From green to mature: LED packaging indicators should be considered comprehensively

China is a big LED package country, with the world's top packaging technology is gradually shrinking, and in the forefront of the local products. At the "Advanced Packaging and Module Technology Branch" of SSL, delegates gave a detailed introduction to their latest research results and the latest products, and shared the latest trends and intelligence of the LED packaging industry.

Compared with the past, the most significant trend now no longer focuses on a single parameter, but comprehensively considers the comprehensive indicators of luminous efficiency, color rendering index, life expectancy and cost. At present, the mainstream way to produce white LEDs on the market is to use blue LEDs to stimulate yellow phosphors. However, the warm white color rendering index produced by this method is relatively low. Lu Pengzhi, assistant researcher of the Institute of Semiconductors of the Chinese Academy of Sciences, pointed out that adding appropriate proportions to yellow phosphors Red phosphors increase the color rendering index, but the luminous efficiency is reduced.

In order to solve the contradiction between color rendering index and luminous efficiency, Professor He Guoxing of the Department of Applied Physics of Donghua University believes that adding red phosphor to improve the color rendering of white LED will greatly reduce the light efficiency. Red LED or chip should be used instead of red phosphor. Achieve high light efficiency and high color rendering LED white light. He also suggested that when designing high color rendering LEDs, you should not only consider the general color rendering index Ra, but also pay attention to the special color rendering index R9 for saturated red, and the special display of four saturated colors such as red, yellow, green and blue. The average value of the color index R (9-12). Because the study found that the general color rendering index Ra has an inconsistency with the visual evaluation of the color rendering of the LED. The white color of the LED white light with a low color rendering index Ra may be visually inferior. On the contrary, the white color of the LED with higher Ra may be better in visual color rendering. The high color rendering of LED white light is guaranteed only when Ra and R9 have higher values ​​at the same time. In addition, Prof. He proposed the spectral model of LED under different currents, and successfully developed LED color rendering simulation software to achieve high color rendering and high light effect color-adjustable temperature LED white light.

For the phosphor link, Inter-Photonics Executive Vice President and Technical Director Yi-Qun Li made a detailed analysis. He believes that the phosphors for TV backlights are mainly green phosphors and red phosphors, and the lighting is mainly YAG phosphors. A silicate phosphor, an aluminate green phosphor, and a mixture of a nitride red phosphor and a yellow, green phosphor. He combined Beta-SiAlON green phosphor, silicate green phosphor, and new aluminate green phosphor with nitride red phosphor R650 for LCD TV backlights and compared their temperature characteristics. Finally, it is believed that the combination of aluminate green phosphor and nitride red phosphor R630 can realize warm white LED for general illumination; phosphors such as YAG, OG450, silicate yellow phosphor can be used for general illumination. Cool white LED.

Wuhan University of Optoelectronics National Laboratory, Director of Microsystems Research Center of Huazhong University of Science and Technology Liu Sheng and everyone's discussion focused on the key process of LED packaging - wire bonding, in the LED packaging process through the pressure welding process to achieve LED The electrical connection between the chip and the package holder. LED packaging companies generally use gold wire bonding, but gold wires are expensive, resulting in higher LED costs. Conversely, copper wire is inexpensive and has great potential for cost reduction. In the report, Professor Liu Sheng established a model by finite element method to analyze and compare the gold wire and copper wire bonding process in high-power LED package, and provide theoretical basis for copper wire bonding process parameter optimization.

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