Automatic bubble defect inspection for microwave communication substrates using multi-threshold technique based co-occurrence matrix

Abstract

Automatic bubble defect inspection for microwave communication substrates using multi-threshold technique based co-occurrence matrixThe microwave communication substrate is currently using manual inspection from ultrasonic image. The bubble defect ratio is an important index for evaluating the quality of the substrate. It is difficult to formalise standards for the quality inspection procedure by an operator since different numbers of bubbles may be realised. This paper proposes a novel inspection procedure for the calculation of the bubble ratio of microwave communication substrate. First, the optimal threshold is determined for binary image segmentation on the basis of a co-occurrence matrix. Further, the image of the microwave communication substrate is divided into three parts, namely, the image skeleton area, soldering area, and IC working area. The image subtraction technique is used to obtain the global and critical regions for bubbles. After data analysis, if the critical region bubble ratio is larger than 10% of the critical region, then it is judged to be a defect. When a substrate is judged to be non-defective, we should further proceed with the global area detection. If the global region bubble ratio is larger than 12.3% of the global region, then it is judged as a defect. An experiment was conducted to demonstrate the application of this technique. The results showed that the inspection accuracy reached 97.49%. The results of this study provide an effective solution for the inspection of the interface bond quality of a microwave communication substrate.

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