X-ray inspection equipment, commonly referred to as Automated X-ray Inspection (AXI) machine, is a type of equipment used to inspect the hidden features of target objects or products using X-rays as the source X-ray inspection machines. Today, automated X-ray inspection is widely used in many applications, including medical, industrial control, and aerospace. For PCB inspection, PCB X-ray inspection is extensively used during the PCB assembly process to test the quality of PCBs, which is one of the most critical steps for quality-conscious PCB manufacturers. This article will explain why PCB X-ray inspection technology is so crucial in PCB assembly.
In recent years, area array packages such as BGA and QFN, flip chips, and CSP have been widely used across various fields such as industrial control, communications, military, and aerospace, making the solder joints hidden under the packages. This fact makes traditional inspection equipment unable to perform perfectly in PCB inspection. Additionally, with the advent of Surface Mount Technology (SMT), packages and leads have become smaller, and traditional inspection methods (including optical, ultrasonic, and thermal imaging) are inadequate due to the higher density of PCBs, with hidden solder joints and buried or hidden holes. Moreover, as semiconductor component packaging continues to miniaturize, the trend of current and future component miniaturization must be considered when evaluating X-ray inspection systems. Compared to other inspection methods, PCB X-ray inspection can penetrate internal packages and inspect the quality of solder joints.
The inspection principle of all PCB X-ray inspection equipment is X-ray projection microscopy. The process begins with an X-ray emitting tube passing X-rays through the PCB being inspected. Due to different materials having different X-ray absorption rates based on material and atomic number differences, a projection is produced on the detector, and the higher the density, the darker the shadow. The shadow will be significantly closer to the X-ray tube, and vice versa.
Therefore, an ideal PCB X-ray inspection system must have clear X-ray images to provide information during defect analysis. To achieve this, the PCB X-ray inspection system must have sufficient magnification to meet current and future demands. Additionally, for analyzing BGAs and CSPs, a tilting angle inspection function must be provided. Without it, you can only inspect solder balls from directly above, losing more detailed analysis information regarding the size and thickness of the solder balls.
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