The LED small-pitch display truly embodies China's "smart" manufacturing, and its rapid development trend proves that the LED small-pitch display has a broad market prospect. Home TV is a big cake with a global market size of nearly one trillion yuan per year. Can small-pitch LEDs share it? From a technical point of view, there are still several problems to be solved when LED-TV enters the home.
1. Electromagnetic Compatibility (EMC). LED-TV as a household appliance, in the national standard and national compulsory certification, its radiated disturbance field strength limit, radiated disturbance power limit, power terminal disturbance voltage limit and conduction common mode disturbance voltage of various signal ports Level limits are equal to CLASS-B in the national standard GB9254-2008 for information technology equipment.
In recent years, some outstanding companies in the industry have achieved results in this research, and the electromagnetic compatibility performance of a single display cabinet has truly reached CLASS-B level. However, household TVs must regard LED-TV as a complete set, and the achievement of CLASS-B level for a single cabinet does not mean that the whole set can reach CLASS-B level. As a compulsory certification of household appliances, we must not have the idea of muddling through. Shielding, grounding, frequency shifting, filtering, balanced transmission, component upgrades, circuit technology improvements, etc., perhaps we need to use all kinds of martial arts to get rid of the devil, and the cost will inevitably increase significantly.
Two, "caterpillar". The "caterpillar" phenomenon is a common name in the industry for the failure of an adjacent LED caused by the failure of one LED, and there are many reasons for it. Among them, the "caterpillar" phenomenon caused by the internal short circuit of a single 3-in-1 LED has not yet been found in the industry to completely cure it. In fact, the root cause of the "caterpillar" is the accumulation of a large amount of metal conductive materials in the small space of the LED. If we can start from the upstream of the chip and package, and greatly reduce the use of metal conductive materials inside the LED, especially the use of silver glue, we may be able to fundamentally eliminate the mechanism of "caterpillars". The good news is that people of insight in the industry have already started research and exploration of many new materials and new processes.
Among the many technical routes, there are three exploration directions worthy of attention: First, the red, green and blue are all double-electrode chips with a horizontal structure, and then all the insulating glue is used as the adhesive during the die bonding, and the use of silver glue is completely eliminated, so as to maximize Eliminate the main cause of "caterpillar" generation. The disadvantage of this solution is that the number of bonding wires has increased from 5 to 6, and the original narrow space is even more cramped. The advantage is that the use of conductive silver glue is completely abandoned, and the technical solution is practical. The second is to use flip-chip LED chips. This solution can greatly reduce the use of metal conductive materials inside the led video screen (their explanation), and the size of the LED can be made smaller, that is, the pixel density of the LED-TV can be made higher, and we can even dare to dream of 4K-LED-TV entering family. The advantages of this technical route are unquestionable, but the disadvantage is that it completely subverts the existing technical route. Therefore, this route is not something ordinary companies can do. The third is to adopt flip chip + flip chip welding process. Once it is maturely applied in the display field, it will bring infinite possibilities for the integration of LED display area array into flip chip + CSP + COB, and may bring us even greater surprises.
3. Color reproduction. LED has many technical advantages, one of which is the high color purity of the three primary colors of red, green and blue, which constitutes a wider color gamut range, thus forming an LED-TV whose color gamut range can reach more than 120% of the NTSC color gamut range . Therefore, LED display has become the darling in the media industry that needs to catch people's attention. When LED-TV enters the home, we not only need high color purity (that is, wide color gamut), but also need realistic color reproduction.
The low color reproduction of LED-TV is mainly due to the distortion (reddish) of human skin color. To solve this problem, the three primary colors of red, green and blue can be adjusted and matched, which can be divided into three levels for practice. The first level is "dominant wavelength matching". The main wavelength matching of red LED is about 612nm, the main wavelength matching of green LED is about 548nm, and the main wavelength matching of blue LED is about 465nm. The second realm is "higher purity of the three primary colors". After realizing the first level of "dominant wavelength matching", we found that if the "dominant wavelength matching" is achieved at the expense of color purity, wouldn't it be "the gain of the mulberry and the loss of the east corner"? Maybe we have to start with upstream chip materials, and even use multi-primary color matching technology to fully realize not only red, green and blue "dominant wavelength matching" but also "higher color purity". The third realm is "balanced enhancement of the purity of the three primary colors". If we match the wavelength and improve the color purity, but the improvement rate of the color purity of the three primary colors is uneven, that is, the red color purity increases by about 6%, the blue color increases by 3% to 4%, and the green color purity is basically the same. Then the phenomenon of "red-faced Guan Gong" is still lingering. Therefore, we also need to start with the epitaxial materials in the upstream, the packaging in the midstream (multi-primary color packaging), and the color space transformation in the downstream, and strive to achieve a balanced improvement in color purity under the condition of matching the dominant wavelengths of the three primary colors.
