Yuting He

Preparation and characterization of ultrasonic electrodeposited copper coating

Copper has replaced aluminum as the main interconnect material in VLSI, due to its low resistivity and high electromigration resistance. The property of copper coating is a key factor that determines the reliability of interconnects. A special copper coating was prepared by ultrasonic-electrodeposition method in this study, and the microstructure, hardness, wear resistance, adhesion and corrosion resistance of it were investigated respectively. Test results show that the crystallite size of it is obviously smaller than that of the ordinary electrodeposited copper coating, and the hardness, wear resistance, adhesion and corrosion resistance of it are all evidently enhanced.

A High-Sensitivity Flexible Eddy Current Array Sensor for Crack Monitoring of Welded Structures under Varying Environment

This paper develops a high-sensitivity flexible eddy current array (HS-FECA) sensor for crack monitoring of welded structures under varying environment. Firstly, effects of stress, temperature and crack on output signals of the traditional flexible eddy current array (FECA) sensor were investigated by experiments that show both stress and temperature have great influences on the crack monitoring performance of the sensor. A 3-D finite element model was established using Comsol AC/DC module to analyze the perturbation effects of crack on eddy currents and output signals of the sensor, which showed perturbation effect of cracks on eddy currents is reduced by the current loop when crack propagates. Then, the HS-FECA sensor was proposed to boost the sensitivity to cracks. Simulation results show that perturbation effect of cracks on eddy currents excited by the HS-FECA sensor gradually grows stronger when the crack propagates, resulting in much higher sensitivity to cracks. Experimental result further shows that the sensitivity of the new sensor is at least 19 times that of the original one. In addition, both stress and temperature variations have little effect on signals of the new sensor.

An assessment method of electronic packaging reliability based on rough set theory

With the continuous improvements of IC integration,the electronic packaging reliability became more and more important. As a result, how to evaluate the reliability of the electronic packaging precisely has become a problem to be solved. In this paper, an index system from the packaging material, packaging process and packaging test is put forward. Then, considering many uncertainties induced by the absence and decentralization of electronic packaging information, a rough set theory based model is established to assess the electronic packaging reliability. It is shown from the case study that the model can make the assessment more objective and feasible because it can take more accounts of the uncertainties in the electronic packaging reliability analysis.

A surface crack monitoring sensor for metallic structures

Crack monitoring plays a great role in modern structural health monitoring. A new scheme of the sensor is developed in this paper. The finite element model (FEM) of the sensor was established, and the output characteristics of the sensor were analyzed by FEM. It was shown that the sensor was sensitive to cracks, and could be used to monitor the propagation of cracks initiating from the edge of the hole. Finally, the sensor was prepared on a specimen, and the feasibility of the sensor to monitor cracks was demonstrated by experiment.