Studies of Visual Inspection

Abstract

This paper describes the results of four experiments in a series aimed at understanding and improving visual inspection in general and of small integrated circuits (i.e. 'chips') in particular. Stimuli consisted of chips that, although electrically sound, contained visual anomalies. The first experiment found that the modal duration of eye fixations of trained inspectors was about 200 msec. The most accurate inspectors made the fewest eye fixations and were the fastest. The second experiment evaluated the performance of inspectors at one of the many sequential stages of chip inspection and found that 23% of the chips containing anomalies were accepted, whereas only 2% of the chips without anomalies were rejected. When the same chip was judged more than once by an individual inspector the consistency of her judgment was very high whereas the consistency between inspectors was somewhat less. The third experiment showed that variation by a factor of six in inspection speed led to variation of less than a factor of two in inspection accuracy. The fourth experiment showed that inspection via a ground glass screen is only a little worse than the usual method of looking through a binocular microscope. This was true even though the inspectors had no previous experience with the screen.