The LED screen encapsulation technology has evolved through traditional LED, Micro-LED and Mini-LED phases. SMD, IMD COB, MiP, and IMD encapsulation techniques have all emerged during these phases, each has own distinct characteristics and applications.
SMD (Surface Mounted Display)
Covers all applications over P0.9, but can be damaged on smaller screens. This leads to a slightly lower level of reliability.
COB (Chip on Board)
COB packaging can omit SMT’s surface-mounting process, covering P0.4 to P2. It offers softer light but encounters module-based color differences.
IMD (Integrated Module Devices)
IMD packaging combines SMD and COB characteristics, which offers a range from P0.4 to 0.9. It is also highly reliable and has strong anti-damage abilities.
Micro-LED Encapsulation Techniques:
It provides a high resolution and brightness, but it struggles to achieve effective colorization.
Micro-Array Lens Optical Synthesis:
It has complex Structure and is unable to meet high brightness and resolution requirements.
UV/B MicroLED array with RGB Quantum Dot color conversion:
Stability issues can be encountered with various methods (spraying or photolithography)
MiP (Micro LED in Package):
MIP packaging uses RGB Micro LEDs to enable comprehensive testing, sorting and binning. This ensures display consistency while reducing downstream repair costs.
What is MIP packaging technology?
MIP packaging technology (Micro LED In Package) is a packaging technique based on Micro LED. The organic combination of Micro LED with discrete devices is achieved by packaging an entire large-area display panel separately. The Micro LED chip is transferred to the substrate using mass transfer technology.
After packaging, it is cut into single or multi-in-one small chips, and then the small chips are split and mixed, and then the chip placement process and screen processing are carried out. The surface of the body is covered with film to complete the production of the LED display.
The advantages of using MiP technology:
Good display effect
MIP devices are able to measure, sort and mix RGB Micropixels, ensuring the panel is displayed in a highly consistent manner.
Diverse product coverage:
MiP covers a wide range of product specifications (P0.9 to P3.0). This eliminates the need for specific encapsulations for each specification. The mass adoption of established specifications reduces costs quickly.
MiP’s wafer-testing, massive transfer, uniform equipment/processes and lower yield requirements provide substantial cost benefits, particularly when leveraging Micro LED’s manufacturing efficiency.
MiP integrates easily into existing COB or SMD production lines. This reduces downstream investments, and allows for standard processes throughout the industry.
The advantages of MIP LED display modules
High black ratio
Black ratio exceeding 99%
Special optical design
Viewing angle horizontally exceedingly large (>=174deg).
It is compatible with existing equipment and machines and can be used to complete testing and sorting.
Micro LEDs are easier to use in end markets
What is COB Packaging Technology ?
Chip-on-board (COB) is a packaging technique that differs from surface-mount(SMD) technology. The method involves attaching the bare chips to a PCB with conductive or nonconductive adhesive. Bonding wires are then attached for electrical connections. The production process is integrated from packaging to the LED display module/unit within a single facility, streamlining operations. Therefore, this allows for a smaller pixel size, increased reliability and cost effectiveness.
COB packaging technology is developing in three major directions:
Single-Chip Packaging Technology: This packaging method is a traditional one with fewer technical hurdles. LED Display manufacturers buy pre-packaged COBs from packaging factories, and assemble them using SMT onto LED display panels.
Limited Integration COB packaging technology: Some manufacturers are looking to improve production efficiency and reduce pixel fail rates without increasing packaging complexity. LED Display manufacturers buy COB LED modules (including brackets), with limited integration, from packaging factories. They then assemble the LED modules on LED display panels using SMT processes.
Integrated COB Packaging Technology: This COB packaging technology is highly integrated and reduces or eliminates SMT processes. LED array integration takes place during packaging, bypassing certain steps in SMT.
It doesn’t eliminate packaging, but it does simplify the process. SMD process involves a number of steps, including die bonding and wire bonding. Other steps include stamping, color sorting, taping and placement. COB simplifies the steps of IC placement, die-bonding, wire-bonding, testing and dispensing.
The challenges faced in COB packaging:
First Pass Yield:
The COB packaging process involves mounting 1024 LEDs on a large circuit board. If even one of the 1024 LEDs is defective, then the integrity of the board is compromised. It is difficult to ensure that all 1024 LEDs are fully functional before encapsulation.
