High speed oblique CT system for solder bump inspection

The high-density LSI packages such as BGA (ball grid array) and CSP (chip scale package) are widely used in the electrical products. Solder bump is used as an electrical junction of these packages, and they cannot be observed from outside. X-ray fluoroscopy is used as inspection method. It cannot evaluate the shape of solder bump correctly because information is compressed along the ray. The oblique CT is considered as a method for accurately examining the shape of the solder bump. Conventional oblique CT still has the speed and mechanical constraint, and it cannot be introduced into the soldering line. In this paper, we propose the novel oblique CT system that can non-destructively obtain the 3D shape of solder bump at a high-speed. This system obtains the projection images from various directions using the rotational transfer of flat panel detector and the fixed mounted open-type X-ray generator that has a wide radiation angle, and reconstructs 3D image using the 3D FBP (Filtered Back Projection) method. In addition, we have developed the reconstruction acceleration unit for oblique CT, and thus the 3D image is obtained in the real time. In our experiments, we evaluated the solder joints of BGA mounted substrate. The result demonstrated that the proposed system obtained the information that was able to determine the good or defective situation in soldering. This system is the world's first CT system, which can be introduced into the soldering line, and it is operated by more than 20 domestic and foreign factories now.