The COG manufacturing process has a history of nearly ten years of development. Its development is inseparable from the miniaturization, ultra-thinness of ICs and the refinement of LCD screen lithography accuracy. Our company has produced COG LCD screens for nearly 6 years. Over time, I have accumulated a lot of valuable experience.
1. The COG process flow is shown below.
LCD display -> Paste the ACF on the screen -> Take out the bare chip from the chip tray -> Check the alignment mark of the bare chip -> Check the alignment mark on the LCD screen -> Align the chip with the LCD screen- >Hot press head to paste the chip and LCD screen->The whole paste process is completed
2. Process points
(1) When bonding the IC, the IC alignment mark is required to match the alignment mark on the LCD screen;
(2) It is necessary to use a dust-free cloth dipped in solvent to remove foreign matter in the pressing area on the LCD screen, and use a UV lamp to remove the organic matter in the pressing area on the LCD screen; (3) ACF attachment accuracy is +100uM;
(4) Pay attention to the ACF storage conditions and control the ACF bonding time, hot pressing temperature and pressure head pressure. The ACF reaction rate is required to reach more than 80%. For example, use Hitachi (HITACHI) AC-8304Y ACF, and its storage conditions are: at room temperature of about 25 ° ℃ and humidity 70% RH, the validity period is 1 month; when the temperature is -10 °C ℃ ~ 5C, the validity period is 6 months. ACF use process conditions: paste ACF temperature 100±10C (actual temperature of ACF), pressure about 1Mpa, time 1~5 seconds, main pressure about 50~150Mpa (refers to the pressure on each ICBUMP, according to the conductive ball in ACF The pressure effect determines the size of the pressure). The ACF temperature is 220±20C (the actual temperature of the ACF), and the time is 7-10 seconds. All ACFs need to be placed at room temperature for 1 hour after being taken out of the refrigerator before opening the package;
(5) It is necessary to ensure the yield rate of the pre-process photolithography process, and strictly control broken pens and continuous pens (mainly at the IC interface); (6) LCD screens need to be strictly tested to prevent waste products from being missed, resulting in material waste and poor quality ;
(7) Full inspection under the microscope to prevent the broken pen from flowing out, requires at least 5 conductive particle indentations on the IC electrode, and adjacent bumps cannot be in contact with each other; (8) COG finished products must be 100% tested;
(9) COG-LCD products are generally high-density products. During manufacturing, the resolution of the photolithography section is required to be higher, and the PI orientation film and friction uniformity are better. When the line gap is less than 15uM, TOP (coated insulating layer) is required. Process to avoid short circuit breaks, uneven display, crosstalk, and large current consumption;
(10) Common defective products of COG include: IC foreign body, IC indentation, poor ACF attachment, IC alignment offset, IC thickness uneven, IC electrical encounter, IC crack/scratch, ICBUMP, etc.
3. Lithography accuracy Lithography accuracy refers to the fine size of lines and gaps that can be etched when making LCD displays. COG products are mostly high-density products, and the wiring between LCD and IC is denser. The PITCH (line width plus line spacing) value of COG product leads is generally below 50uMI, and IC interface lines are generally below 40uM. At present, some domestic manufacturers have controlled the PITCH value of their COG products at 20uM, which means that the processing accuracy of their lead or line gap has reached about 10uM.
4. The material requires transparent conductive glass (that is, a transparent conductive film is plated on the surface of the glass with good flatness, high transmittance, and small warpage). The resistance value is low. The sheet resistance is generally within 30Q, PI (polyamide Materials such as imines, orientation materials), liquid crystals, etc. require high purity, that is, high resistivity. ACF
(Anisotropic Conductive Film) is an anisotropic conductive film that conducts electricity in the vertical direction and is insulated in the horizontal direction. The main components are adhesive and conductive particles.
5. Cleanliness requirements The production process of COG products requires a cleanliness level of 1000, that is, the particle concentration of >=0.5 microns in the clean room <=1000 particles/liter.
