Research On The Higher-precision Optical Automatic Alignment System

An alignment system is one of the key components in flip chip bonders. A vision automatic alignment system comprises an optical lighting system, an optical imaging system, image processing software, a control system and so on. The alignment methods have used the technology of machine vision and image processing, by which the feature marks on die and substrate are recognized or measured for leading machine movement equipments to complete alignment. In this thesis, the high-precision vision alignment is realized by using the technology of optical imaging and the alignment system based on the machine vision is designed and realized. The major works of the thesis are as follows:Firstly, the polarization optical theory is analyzed. The polarization of light is deduced by using the matrix theory. The Jones matrix expression in the different polarization state of nature light is calculated by the theoretical deduction after it go through the polarization beam splitter and the quarter-wave plate and it is reflected by the object. The deduction provides the theoretical basis for the design of the optical imaging system.In the second, an optical imaging system is designed and made. The system avoids the calibration of several cameras because it grabs two objects image by using a CCD camera only. A microscopical objective is chosen because it could be directly coupled with CCD camera and the work distance is longer and the image light path is packaged. The light path is turned and the distance of the two alignment objects is reduced by using the PBS, the quarter-wave plate and the high reflection mirror simultaneously. The light energy is also saved and the quality of the image is improved because the polarization property of light is used.The third step, a new method of high-precision calibration with grating grooves is presented for the optical imaging system. A Lissajous figure could be obtained by calculating and translating the sum of gray-value of pixels in each column. The size mapping coefficient between the grating groove and their image pixels of the optical measurement system is calculated by analyzing and processing the Lissajous figure. The calibration of the system is realized.The final step, an optical automatic alignment system is completed by using the optical imaging system. The images of the chip and the substrate can be grabbed and the alignment can be realized. The results of an example show that the optical automatic alignment system is featured by compact construction, lower costs, and higher precision and so on.