Elk Grove Village, IL-- Sonoscan Inc., a developer and manufacturer of acoustic microscope systems, has been issued a patent (U.S. #6,890,302) that gives engineers a new tool for diagnosing packaging defects. It is one of several patents issued to the company in the past year.
 
Acoustic microscope echoes are typically time-gated on a depth of interest, and echoes from other depths are ignored. This method, known as time domain imaging, has been the standard for many years. If a 230 MHz transducer is being used, the frequency content of the return echoes at an x-y coordinate will range from about 170 to about 260 MHz or more, and the frequency content characteristic typically varies from one pixel to the next. 
 
A new technique, Frequency Domain Imaging (FDI), separates the various return echoes at each x-y coordinate into their individual frequencies. The result is not a single acoustic image, but typically 20 to 40 different acoustic images, each image made from echoes of a single frequency, and each image having its own contrast and resolution.
 
Engineers often solve problems involving internal interfaces by comparing the various FDI images. The results for any particular sample depend on the sample and on the materials involved, but typically some FDI images have high resolution, and are useful for performing diagnoses of critical interfaces, such as those in flip chips. In some cases, FDI images display features that are not visible in the time-domain images.