Three-dimensional metrology of surface extracted from a cloud of measured points using a new point-to-surface assignment method: An application to PCB-mounted solder pastes

This work presents a method of point-to-surface assignment for three-dimensional metrology of solder paste bricks on printed circuit board (PCB). A bounding box enclosing the brick tightly on all sides is introduced to avoid incorrect point-to-surface assignment. The shape of bounding box for solder paste brick is variable according to geometry of measured points. The surface geometry of the bounding box is obtained by using five peaks selected from the histogram of normalized gradient vectors for measured points. By using the bounding box enclosing the solder paste brick, the task of point-to-surface assignment is successfully executed. Subsequently, the geometrical features are obtained via surface fitting.