Automatic Visual Inspection System For IC Bonding Wires

Abstract

This paper discusses a high-contrast imaging capture system and a wire inspection algorithm for an automatic visual inspection system. On IC assembly lines, automated visual inspection is essential to maintain IC productivity and reliability. An automatic inspection system requires realtime inspection without defects overlooked.To overcome the difficulties of getting clear wire images and inspecting flexible object shapes, we developed a high-contrast imaging capture system and a wire inspection algorithm. The imaging capture system consists of a special camera, called a MegaCamera, by Fujitsu Ltd., and structured lighting. The MegaCamera satisfied both the requirements of 10-micron -per -pixel inspection resolution and an image capture area of 20 mm square. The structured lighting optic enabled us to get bright wire images and to reduce background noise. The wire inspection algorithm is based on border following. The algorithm enabled us to inspect curved and straight wires and to detect defects including broken wires, too close wires, and incorrect wiring paths.When we installed the system on an actual IC assembly line, it took 28 s to inspect a 68 -wire IC. The rate of correct detection is 99.7 percent for ICs and the rate of overlooked defects is 0 percent. These results indicate the system can inspect in real time without defects overlooked, which up to now have required visual inspection.

A Survey of Detection Methods for Die Attachment and Wire Bonding Defects in Integrated Circuit Manufacturing

“…Recently x-ray inspection was reported in [68][69][70] in which defects such as high/low loop, missing, sagged, and broken wires were identified.…”

“…In [68], a transformation and threshold segmentation method was used to locate the region of interest (ROI) containing bond wires and a geometric feature extraction mechanism was utilized. In [69,70], similar image processing algorithms were used for detecting wire bonding defects.…”

“…Nearly all of the existing papers just focus on the detection accuracy without discussing these other critical deployment factors. Only in [66,68,70], the inspection speeds were reported.…”