Research On Grate-Shift Control And3D Measurement Technology For Automated SPI

Since the surface mounted technology (SMT) was used in components of circuit boards installed in electronic manufacturing. Size of electronic component is smaller and smaller, the integration higher and higher, the product quality better and better. At the same time, production automation degree is further improved. But the on-line quality inspection of product is the weak link of SMT production line, especially solder paste deposit inspection in the front. As the traditional test methods are slow and poor reliable, more than80%of electronic product quality defect is due to the defects of solder paste deposit.The quality testing of solder paste deposit includes two dimensional area, position defects,3D thickness, volume and shape defects. The paper first reviews the technology development of the printing quality testing in SMT, studies the latest abroad Solder Paste Deposit Inspection (SPI) based on machine vision, analyses research situation of3D measurement technology based on machine vision and study the related key technologies of phase measurement profilometry(PMP) based on the projection grating shift used in SPI.The paper designs the hardware structure of the system, especially to study the piezoelectric ceramic controlling phase shift of glass grating. The paper analyses the nonlinear control voltage and the creep characteristics piezoelectric ceramic and designs the innovation methods of piezoelectric ceramic control voltage based on image correction.In the software algorithm aspects, in view of lens allocation referring to the limited camera view and the big detection object, the paper designs random search method based on prior knowledge guiding to minimize the detecting window, effectively to solve the problem. For phase unwrapping method as one of the key technology, this paper puts forward a rapid partition unwrapping combined with2D image information according to the engineering practice in solder paste deposit inspection. Finally we discuss the phase-height mapping relation in3D measurement. Based on the theory research, we do the experiment with3D measurement system for solder paste deposit, comparing the area and volume accuracy repeatability of the same solder paste at different perspective and position. The experimental results show the system achieved certain measurement accuracy. This paper analyzes the reason why the accuracy is not enough and discusses further research work.