Common Problem

  • Mobile phone touch screens are further divided into resistive touch screens, capacitive touch screens, infrared touch screens, and surface acoustic wave touch screens. At present, capacitive touch screens are the most widely used. Capacitive touch screens have great advantages in use, such as:


    1. The touch operation can be performed by fingers, without the need for a touch pen;


    2. Long service life, easy operation, easy maintenance, wear resistance and low cost;


    3. Can support gesture recognition, real-time feedback can be achieved by sensing the current of the finger, without generating a signal through pressure;


    4. After the production is completed, it only needs to be calibrated once, or it can be used without calibration at all, but its performance and quality must be checked first by testing.


    The touch screen of a mobile phone is composed of multi-layer composite films and relies on sensors to work. The wear resistance of the touch screen refers to the hardness of the screen, and the size of the touch screen refers to the diagonal size of the visible area of the screen. The transmittance of the touch screen of a mobile phone directly affects the sensitivity and comfort of the screen, and is one of the more important performance indicators. Other performance indicators include screen clarity, response speed, stability, reliability, service life, and more.


    When the touch screen of the mobile phone is in use, since the clicked position is different for each touch, it cannot guarantee that the data sampled each time is the same when the touch screen performs touch sampling. phenomenon occurs, the technical term is called drift. The drift phenomenon of the mobile phone touch screen may be caused by changes in the temperature, humidity, electric field, etc. of the environment, resulting in inaccurate touch, which is also a small defect in the capacitive touch screen. But for the mobile phone touch screen with good performance and quality, there is no serious drift phenomenon.

  • 1. Capacitive touch screen jumping point


    Cause analysis: Capacitive touch screens often have jump points, especially in the sample debugging stage, which are mainly caused by electrostatic interference, unstable voltage, driver errors, and CTP short circuits.


    Solution: Electrostatic interference should be considered in the product design stage, especially the design of FPCA must be grounded. If the customer's use of environmental interference is serious, an electromagnetic film must be used to resist interference. In addition, the serial port of the CTP and the main control board is not properly connected. If there are problems such as jumping points, the program must be debugged to the best state in the sample debugging stage. The more serious thing is that the CTP itself is short-circuited. This kind of defect is mainly caused by the short of the sensor or FPC. For fatal flaws, the CTP needs to be replaced.


    2. Water ripple of capacitive touch screen


    Reason analysis: The water ripple of capacitive touch screen is similar to the Newton ring concept of resistive screen. The water ripple of capacitive touch screen is actually a gap between LCM and CTP, and it is also related to the POL of the liquid crystal module.


    Solution: LCM does not have an iron frame. If there is no difference between the POL and the frame, you can consider full lamination. If it is not suitable for full lamination, you can choose frosted POL or increase the distance between LCM and CTP.


    3. Capacitive touch screen failure


    The fundamental reason for the failure of the capacitive screen is that the current that should flow from the finger does not flow due to the charging of the screen. The current flowing from the reference points in the four corners of the screen cannot be determined from which point, so as long as the charge can be balanced, the screen can be repaired. The following methods are available for reference.


    Option One:


    1. Turn off the phone, take out the battery, and let the phone sit for about five minutes.


    2. Find a USB data cable and connect it to the mobile phone.


    3. Wash your hands, or wet your hands (key steps, in order to better export static electricity).


    4. When the hand is wet, the thumb of the same hand touches the metal part of the other end of the USB cable, and the index finger is pressed to the ground for about two seconds (preliminary power off).


    5. After disassembling the back cover, we can see a small metal block next to the battery compartment, which is the generator of the vibration of the mobile phone, commonly known as the vibrator. Since it is also directly connected to the motherboard of the mobile phone, we can do the same, the thumb of the same hand touches the vibrator in the wet hand state, and the index finger is pressed to the ground for about two seconds.


    Option II:

    Remove the HD2 battery, turn on the electric iron, press the sheet on the bed sheet, the temperature should be moderate, remove the electric iron, put the HD2 screen upside down on the hot sheet, and iron the screen cover (the temperature should still be moderate, do not repeat ), and so on for about 5 times.


    third solution:

    Use a hair dryer to blow the screen, pay attention to turn it on to the mid-range, and blow it evenly to feel the screen is hot.

