With the rapid development of semiconductor technology, display technology is also constantly innovating. In recent years, Mini-LED and Micro-LED displays have become hot topics in the large-screen industry as next-generation display technologies. Various packaging technologies such as IMD, SMD, GOB, VOB, COG, and MIP are constantly emerging. Many people may not be familiar with these technologies. Today, we will analyze all the various packaging technologies on the market at once. After reading this, you will no longer be confused.
Q: What are small-pitch, Mini LED, Micro LED, and MLED?
A: Small-pitch: Generally, LED screens with a pixel pitch between P1.0 and P2.0 are called small-pitch displays. Mini LED: The size of the LED chip is between 50 and 200 micrometers, and the pixel pitch of the display unit is maintained within the range of 0.3-1.5 mm; Micro LED: The size of the LED chip is less than 50 micrometers, and the pixel pitch is less than 0.3 mm; Mini LED and Micro LED are collectively referred to as MLED.
Q: What is IMD?
A: IMD (Integrated Matrix Devices) is a matrix-integrated packaging solution (also known as "all-in-one"), currently typically in a 2*2 configuration, i.e., 4-in-1 LED chips, integrating 12 RGB tri-color LED chips. IMD is an intermediate product in the transition from SMD discrete devices to COB: the pitch can be reduced to P0.7 while improving impact resistance, but the four LEDs cannot be separated into different colors, resulting in color differences that require calibration.
Q: What is SMD?
A: SMD is an abbreviation for Surface Mounted Devices. LED products using SMD (surface mount technology) encapsulate the lamp cup, bracket, chip, leads, epoxy resin, and other materials into LED chips of different specifications. High-speed placement machines use high-temperature reflow soldering to solder the LED chips onto the PCB board, creating LED modules with different pitches. Small-pitch SMD typically exposes the LED chips or uses a mask. Due to its mature and stable technology, complete industrial chain, low manufacturing cost, good heat dissipation, and convenient maintenance, it is currently the most mainstream packaging solution for small-pitch LEDs. However, due to serious defects such as susceptibility to impacts, LED failures, and "caterpillar" defects, it can no longer meet the needs of higher-end markets.
Q: What is GOB?
A: GOB, or Glue On Board, is a protective process involving potting adhesive onto SMD modules, solving the problems of moisture and impact resistance. It uses an advanced new transparent material to encapsulate the substrate and its LED packaging units, forming effective protection. This material not only has extremely high transparency but also excellent thermal conductivity. This allows GOB small-pitch LEDs to adapt to any harsh environment. Compared to traditional SMD, it features high protection: moisture-proof, waterproof, dustproof, impact-proof, anti-static, salt spray-proof, oxidation-proof, blue light-proof, and vibration-proof. It can be applied to more severe environments, preventing large-area LED failures and LED drops. It is mainly used in rental screens, but there are issues with stress release, heat dissipation, repair, and poor adhesive adhesion.
Q: What is VOB?
A: VOB is an upgraded version of GOB technology. It uses imported VOB nano-adhesive coating, with nano-level coating machine control resulting in a thinner, smoother coating. This leads to stronger LED protection, lower failure rate, higher reliability, easier repair, better black screen consistency, increased contrast, softer image, and less eye strain, significantly improving the screen's viewing experience.
Q: What is COB?
A: COB (Chip on Board) is a packaging technology that fixes LED chips onto a PCB substrate and then applies adhesive to the entire assembly. Thermally conductive epoxy resin is used to cover the silicon wafer mounting points on the substrate surface. The silicon wafer is then directly placed on the substrate surface and heat-treated until it is firmly fixed. Finally, wire bonding is used to establish an electrical connection between the silicon wafer and the substrate. It features impact resistance, anti-static properties, moisture resistance, dust resistance, a softer image that is easy on the eyes, effective suppression of moiré patterns, high reliability, and smaller pixel pitch. It significantly reduces the "caterpillar effect" of dead LEDs, making it one of the most suitable technologies for the mini-LED era.
Q: What is COG?
A: COG, or Chip on Glass, refers to bonding LED chips directly to a glass substrate and then encapsulating the entire device. The biggest difference from COB is that the chip mounting carrier is replaced by a glass substrate instead of a PCB board. This allows for pixel pitch below P0.1, making it the most suitable technology for Micro LED.
Q: What is MIP?
A: MIP stands for Module in Package, meaning multi-chip integrated packaging. Due to the increasing market demand for light source brightness, the light output achievable with single-chip packaging is insufficient, leading to the development of MIP. MIP achieves higher performance and functional integration by packaging multiple chips within the same device, and is gradually gaining market acceptance. MIP is a hot technology emerging in the Mini/Micro LED field in 2023, primarily addressing the pain points of mass transfer technology in Micro-LEDs. It reduces the difficulty of mass transfer by integrating RGB three-color sub-pixels into the package and then transferring individual integrated pixels.
