An improved method for analyzing the uniformity of white LED spot

White LED is considered to be a “green lighting source” because of its high efficiency, low power consumption, long life, solid-state energy saving, and environmental protection. It is expected to become the third generation of illumination source after incandescent and fluorescent lamps. Development potential. The use of phosphor conversion to achieve white light is currently the most researched and hottest method. At present, the power-type white LED packaging process is still immature, and the heat dissipation and phosphor coating are the key breakthroughs of the two packaging processes. For white light power LEDs used in the field of illumination, the uniformity of spatial distribution of color temperature and chromaticity is an important indicator of product performance. The color temperature difference that can be distinguished by the human eye is 50-100 K. At present, the uniformity of the chromaticity of ordinary LED devices is still not ideal, and even the angular color temperature difference of a single LED can be as large as 800 K. This is because when the concentration of the phosphor is constant, the probability of blue light being converted into yellow light is proportional to the thickness of the phosphor encountered during the blue light emission. The uneven thickness of the phosphor is the main cause of the difference in the angular color temperature of the white light LED. It can be seen that for white LEDs, research and improvement of white spot uniformity is an important issue.

2 sample making process

We use the current mainstream potting and dispensing process, using different phosphor layer shapes and structures, and made five kinds of samples, A1 ~ A5. The phosphor layer is mainly processed in two steps. First, a chip is coated on the chip. A layer of transparent silica gel is dried to form a transparent silica gel layer; a mixture of phosphor and transparent silica gel is applied to the silica gel layer. Figure 1 (a ~ e) is a schematic diagram of five different shapes of structured white LEDs. On the front side of the chip, the phosphor layer has a thickness of about 25 μm.

As shown in Fig. 1(a), the structure of the sample A1 is first coated with a thicker silica gel layer on the light-emitting layer of the LED chip , which is about twice as thick as the phosphor layer, and the silica gel layer covers the substrate base of the entire metal. The seat is coated with a phosphor layer on the dried silica gel layer. As shown in Fig. 1(b), the structure of the sample A2 is basically similar to that of the A1 structure, and a silica gel layer is applied on the light-emitting layer of the LED chip, and the thickness thereof is about 1 /2 of the phosphor layer, and the silica gel layer covers the entire metal. The substrate pedestal is then coated with a phosphor layer, which is slightly different in that the thickness of the silica gel layer is significantly thinner at this time, but the error may be large due to manual operation. As shown in FIG. 1(c), the sample A3 has a structure in which a silica gel layer is coated on the metal base along the edge of the substrate, and the height of the silica gel layer does not exceed the ceramic substrate of the flip chip, and is filled with the ceramic substrate. The luminescent layer on the chip has no silica gel, and after drying, a phosphor layer is coated on the entire chip. As shown in FIG. 1(d), the sample A4 has a structure in which a silica gel layer is coated on the metal base and the ceramic substrate along the edge of the light emitting layer of the chip, and the height of the silicone layer does not exceed the center of the chip of the flip chip, just like The luminescent layer of the chip is filled in, the upper surface of the luminescent layer is exposed, and after drying, a phosphor layer is coated on the entire chip. As shown in Fig. 1(e), the sample A5 has a structure in which a silica gel is applied to the front surface of the light-emitting surface of the chip, the thickness of which is the same as that of the phosphor layer, and then a phosphor layer is applied on the dried silica gel layer.

Figure 1 Schematic diagram of the process of making five white LEDs

3 Establishment of experimental test platform

The 9-point color coordinates and color temperature of each LED were tested by a 9-point method to determine the spatial uniformity of illumination in each direction of a single LED exit spot. The color temperature and chromaticity of the device were tested by the integrating sphere method to investigate the difference between the devices of the same type of sample.

In order to test the spatial uniformity of the exit spot of a single white LED, the following experimental platform was established: the test was carried out in a dark room to reduce the effects of ambient light. First fix the LED on the wall, and place a white screen directly in front of it. The height of the center of the screen is the same as the LED (as shown in Figure 2). The screen and the wall are parallel. In order to facilitate the test and statistics, we selected 9 points that form a square as a representative measurement point.

The Antenna Assembly Harness are passed heat and other kinds of tested.

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