Sub-Pixel Based Alignment of SMT Electronic Components

Rapid growth in modern technology places greater requirements on electronic products' performance and quality. For a PCB (printed circuit board) assembly of SMT (surface mounting technology) electronic components, restricted by its limited vision in image collection, a high-pixel CCD (charge coupled device) can only screen local images, and they need to be mosaiced, through matching and alignment, into a complete image, which is to be matched and aligned with a standard image then for image analysis. Therefore, image matching and alignment are of crucial importance to both the precision of image mosaic and the quality of SMT components. This paper proposed a sub-pixel based method, by which local images are marked, matched and aligned into a mosaiced image, which is matched and aligned with a standard image. The error analyses of matching and alignment for four common markers, i.e. circle, ellipse, square and rectangle, show that a square or rectangle marker is preferred for SMT electronic components; when the marker's center point serves as alignment point and the marked data are processed by sub-pixel algorithm, the alignment error can be reduced to about 0.2 pixel point, besides the sub-pixel based method can greatly improve precision when noise is fixed.