<title>Solder-paste inspection by structured light methods based on phase measurement</title>

Abstract

Solder paste inspection, i.e. reconstruction of the 3D shape of the solder paste printed on surface mount technology component pads, is a major inspection task in the printed circuit board manufacturing process. We have investigated the use of machine vision methods based on structured light and phase measurement for on-line solder paste inspection. With these methods a periodic light pattern is projected onto the object and imaged by a camera from a different viewpoint. Since the imaged pattern is phase-modulated according to the topography of the object, suitable phase- extraction techniques enable reconstruction of the 3D shape. In a previous paper we have shown that the Fourier-based phase-extraction technique allows recovery of the 3D shape of solder paste on pads but is too slow for effective on- line inspection. In this paper we describe a new profilometry technique which uses a fast demodulation scheme and simple DSP operators such as comb filters and moving averages. Experimental results show that the new technique is equivalent to the Fourier technique with respect to reconstruction of the 3D shape of solder paste and computation times measurements indicate that it is roughly 20 times faster.