COB LED display screen refers to an LED display screen that uses COB packaging technology (Chips on Board). It directly integrates and packages the light-emitting chip on the PCB board to achieve a compact structure and high integration.
This kind of display screen has the advantages of ultra-small spacing, delicate pictures, concentrated colors, and fast heat dissipation.
It is widely used in command centers, monitoring and security, advertising media and other fields, providing high-quality, high-definition display solutions for various scenarios.
What is COB LED?
COB stands for chip On board, which means that the bare chip is adhered to the interconnection substrate with conductive or non-conductive adhesive, and then wire bonded to achieve its electrical connection. COB LED is also called COB LED source, COB LED module. There are three packaging forms: long/square/circular.
COB LED display screen process
COB LED surface light source first covers the silicon wafer placement point with thermally conductive epoxy resin (usually epoxy resin doped with silver particles) on the surface of the substrate, then places the silicon wafer directly on the surface of the substrate, and heat-treats it until the silicon wafer is firmly fixed on the substrate. Until then, wire bonding is used to establish a direct electrical connection between the silicon wafer and the substrate.
There are two main forms of bare chip technology: one is COB technology and the other is flip chip technology (Flip Chip).
Chip-on-board packaging (COB), semiconductor chips are hand-mounted and mounted on a printed circuit board. The electrical connection between the chip and the substrate is achieved by wire stitching, and the electrical connection between the chip and the substrate is achieved by wire stitching, and is covered with resin to ensure reliability. .
Although COB is the simplest bare chip mounting technology, its packaging density is far inferior to TAB and flip-chip bonding technologies.
COB LED display screen welding method
(1) Hot pressure welding
Use heat and pressure to weld the metal wire and the welding area together. The principle is to cause plastic deformation of the welding area (such as AI) by heating and applying pressure while destroying the oxide layer on the pressure welding interface, thereby causing attraction between atoms to achieve the purpose of “bonding”. In addition, the interface between the two metals does not When flattened, heated and pressurized, the upper and lower metals can be inlaid with each other. This technology is generally used for chip COG on glass.
(2) Ultrasonic welding
Ultrasonic welding uses the energy generated by the ultrasonic generator. Under the induction of ultra-high frequency magnetic field, the transducer rapidly expands and contracts to produce elastic vibration, causing the riving knife to vibrate accordingly. At the same time, a certain pressure is exerted on the riving knife, so that the riving knife moves Under the combined action of these two forces, the AI wire is driven to rub rapidly on the surface of the metallized layer (AI film) in the welded area, causing plastic deformation on the surface of the AI wire and AI film. This deformation also destroys the AI layer interface. The oxide layer brings the two pure metal surfaces into close contact to achieve interatomic bonding, thereby forming welding. The main welding material is aluminum wire welding head, which is generally wedge-shaped.
(3)Gold wire welding
Ball bonding is the most representative bonding technology in wire bonding, because both semiconductor packages and transistor packages use AU wire ball bonding. Moreover, it is easy to operate, flexible, has strong solder joints (the welding strength of AU wire with a diameter of 25UM is generally 0.07~0.09N/point), and has no directionality, and the welding speed can be as high as 15 points/second or more. Gold wire welding is also called hot (pressure) (ultra) sonic welding. The main bonding material is gold (AU). The wire welding head is spherical, so it is ball welding.
COB LED display screen packaging process
Step 1: expand the crystal. An expansion machine is used to evenly expand the entire LED chip film provided by the manufacturer, so that the closely arranged LED grains attached to the surface of the film can be pulled apart to facilitate the stabilization of the crystals.
Step 2: Adhesive. Place the expanded crystal ring on the surface of the backing machine that has scraped the silver paste layer, and put the silver paste on it. Point silver paste. Suitable for bulk LED chips. Use a dispensing machine to place an appropriate amount of silver paste on the PCB printed circuit board.
Step 3: Put the expanded crystal ring prepared with silver paste into the spine crystal holder, and the operator will stab the LED chip on the PCB printed circuit board with a spine crystal pen under the microscope.
Step 4: Put the crystal-embedded PCB printed circuit board into a thermal cycle oven and let it stand for a period of time at a constant temperature. Take it out after the silver paste solidifies (do not leave it for a long time, otherwise the LED chip coating will be baked yellow, that is, oxidized, and the bonding will be done). cause difficulties). If there is LED chip bonding, the above steps are required; if there is only IC chip bonding, the above steps are cancelled.
Step 5: Stick the chip. Use a glue dispensing machine to apply an appropriate amount of red glue (or black glue) on the IC position of the PCB printed circuit board, and then use an anti-static device (vacuum suction pen or sub) to correctly place the IC bare chip on the red glue or black glue.
Step 6: Dry. Put the glued die into a thermal cycle oven and place it on a large flat heating plate at constant temperature for a period of time. It can also be cured naturally (longer time).
Step 7: bonding. An aluminum wire bonding machine is used to bridge the chip (LED die or IC chip) with the corresponding pad aluminum wire on the PCB board, that is, the inner lead welding of the COB.
Step 8: Pre-test. Use special testing tools (different equipment according to different uses of COB, a simple high-precision regulated power supply) to detect the COB board, and return the unqualified board for repair.
Step 9: Dispensing glue. Use a dispensing machine to place an appropriate amount of prepared AB glue onto the bonded LED die. The IC is encapsulated with black glue, and then the appearance is packaged according to customer requirements.
Step 10: Curing. Put the sealed PCB ( printed circuit board) into a thermal cycle oven and let it stand at a constant temperature. Different drying times can be set according to requirements.
Step 11: Post-test. The packaged PCB ( printed circuit board) is then tested for electrical performance using special testing tools to distinguish between good and bad.
COB LED display screen manufacturing factory
Shenzhen Chifuyi Technology Co., Ltd. is located in Shenzhen, China. We specialize in the research and development of LED displays and creative LED advertising screens for more than 15 years.
After years of continuous development, we have 3 production bases covering an area of 35,000 square meters and more than 500 highly skilled employees. With the spirit of independent research and development and technological innovation, we continuously update our production facilities, introducing and installing multiple fully automatic SMT machines, automatic printing machines, conformal paint machines, CNC screw machines, etc.
Our products have multiple patents and have obtained certificates such as CCC, FCC, CE, RoHs and UL. With good quality and excellent after-sales service, our products sell well at home and abroad and are highly praised by customers.
CHIFE focuses on the R&D, production and manufacturing of COB LED display screens. If you want to know more about COB LED display screen technology, please contact us.