Importance

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Abstract

A textured planar surface (15) on a semiconductor chip (10) is distinguished from a volume of surrounding bonding material (12) by first illuminating the chip and the bonding material with light directed normal to the surface. Thereafter, the image of the surface (15) is captured by a television camera (30) such that the textured planar surface is in focus and the bonding material appears out of focus to the camera. The image captured by the camera is processed by a vision processor (32) which first determines the intensity gradient for each separate small area (pixel) in the image and then creates a gradient image based on the pixel intensity gradients. The gradient image is binarized by causing each pixel to appear dark or bright, depending on whether its intensity gradient is below or above a threshold value. The surrounding bonding material is effectively eliminated from the binarized image because the corresponding pixels associated therewith appear dark since they have a low intensity gradient as a result of the bonding material being out of focus.

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First Claim