Source： RUI JIN
China's LED industry started late. Under the circumstance that the LED core technology is firmly controlled by the international giants, the upstream chip end is difficult to intervene. Chinese enterprises have to choose the technical difficulty is not very high, the entry threshold is relatively low package, and then to this Upstream and downstream extensions. Today, China's LED packaging has reached a world-class level. LED packaging is no longer a simple assembly link, but a test of the production process and technical level.
For LED displays, the LED device package accounts for 30%-70% of the total cost, and the quality of the package directly closes the quality of the LED display. For a long time, the advancement of LED display device packaging technology has promoted the development of LED display screens; and with the development of LED displays towards high-definition displays, their requirements for the technology and processes of LED display device packaging have also become higher and higher. The current LED display industry is mainly based on surface-mount packages. Simultaneously, the in-line package and COB package coexist, but since last year, COB technology has gradually received the attention of display manufacturers, and Mini LED and Micro LED technology have also been widely used. and. In the face of this new trend, how will our LED packaging companies respond? The future of LED display device packaging will eventually go to where these have become the concern of the current business.
LED display device packaging technology development process
To understand the current status of LED packaging industry development and future trends, we must first review the history of China's packaging industry development. China's LED industry probably emerged in the 1980s. The development of LED display packaging devices has undergone several stages: dot matrix module, in-line (lamp), sub-surface, and surface-mount (SMD). Today, dot matrix modules and sub-surface mount packages have been eliminated from the market. In-line packages are still used in large-pitch outdoor markets above P10, while others are superseded by surface mount devices. With the continuous development of the small-pitch LED display market, more display companies are turning their attention to the COB package. At the same time, with the advent of the new generation of display technology Micro LED, which is considered as potentially disrupting the industry, Micro LED packaging technology has also been widely discussed in the industry. Let us take a look at the respective technical characteristics of these types of packaging.
1, in-line (lamp) package
As the in-line package following the dot matrix module, the technical principle is to use a lead frame as a pin for various package shapes. Usually, one end of the bracket has a “cup-shaped” structure to stick and fix the LED chip in the “ In the cup-shaped structure, the liquid epoxy resin is injected into the cavity of the LED mold, then the pressure-welded lead-type LED bracket is inserted, the epoxy resin is cured by high-temperature grilling, and finally the mold is released. forming.
The in-line type can be said to be the first LED product that has been successfully developed and put on the market in a large number, with various types and mature technologies. The manufacturing process is simple and the cost is low. Therefore, the inline package has a very high market share before SMD appears. In-line LED package products are mainly used for outdoor large screens, with advantages of high brightness, high reliability, and strong environmental adaptability.
At present, due to the fact that the distance between outdoor spots is also increasing towards the high density, in-line insertion is limited by the insertion of three components of red, green, and blue, which cannot achieve high density. Therefore, outdoor spot pitch P10 is gradually replaced by surface-mounted LED devices. It is generally believed that the outdoor in-line LED display screen uses P10 as the boundary line, but there are also LED display products in the industry that will be used in the P9 display.
2. Surface Mount (SMD) Package
Surface Mount (SMD) package is to solder single or multiple LED chips to a metal bracket with a plastic “cup” frame (the external pins of the bracket are connected to the P and N poles of the LED chip respectively), and then to the plastic frame. The liquid epoxy or silicone is encapsulated, then baked at high temperature, and finally cut into individual surface-mount packages. Due to the surface mount technology (SMT), it is highly automated. The use of surface mount packaging device display, in the color reproduction, color consistency, uniformity, viewing angle, the overall effect of the screen, especially in terms of volume, all have the advantages of in-line display can not be compared. However, SMDLEDs are also congenitally deficient, with high failure rate and decay rate, and relatively poor adaptability to harsh environments.
At present, SMD LEDs are mainly classified into TOP LED and Chip LED. The former often uses a PLCC (Plastic Leaded Chip Carrier) bracket, and the latter uses a PCB circuit board as a carrier for the LED chip. The cost of the PLCC support is low, but there are problems such as poor air tightness, poor heat dissipation, uneven light emission, and decreased luminous efficiency in applications. Although there are also PCT and EMC material holders with better performance and light efficiency, they are not widely used in the industry because they are expensive and costly.