Q: What is CSP?
A: CSP stands for Chip Scale Package, meaning chip-level packaging. CSP (Converterless Package) is a further miniaturization of SMD (Surface Mount Device) technology. While also a single-chip package, it's currently only used for flip-chip packaging. By eliminating leads, simplifying or removing the lead frame, and directly encapsulating the chip with packaging material, the package size is significantly reduced, typically to about 1.2 times the chip size. Compared to SMD, CSP achieves smaller size, and compared to COB (Chip-on-Board) multi-chip packaging, it offers better chip performance uniformity, stability, and lower maintenance costs. However, due to the smaller flip-chip pads, it requires higher precision in the packaging process, as well as more demanding equipment and operator skills.
Q: What is a standard LED chip?
A: A standard chip refers to a chip where the electrodes and light-emitting surface are on the same side. The electrodes are connected to the substrate via metal wire bonding. This is the most mature chip structure, mainly used in LED screens with a resolution of P1.0 and above. The metal wires are mainly gold and copper. A tri-color LED has five wires. It is susceptible to moisture and stress, which can cause wire breakage and lead to LED failure.
Q: What is a flip chip? A: Flip-chip LEDs differ from standard-chip LEDs in the layout of the electrodes and the way they perform their electrical functions. The light-emitting surface of a flip-chip faces upwards, while the electrode surface faces downwards; it's essentially an inverted standard-chip, hence the name "flip-chip." Since it eliminates the bonding process required for standard-chip LEDs, it significantly improves production efficiency. Advantages of flip-chip LEDs include: no wire bonding required, resulting in higher stability; high luminous efficiency and low energy consumption; larger pitch, effectively reducing the risk of LED failure; and smaller size.
Q: What is a synchronous control system?
A: A synchronous control system means that the content displayed on the LED screen is consistent with the content displayed on the signal source (such as a computer). When the communication between the display screen and the computer is lost, the display screen stops working. Indoor small-pitch LEDs often use synchronous control systems.
Q: What is an asynchronous control system?
A: An asynchronous control system enables offline playback. Programs edited on a computer are transmitted via 3G/4G/5G, Wi-Fi, Ethernet cable, USB flash drive, etc., and stored on an asynchronous system card, allowing it to function normally even without a computer. Outdoor screens generally use asynchronous control systems.
Q: What is a common anode driver architecture?
A: A common anode architecture means that the positive terminals of all three types of LED chips (RGB) are powered by a single 5V source. The negative terminal is connected to the driver IC, which activates the circuit to ground as needed to control the LED. This is the most mature and cost-effective driving method, commonly used in conventional LED displays. Its disadvantage is that it is not energy-efficient.
Q: What is a common anode driver architecture?
A: "Common cathode" refers to a common cathode (negative terminal) power supply method. It uses common cathode LEDs and a specially designed common cathode driver IC. The R and GB terminals are powered separately, with current flowing through the LEDs to the negative terminal of the IC. With common cathode, we can directly supply different voltages according to the different voltage requirements of the diodes, thus eliminating the need for voltage divider resistors and reducing energy consumption. Display brightness and effect remain unaffected, resulting in energy savings of 25%~40%. This significantly reduces system temperature rise; the temperature rise of the metal parts of the screen structure does not exceed 45K, and the temperature rise of the insulating materials does not exceed 70K, effectively reducing the probability of LED damage. Combined with the overall protection of COB packaging, this improves the stability and reliability of the entire display system, further extending system lifespan. Simultaneously, due to the common cathode drive control voltage, heat generation is greatly reduced while power consumption is lowered, ensuring no wavelength drift during continuous operation. Displays true-to-life colors.
Q: What are the differences between common-cathode and common-anode driving architectures?
A: First, the driving methods differ. In common-cathode driving, current flows through the LED chip first, then to the negative terminal of the IC, resulting in a smaller forward voltage drop and lower on-resistance. In common-anode driving, current flows from the PCB board to the LED chip, providing unified power to all chips, leading to a larger forward voltage drop. Second, the supply voltages differ. In common-cathode driving, the red chip voltage is around 2.8V, while the blue and green chip voltages are around 3.8V. This power supply achieves accurate power delivery with low power consumption, resulting in relatively low heat generation during LED display operation. In common-anode driving, with a constant current, higher voltage means higher power consumption and relatively greater power loss. Additionally, because the red chip requires a lower voltage than the blue and green chips, a resistor divider is needed, leading to more heat generation during LED display operation.
