TAB bonding, which stands for Tape-automated bonding, is a process used to attach bare semiconductor chips (dies) onto a flexible circuit board (FPC) by connecting them to fine conductors in a polyamide or polyimide film carrier [1]. This bonding technique is commonly used in the electronics manufacturing industry, particularly for achieving chip-on-flex (COF) assembly .
Process:
TAB bonding involves placing the bonding sites of the semiconductor die, usually in the form of bumps or balls made of gold, solder, or anisotropic conductive material, onto fine conductors on the tape .
The bumps or balls can be located either on the die or on the TAB tape .
TAB compliant metallization systems include various combinations of materials such as gold-plated copper, gold or tin bumped tape areas, and solder-plated tape areas .
The tape, which may already contain the application circuit of the die, is moved to the target location, and the leads are cut and joined to the chip as necessary .
Joining methods used with TAB bonding include thermocompression bonding, thermosonic bonding, and other techniques .
After bonding, the bare chip may be encapsulated with epoxy or a similar material .
Merits of TAB bonding:
All chip interconnections are made during one bonding process, distinguishing TAB from wire bonding .
TAB bonding can be highly automated and fast, making it suitable for high-volume electronics production.
It produces lightweight and thin assemblies due to the thin substrate and minimal glob topping, which is beneficial in applications where small weight and thinness are desired .
In some cases, additional packaging may not be necessary, potentially replacing metallic lead frames in certain packaging approaches .
Challenges of TAB bonding:
Specific machinery is required for TAB manufacturing .
The chips need to have bumps on the input/output (IO) pads or bumps need to be on the tape, and the bumps and metals on the chip and tape must be compliant to ensure reliability in various environmental conditions .
The speed advantage of TAB bonding has diminished with the development of flip chip manufacturing, which also enables simultaneous bonding of all IOs of the die .
FOG bonding and COG bonding are two different methods used in the manufacturing of displays, particularly LCDs (Liquid Crystal Displays). While both methods involve bonding a flexible printed circuit (FPC) onto a glass substrate, there are some key differences between FOG bonding and COG bonding.
Definition:
FOG Bonding (Film On Glass): FOG bonding refers to the process of mechanically fixing and conductively bonding an FPC onto a glass substrate [1].
COG Bonding (Chip On Glass): COG bonding involves directly bonding the driver IC (Integrated Circuit) onto the glass substrate of the display [1].
Bonding Method:
FOG Bonding: In FOG bonding, the FPC is mechanically fixed and conductively bonded to the glass substrate using an adhesive, such as anisotropic conductive film (ACF) .
COG Bonding: In COG bonding, the driver IC is directly bonded onto the glass substrate using a thermal crimping process with ACF .
Purpose:
FOG Bonding: FOG bonding is primarily used to bond the FPC onto the glass substrate, providing the necessary electrical connections for driving the display .
COG Bonding: COG bonding is used to directly bond the driver IC onto the glass substrate, eliminating the need for a separate PCB (Printed Circuit Board) .
Advantages and Disadvantages:
FOG Bonding:
Advantages: FOG bonding allows for a narrow frame display, as the driver bonding can be done on the FPC, reducing the overall frame size . It also provides flexibility in design and allows for easier mass production .
Disadvantages: FOG bonding may require additional components and assembly steps compared to COG bonding .
COG Bonding:
Advantages: COG bonding reduces the size and weight of the display module, as the driver IC is directly bonded onto the glass substrate . It also simplifies the manufacturing process by eliminating the need for a separate PCB .
Disadvantages: COG bonding may limit design flexibility, as the driver IC is directly bonded onto the glass substrate . It may also require more precise alignment during the bonding process .
COG bonding, which stands for Chip-On-Glass bonding, is a method used in the manufacturing of flat-panel displays, particularly LCDs (Liquid Crystal Displays). It involves directly bonding the driver IC (Integrated Circuit) onto the glass substrate of the display panel. This bonding technique offers several advantages, including space-saving, improved electrical performance, and reduced manufacturing complexity.
The COG bonding process typically involves the following steps:
Flip Chip Bonding: In COG bonding, a flip chip technique is used, where the driver IC is flipped and bonded onto the glass substrate. This bonding is achieved through thermal crimping using ACF (Anisotropic Conductive Film) .
Mainstream Method: The driver IC required to drive the flat-panel display, such as an LCD, is directly bonded onto the glass panel. This is known as COG bonding. Additionally, for narrow frame displays, driver bonding can also be done on the FPC (Flexible Printed Circuit) known as COF (Chip-On-Flex). Another approach to narrow the total frame is by pinching the pitch FOG (Film-On-Glass) .
Improved LCD Resolution: With the advancement in LCD resolution and definition, driver ICs are becoming more densely packed and have elongated shapes. COG bonding allows for efficient and compact integration of these driver ICs onto the glass substrate .
Experience and Expertise: COG bonding requires specialized knowledge and experience. Manufacturers with expertise in COG bonding can handle various bonding requirements and ensure reliable and high-quality bonding .
COG bonding offers several benefits, including reduced space requirements, improved electrical performance due to shorter interconnects, and simplified manufacturing processes. It enables the production of sleek and compact display modules, making it a preferred bonding method in the flat-panel display industry.
