Papers by Author: Sang Joo Lee

Abstract: Mechanical behavior of small size materials has been explored due to many industry applications such as MEMs and semiconductors. The accurate measurements for mechanical properties of thin films are very challenge due to several technical difficulties. The proposed solution is the Visual Image Tracing (VIT) strain measurement system coupled with a micro tensile testing unit, which consists of a piezoelectric actuator, load cell, microscope and CCD cameras. This system has shown advantages of real time strain monitoring during the test and ability to measure the Young’s modulus, yiled strength and Poisson’s ratio of the material. Free standing Au films 0.5, 1 and 2 μm thick with average grain sizes of 104, 148 and 219 nm prepared by sputtering were studied using VIT system. The yield stresses of the films are dependent on film thickness and grain size.

Abstract: In the semiconductor inspection, number of pads at unit area is increasing and pad array have become irregular 2-dimensional. So we develop a bellows type micro contact probe. Our micro contact probe is a vertical-type micro contact probe for area arrays and narrow pitch electrode pads. We choose bellows type micro contact probe to prevent stress concentration. Our design targets are 120 um pad pitch, 20-50 um OD(over drive) and over 5 mN reaction force. In this research, micro contact probe is made by electroplating(Ni-Co). structural analysis is accomplished by FEM. And characterization of micro contact probe is done by our own mechanical tester. So material property is measured for structural analysis and structural analysis result will be compared with experimental result.

Abstract: It is quite difficult to accurately measure the mechanical properties of thin films. Currently, there are several methods (or application) available for measuring mechanical properties of thin films. Their properties, however, have been determined by indirect methods such as cantilever beam test and diaphragm bulge test. This paper reports the efforts to develop a direct strain measurement system for micro/nano scale thin film materials. The proposed solution is the Visual Image Tracing (VIT) strain measurement system coupled with a micro tensile testing unit, which consists of a piezoelectric actuator, load cell, microscope and CCD cameras. The advantage of this system is the ability to monitor the real time images of specimen during the test in order to determine its Young’s modulus and Poisson’s ratio at the same time. Stress-strain curve, Young’s modulus, yield strength and Poisson’s ratio of copper thin film measured using VIT system are presented.