Apr. 09, 2021< Back to list
Several common applications of LED display MiniLED
As the display screens are getting closer, the volume of LED chips is getting smaller. We call LED chips with a chip size in the range of 50-200um as MiniLED. This chip is divided into front-mounted and flip-chip (as shown in the figure below). At present, the application of MiniLED in the LED display market can be roughly divided into three major applications: COB, conventional packaging, and CSP.
COB stands for Chip On Board, which is to directly fix the chip on the board. The chip here can be either a formal MiniLED or a flip-chip MiniLED. The main process difference between formal and flip-chip is that flip-chip directly fixes the chip on the PCB with conductive glue, eliminating the need for gold wire in the formal installation. The general production process of COB is shown in the figure below:
This approach has the following advantages and disadvantages:
1.1 A layer of GOB protection is added to the surface of the product. Anti-scratch and anti-knocking, surface waterproof, low failure rate.
1.2 The LED chip is in direct contact with the board, so the LED has good heat dissipation performance.
1.3 Small pitches can be made.
1.4 It is difficult to maintain dead pixels.
1.5 The consistency of the chip parameters is poor, and it takes a lot of time to calibrate.
1.6 Due to the problem of expansion and contraction, the PCB size cannot be enlarged, the ink color is difficult to control, and the product modularity is serious.
1.7 It requires production equipment that is completely different from the SMT process.
The main method to solve the problem of poor chip parameter consistency is to correct it point by point.
In addition, some companies add colored substances like matte powder to the epoxy of GOB to reduce the impact of PCB ink color and chip parameter inconsistency. However, this approach will cause the LED color gamut to change, and the display image reproduction will be reduced.
2. Application of conventional package MiniLED.
This approach is to package MiniLEDs into SMD components that can be operated on the SMT production line. The method is the same as the traditional SMD lamp beads, except that the chip inside the lamp beads becomes a Mini chip. The chip can be either formal or flip-chip, and there is an all-in-one package.
The difficulty of the MiniLED application process has been solved by the packaging factory, and the user only needs to mount it with the conventional SMT process. Considering product performance, yield, and price, there are also red-light formal installations and blue-green inverted installations on the market.
This approach has the following advantages and disadvantages
2.1 The conventional SMT process is mature; the defective rate of one-time operation is low
2.2 The materials provided by the supplier have been subjected to light separation and color separation, so there will be no blurring caused by inconsistent chip parameters.
2.3 It can be maintained with conventional maintenance tools.
Compared with a single LED, the chip efficiency of N-in-1 is greatly improved.
2.4 The size of N in one lamp bead is fixed, and the dot pitch is fixed.
2.5 It is impossible to achieve extremely small pitches like COB and CSP.
2.6 The heat dissipation of the lamp bead chip is worse than that of COB and CSP.
3. Application of CSP package.
CSP (Chip Scale Package) package means chip-scale package. This application method is to package the flip-chip MiniLED in the smallest package. The final size after packaging can satisfy conventional SMT production line operations. But because it is a CSP package level, the equipment should have higher accuracy.
This product has the following advantages and disadvantages:
3.1 A layer of GOB protection is added to the surface of the product to prevent scratches and bumps. The surface is waterproof and the failure rate is low.
3.2 The LED chip is a flip-chip with high luminous efficiency; the metal electrode is directly in contact with the plate, and the heat dissipation performance is good.
3.3 Small pitches can be made.
3.4 The production rate is higher than that of COB.
3.5 Strict requirements on the accuracy of production equipment.
3.6 As the red light chip material gallium arsenide is a very brittle material, the chip bonding part is easy to fall off during the bonding process, and the yield rate is not high.
3.7 Due to the problem of expansion and contraction, the PCB size cannot be enlarged and the ink color is difficult to control. The product modularity is serious.
3.8 It is difficult to maintain the dead pixels.
3.9 The consistency of the chip parameters is poor, and it takes a lot of time to calibrate.