Research On The Key Technologies Of3D Inspection For Solder Paste Deposit Quality On SMT Production Line

In the field of electronic manufacturing, surface mounted technology(SMT) which has greatly reduced the component size and enhanced the mounting density and reliability, and facilitated the automated production, has been widely used in the installation of the components on the printed circuit board. Solder paste deposit is an important part of the SMT production line. More than eighty percent defect of surface mounted electronic products is due to deposit quality defect of solder paste. And repair cost in the front of production line is lower. So it is necessary to inspect the solder paste deposit quality. Traditional visual inspection, laser triangulation inspection method and the semi-automatic inspection method of their combination have been unable to meet the rapid, real-time and accuracy requirements of inspection capability. Rapid, real-time, accurate and automatic solder paste inspection(SPI) has become an important technology which can improve the level of electronic manufacturing industry and product quality. The automatic3D SPI technology based on machine vision is an international advanced technology. It can achieve the rapid, real-time and accuracy requirements of SPI.After analyzing the history and current situation at home and abroad about the technology of inspection for solder paste deposit quality, this paper has researched the key technologies of3D inspection for solder paste deposit quality. Specific research include:(1) Hardware and inspection software algorithm design of3D solder paste measurement system:Research on the raster projection system, the image acquisition and processing system. Choosing right hardware to build the three-dimensional solder paste measurement system. An innovative method of calibrating piezoelectric ceramic(PZT) positioning accuracy based on gray-scale image has been used to improve the positioning accuracy of PZT in the grating projection system, which can improve the accuracy of3D solder paste measurement.(2) Designing a method of camera calibration which can correct lens distortion, transform the image coordinates to the world coordinates. Using radial alignment constraint(RAC) to realize camera calibration.(3) Using grating projection phase measuring profilometry to achieve3D solder paste measurement with four-step phase shift method. In the link of phase unwrapping some innovative phase unwrapping program combined with two-dimensional image information are used to obtain the phase value on behalf of solder paste thickness. And then using the mapping of phase and height to obtain the thickness data of solder paste. In addition, the collected images contain noise which will affect the phase unwrapping effect and further affect the3D measurement accuracy of solder paste. Using appropriate image filtering method to solve this problem. Minimizing the impact of noise after image pretreatment.(4) After obtaining the thickness data of solder paste using phase measuring profilometry, it is necessary to display these3D data on a computer screen, and this paper has designed a method of programming in Delphi platform with OpenGL to develop three-dimensional demonstration module of solder paste. Experimental results show that programming in Delphi platform with OpenGL to develop the3D display module can not only improve the efficiency of programming, but also improve the demonstration speed of graphics. The3D demonstration module can realize the rotate, zoom and other interactive functions of3D solder paste graphics. It can also display the3D effect of solder paste deposit from multiple perspectives.This paper has had a research on the specific application about3D inspection for solder paste deposit quality on SMT production line, solved some key engineering and technical problems about3D solder paste inspection, and provided some valuable references of the further development of3D online inspection for SMT solder paste deposit quality.