What is a COB display?

COB (chip-on-board) is a chip-on-board package. It is a new product COB full-color display screen developed by Oreda Technology based on the glue-bonding planar technology + SMD precise glue-dispensing technology. The process of this product is to first cover the placement point of the silicon wafer with thermally conductive epoxy resin (generally epoxy resin doped with silver particles) on the surface of the substrate, then place the silicon wafer directly on the surface of the substrate, and heat treatment until the silicon wafer is firmly fixed on the substrate. So far, wire bonding is then used to directly establish an electrical connection between the silicon wafer and the substrate. Compared with the dot matrix module full-color and SMD full-color, this process is simpler, so it is convenient for mass production.

Process cost

SMD full color: The raw material cost of this product is more expensive, the production and processing technology is more complicated, and the input and cost costs are high.

COB display full color: COB eliminates the concept of bracket, no electroplating, no reflow soldering, no patch, and the process is reduced by 1/3. The efficiency of the die bonding and wire bonding process is comparable to that of SMD, but the efficiency of COB packaging is much higher in dispensing, separation, light separation and packaging. The labor and manufacturing costs of traditional SMD packaging account for about 15% of the material cost, while COB only accounts for 10%, and the cost of construction is at least 5% compared to SMD full color.

Optical and electrical

COB full-color has good color consistency, large viewing angle, uniform light spot, high brightness, and good color mixing effect. These are the features and advantages that SMD full-color and dot-matrix full-color cannot surpass. The viewing angle is large and the brightness is high. COB adopts heat sink technology, which can ensure that the LED has an industry-leading thermal lumen maintenance rate (95%). The following are the comparison pictures of the appearance and angle light shape of dispensing and SMD

COB Full Color Display Appearance SMD Full Color Appearance

The visual consistency of COB is better. From the appearance alone, it can be seen that there are hundreds of light-emitting points on the dispensing board, which are all on the same PCB board, that is, on the same level, so the light-emitting points are all on the same reference point, so the light spot is more uniform. , However, the SMDs are attached to the PCB one by one, and there will definitely be high and low spots, so the light spot is not uniform, so that the visual effect is worse than the effect of COB packaging.

COB has better light quality.

The traditional packaging form of SMD is to mount multiple discrete components on the PCB board to form LED applications. This method has the problems of point light, glare and ghosting, which is obvious from the figure; while COB is an integrated package and is a surface light source, which not only has the large viewing angle of advantage 1, but also reduces the loss of light refraction.

The COB display panel has a larger viewing angle. It can be seen from the light diagram below that the viewing angle of Aureda COB full color is much larger than that of SMD full color. will weaken, and the vertical angle also has a wide viewing angle of 140-170 degrees, these characteristics are particularly advantageous in some applications. Here’s a comparison of the two light charts:

COB screen angle light pattern SMD angle light pattern

Judging from the actual lighting effect diagram, such as the dispensing lighting effect diagram SMD lighting effect diagram From the above comparison, the visual effect of COB full-color display is better than that of SMD full-color in terms of viewing angle and luminous effect.

die placement

COB solid crystal placement method: RGB wafers are placed in a straight line, the lens above the wafer is a smooth curved surface, and the lens has a very good refraction effect on light. If the color and light are mixed more uniformly, the color mixing effect is good, and the light spot is uniform, so that the visual effect is good, and the display effect is more realistic. However, SMD full color does not have this feature, because the top of SMD is a flat surface, so the refraction effect is average, so the color matching The effect is worse than that of COB. The following is a comparison of the light distribution curves of the two, and the advantages of COB full color can be seen more clearly: COB full color R/G/B light distribution curve SMD full color R/G/B light distribution curve

From the light distribution curve, it can be seen that the curves of COB full-color are in good agreement, while the SMD full-color curves are not consistent. The red light curve and the blue/green light curve have a large separation, so the effect is better than that of COB full-color. worse.

reliability

Low thermal resistance

The system thermal resistance of traditional SMD packaging applications is: chip-die glue-solder joint-solder paste-copper foil-insulation layer-aluminum, while the system thermal resistance of COB packaging is: chip-die glue-aluminum, obviously The system thermal resistance of the COB package is much lower than that of the traditional SMD package, which greatly improves the life of the LED.

In addition, Alleda COB dispensing chip is directly fixed on the PCB board, so the heat dissipation area is large, so that the junction temperature of the chip is not easy to rise, resulting in better light decay and stable product quality; while the SMD chip is fixed in a bowl, It is not in direct contact with the PCB board, so that the heat dissipation area is small, which directly leads to its poor heat dissipation performance, so it will cause the junction temperature of the chip to rise, resulting in greater light decay. These reasons are the bottleneck in the development of SMD full-color technology.

Waterproof, moisture-proof and UV-proof

COB adopts the packaging method of dispensing on the board to form a lens, so when it is used outdoors, it has better performance in terms of waterproof, moisture-proof and UV-proof, while SMD generally uses a PPA material bracket, which is waterproof, moisture-proof and UV-proof. Poor, and the waterproof and moisture-proof problems are not solved, it is easy to have quality problems such as failure, dark and bright, and rapid attenuation.