The mechanical strength of layers used in microelectronic circuits is not well understood. In this study in situ microtensile tests were performed in a scanning electron microscope on various multilayers of Al-0.5%Cu, Ti and TiN deposited on a Ti substrate. Film fracture occurred in two distinct modes, either perpendicular to the loading or at a 45 degrees angle to the loading direction. Samples were loaded until the cracked films began to debond from the substrate. By using X-ray diffraction (XRD) and energy dispersive spectroscopy (EDS) the weak interface was determined to be the Al to Ti interface. The strength of this interface was calculated to be 0.5 J/m(2), which is in good agreement with theoretical predictions.