How do I implement automated visual inspection for RF solder joint quality?

Automated optical inspection (AOI) and automated X-ray inspection (AXI) are complementary tools for ensuring RF solder joint quality in production: (1) AOI (Automated Optical Inspection): uses high-resolution cameras and image processing to inspect the visible surfaces of the PCB assembly. Detects: missing components, tombstoned (lifted) components, solder bridges (shorts between adjacent pads), insufficient solder (dry joints), component misalignment (offset, rotation), and wrong component (incorrect part placed). Limitations: cannot inspect hidden joints (BGA/QFN solder joints are underneath the component, invisible to cameras). Cannot measure void content in solder joints. Cannot detect hairline cracks in solder. Speed: 1-10 seconds per board (fast enough for in-line production). (2) AXI (Automated X-ray Inspection): uses X-ray imaging to see through components and inspect hidden solder joints. Detects: solder voids (the primary concern for RF power devices), head-in-pillow defects (BGA balls with incomplete wetting), open joints under QFN/BGA packages, and solder bridges under fine-pitch components. 2D X-ray: fast (seconds per board), measures void percentage, resolution ≈ 5-10 μm. 3D X-ray (computed tomography, CT): slower (minutes per board), provides volumetric void analysis, reveals defects in multi-layer solder joints. Limitation: X-ray cannot distinguish cold joints (poor wetting) from good joints if the solder shape is similar. (3) For RF assemblies: use AOI as the first-pass inspection (catches obvious assembly defects). Use AXI for all boards with QFN, BGA, or power device thermal pads (catches hidden solder defects and measures voiding). Set void acceptance criteria per IPC-7095 (< 25% void area for Class 3). For critical RF power devices: 100% AXI inspection with void area measurement and automatic pass/fail.