Showing papers by "Yutaka S. Sato published in 2012"
TL;DR: In this paper, the relationship between material flow and abnormal grain growth in friction-stir welds was analyzed, and it was found that the deformation induced by the tool shoulder during friction stir welding may lead to the formation of a fine-grained layer at the upper surface of the weld, which may give rise to abnormally large grain growth during subsequent annealing.
41 citations
TL;DR: In this paper, a Co-based alloy tool was used to weld a zirconium alloy, Zircaloy-4, and a shiny, smooth surface was obtained.
39 citations
TL;DR: In this article, a novel technique of vacuum assisted via filling with molten solder was developed in which the diameter of the TSV was 30mm and its depth was 100-200mm.
34 citations
TL;DR: In this article, the hardness distribution and texture evolution in a friction stir welded oxide dispersion strengthened (ODS) ferritic steel was studied by electron backscattering diffraction (EBSD) and the results showed that regions near the bottom of the stir zone were the weak points in hardness, as those regions comprise coarser grains compared with adjacent regions.
Abstract: The goal of this study is to characterize the hardness distribution and texture evolution in a friction stir welded oxide dispersion strengthened (ODS) ferritic steel. Hardness profiles were plotted by collecting data on the transverse cross section of the joint. The texture evolution and microstructure characteristics were studied by electron backscattering diffraction (EBSD). Results showed that regions near the bottom of the stir zone were the weak points in hardness, as those regions comprise coarser grains compared with the adjacent regions. EBSD results showed that the grain characterization (size, shape, and aspect ratio) varied within different regions and provided important insight into the material flow within the stir zone. EBSD results also revealed that textures within different regions presented some features of rotating coincidence. By suitable rotations of the poles figures, textures within different regions could superpose with each other almost exactly.
20 citations
01 Dec 2012
TL;DR: The chip-based 3D heterogeneous integration technology for realizing highly parallel 3D-stacked image sensor that combines through-Si vias and metal micro-bumps formed in chip-level before stacking.
Abstract: We demonstrate the chip-based 3D heterogeneous integration technology for realizing highly parallel 3D-stacked image sensor. Three kinds of chips, CMOS image sensor chip, analog circuit chip, and ADC array chip, which were fabricated by different technologies, are processed and stacked vertically to form a prototype 3D-stacked image sensor. Through-Si vias (TSVs) and metal micro-bumps are formed in chip-level before stacking. The fundamental characteristics are evaluated in the fabricated prototype 3D-stacked image sensor.
15 citations
16 Aug 2012
TL;DR: Low cost and high speed molten solder-filling process of through silicon via (TSV) for 3D packaging was investigated and molten solder was filled into the TSV without voids by using vacuum system.
Abstract: Low cost and high speed molten solder-filling process of through silicon via (TSV) for 3D packaging was investigated Present filling methods, such as Cu electroplating and chemical vapor deposition (CVD), have some problems like low process speed and complicated process factors In this study, molten solder was filled into the TSV without voids by using vacuum system The thickness of wafer was 200 μm and the hole diameters were 20 and 30 μm respectively TSVs were formed by deep reactive ion etching (DRIE) process As the wetting layer, Ti and Au was sputtered on the wall of the TSVs Vacuum pressure was ranged from 006 ∼ 002MPa In 002MPa condition, via was filled perfectly within only few seconds To evaluate reliability of the filled TSV, thermal cycle test were carried out And interface between TSV wall and filled Sn alloy was observed by focused ion beam (FIB)
11 citations
TL;DR: The Texture developed in high-temperature β phase during Friction Stir Welding of Ti-6Al-4V was studied in this article, and it was found to be a mixture of {hkl}-fiber texture and D2(112]-simple-shear texture component.
Abstract: The Texture Developed in High-Temperature β Phase during Friction Stir Welding of Ti-6Al-4V Was Studied. It Was Demonstrated that 0002 and 1120 Pole Figures Calculated from α Phase May Be Employed for Interpretation of Material Flow in the β Phase. Together with Orientation Measurements in Retained β Phase, this Approach Was Shown to Be a Very Simple and Effective for the Texture Analysis. The β Texture Was Found to Be a Mixture of {hkl}-Fiber Texture and D2(112)[111](Simple-Shear Texture Component.
6 citations
01 Dec 2012
TL;DR: Wang et al. as mentioned in this paper developed a 3D-stacked image sensor chip composed of CMOS image sensor (CIS) layer, correlated double sampling circuit (CDS) layer and analog-to-digital converter (ADC) array layer using the chip-based 3D heterogeneous integration technology.
Abstract: We have developed a 3D-stacked image sensor chip composed of CMOS image sensor (CIS) layer, correlated double sampling circuit (CDS) layer, and analog-to-digital converter (ADC) array layer using the chip-based 3D heterogeneous integration technology Three kinds of chips, CIS chip, CDS chip, and ADC chip, which were fabricated by different technologies, are processed and stacked vertically to form a prototype 3D-stacked image sensor Through-Si vias (TSVs) and metal micro-bumps are formed in chip-level before stacking The fundamental characteristics are evaluated in the fabricated prototype 3D-stacked image sensor
5 citations
TL;DR: In this paper, a Co-based heat-resistant alloy strengthened by precipitating intermetallics, Co3(Al,W), with a L12 structure at high temperatures was used for friction-stir welding.
Abstract: The authors have developed a new friction-stir welding (FSW) tool that enables to weld high-softening-temperature materials (HSTMs), such as steels, titanium and zirconium alloys. The new tool is made of a Co-based heat-resistant alloy strengthened by precipitating intermetallics, Co3(Al,W), with a L12 structure at high temperatures. The Co-based alloy tool exhibits yield strengths higher than 500 MPa at 1000 deg C, so it might have a great potential as a tool material for FSW of HSTMs. In this study, the feasibility of using the Co-based alloy tool with various HSTMs was examined. Changes in the tool shape during FSW and the weld appearances produced with the Co-based alloy tool will be briefly shown.
3 citations