Study On SMT Solder Joints Quality Inspection And Intelligent Discrimination Based On Solder Joint Virtual Evolving Technology

The reliability of the solder joints formed by the surface mount technology (SMT) is the core of the SMT productions. The inspection of the soldered joints defects and the control of the assembly quality are the key technology to ensure the quality and the reliability of SMT products. In order to get high production yield, the goals we pursued in SMT manufacture are to inspect the assembly defect, to feedback the defects, to adjust the technology parameters in time according to the feedback information and to achieve the inspection and the feedback control of the SMT products quality.In this paper, the solder joints quality inspection and intelligent discrimination are all-around studied based on the virtual evolving technology. The key technology including solder joint three-dimensional surface reconstruction, solder joint three-dimensional information measurement, solder joint defects intelligent discrimination and solder joint defects causation intelligent analysis are solved. The system model and software are developed. The achievements in our research have the advantages of remarkable real-time characteristic in the assembly quality information measurement, feedback and control of the solder joints, which applies to the small batch SMT manufacturing that requires the technology parameters being adjusted and the mound production being carried through rapidly to get the high primary production yield. The research, which meets the engineer and reality demands, is of great practical, economic and technical values.Based on the minimum energy principle the three-dimensional shape predictive models of such typical SMT solder joints as chip components, leadless ceramic chip carrier (LCCC) components, quad flat no-lead (QFN) components and plastic ball grid array (PBGA) components are set up and the three-dimensional shapes of above solder joints are predicted. The influence of the correlative technology parameters on the solder joint volume, the pad length and the pad width on the joint shapes is analyzed. Results reveal that all the parameters affect the joint shape and each of them impacts the joint shape in varying degrees,。The predictive results for the lead-free solder joints of chip components and lead solder joints of PBGA components are demonstration tested and the experimental results show that the shapes of predictive the solder joints fit those of the real joints very well. The research results might be widely used in the design and control of the solder joint shape.The constitutive relation to SMT solder is described through the unified viscoplastic Anand model. Based on the solder joints three-dimensional shape, the finite element (FEM) model is built to analyze the mechanical characteristic and to get the prediction of the solder joints thermal fatigue life of LCCC component, chip component, QFN component and PBGA component. The reliability of PBGA solder joints under the multi-technology parameters combination (the specification size, the chip weight, the pad diameter and the stencil thickness) is studied. The influence order and significance of the technology parameters that affect the PBGA component solder joints reliability is achieved.The image processing algorithm of SMT solder joints in three-dimensional area are studied. By the processing effect comparison of different algorithm, the appropriate algorithm is selected to obtain and process the computer optical information.Based on the laser triangulation method, the mathematic model for SMT solder joint measurement system is built, the hardware to measure the solder joint shape is designed and implemented, the solder joints system test parameters are calibrated and the three-dimensional surface reconstruction method is studied and applied to practice. The algorithm is adopted to fillet the physical model, to locate the key section of the solider joints and to measure the solder joint shape parameters as wetting angle, solder joint height and the area of the key section. In this way, the three-dimensional quality information of the solder joints is obtained. The accuracy of the reconstructed solder joints is gained through the three-dimensional reconstruction precision testes and the error analysis. The test result approved that the three-dimensional reconstruction method we adopted in the paper is effective and accurate in the study of the solder joints shape.The characteristic information parameters to describe solder joints defects is determined by using the least square method. The sample data, which is used in the solder joints defects intelligent discrimination and defects causation intelligent analysis is measured. The standard BP algorithm is improved in this paper. The test results of the algorithm proved that the improved measures might satisfy the service demands. The improved BP algorithm is trained successfully by using the virtually formed data samples that are used to describe the chip component solder joints defects information. The defects in the chip components solder joints are discriminated intelligently. The discriminated results are identical with the actual defects. This work meets the precision requirement of the solder joint intelligent discrimination. The intelligent analysis and estimate model for the solder joints defect causations is built based on the fuzzy neural network. With the output variables of the training samples in the intelligent discrimination being selected as the input variables of the training samples in the fuzzy neural network to train the fuzzy neural network and the output variables of the testing samples in the intelligent discrimination being selected as the input variables of testing samples in the fuzzy neural network to test the fuzzy neural network, the fuzzy neural network is tested and the relatively rational intelligent analysis results are obtained.The SMT solder joints quality estimate, the SMT solder joint defects intelligent discrimination and defects causation intelligent analysis software is developed based on the research achievements in this paper which include the technology of the image process, three-dimensional shape reconstruction, quality information measurement, defects intelligent discrimination and the defect causations intelligent analysis of the SMT solder joints. This software is proved to be practical through the experiments of the image collection and process of the actual solder joints, the three-dimensional reconstruction of the solder joint shape, the measurement of the reconstructed solder joint shape parameters, the defects test and defect causation discrimination of the solder joints.