iPhone adopted a projected capacitive touch screen, a large number of structural designs have emerged in a short period of time. The projected capacitive touch screen is characterized in that the sensor is placed under the surface of the touch screen and covered with a protective glass. Some new products are being developed with a one-sided design where all sensing layers are designed on one side of a single substrate. In this current thinnest projected capacitive touch screen design, each layer uses a multilayer sputtering process. Based on the basic principle of a projected capacitive touch screen with two layers of transparent conductive layers, various changes can be made in the design. For example, a layer of ultrafine (10 μm) wire can be used instead of a layer to sputter less ITO. At present, most mobile phones and signature acquisition boards on the market are plated with IT0 on different PET layers. In addition, common touch screens are ITO coated glass which is double-coated or single-sided coated on two substrates.


(1) film pattern


In projected capacitive touch screens, ITO films can be etched into a variety of shapes, but the manufacturing cost is the same, and due to the high correlation of touch sensors and electronic control systems, it is difficult to say which pattern is superior to other patterns.


The pattern of the projected capacitive touch screen of the early iPhone is the simplest one: the IT0 on both sides of the glass is engraved into 10 columns, the line width lram, the column arrangement layer with a pitch of 5 mm, the back surface is etched into 15 lines, the line width is 5 mm, and the pitch is The row arrangement layer of 37 ^ m, the columns of the column arrangement layer 10 are left unconnected (isolated) to maintain a uniform optical effect. This design requires simple process, but requires the controller's processing power to generate accurate coordinates.

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Learn about the structure of a projected capacitive touch screen


The most common pattern is the Lian Ling diamond (actually square 45° oblique), the connection between the electrode islands of this pattern is reliable (the shortest connection), and the screen area is fully utilized to sense the finger capacitance, and the diamond pattern is divided into Complementary two layers, one layer is a horizontal diamond row, one layer is a vertical diamond column, and the intersection of the wires is like a small bridge. The size of the diamond island depends on the manufacturer, usually between 4 and 8 mm. Currently, most of the projected capacitive touch screens use a diamond pattern.


(2) Touch screen conductor block resistance is usually processed by 15011 / port (unit: n / (m2 * mil)) ITO coated glass. To form a pattern with a line width of 20 pm, it needs to be completed by photolithography, such as in LCD panel factory. The lithographic ablation agent used in the process. The thicker the IIS, the smaller the resistance, the better the signal-to-noise ratio, but the light transmittance is poor; on the contrary, the thinner the ITO, the better the light transmittance, but the signal-to-noise ratio is worse. Transparent plastic, mainly used to make mineral water bottles. When the substrate is used as a substrate, the line width is usually 100~200jim. It can be screen printed, photoetched or laser cut, and the process of making a line width of 30~5 (Vm) on PET. In the actual application, the third layer of IT0 is used as the shielding layer to isolate the interference of the LCD. The shielding layer usually uses a sheet resistance of 150~300fi / □. The signal line on the border of the touch screen is usually molybdenum/ The aluminum/molybdenum material is also plated after ITO sputtering using a vacuum magnetron sputtering process.


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