Micro LED, Mini LED, COB, GOB, TOPCOB... what is the specific meaning of this dazzling string of letter names? How to distinguish? And which of these emerging new terms represents the birth of innovative technology or is it the bluff market hype of businessmen?
The popularity of mini LED display technology in the commercial market has greatly encouraged the research and development of manufacturers, and has given birth to the continuous emergence of many innovative technologies and products. At the same time, a variety of new terms come one after another. And the promotion of each new term is an endorsement or evidence of the significance of the change of the product. It seems that it has a great name, and this technology has epoch-making significance.
In fact, the realization of every revolutionary innovative technology and product is difficult to achieve overnight. It requires a hard and long exploration process, during which there will be some transitional intermediate technology and products. As far as these intermediate technologies and products are concerned, they also have certain progressive significance. However, sometimes businesses exaggerate their propaganda and consciously pack various terms, which results in market disruption and misleading.
This paper will start from a simple chart to clarify the meaning of various nouns, technical origins, and innovative gold content related to LED display design.
The following table, starting from three basic elements, evaluates and classifies products with small spacing. The three elements are:
1. Chip size
2. Point spacing
3. Technical route
Using these three basic elements, we can accurately measure the technical content of a product.
Definition: chip size is less than 50um
Micro LED is a hot word that appears with high frequency. Generally speaking, the current industry-recognized standard is that it can be called micro LED technology when the chip size of the display screen is less than 50um. At present, the conventional chip size of small spacing LED display is more than 100um. Therefore, in order to challenge the existing technology, Micro LEDs are also more strictly defined as chips smaller than 20um or 30um.
When the chip size is below 50um, the pixel spacing is also defined in the order of micrometer. For example, when the pixel density of the mobile phone is 432ppi, the pixel spacing is 118um * 118um (μ m).
At present, Micro LED technology is still in the research and development stage. In addition to the micro chip technology, how to transfer a large number of micro chips to the circuit board is the biggest technical bottleneck of Micro LED at present. However, there is no doubt that the breakthrough in this field is a new technology with epoch-making significance.
Narrow meaning: chip size is 50-100um
Generalized meaning: the distance between points is less than P1.0
Mini led screen was first proposed by chip manufacturers. And the micro LED technology will take a long time to be realized. At the same time, for our large screen display, in most application scenarios, pixel density does not need to reach micron level. Therefore, compared with Micro LED, Mini LED panel has larger chip size and is easier to realize technically.
At first, mini led was defined strictly. The chip size was between 50-100 um. This chip of this size can only be realized by flip chip technology. It should be said that the initial definition of Mini LED has a great breakthrough in technology.
However, with the increasing heat of micro spacing LED, domestic display industry manufacturers call the display screen with a point spacing of less than 1.0mm the Mini LED due to the need of market promotion of “heat”. This kind of appellation is easy to be confused. Because the traditional surface mount package can also be used to achieve P1.0 or below, the n-in-1 package can also be used, and the positive chip COB package can also be used, and of course, the inverted cob can also be used. Therefore, many of the display screens known as mini led, which have not made a breakthrough in chip technology, are still widely used in small spacing LED display chips.
For example, the N-in-One integrated packaging introduced by some domestic packaging factories still uses chips larger than 100um, and the packaging technology route is SMD surface mount packaging technology. It is a set of 1R1G1B chips, which are originally packaged in a single package, and integrated into 4 groups, 6 groups or 9 groups, etc. It should be said that N-in-One is an exploration of the extension and improvement of traditional SMD packaging technology. It's not to say a technology update.
Qualitative: intergenerational change of packaging technology route
Highlight: the minimum distance between inverted cob points can reach P0.1
COB is the abbreviation of CHIP ON BOARD, which is an innovation of the existing SMD packaging mode, and also can be called the transformation of SMD small spacing led.
COB packaging is to put the chip direct to the solid-state welding line on the PCB board, and then protect it by glue coating technology. In SMD mode, the solid crystal, the solid crystal, welding wire and dispensing of the chip are packaged into an independent lamp bead, which is then pasted and welded on the PCB through the surface. The two packaging structures are shown in the figure below:
COB package completely abandons SMD bracket or base plate, and the structure is more concise. At the same time, because there are no exposed welding feet and not affected by the external environment, it greatly improves the sealing of the entire display structure. Therefore, COB packaging can greatly improve the reliability and stability of small spacing led. At the same time, COB technology can also achieve smaller spacing and lower material cost, which is a subversion of traditional SMD.
At present, COB can be divided into two types: positive chip cob and flip chip cob.
The minimum distance between points that can be achieved by the positive COB is p0.5. The flip COB can also remove the wires between the chip and the substrate shown in the figure above. Flip cob can further reduce the point spacing to P0.1.
One of the most representative products of the flip cob is the CLEDIS display screen displayed by Sony at major exhibitions, and the other is the p0.84 point pitch thewall display screen launched by Samsung. It can be said that in a period of time of the future, the flip cob represents the direction of the development of small spacing led.
Sony CLEDIS Display
Samsung THEWALL Display
Qualitative analysis: modified SMD with small space
GOB is the abbreviation of GLUE ON BOARD. It is to apply a whole layer of glue on the surface of display module of SMD to improve the sealing of SMD. It is an improvement of SMD surface mount.
It should be said that GOB is a kind of technological improvement of display manufacturers, which improves the performance of moisture-proof, water-proof and anti-collision of display screen. And to a certain extent, it makes up for the lack of reliability and stability of small spacing display screen. However, this technical scheme puts forward a very high requirement for SMD surface sticking process. Once there is a faulty welding, it is difficult to repair. In addition, it also needs time to verify whether the colloid will change color, degumme and affect heat dissipation during long-term use.
Qualitative analysis: modified SMD with small space
This product, called TOPCOB, has nothing to do with COB what we usually call. It still adopts the current SMD surface mount package and then the module surface is covered with glue, which is completely consistent with the gob technology mentioned above. It is a patch to the technical defects of surface mount, which is hard to be called a revolutionary intergenerational product.
In addition to the above mentioned terms, there are many new terms that have emerged or are emerging in the industry. To judge and measure these technologies and products, we need rational analysis. From chip technology, packaging technology to the final display production and assembly, what level does the new technology update take place at? Is it improvement of traditional technology or an update? Only by deeply analyzing the causes of technology can we not be misled by the exaggerated market propaganda of the businessmen. I hope this article will be helpful to your objective evaluation.
Lin, J. Y., & Jiang, H. X. (2020). Development of microLED. Applied Physics Letters, 116(10), 100502. doi:10.1063/1.5145201
Greig, W. J. (2011). Integrated circuit packaging, assembly and interconnections. New York: Springer.