Hochauflösende zerstörungsfreie Prüfung an Lötverbindungen mittels Hochfrequenz-Ultraschall

The detection of defects with ultrasonic waves can be optimized if the ultrasonic wavelength lambda is comparable to the defect size d. This implements the other boundary conditions too: pulse length equal or bigger than 1.5 lambda, sound beam diameter without focussing about 10 lambda, with focussing about lambda. Related to soldered joints and sound velocities inside the solder itself ultrasonic frequencies equal or bigger than 50 MHz are necessary. While qualifying bonds with lower frequencies (10-50 MHz) by phase boundary echo amplitudes, high frequency ultrasonic testing UT enables locating and sizing of defects. Quality assurance for high temperature and high strength ceramics recently improved the high frequency UT. Probes made by piezoelectric foils (PVF2), thin films (ZnO, CdS) or buffer rods (Al2O3,Si3N4) and piezoelectric single crystals (LiTaO3) allow to reach the frequency region above 250 MHz too. Imaging systems like the Scanning Laser Acoustic Microscope (SLAM) are anal yzing macroscopic volumes (cube millimeter) with microscopic resolution (some ten microns). Examples are given and discussed for soldered joints.