Study On 3D Laser Measurement System Of Solder Paste

In SMT(Surface Mounting Technology) process, chip mounting quality is largely depended on solder paste printing quality. For instance, lack of solder paste would result in open soldering, solder bridge would result in short-circuiting, collapse of solder paste would result in pseudo soldering. And solder paste thickness is one of the most important indicators to judge the quality and reliability of solder joint. In the actual production, for many uncontrollable factors in the printing process, the surfaces of solder pastes are not flat. In this case, 3D testing technique of solder paste thickness is invented. And its measuring results are more representative and stable, because of the technique which uses the average height of multi-group data in scanning area to represent the height of the solder paste.Used by most domestic PCB(Printed Circle Board) plant manufacturers, 3D measurement systems of solder paste rely on imports presently. But the imported equipments are more expensive. So that, developing 3D measurement systems of solder paste with independent intellectual property is meaningful to domestic PCB plant manufacturers and IC industry.In this paper, 3D laser measurement technique of solder paste, which is based on laser vision survey principle, adopts scanning measurement mode to gather the 3D data of of solder pastes. By solving the data, precise height and 3D appearance of solder pastes, such as the width and length of solder pastes, are obtained. The application of the technique would rather be propitious to economize the semiconductor manufacture costs and to improve the reliability of chip mounting.The measuring method of 3D laser measurement system of solder paste is studied. And the mathematical model of the system is built. The structure of the system is designed. The main components are line-structured laser, CCD camera, frame grabber and electric control precision translation stage. Related image processing method, the definition of datum plane using Principle Components Analysis (PCA), and also the measuring method of three-dimension of solder pastes are studied. the measuring software is programmed, according to the collaborator's request.In the experimental process, a standard part with 1mm as the width and length, 0.213mm as the height, and 1μm as the accuracy was measured ten times. The average of the measuring result is 0.2132mm. And the standard deviation is 0.8μm. The system also did a lot of measurement on various types of solder paste package in PCB manufacture factory, such as BGA and QFP. Experimental results prove that the system is a more easily operated device with high performance.