Yoshitaka Oshima

Novel high-spatial resolution probe for electric near-field measurement

A new probe with a micro-hole chip has been developed for measurement of near-field electrical radiation from printed circuit boards. The chip is fixed onto a semi-rigid cable probe facet and the radiated electric field is coupled with the surface of its inner conductor through an aperture with a diameter of 100 µm. Using a 50-µm-wide microstrip line for the device under test, we obtained a distance of 100 µm where the probe output decreases by 6 dB at a measurement height of 50 µm. This distance is in good agreement with our simulation results based on FDTD analysis. With a rectangular aperture of having a 50 µm width, we obtained a 72 µm distance at a 25 µm height. In addition, we confirmed that both the S21 characteristics of the measured line and the frequency characteristics of the probe can be dramatically improved by covering the outside of the probe with magnetic film.

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.