Image Matching Technology Research In High Power LED’s Eutectic Welding Package

With the advantages of high efficiency, energy saving, long life, environmental protection and so on, LED is considered as new energy-efficient lighting fixture in the 21 st century. Currently, LED is widely used in various fields including lights, displays and landscape lighting. High power LED, regarded as the core of semiconductor lighting for the future, has increasingly gained people’s attention and favor due to its high light efficiency and long life. LED packaging technology is the most important part that makes LED from the semiconductor chip to the final product. And it has some functions such as protecting chip, connecting electric signal, which directly affects the development of the whole industry chain. As the integrated packaging density of high-power LED chip modules becomes higher and higher, the accuracy, speed and reliability of visual inspection require higher demands correspondingly. Especially, for high power LED flip chip, on one hand its positive and negative electrodes are extremely close, so in the welding process, if the positional relationship of LED chip and ceramic substrate exits a slight deviation, it will cause a short circuit. On the other hand, the matching speed of LED chip and ceramic substrate is slow in the automatic eutectic welding process, which will restrict the efficiency of production severely. Therefore, it has important practical significance for researching on high-speed and high-precision position matching system of LED chip and ceramic substrate.In this paper we do numerous studies on these issues for image matching technology in high power LED’s eutectic welding, and propose creatively a complex positioning matching method based on features and gray correlation, and the basic principle is: firstly extract edge features of the images of LED chip and substrate; then apply respectively projection algorithm and interconnected domain algorithm to locate notable features of the chip and the substrate; final y, complete the matching based on the located key features. The concrete matching process is as follows: Firstly, the substrate images and the flip-chip images are pre-processed respectively to obtain edge detection images(binary images). Then we apply Hough transformation to detect straight lines on the edge detection images, and compute the main linear directions to trigger the mechanical arms to adjust the positions of the substrate and the chip initial y. Thirdly, we use eight neighbors interconnected domain algorithm to locate two holes of the substrate, and pass the located information to the control system to trigger the mechanical arm to adjust the substrate for the second time. At the same time, projection algorithm is applied to locate the anode of the flip-chip to drive the mechanical arm to adjust the position of the flip-chip again. Finally, two holes of the substrate image and four vertices of the flip-chip image are located, thus triggering the mechanical arm to accomplish the matching of the two.To verify the effectiveness of the proposed algorithm, multiple images of LED chip and substrate with different tilted angles captured by random are used in our experiment. The experiment results show that the mean error of calibrated angles for thirty pairs of substrates and chips are respectively 0.020 o and 0.025 o, and the standard deviation are respectively 0.086 o and 0.0959o; the whole matching process costs 92.11 ms on average. Thus, the proposed matching method improves the speed of matching on the basis of the accuracy of matching, which achieves the requirements of real-time applications.