CIRCULAR FEATURE FILTER

摘要

A method for recognizing circular features and determining the true centers of the circular features calculates a fitted circle that has a radius within a small range of the known radius of a known model. This method recognizes circular contact features on electronic components such as bumps on a flip chip and pads on a substrate and other visually similar applications and employs an algorithm which is unaffected by circular feature damage, artifact illuminations or traces connecting pads and contact bumps which create distortions that typically result in inaccuracies in determining the true center of the circular feature when using conventional center of mass or 'centroid' algorithms. The method for filtering out the distortions includes determining the distance from the centroid of the circular contact feature to the boundary as a function of angle. Determining the boundary data in this manner creates a signature which provides a one dimensional representation of a two dimensional boundary. Once the signature is plotted the data can be passed through a low pass filter to reduce noise or small scale distortions. Acceptable bounds for the variation of the radius can be selected and all points along the boundary that do not fall within the selected bounds can be eliminated. The remaining points are used to fit a circle and compute a new centroid for the circular feature.