Final Product Yield
After LED encapsulation, IC driver components undergo reflow soldering. The challenge lies in protecting the LEDs during the high-temperature (240 degrees) reflow process. COB saves the LEDs from one reflow process but exposes them to potential damage during the second reflow. High temperatures can cause wire breakage and micro-damages difficult to detect but can lead to eventual failure.
Repairing COB LEDs requires special handling. The maintenance of individual LEDs can be difficult because the heat generated by soldering often causes the LED to affect the area around it, making repairs harder.
These challenges are being addressed by companies with specific solutions. Protective measures such as shielding of the LED surface and point-by-point calibrating during maintenance are used to ensure consistency.
The advantages of COB packaging
Ultra-thin and thin: According to the actual needs of customers, PCB boards with thicknesses ranging from 0.4 -1.2mm can be used to reduce the weight to at least 1/3 of the original traditional products, which can significantly reduce structural, transportation and engineering costs for customers.
Anti-collision and compression resistance: COB LED display products directly encapsulate the LED chip in the concave position of the PCB board, and then encapsulate and solidify it with epoxy resin glue. The surface of the light spot is raised into a raised surface, which is smooth and hard, impact-resistant and wear-resistant.
Large viewing angle: The COB package uses shallow well spherical luminescence, the viewing angle is greater than 175 degrees, close to 180 degrees, and has a better optical diffuse light effect.
Strong heat dissipation ability: COB products encapsulate the lamp on the PCB board, and quickly transfer the heat of the wick through the copper foil on the PCB board, and the thickness of the copper foil on the PCB board has strict process requirements, coupled with the immersion gold process , will hardly cause serious light attenuation. Therefore, the lamp rarely dies, greatly extending the life of the lamp.
Wear-resistant and easy to clean: The surface of the lamp points is raised into a spherical surface, smooth and hard, impact-resistant and wear-resistant; if there are bad pixels, they can be repaired point by point; without a mask, if there is dust, it can be cleaned with water or a cloth.
Excellent all-weather characteristics: It adopts triple protection treatment, with outstanding waterproof, moisture, corrosion, dust, static electricity, oxidation, and ultraviolet effects; it meets all-weather working conditions and can still be used normally in a temperature difference environment of minus 30 degrees to above zero 80 degrees.
COB and MIP Packaging Development
Many companies are currently developing SMD and COB technology. IMD and COB are primarily used for pitches below P1.0. Both technologies are suited to specifications between P0.4-P0.9. MIP is similar to COB pixels that are individually encapsulated: it offers COB-level reliability for integration and flexibility of individual LEDs, but requires lower reliability when transferring large amounts. MIP technology is still a good choice for mainstream applications such as P1.2,P1.5 and P3.0.
COB is a leader in high-integration and high-pixel density encapsulation. It targets products that are mid-to-high-end, selling mainly below P1.6. P1.2 LED displays are more prevalent. COB’s cost-effectiveness increases as the pitch decreases. COB has a lower cost of production than SMD for pitches less than P1.2.
COB technology is a good choice for applications that require a high-density encapsulation. It offers cost savings in smaller pitches and can be used in varying applications.
Differentiating between COB and MIP packaging:
COB: COB packaging of LED display involves higher-quality assembly without brackets. The chips are directly attached to the substrate with silicone or conductive glue, then wire-bonded for electrical connections.
MIP: MIP packaging links LED chip electrodes to substrate electrodes after the electrodes are completed.
COB: A popular choice for its simplicity, aesthetic appeal and cost-effectiveness.
MIP: Recognized as a packaging solution that achieves ultra-thin packaging and high production efficiency. It also provides superior heat dissipation. COB technology integrates downstream LED display technology with midstream LED packaging, reducing brackets costs and streamlining production processes to achieve higher efficiency.
MIP technology, on the other hand is a cost-effective and high-quality way to produce Micro LEDs. MIP-produced P1.2 products are the same price as COB or SMD made at the same pitch. However, MIP has a lower cost when it comes to manufacturing smaller pitches than P1.2.