  • Resistive touch screens have a variety of top and bottom electrode support components. The basic structure is F/G, which is widely used due to its low cost. F/F/G are also widely used, but their usage is decreasing recently due to problems such as low transmittance. The film/plastic (F/P) structure is widely used because of its advantages in lightening and thinning of portable game machines or the like, or not being damaged when dropped. The F/F type refers to a method in which an optical bonding material or the like is directly attached to a liquid crystal display device, and is called an optical bonding method. In terms of reliability, the standard for pure car navigation devices (MOPs) that enter the production line of car manufacturers is G/G. In order to minimize the reflection of sunlight, car navigation is attached with linear polarizers, but high-end products use circular polarizers with a phase difference of 1/4 up and down.


    1. Improvement of optical properties


    One of the disadvantages of resistive touch screens is the optical properties, especially the low transmittance. There is an air layer between the top and bottom electrodes, which reduces transmittance due to internal reflection. In the past, some methods of injecting liquid into the air have been developed to improve the permeability, but due to insufficient reliability or price problems, it was not able to switch to mass production and remained in the development state.


    Recently, in order to improve the transmittance, it has been proposed to improve the transmittance of ITO glass and ITO film materials. For example, the transmittance of ITO glass is usually 90%. By improving each interface, the transmittance can be raised to 97%. The transmittance of ITO film is usually 88%, and some developed products can reach 95%, but the products with high transmittance in the use stage are about 91%. Table 2-2 is the transmittance of the theoretical panel. Using the materials at the practical stage, the transmittance of the F/G panel should be theoretically increased to 88%, but the unit price of each material will increase several times, so it is not realistic. The transmittance of the G/G touch screen can also reach 94%, but in practice, it is difficult to exceed 90% unless a film to prevent scattering is attached.


    A touch screen with a polarizer attached, there is a layer of polarizer in the middle that is not necessary (needed for liquid crystal). If the polarizer on the top of the liquid crystal is removed, its optical properties will be greatly improved. Because its structure is similar to putting a touch screen inside a liquid crystal, it is called "Inner TP". It seems relatively simple in the picture, but it needs to cooperate with LCD manufacturers, and there are relatively few manufacturers who actually carry out this.


    2. Improvement of other features


    Although the resistive touch screen has many requirements in terms of characteristics, most of them are to improve the ITO film on the side of the touch surface. Table 2-3 is the relevant content. While there are many requirements, there are three recent trends:


    (1) Liquid crystal display and Super Glass


    (2) Anti-fouling/fingerprint resistance


    (3) Scratch resistance


    Recently, the level of liquid crystal display has become higher and finer, and the RGB light-emitting phenomenon of the AG-treated touch screen is prominent. Also, there are more opportunities to watch single-segment broadcast TV with mobile phones or car navigation, so that obvious fingerprints can make consumers unpleasant. Like mobile phones, people often use clothes to wipe oil and fingerprints off mobile phones.

  • More and more things in life need to be operated with touch screen, such as home appliances, car navigation and so on. In daily life, the most common touch screen is capacitive touch screen, so what are the precautions when operating them. Today, Zhiling Weiye will tell you about the things you need to pay attention to when trying out the capacitive touch screen.


    1. If the user is using the capacitive touch screen for the first time, it is recommended that the user install the driver correctly according to the requirements of the manual, and then follow the on-screen prompts to calibrate the screen.


    2. In addition to ensuring the correct installation of the system software, remember not to install two or more touch screen drivers on one host, which will easily lead to conflicts during system operation, so that the touch screen system cannot be used normally. .


    3. Try not to let water droplets or other soft things stick to the surface of the touch screen, otherwise the touch screen will easily mistakenly think that there is a hand touching the surface. In addition, when clearing the dirt on the surface of the touch screen, try to use a soft dry cloth or detergent to carefully wipe from the center of the screen outward, or use a dry cloth dipped in denatured alcohol to clean the touch screen.


    4. If the touch screen responds very slowly when you touch the surface acoustic wave touch screen with your hand or other touch objects, it is likely that the touch screen system is outdated, the internal clock frequency is too low, or there are water droplets moving on the surface of the touch screen. In order to restore the quick response of the touch screen, the system must be replaced or upgraded, or the water droplets on the surface of the touch screen must be wiped off with a rag.


    After reading the above precautions about capacitive touch screen, do you have a deeper understanding of the touch screen around you? For more knowledge about touch screen, please go to the industry news to watch it yourself.


