A study of using nonnegative matrix factorization to detect solder-voids from radiographic images of solder

Abstract

Accurate detection of voids in solder bumps on ball grid arrays (BGAs) is important for improving device quality.Radiographic imaging is commonly used to inspect BGA packages incorporate into LSI circuits. In the case of conventional method, imaging is normally done four times, and the images obtained are averaged to reduce noises. We have developed a nonnegative matrix factorization method for detecting solder-voids using only three radiographic images. Computer simulation demonstrated that it has the same level of accuracy as the conventional method.

A Simple Automated Void Defect Detection for Poor Contrast X-ray Images of BGA

“…We claim that the new ideas mentioned in 2) and 3) are different to previous existing methods (2)(3)(4)(5) .…”

“…2a; although the physical fact suggests the void regions are brighter than neighborhood inside the solder ball, however, in reality these voids are quite difficult to be detected because of poor image contrast, irregular shapes, different void sizes and positions (2)(3)(4) , and high noise level (5) . These issues are what we have to overcome in practice.…”

“…Finally, the number of voids, the ratio between void area and solder ball area (1)(2)(3)(4) and the height of peak (5) are normally used as the indicators of severity levels.…”

“…Void defect can be defined as holes formed inside a solder ball due to the amount of outgassing flux that gets entrapped in the solder ball during the reflow process. Based on the inspection techniques (1)(2)(3)(4)(5) , the void can be visualized as a brighter area inside the solder ball on a 2D X-ray image.…”

“…Therefore, the research of automated void detection algorithms has been actively developed (2)(3)(4)(5) in order to obtain the better accuracy, speed and robustness when dealing with different types of practical factors, e.g., noise, interference, and various quality of images acquired from different setting in X-ray machines, especially the case of low contrast images.…”