3, COB package
A COB (chip on board) package is a method for attaching a bare chip to an interconnect substantially with conductive or non-conductive adhesive, and then performing wire bonding to achieve its electrical connection. The COB package is a stand-less technology without the stand's solder PIN pin. Each lamp bead and solder wire is tightly encapsulated in epoxy by colloidal epoxy without any exposed elements.
Compared to SMD-packaged displays, the COB display uses integrated packaging technology. This eliminates the need for a single LED device package and then the SMT packaging process, which can effectively solve the SMD packaging display, due to the ever-decreasing point spacing. The difficulty of the process is increased, the yield is low, and the cost increases. However, COB packaging has not been widely used in the display industry since COB packaging integrates upstream chip technology, midstream packaging technology and downstream display technology. To realize the large-scale application of COB packaging, it needs the close cooperation of upper, middle, and downstream enterprises to complete.
4, Micro LED package
The full name of the Micro LED is "Micro Light Emitting Diode," and Chinese is also called a micro light emitting diode. It can also be written as "μLED."
Micro LED's thinning, miniaturization and arraying of its LED structure make its volume about 1% of the size of mainstream LED. Each pixel can be addressed and driven independently to reduce the pixel pitch from millimeter to micrometer. Thus the theory reaches 1500 ppi and even 2000 ppi ultra high resolution.
Micro LED inherits the advantages of low power consumption, high brightness, ultra-high resolution, color saturation, fast response speed, ultra-power saving, long life, and high efficiency. Its power consumption is about 10% of LCD, OLED 50%. Therefore, MicroLED is seen as a new generation of display technology that may disrupt the industry.
Current Problems of LED Display Device Packaging Technology in China
The development of LED displays has experienced the rapid development of single-color, full-color displays, and small-pitch HD displays. Nowadays, 2K has become popular, 4K&HDR technology has risen, and ultra-high-definition 8K has also been proposed. With the constant pursuit of display effects, LED display companies are constantly making technological improvements. However, people's pursuit of high-definition picture quality is endless, and the development of a technology may face the ceiling and face the problem of replacement of old and new technologies. LED display industry as an emerging industry, of course, technology can not be eliminated so soon, but now the LED display industry is just like a crossroads, facing the "left" or "right" problem.
Although “all roads lead to Rome”, the number of ways to reach the destination is much, but the difference is that there are both detours and shortcuts. In the current industry, LED display screens are advancing towards the development of high-definition, and some have chosen to continuously improve the small spacing of SMD, while others have chosen COB small pitch display screen this route.
For SMD small-pitch LED display screens, we have to mention that it is the appearance of SMD's small pitch that allows LED display screens to enter the room from the home screen area, thus opening up a vast commercial display market. In the professional indoor large-screen display area, there are mainly DLP rear-projection splicing, LCD splicing and other technologies, each of which has its own advantages and disadvantages. With the advantages of seamless splicing, low-light and high-gray, the small-pitch LED display has rapidly gained market recognition and has been advancing rapidly, gradually replacing a portion of the market that originally belonged to DLP and LCD. SMD's small gaps are now widely used in high-end applications such as command rooms, control rooms, and conference rooms.
SMD small-pitch LED display greatly expands the application space of LED display. In order to meet the development trend of high-definition display, many companies are now focusing on the continuous improvement of the small pitch, and some manufacturers have already launched a 0.7 mm pitch. The display products, but limited by the process and cost, this very small pitch display product has not been applied in the market.
It is also due to SMD's small spacing in the technical process and manufacturing costs will soon reach the limit, so some of the industry's display companies have turned their attention to the COB display.
Above, we have already mentioned some technical principles about COB packaging. Compared with SMD packaging, COB is easier to achieve a small pitch, but COB is unable to solve the problems due to its uneven ink, poor consistency, and low yield once. Large-scale mass production has occupied a relatively small market share in recent years. However, in 2017, the sales of COB small-pitch displays increased by more than 200%, which was nearly 4 times that of the entire small-pitch LED market. Therefore, some people in the industry believe that the COB small-pitch display is about to usher in a period of rapid development, and COB is expected to reach 2018. Small pitch display products will grow by more than 15%.
