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Finite Element Analysis for Reliability of Solder Joints Materials in the Embedded Package
Seunghyun Cho,Seunghyun Cho 대한금속·재료학회 2019 ELECTRONIC MATERIALS LETTERS Vol.15 No.3
This paper is about study on warpage, creep strain and the total strain energy density (TSED) eff ect on fatigue life of thesolder joints in the embedded package under thermal cycling conditions by fi nite element method. In order to investigate theinfl uence of material of solder joints in embedded package, four materials (SAC305, SnAgCu, Sn96.5Ag3.5, Pb97.5Sn2.5)of solder joints were used. Calculated results show that warpage of package was low, creep strain and TSED of solder jointswere low in embedded package. Therefore the fatigue life of the solder joint in embedded package increases. Also, the fatiguelife of solder joints of Sn96.5Ag3.5 would be highest among solder materials because of the lowest of TSED.
Fast CU Splitting and Pruning for Suboptimal CU Partitioning in HEVC Intra Coding
Seunghyun Cho,Munchurl Kim IEEE 2013 IEEE TRANSACTIONS ON CIRCUITS AND SYSTEMS FOR VIDE Vol.23 No.9
<P>High Efficiency Video Coding (HEVC), a new video coding standard currently being established, adopts a quadtree-based Coding Unit (CU) block partitioning structure that is flexible in adapting various texture characteristics of images. However, this causes a dramatic increase in computational complexity compared to previous video coding standards due to the necessity of finding the best CU partitions. In this paper, a fast CU splitting and pruning method is presented for HEVC intra coding, which allows for significant reduction in computational complexity with small degradations in rate-distortion (RD) performance. The proposed fast splitting and pruning method is performed in two complementary steps: 1) early CU split decision and 2) early CU pruning decision. For CU blocks, the early CU splitting and pruning tests are performed at each CU depth level according to a Bayes decision rule method based on low-complexity RD costs and full RD costs, respectively. The statistical parameters for the early CU split and pruning tests are periodically updated on the fly for each CU depth level to cope with varying signal characteristics. Experimental results show that our proposed fast CU splitting and pruning method reduces the computational complexity of the current HM to about 50% in encoding time with only 0.6% increases in BD rate.</P>
Zirconia-Polyurethane Aneurysm Clip
Cho, Won-Sang,Cho, Kyung-il,Kim, Jeong Eun,Jang, Tae-Sik,Ha, Eun Jin,Kang, Hyun-Seung,Son, Young-Je,Choi, Seung Hong,Lee, Seunghyun,Kim, Chong-Chan,Sun, Jeong-Yun,Kim, Hyoun-Ee Elsevier 2018 World neurosurgery Vol.115 No.-
<P><B>Objective</B></P> <P>Susceptibility artifacts from metal clips in magnetic resonance (MR) imaging present an obstacle to evaluating the status of clipped aneurysms, parent arteries, and adjacent brain parenchyma. We aimed to develop MR-compatible aneurysm clips.</P> <P><B>Methods</B></P> <P>Considering the mechanical and biologic properties, as well as MR compatibility of candidate materials, a prototype clip with a zirconia body and a polyurethane head spring (zirconia clip [ZC], straight, 9-mm long) was developed. The closing forces, opening width of blades, and in vitro and in vivo artifact volumes in 3 tesla MR imaging were compared among the prototype and commercial metal clips such as a Yasargil clip (YC, curved type, 8.3-mm long) and a Sugita clip (SC, straight type, 10-mm long). An in vivo animal study was performed with a canine venous pouch aneurysm model.</P> <P><B>Results</B></P> <P>The closing forces (N) at 1 mm and 8 mm from the blade tip were 2.09 and 3.77 in YC, 1.85 and 3.04 in SC, and 2.05 and 4.60 in ZC. The maximum opening widths (mm) was 6.8, 9.0, and 3.0 in YC, SC, and ZC, respectively. The in vitro artifact volumes of YC, SC, and ZC in time-of-flight MR imaging were 26.9, 29.7, and 1.9 times larger than the respective real volumes. The in vivo artifact volumes of YC, SC, and ZC were respectively 21.4, 29.4, and 2.6 times larger than real ones.</P> <P><B>Conclusions</B></P> <P>ZC showed the smallest susceptibility artifacts and satisfactory closing forces. However, the narrow opening width of the blades was a weak point.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Our prototype of a zirconia-polyurethane aneurysm clip showed the much smaller susceptibility artifact, compared with the commercial clips, in about 2 versus 30 times larger than the real volumes of clips. </LI> <LI> This clip showed satisfactory closing forces comparable with the commercial clips. </LI> <LI> This clip showed a narrow opening width; however, this weak point is expected to be overcome by design modification. </LI> </UL> </P>
Study on the Nonlinear Characteristic Effects of Dielectric on Warpage of Flip Chip BGA Substrate
Cho, Seunghyun The Korean Microelectronics and Packaging Society 2013 마이크로전자 및 패키징학회지 Vol.20 No.2
In this study, both a finite element analysis and an experimental analysis are executed to investigate the mechanical characteristics of dielectric material effects on warpage. Also, viscoelastic material properties are measured by DMA and are considered in warpage simulation. A finite element analysis is done by using both thermal elastic analysis and a thermo-viscoelastic analysis to predict the nonlinear effects. For experimental study, specimens warpage of non-symmetric structure with body size of $22.5{\times}22.5$ mm, $37.5{\times}37.5$ mm and $42.5{\times}42.5$ mm are measured under the reflow temperature condition. From the analysis results, experimental warpage is not similar to FEA results using thermal elastic analysis but similar to FEA results using thermo-viscoelastic analysis. Also, its effect on substrate warpage is increased as core thickness is decreased and body size is getting larger. These FEA and the experimental results show that the nonlinear characteristics of dielectric material play an important role on substrate warpage. Therefore, it is strongly recommended that non-linear behavior characteristics of a dielectric material should be considered to control warpage of FCBGA substrate under conditions of geometry, structure and manufacturing process and so on.
Seunghyun Cho,HyunMi Kim,Hui Yong Kim,Munchurl Kim IEEE 2015 IEEE transactions on multimedia Vol.17 No.6
<P>HEVC is a next generation video coding standard designed with modern coding techniques to be especially efficient for coding high-resolution video such as 4 K/8 K-ultra high- definition (UHD) video. Among the advanced coding tools of HEVC, tiles and wavefront parallel processing (WPP) have been newly adopted for parallel processing of such high-resolution (4 K/8 K-UHD) video. To realize UHD video services over portable devices with limited battery power, it is essential to implement multi-core-based and dedicated HEVC hardware decoders that support the tile- and wavefront-based parallel processing. By doing so, each frame is divided into a multiple number of picture partitions which can then be processed by multiple hardware decoder cores in parallel. However, in-loop filtering (ILF) at tile boundaries cannot be easily parallelized by a multi-core HEVC hardware decoder because of the data dependency between samples in different tiles. In this paper, an efficient control method for ILF across tile boundaries is proposed for multi-core HEVC hardware decoders. The proposed method does not require additional in-loop filters for ILF across the tile boundaries and it allows a decoder core to continue to process the next coding tree unit (CTU) without waiting for other decoders until they finish their ILF processing for the neighboring CTUs in other tiles. From experiments, we show the effectiveness of our ILF control method via a quad-core HEVC decoder for 4 K-UHD video implemented on a prototyping FPGA board.</P>