  • Nowadays, display devices are now an indispensable part of people's life and work, and it changes our lives to make them more convenient and efficient. There are several types of touch screens, mainly divided into capacitive touch screens and resistive touch screens. Capacitive touch screens are more commonly used now. Today, Zhiling Weiye will share with you the advantages and disadvantages of capacitive touch screens.


    Advantages of capacitive touch screen:


    1. Novel operation: The capacitive touch screen supports multi-touch, making the operation more intuitive and interesting.


    2. Not easy to touch by mistake: Because the capacitive touch screen needs to sense the current of the human body, only the human body can operate it, and it will not respond when touched with other objects, so the possibility of false touch is basically avoided.


    3. High durability. Compared with resistive touch screen, capacitive touch screen has better performance in dustproof, waterproof and wear-resistant.


    As a popular touch screen technology, although capacitive touch screen has the advantages of rich interface, multi-touch, and only human body induction, it also has the following defects:


    1. Susceptible to environmental influences. When environmental factors such as temperature and humidity change, it will also cause instability and even drift of the capacitive touch screen. For example, when the user is using the body close to the screen, it may cause drifting, and even operating in a crowded crowd will cause drifting. This is mainly caused by the working principle of capacitive touch screen technology. Although the user's finger is closer to the screen, there are many electric fields near the screen that are much larger than the finger, which will affect the judgment of the contact position. .


    2. The cost is high. In addition, at that time, the capacitive touch screen still had certain technical difficulties in the process of attaching the touchpad to the LCD panel, and the yield rate was not high, so the cost of the capacitive touch screen was also increased invisibly.

  • In real life, our living standards have improved significantly, and there are many electronic products around us. As far as I know, the anti-interference problem of capacitive touch screen is a very headache for touch screen manufacturers now. The anti-interference of capacitive touch screen is one of the performance requirements of touch screen. If the anti-interference is weak, it will affect the touch screen effect of the switchboard, such as The touch is not sensitive, the problem is inaccurate, and it is very affected by the outside world.


    First of all, we must understand the structure of capacitive touch screen and the principle of capacitive touch screen, and then find the reason for the anti-interference of capacitive touch screen, what is the general impact: capacitive touch screen anti-interference problems are manifested as: screen jumping, inaccurate touch, or complete failure. Then first determine whether there are external factors, such as the power supply is not timely, the signal is weak, the antenna signal is not strong, these are common, just need to detect whether there are any of the above phenomena, and then adjust.


    Then, in order to solve the anti-interference problem when designing a capacitive touch screen, the following adjustments must be made: first, add virtual wiring to the blank area on the touch screen panel, that is, fill the wiring outside the display area, and connect the added virtual wiring to each other to form virtual circuit; secondly, the virtual circuit is connected with the ground part of the touch chip to form a shielding circuit. This design eliminates the interference caused by temperature, humidity, environmental electric field, reflection and other factors to the capacitive touch screen, and has low cost and high efficiency.


  • The sensing screen of the capacitive touch screen is a four-layer composite glass screen. The inner surface and the interlayer of the glass screen are each coated with a conductive layer, and the outermost layer is a thin layer of silica glass protective layer. When we touch the sensor screen with a finger, the electric field of the human body makes the finger and the touch screen surface form a coupling capacitance. For high-frequency current, the capacitance is a direct conductor, so the finger sucks a small current from the contact point. . This current flows out from the electrodes on the four corners of the touch screen, and the current flowing through these four electrodes is proportional to the distance from the finger to the four corners. The controller obtains the position of the touch point by accurately calculating the ratio of the four currents. .


    Compared with the traditional resistive touch screen, the advantages of capacitive touch screen mainly include the following aspects:


    1. The operation is novel. The capacitive touch screen supports multi-touch, making the operation more intuitive and interesting.


    2. Not easy to touch by mistake. Since the capacitive touch screen needs to sense the current of the human body, only the human body can operate it, and it will not respond when touched with other objects, so the possibility of accidental touch is basically avoided.


    3. High durability. Compared with resistive touch screen, capacitive touch screen has better performance in dustproof, waterproof and wear-resistant.


