The multi-chip LED integrated package is one of the ways to achieve high-power white LED lighting. This paper summarizes the characteristics of integrated packaging, from product application, packaging mode, thermal processing and optical design, and analyzes the development trend of integrated packaging, with the wide application of high-power white LED in the field of lighting. The integrated package will also be developed rapidly.
At present, there are two ways to achieve high-power LED lighting: one is to package a single high-power LED chip, and the other is to use a multi-chip integrated package. For the former, with the development of chip technology, the size is increased, the quality is improved, and high-power LED can be realized by high-current driving, but at the same time, it is limited by the chip size, and the latter has greater flexibility and development potential. The number of chips can be changed according to the illuminance, and it has a high cost performance, making LED integrated packaging one of the mainstream directions of LED packaging.
Integrated packaged product applications
According to reports, UOE Corporation of the United States introduced the Norlux series of LEDs in a multi-chip package using hexagonal aluminum plates as substrates in 2001; Lanina Ceramics introduced low-temperature sintered ceramics (LTCCM) on the company's unique metal substrate in 2003. High-power LED arrays packaged in technology; Panasonic introduced high-power white LEDs packaged in a combination of 64 chips in 2003; 6.6-W, 8W, 12W COB LED series light sources from Everlight, using multi-chip integration on MCPCB substrates The way to reduce the heat transfer distance and lower the junction temperature.
On the basis of analyzing various technical schemes of LED fluorescent lamps, Li Jiansheng used COB technology to directly fix small power chips on aluminum substrates to produce COB LED fluorescent lamps with high efficiency. Since 2009, 45,000 LED fluorescent lamps have been used. The Expo bus and nearly 4,000 city buses were modified to replace the original fluorescent lamps and received favorable comments from users, serving the Shanghai World Expo and urban traffic.
Yang Wei developed an LED explosion-proof lamp using a multi-chip integrated package LED light source module, which uses heat pipe cooling technology. The LED explosion-proof lamp has high brightness, long irradiation distance, high reliability, good heat dissipation performance and long service life.
LED integrated package features
Integrated package, also called polycrystalline package, determines the number of LED chips on the substrate base according to the required power. It can be packaged into high-power LED devices with high brightness such as 1W, 2W, 3W, etc. Finally, high refractive index materials are used. The chip is packaged in an optically designed shape.
The unique packaging principle of integrated package determines its many advantages, such as: (1) As far as China is concerned, the research and development of high-power chips is in a backward position. The use of integrated packaging is a shortcut for development, and is more in line with China's basic national conditions; (2) The chip can be designed to be connected in series or in parallel, flexible to adapt to different voltages and currents, to facilitate the design of the driver, to improve the light efficiency and reliability of the light source; (3) the number of chips on a certain area of ​​the substrate can be freely controlled, according to The customer's requirements can be packaged into point light source or surface light source in various forms. (4) The chip is directly connected to the substrate, which reduces the thermal resistance of the package, and the heat dissipation problem is easy to handle.
However, for integrated packaging, there are also some shortcomings: (1) due to the multi-chip integrated package on a substrate, resulting in a larger volume of the resulting light source; (2) multiple chips are combined by series and parallel, relative In the case of a single chip, its reliability is poor, which will cause the overall light source to be affected. (3) Although the multi-chip package has a strong heat dissipation capability compared to a single chip of the same power, the heat is dissipated by multiple chips at the same time. Different degrees of loss will cause different temperatures between the chips and affect the life. Therefore, the handling of heat dissipation is also critical. (4) The design problem of secondary optics, the multi-chip light extraction angle is different, and it is necessary to carry out the second optical design. Sub-optical design to meet user requirements.
Mechanical, thermal, and optical research in integrated packaging processes
Due to its outstanding advantages, integrated packaging has become the mainstream of LED packaging. In recent years, it has attracted the attention of many companies and research institutes and carried out a large number of research and applied for related patents. These are extremely Promote the development of integrated packaging technology.
(1) Package structure mode
The current mainstream form of multi-chip integrated package is that multiple chips are directly connected to the substrate in series and parallel, and then the chips are individually packaged or packaged under the same lens.
In the patents applied by Xu Xiangyang, a plurality of chips are directly fixed on an aluminum substrate, and after coating the phosphor, an optical lens is sealed on the outside of each LED chip. The process is simple, the packaging material is simplified, the thermal resistance is reduced, the light efficiency is improved, and the LED lighting product is easily assembled. Compared with the single chip packaging mode of the same power, the COB modular LED packaging technology has many advantages.
Li Jiansheng proposed a COB integrated packaging process based on the layer bonding surface and long heat conduction distance existing in the general integrated package. That is, the aluminum PCB integrated circuit board is engraved with some reflective cavities which are favorable for the diffusion of the illuminating light of the chip, and a plurality of chips are implanted one by one into the cavity, and a PCB line is drawn around the chip, and the chip electrode leads are soldered thereto, and the conduction circuit is Finally, a barrier is formed around the cavity to form a ring-shaped fence, and silica gel and phosphor are coated therein to form an integrated LED COB assembly at a time. This design directly connects the chip to the heat sink, which reduces the structural thermal resistance, and the heat dissipation effect is much better than the ordinary package structure, which improves the light output rate of the LED.
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