The High Density Electronics Center (HiDEC) at the University of Arkansas is developing advanced electronic packaging methods including multi-chip modules which utilize high temperature superconductor interconnects. A wide variety of materials have been proposed and investigated for these applications. Good knowledge of the mechanical properties of the candidate thin film materials is important for reliable device design.
Two new techniques have been developed to measure strain at fracture of thin film materials. The first is an acoustic technique in which an accelerometer is attached to the film. The film is then gradually strained. When the film fractures, an acoustic wave propagates through the film thereby creating a transient signal from the accelerometer. This signal is used to trigger an oscilloscope. The second technique is similar except that it utilizes a laser probe to detect the acoustic wave. In this photo-acoustic technique, the laser is reflected from the film onto a bi-sectional photodetector while the film is gradually strained. Upon film fracture, the acoustic wave modulates the laser beam and a transient voltage pulse is produced by the photodetector. Both techniques are capable of detecting extremely small cracks.