System and method for three-dimensional inspection using patterned light projection

Abstract

A three-dimensional inspection system is used to obtain three-dimensional information pertaining to an article having specular surfaces, such as a BGA device, by projecting a pattern of light onto the article at an oblique angle with respect to the article. The system includes patterned light projector having an optical axis disposed at an oblique angle with respect to the plane of the article being inspected and an image detector or camera disposed generally above the article being inspected to detect the image of the pattern projected on the article. The patterned light projector includes an extended light source that directs light along the optical axis and a light patterning member disposed at an angle with respect to the optical axis such that the light pattern is in focus in an image plane parallel to the plane of the article, thereby satisfying the Scheimpflug condition. The light pattern preferably includes lines of light projected onto the article with a substantially equal thickness and spacing. The spacing of the lines is preferably greater than a spacing or pitch of the specular elements, such as the solder balls on a BGA device. An image processor is coupled to the image detector to receive the image, locate the lines, and measure the lateral shift of the lines. Height information is determined from the lateral shift and projection angle using triangulation.