Identification of Faulty BGA Solder Joints in X-Ray Images

The advantages of X-ray inspection are extensive in scope due to the ability of X-rays to see through packages including heat sinks, welds, encapsulation, and metallic shielding to reveal obscured connections and identify potential quality non-destructive issues. Many assembly line manufacturers rely on real-time X-ray technology to evaluate solder joint integrity for BGAs and other leadless packages that cannot be inspected by conventional vision systems. X-ray inspection is particularly beneficial to applications that involve advanced surface-mount packaging technologies such as Ball Grid Array (BGA) used for integrated circuits. This paper proposes a method that relies on computer vision and image processing techniques that inspects each ball image of a BGA chip and indicates the faulty balls for further assessment. The defective balls that are typically circular change into elongated or elliptical shape. Therefore, it exploits the use of the basic geometric distinction between a circle (perfect soldered ball) and an ellipse or any other shape (ball with reshaped solder joint). A contour analysis method is defined in this paper in terms of the angle changes that occur along the outline profile of a solder joint by moving three equal distant points located on the border. This angle change is plotted to detect the faulty ball joints.