ACF bonding, also known as Anisotropic Conductive Film bonding, is a method used in various industries, particularly in the manufacturing of liquid crystal displays (LCDs) and other electronic devices. It involves the use of an adhesive interconnect system to create electrical and mechanical connections between different components.
Here is some information about ACF bonding:
What is ACF bonding?
ACF bonding refers to the process of using anisotropic conductive film, which is a type of adhesive, to establish electrical connections between components in electronic devices .
The film is made of resins, such as thermoset epoxy resin, in which conductive particles are dispersed. It can achieve conductivity vertically, or in the direction of compression, and insulation quality horizontally, or in the perpendicular direction to compression .
ACF bonding is commonly used in LCD manufacturing to connect the electrodes of glass substrates to the electrodes of IC chips or flexible substrate circuits .
Usages of ACF bonding:
1.LCDs and OLED displays: ACF bonding is extensively used in flat panel displays, including smartphones, tablets, PCs, and televisions. It is used to electrically connect the electrodes of the glass substrates to the electrodes of IC chips or flexible substrate circuits, and also physically fix them .
2.Touch sensors: ACF bonding is also used in touch sensors, which are built on or in the display of smartphones and tablets. It helps connect the transparent electrodes on a transparent film substrate or glass substrate to the electrodes and driver ICs for sensing .
3.Semiconductor device connection: ACF bonding is adopted in various semiconductor devices, such as CMOSs or CCDs in camera modules, micro-LEDs, and secondary mounting processes .
How to use ACF bonding:
ACF is attached to the cleaned surface of a substrate, such as a glass substrate or flexible printed circuit (FPC) .
Heat and pressure are then applied to the ACF without removing the film liner .
This process compresses the conductive particles in the ACF, creating a conductive path between the electrodes and forming a secure bond .
COF bonding, also known as Chip-on-Film bonding, is a process used in LCD screen repair to connect the COF (Chip-on-Film) component to the ITO (Indium Tin Oxide) glass and PCB (Printed Circuit Board). This bonding process ensures proper electrical connection and functionality of the LCD screen.
The COF bonding process involves several steps, which are outlined below:
1.LCD Fault Mark: Make a mark on the screen where the fault appears before bonding. This helps to identify if the fault disappears after bonding.
2.Glass and Side PCB Fixation: Fixate the glass and side PCB to prevent damage to other COFs during the bonding process .
3.Polarizer Protection: Apply a film, like a preservative film, on the polarizer to prevent scratches during bonding. Ensure the film is smooth and flat .
4.Wind Station Parameter Setting: Set the parameters of the wind station to ensure the COF remains flat, non-deformed, and unshrinking during removal. The temperature range is typically set between 300-330°C, and the wind power is set at 3-4 degrees .
5.COF Disassembly: Remove the sealing glue and disassemble the COF, starting with the PCB side and then the glass side .
6.ACF (Anisotropic Conductive Film) Removing Liquid: Apply the right amount of ACF removing liquid on the ITO glass and COF. Avoid applying the liquid on other parts, as it can damage the polarizer film or protection film. Take precautions to avoid contact with the liquid .
7.ACF Removing Liquid Chemical Reaction: Allow the ACF removing liquid to react for a specific time period (1-5 minutes for G-450) to make the ACF soft, loose, and easy to clean. After the reaction, clean the ACF with alcohol or acetone .
8.ITO and PCB Cleaning: Clean the ITO using cotton swabs with alcohol and electrostatic cloth with acetone until it is clear .
9.Old COF Cleaning: Clean the old COF on a clean glass table using a clean cotton swab with alcohol. Clean the ACF in one direction, following the direction of the pins from the inside to the outside of the COF .
10.ITO Checking: Check the ITO under magnification to ensure there are no residual ACF, dirt, scratches, or corrosion before bonding.
11.Clean ITO Under Microscope: For small residual ACF and dirt, clean the ITO under a microscope using a proper direction and force. Use cotton swabs and alcohol for cleaning.
12.COF Checking: Check the COF under a microscope for residual ACF or dirt on the pins. Scrape them carefully with a toothpick. If the pins are curved or broken, discard the COF. For new COF reels, cut them separately before bonding .
13.ACF Model: Choose the correct ACF for bonding. The ACF for the ITO side and PCB side may differ. Store the ACF in low temperature, and check the expiration date before use .
14.ACF Attaching: Cut the ACF from the reel slightly longer than the COF. Attach the ACF to the COF pins using tweezers and pre-heat it with a T-type iron for a good connection .
15.ITO Moving and Placing: Move the ITO to the bonding machine platform, ensuring it is smooth and steady. Take care not to strike other parts of the machine .
16.Bonding Machine Operation: Set the parameters and align the head, camera, COF fixture, and COF-ITO pins .
17.Teflon Tape and Bonding Pressure: Place a Teflon tape on top of the COF for protection and set the bonding pressure between 2.0Mpa to 4.0Mpa .
18.Alignment Image: Ensure proper alignment between the COF and ITO before starting the bonding process .
