Robust automatic void detection in solder balls

Abstract

Voids in solder balls can cause board failures. The detection and assessment of voids in solder balls can help in reducing board yield issues caused by incorrect scrapping and rework. X-ray imaging machines make voids visible to the operator for manual inspection. Some existing x-ray inspection systems have void detection algorithms that require the use of intensive manual tuning operations that are time consuming, and inaccurate due to the inability to examine balls overshadowed with other components. In this paper, a robust automatic void detection algorithm is proposed. The proposed method is able to detect voids with different sizes inside the solder balls, including the ones that are overshadowed by board components and under different brightness conditions. Results show that the proposed method achieves a correlation squared in the range of 91% to 97 % with ground truth data from a 3D x-ray scan. The proposed algorithm is fully automated and benefits the manufacturing process by reducing operator effort and by providing a cost effective solution to improve output quality.

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) .…”

“…In typical 2D X-ray images (gray scale image, 0-255 levels), the solder balls are often interfered by other board components (2)(3) , for example some joints normally create some occluded solder balls. Then, the robust segmentation algorithms that are able to deal with different kinds of interfering backgrounds are essentially preferred.…”

“…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.…”

“…1c) in the sense of giving a good estimate of void location and a fair estimation of void area. The first parameter, void location inside ball, is emphasized as the primary root cause for the loss of solder joint integrity (1) and the second parameter, void area, is required as 25% or less cumulative voiding percentage in solder balls based on the IPCA610D standard (1)(2)(3) .…”