Reconstruction of Solder Joint Surface Based on Shape from Shading

Inspection of solder joint is a critical step in the assembly of PCB (Printed Circuit Board) which requires high reliability. Previous studies have shown that a visual inspection is tedious and unreliable because the inspection process varies with the mood, time, experience and interpretation skills of an inspector. So, non-destructive inspection technology based on image captured by CCD (Charge Couple Device) has been widely used in a production of PCB because of their excellent characters. This paper deals with the reconstruction of the solder joint's surface in PCB based on shape form shading technology. Shape-from-shading (SFS) is an important non-contact measurement method that can be applied in the fields of remote sensing technology, industrial measurement, pattern recognition, product monitoring and micrograph measurement, etc. Therefore, more and more researchers pay more attention to this field recently. However, the application of SFS for reconstruction of solder joint surface has yet to be fully investigated. In this paper, compared to other measurement methods, the advantages of SFS method are analyzed firstly. Then, theory and survey of SFS method is introduced. To overcome the disadvantages existing in conventional SFS methods, some improved algorithms are provided and proved by experiments. 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.