Detection of defects at BGA solder joints by using X-Ray imaging

In the surface mount technology, Ball Grid Array(ElGA) has been used in a production of PC boards, because of their excellent characters such as high density of the lead pin pitch, better lead rigidity and self-alignment during re-flow processing. This paper deals with the detection of defects at BGA solder joints in PC boards by using X-ray imaging. In the conventional IC boards, it is possible to detect defects of solder joints by visual inspection, because the lead of IC package is set at its outside. However, we can not to detect visually defects at BGA solder joints, because they are hidden under the IC package. In a production line, the inspection of BGA in PC boards depends on the function test of electric circuits in the final process. To improve a cost performance and reliability of PC boards, an inspection of BGA is required in the surface mount process. Types of defects at BGA solder joints are solder bridge, missing connection, solder voids, open connection and misregistration of parts. As we can find mostly solder bridge in these defects, we pick up to detect solder bridge in a production line. The problems of image analysis for the detection of defects at BGA solder joints are the detection accuracy and image processing time according to a production line speed. To get design data for the development of the inspection system used easily in the surface mount process, it is important to develop image analysis techniques based on X-ray image data. At the first step of our study, we attempt to detect the characteristics of the solder bridges based on an image analysis.