Stereoscopic Imaging of Solder Pads
Original Publication Date: 1985-Oct-01
Included in the Prior Art Database: 2005-Feb-19
Variations in volumes of deposited and reflowed solder pads is determined by stereoscopic viewing and triangulation. When orthogonally polarized, a pair of light beams impinge on a viewed pad surface from different angles, then undergo Fresnel diffraction to provide a stereo pair of images sensitive to surface quality and show features in surface relief. One arrangement for producing stereo images is shown in the figure where unpolarized light from laser 1 is directed through beam-expanding lenses 2 and 3 and diverging lens 4 to polarizing beamsplitter 5. Beamsplitter 5, which may be a birefringent single crystal of calcite in cleavage form, is placed near the focal point of either lens 4 or 2 to use a small, aberration-free region of the crystal.