    As the current popular touch screen technology, although capacitive touch screen has the advantages of gorgeous interface, multi-touch, only human body induction, but at the same time, it also has the following shortcomings:


    1. The accuracy is not high. For technical reasons, capacitive touchscreens are less accurate than resistive touchscreens. Moreover, only fingers can be used for input, and it is difficult to recognize complex handwriting input on a small screen.


    2. Susceptible to environmental influences. When environmental factors such as temperature and humidity change, it will also cause instability or even drift of the capacitive touch screen. For example, the user may cause drift by bringing his body close to the screen while using it, and even operating in a crowded crowd will cause drift. This is mainly due to the working principle of capacitive touch screen technology. Although the user's finger is closer to the screen, there are many electric fields near the screen that are much larger than the finger, which will affect the judgment of the touch position.


    3. The cost is high. In addition, the current capacitive touch screen still has certain technical difficulties in the step of attaching the touch panel to the LCD panel, and the yield is not high, so the cost of the capacitive touch screen is also increased invisibly.


    Outlook


    In the past, due to factors such as cost and technology, resistive control panels have been adopted far more than capacitive touch technology. However, in the recent stage, with the progress of technology and mass production, the price of capacitive touch screen is constantly falling, and the price gap with resistive touch screen is getting smaller and smaller, and the price gradually has the ability to compete with resistive touch screen. .


    With the booming of Apple's iPhone, iPod Touch and other products, not only major manufacturers have started the research and development of capacitive touch screen products, but many touch screen manufacturers such as 3M and Synaptics have also followed up in large numbers and invested in the research and development of capacitive touch screens. and in production. It is believed that with the continuous escalation of competition, capacitive touch screen will have great development in the short term; and the application of capacitive touch screen will not be limited to existing mobile phones, portable audio and video players and other products, but may also be used in cameras, Expand on more products such as GPS navigators, game consoles, etc.


  • The technical principle of projected capacitive touch screen technology is still mainly based on capacitive sensing, which is basically an extension of surface capacitive touch screen. Technically, it uses one or more etched indium tin oxide templates that have been rigorously designed, and increases the number of arrays (the more groups, the higher the detection accuracy and richness). Similar to X, F axis drive line.


    These wires are controlled by the capacitance detection chip. When the current drives the wires through the driving line, it is connected to the wire that detects the change of the capacitance value. The control chip takes turns to detect the change of the capacitance value and input the data to the main controller. After the point position, because the transparent wire forms a three-dimensional electric field on the panel, the proximity detection of the contact can occur without touching the screen, and even this technology can be applied to Z-axis detection and discrimination.


    In simpler terms, the projected capacitive touch screen can be said to change the state according to the X and F axis electrode signal distribution on the screen surface, and then calculate the cross geometric coordinates of the actual touch point on the screen surface. The panel achieves 1024 x 1024 touch point detection resolution.


    In a touch screen, ITO exists in the form of a planar conductor, and each square area corresponds to the same impedance. According to this principle, it is recommended to use diamond-shaped sensing elements, because the wires connecting these diamonds can be spliced with the least square area (less than or equal to 2).


    The projected capacitive touch screen also uses ITO to make horizontal electrodes and vertical electrodes on the glass surface. The difference between it and the surface capacitive touch screen is that a capacitor will be formed where the two sets of electrodes intersect, that is, the two sets of electrodes constitute the two poles of the capacitor respectively. . When a finger touches the capacitive touch screen, it affects the coupling between the two electrodes near the touch point, thereby changing the capacitance between the two electrodes. When detecting the mutual capacitance, the horizontal electrodes send out excitation signals in turn, and all the vertical electrodes receive signals at the same time, so that the capacitance value of the intersection of all horizontal and vertical electrodes can be obtained, that is, the two-dimensional planar capacitance of the entire touch screen. According to the two-dimensional capacitance change data of the touch screen, the coordinates of each touch point can be calculated. Therefore, even if there are multiple touch points on the touch screen, the real coordinates of each touch point can be calculated.


    Apple's iPhone has re-emphasized the touch screen industry. In the past, the touch screen technology was mainly based on 4-wire resistive touch screen, while the iPhone uses a projected capacitive touch screen, which makes the touch behavior detection more detailed. Due to its near-field detection and high sensitivity, It also avoids scratches and screen cracks.


    Projected capacitive touch screen has the advantage of supporting multi-touch, only need to touch with fingertips without using a touch pen, with higher screen light transmittance, overall power consumption will be more power saving, longer service life and no need for correction.

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