Development of high-speed 3D inspection system for solder bumps

We developed a high-speed 3D inspection system for solder bumps. The system applies laser-based triangulation with a laser diode, an acousto-optical deflector (AOD), and a position sensitive detector. The system scans LSI surfaces with a laser beam at a 15 m/s scanning speed, and can acquire height data at rate of up to 7 X 106 samples/sec with 0.8 micrometers resolution. For high-speed laser beam scanning with the AOD, we developed a technique to correct for the cylindrical lensing effect that causes astigmatism on a focal plane. Our correction method is unique in that it notices the scanning speed being constant in order for the dynamic deviation to be erased. This technique can suppress these deviations enough to enable accurate laser scanning. When installed on an LSI chip assembly line, the system can measure each bump height to within +/- 2 micrometers in 5 ms. This will allow for a 100% inspection to be achieved.