[analysis] package and performance of color temperature adjustable LED

LEDs are increasingly used in indoor and outdoor lighting applications because of their excellent performance combined with intelligent control systems, but at the same time, they also set new requirements for color temperature and color rendering index. In order to cope with this challenge, a new color temperature adjustable LED was designed. The high-power LED chip combined with the metal substrate was used to package the warm white light high color rendering index LED sample with adjustable color temperature, and its luminescence spectrum, color temperature and color rendering. The index was tested with changes in current. It was found that the spectrum of the LED has three peaks. The color temperature can be changed from 5000K to 3300K, covering the range of cool to warm light. The color rendering index can be increased from 68 to over 90, which can meet indoor lighting. Requirements. The LED with adjustable color temperature is applied to the downlight, and its luminous effect and heat dissipation performance are tested, indicating that the LED has the characteristics of uniform luminous surface, no glare, small thermal resistance, and the like, and is particularly suitable for indoor lighting applications such as downlights.

1 Introduction

Since the invention of blue LEDs, people have begun to develop various high-power white LED packaging technologies, and hope that white LEDs can replace traditional lighting sources. At present, the white LED production technology on the market is mainly divided into two major mainstreams. The first is to use the phosphor to convert the blue or ultraviolet light generated by the blue LED or the ultraviolet LED into two-wavelength or three-wavelength white light respectively. This technology is called fluorescence. The powder is converted into a white LED; the second type is a multi-chip white LED, which is combined to form white light by combining two (or more) LEDs of different color lights. The first method can obtain white light with medium to high color temperature, and poor color rendering for warm color temperature. In order to solve this problem, a red phosphor is usually added, but the red phosphor has a low excitation efficiency, resulting in a low overall light efficiency.

The second method needs to supply power to the three chips separately, the driving circuit is complicated, and the aging attenuation of the three chips is inconsistent, and the long-term work will cause the color temperature to shift.

2 color temperature adjustable LED package

LED packaging technology actually borrows from traditional microelectronic packaging technology, but LED has its own unique features, and can not be completely in accordance with microelectronic packaging. The whole LED packaging process mainly includes the selection of packaging materials, the design of the package structure, the control of the packaging process, and the optical design and heat dissipation design. In general, it is thermo-electric-machine-light (TEMO), as shown in Figure 1, this is The key technology of LED packaging.

Figure 1 LED packaging key technology The traditional multi-chip integrated package is to fix the LED chip on the circuit board according to certain rules, such as aluminum-based copper clad laminates, ceramic circuit boards, etc., because aluminum-based copper clad laminates and copper-based copper clad laminates are inexpensive. They are widely used, but they also have inherent disadvantages. They are usually laminated by a circuit layer (copper foil layer), a thermally conductive insulating layer and a metal substrate, but the thermal conductivity of the thermally conductive insulating layer is extremely low, which becomes a thermal bottleneck of the circuit board, resulting in a thermal conductivity of only 1.5 W/ of the entire circuit board. mK or so. The ceramic circuit board has good thermal conductivity, but it has the disadvantages of high cost, unsuitable processing, and high brittleness, and it has a high proportion in the overall cost of the LED device, and its application is also limited. In order to solve the above problems, an LED package structure has been developed. A window is opened at the solid crystal position of the aluminum-based copper clad plate, and the pad needs to be placed at the position of the bonding wire, and an aluminum plate having the same shape as the aluminum-based copper clad plate is attached to the aluminum substrate. Under the copper plate, the LED chip is placed on the area passing through the window, which can greatly improve the heat dissipation performance of the LED.

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