Leading LED display manufacturers discuss the differences
For Micro in package, only a few companies have achieved mass production. MiP’s advantage lies in the miniaturization of packaging and the smaller size packaging, while still maintaining brightness, color consistency, and other product characteristics. MiP has a strong industrial chain that can replace products seamlessly without changing their electronic structure and improve performance.
MiP offers many advantages, including light mixing, uniformity, low cost of repairs, reduced difficulty for spot testing and sorting and no Mura Effect. MiP also has the unique advantage of being compatible with mass-production Micro LEDs in large sizes and is accepted by LED display manufacturers.
In terms of LED display applications for smaller pitch and larger sizes, MiP can avoid core bottlenecks in yield, ink color consistency, uniformity, inspection and repair, cost, etc., making it an ideal choice for Micro LED display production.
In addition to its technical advantages, MiP can match the original process of LED displays in terms of manufacturing process and process, which means that MiP has higher compatibility in terms of manufacturing process, technology and other aspects.
If we look at MiP and COB technologies from a comparative perspective:
Regarding the LED chip size requirements, usually, COB can only encapsulate LED chips with a bilateral size greater than 100μm, while MiP can encapsulate LED chip sizes below 60um; at the display level, MiP can have the smallest pixel pitch, followed by COB. Generally speaking, MiP is superior to COB in terms of LED chip size, electrical connection, contrast, mounting process, repairability, flatness, mixed light bins, etc.
COB and MIP differ in their manufacturability and usage scenarios, as well as the display performance.
Manufacturing: MIP (Mini LED in package) can reuse SMD production equipment, which reduce heavy asset investment; MIP, or Micro LED in Package, may also be able to use some of the SMD equipment. COB, (Chip on board) requires an investment in its own production line.
Use scenarios: COB and MIP (MicroLED in package) are used primarily for large-size LED displays such as in control rooms, large meeting rooms, exhibitions, and other indoor scenes. The MIP chip size is getting smaller. In the future, Micro LEDs will mainly be used for small LED displays, including wearable devices, Micro LED televisions, vehicle displays, and other scenarios.
Display performance: COB LED displays high brightness and high contrast, while presenting HDR effects. It also has many advantages over SMD products, such as display stability. MIP’s display performance is comparable to COB and its large viewing angle consistency is superior. Display stability is less stable without surface integration packaging than COB.
Micro LED in Package (MIP) is currently the most popular and easy-to-mass produce route. It can achieve ultra-high resolution display and can realize display products below P0.4mm. It requires higher precision in the driving scheme, so in ultra-small The spacing display will be better.
MiP is currently divided into two categories on the market: package level and chips level. Kinglight and Lijing are the companies that represent MiP package level, which is still a continuation of SMT. Chip-level MiPs are mainly from international brands such as Seoul Semiconductor and Samsung.
The main difference between COB and MIP package-level is the SMT and COB packaging process. COB is the absolute leader in reliability and stability. COB also does not use a lamp cup packaging connection, and the Chip can be directly attached to the PCB board. Therefore, the cost of COB at the same scale than package-level MIP.
Mini LED is the main field of battle for MiP package level. The products are used primarily in commercial displays, XP Photography, consumer fields, etc. It’s not suitable for professional applications such as medical and government. Its spacing limits its ability to enter the Micro LED market. Package-level MiP represents a continuation and extension of original capabilities. This does not mean there will be an incredibly bright future.
The main difference in chip-level MiP is the arrangement of the RGB chip. The process used is mass transfer or solid crystal, which is similar to the future technology of COB. Batch production is not possible in the near future due to high costs and unreliable mass production capacities. The Micro LED market will continue to be parallel to COB as long as the industry’s technology, manufacturing costs and production equipment are not unified. COB Packaging will be the mainstream technology of Mini LED and the only way to Micro LED.
The debate over whether COB or MiP is superior has never ended. In general, LED display manufacturers tend to focus on the maturity and reusability of MiP’s technology, while COB’s growth is their main focus.
Some LED display manufacturers take a clear stand, but most choose to follow both paths in parallel. Manufacturers all agreed that MiP’s importance is unquestionable, it will take time to make breakthroughs in COB cost reduction, and the large-scale market application of Micro LED still has a long way to go.