LED chip is the core component of the LED industry. The high temperature of the chip will seriously affect the quality of the LED product. However, the temperature distribution inside the chip and the chip has always been a difficult point of detection. The main problem is that the internal device is too small, especially the micron level of gold. Line (about 10 microns), can not be detected by traditional thermocouple / thermal resistance; using infrared thermal imaging camera and special accessories can detect the inside of the LED chip, the temperature of the gold wire inside the chip and the positive and negative electrode temperature distribution can be for developers Providing the basis for wiring design, as well as developing a heat dissipation system for the chip, it is also necessary to confirm the heat generation of each part of the chip and improve the quality of the LED chip.
However, it is difficult to detect the micron-level LED gold wire and positive and negative electrodes by the thermal imager. The commonly used infrared thermal imager can only detect a target of 0.2mm, so special accessories are needed for testing.
First, the infrared camera uses the standard lens and wide-angle lens detection effect
The target is a 3mm LED chip, and the thermal image below is the same type of thermal imager (TI50) with different lens shots:
The standard lens is shot at 150mm (150mm is the minimum focus distance of the TI50 camera)
Replacing the wide-angle lens at 10mm
Note:
1. Minimum focus distance: The minimum focus distance is an important parameter of the infrared lens. Generally speaking, the closer the distance is, the better the resolution will be under the same conditions; but most of the lenses cannot be close to the detection, and the target can How close is the minimum focus distance.
2. At present, most thermal imaging cameras have dual imaging modes of infrared and visible light. However, due to the small size of LED chips, thermal imaging cameras need to be shot at the nearest extreme distance, which is far below the minimum focusing distance of visible light, so visible light is generally not hot. The figure shows that there is a large difference between the position of visible light and infrared heat map.
From the effect of the thermal image, both the standard lens and the wide-angle lens can only see the approximate temperature distribution of the surface of the LED chip, and the temperature distribution of the details such as the gold wire and the positive and negative electrodes cannot be clearly seen. The configuration does not meet the requirements of the test.
Second, use the macro lens to detect the LED chip
The thermal imager is equipped with a 13.5μm macro lens to shoot a 3mm blue LED chip at 20mm.
LED chip infrared heat map, can see gold wire and positive and negative electrodes with a width of 10μm
Using the software, set a straight line in the chip range of the thermal image (left left). In the right right of the figure below, you can see the temperature change curve of the line according to the position (the horizontal axis is the pixel coordinate axis and the vertical axis is the temperature axis). Attacking 250 pixels on the line, the chip size is 3mm, the size of each pixel on the chip is 3mm/250=12μm, that is, the thermal imager can distinguish the subtle temperature difference of the 12μm diameter component.
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This article is selected from the Electronic Consumers Network November "Test and Measurement Special" Change The World column, please indicate the source!
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