Reconstruction of Solder Joint Surface Based On Hybrid Shape from Shading

Inspection of solder joint is a critical step in the assembly of printed circuit board (PCB) which requires high reliability. Shape-from-shading (SFS) is an important non-contact measurement method. However, the application of SFS for reconstruction of solder joint surface has yet to be fully investigated. In this paper, a algorithm of shape from shading based on hybrid reflection is proposed. Hybrid reflection models which containing diffuse reflectance and specular reflectance are used based on Tsai and Shash algorithm. For solder joint inspection, the images contain specular reflectance component, one of the problems that hinders conventional methods for shape-from-shading is the presence of local specularities which may be misidentified as high curvature surface features. Traditional shape from shading method directly used to reconstruct the surface of solder joint will obtain the result combined structural error, so considering the effect of specular reflectance will improve the precision. This paper summarize the existing method in hybrid reflection, selected a simple model joint with Tsai and Shash algorithm in order to improve the quality of surface normal information recoverable using shape-from-shading This paper discusses the flow of solder joint inspection based on SFS. Experimental results reveal that the proposed method shows practical value in solder joint inspection.