Three-dimensional inspection of printed circuit boards using phase profilometry

Reconstruction of 3D shape of the solder paste printed on SMT component pads is a major inspection task in the PCB manufacturing process. The paper reports on the use of phase profilometry for this inspection task. In phase profilometry a structured light pattern is projected onto the object and viewed by a camera. Since the imaged pattern is phase-modulated according to the topography of the object, the extraction of phase information from the image enables reconstructing the 3D shape. In this paper two phase-extraction methods, Fourier Transform Profilometry and Signal Domain Profilometry, are compared by means of simulations and experiments. Results show that the Fourier method performs better, yielding neat detection of the elevation with respect to PCB surface associated with solder paste.