A Proposal of a Visual Inspection Method for Detecting Low Contrast Defects of an IC Lead Frame by Using a Spline Function

Abstract

An automatic visual inspection method for an IC lead frame, which is effective to detect low contrast defects called stains and irregular luster, is desired. Low contrast defects are usually difficult to be distinguished clearly from the normal area by the difference of intensity level. Therefore, a simple subtraction technique using a good product as a reference image is not effective for detecting low contrast defects. This paper proposes a novel automatic visual inspection method effective to detect low contrast defects by using a spline function. In our method, a virtual good-product image is created for each product under the visual inspection by using a spline function. And the intensity subtraction technique is applied between a target image and a virtual good-product image. The intensity deviation of the virtual good-product image from the normal one can be made small enough to distinguish low contrast defects. Thus, the proposed method realizes an effective detection of low contrast defects and the reduction of false detection for the good product.