Development status of high power LED packaging technology - next

Author: Zheng Jing too

Although the world has paid more and more attention to energy saving and power saving, and LED lighting is regarded as the most popular application in the next decade, there are still many thresholds for LEDs to enter into general lighting in the short term. It is due to two limitations of low luminous efficiency and high cost. However, these two limitations are closely related to the development of high-power LED packaging technology. If LED lighting technology can be used to increase its luminous efficiency to 150lm/W and significantly reduce its cost, it is expected that the LED lighting market will be promising in 2012~2013.

Japan's Intellectual Property Bank (hereinafter referred to as IPB) ranks the technical competitiveness of LED lighting manufacturers based on their own set of “Applicant Score Ranking”. According to the ranking results, the manufacturer with the highest technical competitiveness in the field of LED lighting is Nichia Chemical Industry. According to IPB, “applicant score” refers to the applicant's patent level from the quality and quantity of the patent applied for, and the target audience includes enterprises, universities, research institutions and individuals who apply for patents related to LED lighting technology to the Japanese Patent Office. According to the scoring project, “LED packaging” is one of the indispensable technological development projects to develop LED lighting business. What details must the LED package pay attention to? What is the development trend of its packaging technology? This article will provide a detailed explanation of these questions. Analyze each process required for LED packaging. High-power LED packaging technology can be subdivided into: 1. Bracket design (including light extraction and heat dissipation); 2. Chip selection and arrangement; 3. Solid crystal mode; Gold wire type and thickness; 5. Phosphor type and coating structure; 6. The curvature and refractive index of Silicone Lens. These six processes all have an impact on the thermal performance (thermal resistance), luminous flux (lumen), luminous efficiency, relative color temperature (CCT), color rendering (CRI), uniformity of light color, and lifetime of the LED. Every link should not be ignored. The following will be a detailed analysis of four of them, and explain their relationship to the characteristics of LEDs one by one.

Phosphor Coating Structure <br> In order to pursue high color uniformity and high output lumens, the traditional phosphor coating method (Uniform Distribution) has been unable to achieve this requirement, so many manufacturers have developed new phosphor coatings. Techniques such as Conformal Distribution and Remote Phosphor (Figure 1); application coatings focus on improving the uniformity of white LED color, while Remote Phosphor coating focuses on enhancement The light output of a white LED. Each of the three phosphor coating methods has its own proponents. For example, Nichia's NS6W083A product has a phosphor coating method for conventional phosphor coating; Lumileds uses electrophoretic coating technology to coat the phosphor on the chip (see figure). 2), in order to form a uniform thickness of the coated structure, so that a very uniform white light can be obtained, the technology has also been successfully applied to the Luxeon I and K2 products, and has been patented, the patent number is US 6576488 B2, however, the electrophoretic coating process is expensive to manufacture, which is not conducive to reducing the price of LEDs. In 2008, Lumileds proposed a new coating method called Lumiramic Phosphor Plate, which is directly attached to the chip. It converts blue light into white light. This method has a high degree of color control and can effectively reduce the number of Binning.


Figure 1. Schematic diagram of three phosphor coating structures (a) Uniform Distribution; (b) Conformal Distribution; (c) Remote Phosphor


Figure 2. Schematic diagram of a phosphor-forming Conformal Coating by electrophoretic coating technology

The Curvature and Refractive Index of Silicone Lens (Silicone Lens) As the operating power of high-power LEDs continues to increase, the temperature of the LED components will also increase. In this working environment, the traditional epoxy resin The packaging material can cause material degradation (yellowing) due to the inability to withstand this high temperature, and causes the brightness of the LED to decay. To avoid this, you must find a package that is suitable for high-power LEDs. Silicone is the best high-power LED packaging material due to its high refractive index, high temperature resistance, insulation, chemical stability, high light transmission (wavelength range between 300~700nm) and high reliability. Select the object.

At present, the most important manufacturers of silica gel are Shin-Etsu, Dow Corning, NuSil and Momentive (formerly GE Toshiba). The product characteristics of high-power LED packaging materials are listed in Table 1 for readers' reference. It can be seen from the table that the refractive index of the Silicone is between 1.4 and 1.41, and it can be inferred that the functional group of Silicone should be dimethyl (Dimethyl), and its hardness should fall within the Shore A range. Based on this hardness value, these silicone encapsulants can be classified as soft materials and referred to as Rubber or Elastomer; if a high-hardness silicone encapsulant is to be used, the functional groups of the silicone material need to be adjusted. In addition, the curing conditions of these silicone encapsulants generally require baking in an oven at 150 ° C for more than 1 hour to achieve hardening and obtain the hardness indicated.

Table 1. List of Silicone packaging materials and their characteristics commonly found on the market


1. The curvature of a silicone lens is not difficult to find from commercially available products. Some high-power LEDs contain a lens structure, while others do not. Since the design of the lensless structure is relatively inexpensive, it is often used, but its luminous flux is not the most superior. Therefore, it is often necessary to add a lens structure to increase the luminous flux of the LED, as shown in FIG. When the height (h) of the lens is equal to the radius of the lens, the light output rate of the LED will be higher than that of the flat panel LED, but when the height of the lens is equal to half of the lens radius, the light output rate of the LED will be lower than that of the flat LED. These results show that the light extraction rate is related to the lens structure, and the curvature of the lens also affects the total reflection. When light enters the low refractive index medium from the high refractive index medium, total reflection occurs. If the LED has a lens structure, the total reflection can be reduced, and thus the light extraction rate can be increased.


Figure 3. Relationship between light extraction rate and lens structure

2. The refractive index of Silicone Lens (omitted)
3. Silicone lens manufacturing technology (omitted)

Conclusion <br>If you want to bring high-power LED packaging technology to the fullest, you must focus on every aspect of LED packaging technology, including the design of the bracket, the choice and arrangement of the chip, the die bonding method, the gold wire type and thickness, The type of phosphor and coating structure, the curvature and refractive index of the Silicone Lens, etc., can only be used to create an ultimate LED package. From the number of patent applications, it can be found that domestic manufacturers have very little ink for LED packaging technology. Only a small number of patents are concentrated on the design of the brackets. As for other technologies, there are few disclosures, which will not be competitive with competitors. In view of this, this article will use this to attract more attention, and hope that domestic manufacturers can make more efforts to expose patents, and hope to have a place in the future lighting market.


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