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Surface profile measurement by grating projection method with dual-projection optics

Recently, various investigations have been carried out using grating projection method based on triangulation. It has advantages such as simple optical arrangement and full-field measurement with high accuracy, and moreover measurement time is shorter compared with other methods like point and/or line scanning. However, it has such problems as occlusion and phase error due to halation. The first problem is inevitable due to principle of triangulation. The second problem is caused mainly by unequal surface reflectivity of the BGA, CSP and solder bumps, etc. Therefore we propose dual projection method to solve these problems. This proposal consists of one camera and dual projection units with specified liquid crystal gratings. These problems can be avoided owing to measurement from two directions. Finally, three-dimensional profiles are obtained by combining these two results. We intend to present a method that can extend the use of fringe projection method based on triangulation. In addition to the principle of this system, BGA sample applications are to be shown up.