Key Engineering Materials Vols. 326-328

Abstract: An indentation method to determine equi-biaxial residual stress is proposed by examining the data from the incremental plasticity theory based FE analyses. We found that hardness is strongly dependent of the magnitude and sign of residual stress and material properties. We then selected some normalized parameters minimally affected by material properties and tip radius. With numerical regressions of the data obtained, we proposed new formulae for residual stress evaluation. The new approach provides a substantial enhancement in accuracy compared with the prior methods.

Abstract: Flow properties and stress state are indispensable factors for safety assessment of structural materials in operation, which were evaluated using instrumented indentation tests (IITs). Flow properties were obtained by defining representative stress and strain, and IIT results for 10 steel materials were discussed by comparing with those from uniaxial tensile tests. The indentation load-depth curve is significantly affected by the presence of residual stress, and the stress-induced load change was converted to a quantitative stress value. The stress state of a friction stir-welded joint of API X80 steel was evaluated and compared with that measured by energy-dispersive X-ray diffraction.

Abstract: Signals acquired from a Combo calibration standard tube used to calibrate for inspection and evaluation of motorized rotating pancake coil probe signals from steam generator tubes. So, Combo tube signals should be consistent and accurate since they have strong influence on evaluation procedure of signals. However, motorized rotating pancake coil probe signals are very easily affected by various factors so that they can distort amplitudes and phase angles which are quantitative terms for signal evaluation. To overcome this problem, we explored possibility of using numerical simulation as a practical calibration tool for the evaluation of real field signals. In this study, we investigated the characteristics of a motorized rotating pancake coil probe and a Combo tube. And then we used commercial software to produce a set of calibration signals and compared to the experiments. Using simulated Combo tube signals, we evaluated deliberated single circumferential indication defects, and these results were compared with experimental signal evaluation results.

Abstract: The objective of this study is to estimate the feasibility of X-ray diffraction method application for fatigue life assessment of the high-temperature pipeline steel such as main steam pipe, re-heater pipe and header etc. in power plant. In this study, X-ray diffraction tests using various types of specimen simulated low cycle fatigue damage were performed in order to analyze fatigue properties when fatigue damage conditions become various stages such as 1/4, 1/2 and 3/4 of fatigue life, respectively. As a result of X-ray diffraction tests for specimens simulated fatigue damages, we conformed that the variation of the full width at half maximum intensity decreased in proportion to the increase of fatigue life ratio. And also, the ratio of the full width at half maximum intensity due to fatigue damage has linear relationship with fatigue life ratio algebraically. From this relationship, it was suggested that direct expectation of the life consumption rate was feasible.

Abstract: Natural hazards, and especially earthquakes, are often recurring phenomena. Therefore, there is a permanent need for solutions to reduce earthquake losses by developing technologies, procedures, knowledge, and tools for seismic design and rehabilitation of buildings and infrastructure. A key point to an effective decision making process that aims at mitigating their effects is building a model of the underlying facts. A Geographical Information System (GIS) is a framework able to assemble, keep, process and display specific information, identified by geographical location, which can combine layers of information to give the user a better understanding about that location. By using a Geographical Information System containing geospatial data, one can develop useful scenarios to reduce natural disaster risk and vulnerability of structures. In this paper, we describe a way of applying data mining techniques from the artificial intelligence field to earthquake analysis in order to make a better investigation of the available data. These methods are capable of finding “hidden” correlations among different subsets of data, which cannot be revealed by means of simple statistics.

Abstract: In the manufacturing process of flip-chips, ultrasonic bonding has been widely used. In the past, however, the ultrasonic horn was designed to move horizontally while the bonding force was applied vertically, the motion control of the horn thus cannot be controlled accurately. In addition, non-coplanar effects were unavoidably occurred and the quality of bonding became unacceptable. In this paper, the non-coplanar phenomenon between the horn and the substrate was attempted to improve by designing the horn with the following features: 1. The resonant mode of the horn is purely longitudinal; 2. The contact surface between the horn and the flip-chip in the substrate remain plane; The finite element method (FEM) was used to design the ultrasonic horn with the above features. In the future, the amplitude-fluctuation electronic speckle pattern interferometry (AF-ESPI) will be used to verify the FEM results.

Abstract: In low temperature co-fired ceramic (LTCC) packaging which offers a good performance to produce multilayer structures with electronic circuits and components, the via-hole fabrication of LTCC ceramic-PET double layer sheets (green sheets or green tapes) by micro-scale punching plays an important role in providing an electric path for the interconnection between layers. Although conventional punching has been used widely and many researchers have provided useful insights of the process, they are restricted to the punching of single layer material. This paper discusses the characteristic of micro via-hole punching of double layer sheets and the optimum process condition for via-holes of good quality. Workpiece (double layer sheet) used in the present investigation consists of LTCC ceramic composite material layer (ceramic layer) of 20~100*m in thickness and PET layer of 38 and 75*m in thickness by tape-casting. The diameter of via-holes ranges from 100~300*m.

Abstract: For measuring deformation of electronic packages, various techniques have been used. Each technique has some merits and demerits. Some techniques have very high resolution but small measuring area. On the contrary, other techniques have large measuring area and low resolution. So the judicious selection of techniques with a trade-off between the resolution and available measuring area is important. In this research, a new laser profiler was developed by integrating high resolution laser displacement sensor into the x-y scanner. This system has 10nm vertical resolution and 100nm horizontal resolution with a measurement area up to 25mm by 25mm. The residual deformation of a lead-contained and lead-free PBGA package after reflow process was measured by the newly developed system. And the effect of aging was evaluated.

Abstract: Among many factors that influence the reliability of a flip-chip assembly using NCF interconnections, the most effective parameters are often the coefficient of thermal expansion (CTE), the modulus (E), and the glass transition temperatures (Tg). Of these factors, the effect of Tg on thermal deformation and device reliability is significant; however, it has not been shown clearly what effect Tg has on the reliability of NCF. The Tg of a conventional NCF material is approximately 110°C. In this study, a new high Tg NCF material that has a 140oC Tg is proposed. The thermal behaviors of the conventional and new NCFs between -40oC to 150oC are observed using an optical method. Twyman-Green interferometry and the moiré interferometry method are used to measure the thermal micro-deformations. The Twyman-Green interferometry measurement technique is applied to verify the stress-free state. The stress-free temperatures of the conventional and new Tg NCF materials are approximately 100oC and 120oC respectively. A shear strain at a part of the NCF chip edge is measured by moiré interferometry. Additionally, a method to accurately measure the residual warpage and shear strain at room temperature is proposed. Through the analysis of the relationship between the warpage and the shear strain, the effect of the high-Tg NCF material on the reliability is studied.

Abstract: As the interconnection density of electronic packaging continues to increase, the fatigueinduced solder joint failure of surface mounted electronic devices become one of the most critical reliability issues in electronic packaging industry. Especially, prediction of the shape of solder joint is a major event in the development of electronic packaging for its practical engineering application. In conventional electronic packages, the geometrical dimensions of solder balls and solder pads of the package are the same. In this research, a hybrid method combined with analytical and energybased methods is utilized to predict force-balanced heights and geometry profiles of solder balls under various solder volume and pad dimensions as well as their relative location during the reflow process. Next, a non-linear finite element analysis is adopted to investigate the stress/strain behavior of solder balls in flip chip package. The results reveal that as the flip chip package contains larger solder balls located at the corner area underneath the chip, the maximum equivalent plastic strain/stress is evidently reduced and the reliability cycles under thermal loading are enhanced. Furthermore, the results presented in this research can be used as a design guideline for area array interconnections.