Xinhechang Takes You To Understand The Structure Of The Projected Capacitive Touch Screen

- Nov 08, 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 design. For example, an ultra-fine (lO^ni) wire can be used to replace a layer, thereby sputtering a layer of ITO less. Most mobile phones and signature acquisition boards currently on the market are plated with IT0 on different PET layers. In addition, common touch screens are ITO coated glass that is coated on both sides or on one side of a two-layer substrate.


(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 was the simplest one: the front side of the glass on which the IT0 was etched into 10 columns, the line width lram, and the pitch of 5 mm, and the back surface was etched into 15 lines, the line width was 5 mm, and the pitch was 37. The row arrangement layer of ^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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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 design. For example, an ultra-fine (lO^ni) wire can be used to replace a layer, thereby sputtering a layer of ITO less. Most mobile phones and signature acquisition boards currently on the market are plated with IT0 on different PET layers. In addition, common touch screens are ITO coated glass that is coated on both sides or on one side of a two-layer substrate.


(1) Film pattern


The most common pattern is a chain of diamonds (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 The 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, and most of the projected capacitive touch screens now use a diamond pattern.


(2) The 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. A lithographic ablating agent used in the process. The thicker the ITO, 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. When using PET (transparent plastic, mainly for manufacturing mineral water bottles) as the substrate, the line width is usually 100 ~ 200jim, and you can use screen printing, photo etching or laser cutting to make a line width of 30 ~ 5 (Vm on PET). The pattern of the process is still under study. In practical applications, the third layer of IT0 is used as a shielding layer to isolate the LCD interference. The shielding layer usually uses a sheet resistance of 150 ~ 300fi / □. The signal line on the touch screen frame is usually The molybdenum/aluminum/molybdenum material is also plated after ITO sputtering using a vacuum magnetron sputtering process.