Papers by Author: H. Du

Abstract: Piezoelectric bimorphs were assessed for their capabilities to be used as control actuators for vibration suppression of the print circuit boards (PCBs). Plate structures made of FR-4, a widely used industrial-grade material for manufacture of PCBs, were considered. An advanced and structured control algorithm, linear quadratic regulator with output feedback (LQROF), was used for active vibration control of the PCB structures. Experimental results showed that the LQROF control is a more robust algorithm than the classic control using the direct velocity feedback, and piezoelectric bimorph actuators present a great potential for active vibration control of the PCBs, and smart composites with embedded actuators.

Abstract: The quality of the interfaces in multilayer composites is a critical issue in the reliability testing of the composite product during the manufacturing process and in-service. Weak interfaces have often gone undetected and may become potentially defective at a later stage. One example is the interface between mold compound and silicon (MC/Si) in IC packaging. There is a desire to study the interface quality quantitatively, so the potential defective area can be evaluated and identified early. In this paper, a nondestructive evaluation methodology is proposed to measure the available strength of the interface by using ultrasonic reflection coefficients. It is known that interface degradation can be either due to poor manufacturing process and stress loading. Characterization of the interface quality of the MC/Si interface is first conducted by measuring longitudinal ultrasonic wave reflections from the interface samples fabricated under varying conditioning processes that simulate the degradation. A combined test that measures the reflection coefficient of the interface under stress load has also been conducted to quantify the effect of the load. Finally, it is shown that the overall effect on the reflection coefficient and available strength of the interface is derived and can be used as a quantitative indicator.

Abstract: Nanocrystalline TiN (or nc-TiN) has been imbedded in amorphous silicon nitride (a-SiNx)matrix to form a nanocomposite thin film (nc-TiN/a-SiNx) via magnetron sputtering deposition on silicon wafer. Two important effects of the Si3N4 sputtering target power on the formation of nc-TiN/a-SiNx have been studied: (1) Aside from forming a-SiNx in the matrix, Si atoms also imbed into TiN to form (Ti,Si)N solid solution crystallites. At low target power, the solid solution is substitutional. With increase of power, the amount of silicon “dissolved” in the TiN crystallite increases, and in the meantime, the interstitial components increase which is manifested in the increase in the TiN lattice parameter. (2) The crystallites have a preferred orientation varying with the deposition target power. As conveniently described by the coefficient of texture, the degree of preferred orientation along [111] direction decreases and finally tails off with increase of power. At the same time, the crystallites orient along [200] and [220] direction and eventually [220] direction dominants.