In the past, companies engaged in COB display screens were only a small number of players such as Changchun Xida, Wei Qiaoshun Optoelectronics, and Oleida. Nowadays, with more and more companies participating, especially the listed company Lehman's participation, it has become even more prominent. Many companies pay attention to COB small-pitch displays.
The rise of new technologies, LED display device packaging companies have different attitudes
As the industry continues to improve technology on SMD and COB technology, the emerging Micro LED technology is increasingly attracting the attention of major companies in the industry. Even the concept of the Mini LED has recently been brought up. The discussion and interpretation of the two are overwhelming.
If everyone said that Micro LED was relatively unfamiliar a few years ago, now it is impossible for either LED display companies, packaging companies, or third-party supporting companies to ignore it. Micro LED seems to be lurking in the industry for many years, but is about to go in the "ghost" of the broad daylight.
We will trace the source, we will find that the development of LED display for nearly three decades, and the emergence of Micro LED, can be traced back to at least 17 or 8 years ago. For example, as early as 2001, the team of Satoshi Takano of Japan announced a set of Micro LED arrays they studied. The array adopts a passive driving method, and uses a wire to connect the pixels and the driving circuit, and places three red, green and blue LED chips on the same silicon reflector to achieve colorization through RGB. Although the array has achieved initial success, it also has disadvantages that cannot be ignored. The resolution and reliability are still very low, and the forward conduction voltages of different LEDs are quite different.
Subsequently, the results released by multiple project teams in the world continue to promote the development of Micro LED related technologies. However, Micro-LED led the attention of a large number of people for the first time in the LED display industry, and everything was due to the influence of Apple.
In 2014, Apple acquired LuxVue Technology, a Micro LED display technology company, and obtained a number of patented Micro LED technologies. At that time, it was widely believed that Apple wanted to use the new generation of Micro LED technology on Apple Watch and iPhone. However, because they were reluctant to rely too heavily on panel makers, they acquired LuxVue in order to obtain technical leadership in the field of Micro LED. This acquisition of Apple has caused market attention and led to some discussions in the LED display industry. However, at this time, the small-pitch LED display screen has just begun to emerge. LED display companies have adopted a wait-and-see attitude for the next generation of Micro LED display technology. Many people even think that this has little to do with the LED display industry, at least still far away.
Until this year, Samsung’s “The Wal l” TV again triggered the industry’s focus on Micro LED. According to reports, at the CES 2018 show in January, Samsung introduced the new "The Wall" TV, stunning the entire industry with its outstanding image quality. This product is equipped with Micro LED technology, which is also the world's first 146-inch. Micro LED modular TV. However, some people in the industry think that Samsung's "The Wall" TV is not a true Micro LED technology, but a technology that lies between traditional SMD and COB.
Regardless of whether Samsung's technology belongs to the Micro LED, at least Samsung’s “The Wall” TV will lead people to pay attention to Micro LED technology.
It is generally believed that Micro LED is technically feasible and its advantages are also visible. However, the problem of Micro LED in the "mass transfer" has become the biggest "stumbling block" to the market.
Mass transfer is an academic term that is often used in the engineering design of material handling processes. It involves the diffusion and convection of substances or particles within a physical system. More specifically, a huge amount of transfer is to describe a chemical or physical mechanism, which is a transport phenomenon, which means that a large number of points (molecules or particles) move from one end to the other. It can be a single stage, or multiple stages, and involves a liquid or gas phase, and sometimes it can occur in solid matter. In the production of Micro LED, it is necessary to correctly and efficiently move millions or even tens of millions of micron LED die to the circuit substrate. However, it is not an easy task to place a large number of micron-scale LED die on a target substrate or circuit through high-precision equipment. Taking a 4K TV as an example, the number of crystals to be transferred is as high as 24 million (calculated as 4000 x 2000 x RGB three colors). Even if 10,000 are transferred at a time, it is necessary to repeat 2400 times.
Although a technical problem can be overcome, it will be overcome sooner or later. However, industry insiders conservatively estimate that it will take at least 2 to 3 years for the Micro LED to actually go to market. It may be the time Micro LED was used in the market that some companies saw the opportunity, so Mini LED as a "transition technology" came into being.