19.Double Start: Start the automatic bonding process, ensuring the alignment, parameters, and pressure are set correctly. The head will heat up, apply pressure, cool down, and then retract automatically .
20.Automatic Bonding: After bonding, check the quality of the connection between the COF and ITO. If necessary, disassemble and re-bond carefully. If the bonding is successful, proceed to PCB side bonding .
21.PCB Side Alignment: Align the PCB and COF pins, similar to the ITO side alignment
Please note that this is a general overview of the COF bonding process, and specific procedures may vary depending on the equipment and materials used.
We have mentioned that the principle of COF bonding machine is to bond ACF and explode another ACF conductive particle at a certain temperature, pressure and time to solidify ACF adhesive, so as to realize mechanical connection and electrical conduction between liquid crystal glass or PCB and flexible circuit board (FPC).
The simple understanding is to replace the faulty drive soft wire (COF), and the equipment used in this process is called a hot press.
First, the following are the problems we often encounter. In fact, COF (the technology of connecting chips to FPC soft-wires is called COF(chip on film), and we are also used to using LCD-driven soft-wires as COF) causes the following main faults:
1. Black screen: COF power supply short circuit, DC-DC circuit into a protective state after short circuit, the main voltage has no output, the whole machine stops working, the fault phenomenon is black screen.
2. Line or band: For example, according to the resolution of 1024*768, the driving electrode of source driver is 1024*3 (a pixel unit consists of three RGB pixels)= a total of 3072 driving electrodes. If these electrodes are divided into four regions driven by four COFs, each COF driving pin is 768, and the width of the pin is usually 0.0. Between 05mm and 0.01, it is thinner than hair. If contact is bad or open circuit breaks, the corresponding pins will lose drive, and the screen will appear bright lines, dark lines, large area of bad will form bright or dark bands.
3. Colour band, dark band, interference: What we are talking about here is that a single driving area has an image but the image is not normal, the color bias or brightness is abnormal or the color interference; the source driver driver (also known as data driver, vertical driver, source driver or X-axis driver), because X is good at expressing an English letter, we are used to it. It is called X-axis. In addition to the connection with the panel electrode, the other end is connected with the PCB end, which is also bonded by ACF and formed by hot pressing to form an on-line circuit. The PCB end provides power supply for the source driver, signal transmission and gamma voltage, etc.
Abnormal A. LVDS signal: color interference or discoloration.B. Gamma voltage anomaly: gray scale and color anomaly. C. Abnormal power supply: dark band or not working (if power supply or STH output open circuit, look at the location of the driver, will affect the driving work behind, resulting in a large area of failure).Most of the above are caused by poor PCB end (not excluding the COF drive itself fault), just remove the PCB end and clean it again, paste ACF glue and press it again by hot press.
4. X-axis regional anomalies: X-axis scanning depends on the design of different manufacturers. It can scan from left to right, or from right to left, or from middle to both sides. Either way, it is a relay running mode, just like an athlete passing a baton to another sport after a lap. He was asked to finish the next lap… a lap is equivalent to a COF working area, and the baton is equivalent to STH (STH source source driving start pulse, equivalent to gate driving STV signal). If the last athlete had fallen before he finished the lap, the latter athlete could not wait for the baton to run! That is to say, the rear COF drivers will not work properly, so the whole screen will not work or the front can work, and the back will not work properly (flashing, jumping, black and black).
5. Flower screen: slow response, drawing, flickering, jumping, deformation, disorder, black screen
Gate driverr driver/gate driver/Y-axis driver. At present, the signal power supply driven by gate driverr in LCD panel is driven by PCB through COF and ITO along the edge of the panel, and finally arrives at gate driverr. Any link in the whole circuit may cause errors in scanning timing, slow image response, wire drawing and flickering. Vibration, jump, deformation, disorder, black screen protection stop working, etc.
In addition, we mentioned above what failures can not be repaired, here we also reply, we usually receive calls from some customers, ask if the broken screen can be repaired? Unified reply here, this really can not be repaired!!!
A. Screen leakage can not be repaired, even if repaired by special means can not stand the use, soon the problem is still!
B.Y axis is driven by non-discrete external COF, the corresponding area is usually not repairable, but this is not absolute, individual can be repaired by special means.
C. Short circuit or open circuit inside the screen: Compared with the overall failure rate, it has a relatively low proportion of failure (can be repaired by laser, but the price is very expensive, imported laser must be used, the current domestic technology level is limited, repaired faults quickly, not durable! We only import, we can contact our company. We do not stock this kind of equipment, we need to pay a certain proportion of deposit before production.
Crossroads – X and Y are short-circuited at some intersection point to form two vertical and horizontal lines. A bright spot can be seen at the intersection point.
Big and small headlines – X or Y are short-circuited somewhere with the back panel (VCOM), and the line near the COF driver is relatively not obvious, the closer the short-circuited point line is, the more obvious it is.
Half-line – X or Y open at some point, the second half of the open circuit can not get signal power supply, so the second half does not work, forming a half-line.
More technical problems of LCD maintenance, please call our company, purchase equipment tuition free, we have a large number of LCD screens in maintenance every day, the practice of true knowledge!
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