Electronic scanning of 25 MHz ultrasound for imaging IC packages

An electronic scanning technique using high-frequency ultrasound was developed as the basic technology for inline testing of fine defects in IC packages. Newly developed components are linear array transducers (frequency: 25 MHz, pitch: 0.2 mm-, elements: 128), a phase control circuit that utilizes quasi-distributed delay lines, and a matrix-type electronic scanning circuit. Beam width along the array is 0.37 mm at the focal point, while the focal length is 15 mm in water. The imaging process is executed with Cartesian-coordinate two-dimensional scanning, one axis being electronic and the other mechanical. Images of voids between an IC chip and the mold material are displayed with the system in combination with a scanning acoustic tomography apparatus. C-scan imagining of the IC internal structures (22 mm×15 mm) is completed in 2 s with the system, 30 times shorter than with a conventional mechanical one