Patent ID: 7191929
Filing Date: 2007-03-20
Classification: B23K,H01L

Abstract:
1. A method of measuring a thickness of a ball bonded to a pad of a semiconductor chip in wire bonding which attains wiring between the pad of the semiconductor chip and an external electrode, comprising the steps of: taking a plane image of a bonding portion between the pad and the ball at each step position through an image taking means being shifted in a vertical direction at predetermined step intervals; obtaining luminance variations at an edge portion of the pad in each taken image and determining an in-focus height of the pad based on an image taking height position at which the taken image has the largest luminance variation at the edge portion of the pad; obtaining luminance variations on an upper surface of the bonded ball in each taken image and determining an in-focus height of the upper surface of the ball based on an image taking height position at which the taken image has the largest luminance variation on the upper surface of the ball includes setting a luminance detection window with a predetermined size and constituted by an array of pixels at a portion of the upper surface of the ball on the taken image so as to extend the luminance detection window in a radial direction of the ball, obtaining, for the pixels in the luminance detection window, luminance differences between the adjacent pixels in the radial direction of the ball to define a luminance level of the upper surface of the ball in the taken image at one image taking height position by adding the obtained difference luminance values, and defining, as the in-focus height of the upper surface of the ball, the image taking height position at which the taken image has the highest luminance level in all the taken images; and calculating a thickness of the ball bonded to the pad by finding a difference between the obtained in-focus height of the pad and the obtained in-focus height of the upper surface of the bonded ball.