3-D reconstruction for SMT solder joint based on joint shadow

3-D reconstruction is essential for Surface Mount Technology (SMT) solder joint defect inspection. Conventional vision-based reconstruction methods are very sensitive to the surface reflectivity variation or require sequential images from multicamera system which would increase calibration difficulty and computation complexity. To solve the problem mentioned above, a novel shadow based 3-D reconstruction method for solder joint reconstruction is proposed. A paralleled light casts a joint shadow on PCB (Printed Circuit Board), and then the shadow is captured by a camera and used to reconstruct the joint. To make a single shadow obtain the 3-D model totally, a joint shape model is proposed based on consistent joint characteristics which produced by soldering tin surface tension when the tin is still liquid during the manufactory process. Compare the reconstruction results of this method with that of Shape from Shading (SFS) reconstruction method, this method can reduce the hardware cost and algorithm complexity significantly, which at the same time obtains better accuracy and efficiency.