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.

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.

Evaluation of Mechanical Properties of Low Temperature Space for Automotive Material Applications

Seunghyun Cho(조승현),Jungsoo Oh,Sungjae Won,Gwango Park 한국자동차공학회 2017 한국자동차공학회 부문종합 학술대회 Vol.2017 No.5

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>

Efficient In-Loop Filtering Across Tile Boundaries for Multi-Core HEVC Hardware Decoders With 4 K/8 K-UHD Video Applications

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>

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>

종방향 스트립을 이용한 낮은 레이놀즈 수 익형 주위의 유동 제어

조승현(Seunghyun Cho),김주하(Jooha Kim),최해천(Haecheon Choi) 대한기계학회 2017 대한기계학회 춘추학술대회 Vol.2017 No.11

124-Mpixels/sec 하드웨어 HEVC 인코더의 화면간 예측 구현

조승현(Seunghyun Cho),김현미(Hyunmi Kim),이석호(Sukho Lee) 한국방송·미디어공학회 2014 한국방송공학회 학술발표대회 논문집 Vol.2014 No.11

전기차 인너벨트 웨더스트립용 EPDM/PP Thermoplastic Vulcanizates 재료설계인자에 따른 점탄성과 글라스 마찰 소음 상관관계 연구

조승현 ( Seunghyun Cho ),윤범용 ( Bumyong Yoon ),이상현 ( Sanghyun Lee ),홍경민 ( Kyoung Min Hong ),이상현 ( Sang Hyun Lee ),서종환 ( Jonghwan Suhr ) 한국복합재료학회 2021 Composites research Vol.34 No.3

전기차의 수요 및 보급이 확대됨에 따라 차량 내 이음(buzz, squeak, rattle, BSR) 개선에 대한 요구가 커지고 있다. 이에 풍절음, 도어 글라스 및 차량 진동을 차단하는 인너벨트 웨더스트립(innerbelt weatherstrip)의 댐핑(damping) 특성 향상을 통해 BSR을 저감하는 기술 개발이 필수적이다. 기존 열경화성(thermoset) 탄성체 대비 가볍고 재활용이 가능한 열가소성(thermoplastic) 탄성체가 주목을 받고 있지만 낮은 소재 댐핑과 영구압축줄음률(compression set)로 인해 도어 글라스와 웨더스트립 간 마찰 소음을 발생하는 문제가 있다. 고분자 댐핑 특성은 점탄성(viscoelastic)에 좌우되므로, 본 연구에서는 인너벨트 웨더스트립과 도어 글라스 간 마찰 소음을 개선하기 위해 EPDM (ethylene-propylene-diene monomer)/PP (polypropylene) thermoplastic vulcanizates (TPV)의 재료설계인자(EPDM/PP 비율, EPDM 내 ENB 함량)에 따른 점탄성 분석을 통해 소재 댐핑 특성을 평가하였다. EPDM/PP 비율에 따른 분석을 통해 PP 비율이 낮을수록 소재가 연화되고, 탄성회복력(resilience)이 증가하여 저장탄성률(storage modulus)은 10.8% 감소하고 댐핑 특성을 의미하는 감쇠계수(tanδ)는 88.2% 증가함을 확인하였다. 또한 EPDM 내 ENB 함량이 높을수록 소재의 가교밀도(crosslink density)가 증가하지만, 동적가교(dynamic vulcanizate) 과정 중 PP에 분산된 EPDM particle의 크기가 감소한다. 이로 인해 증가된 EPDM/PP 계면 간 면적 증가로 인해 계면 미끄러짐에서 기인한 손실탄성률(loss modulus)이 24.7% 증가하여 댐핑 특성이 향상되었다. 재료설계인자에 따른 물성 분석을 바탕으로 최적 소재(낮은 PP 비율(14 wt%), 높은 ENB 함량 (8.9 wt%))를 배합한 결과 소재 댐핑 특성(tanδ peak)은 기존 소재(PP27, EPDM/PP 30/27, ENB content 5.7 wt%) 대비 140% 증가하여 재료설계인자에 따라 댐핑 특성을 제어할 수 있음을 확인하였다. 설계된 소재의 글라스 마찰 소음 개선 효과를 확인하기 위해 stick-slip 시험을 통해 마찰 소음을 평가하였다. 소재 댐핑 특성이 향상됨에 따라 마찰 진동의 가속도 peak가 약 57.9% 감소하였다. 이러한 결과로부터 재료설계인자에 따른 소재 댐핑 특성 향상을 통해 인너벨트 웨더스트립의 글라스 마찰 소음을 개선할 수 있음을 확인하였으며, 향후 소재 재료설계인자에 따른 물성 제어를 통해 부품의 요구 성능에 맞는 다양한 재료설계에 활용할 수 있을 것으로 기대된다. Due to enormous market growing of electric vehicles without combustion engine, reducing unwanted BSR (buzz, squeak, and rattle) noise is highly demanded for vehicle quality and performance. Particularly, innerbelt weatherstrips which not only block wind noise, rain, and dust from outside, but also reduce noise and vibration of door glass and vehicle are required to exhibit high damping properties for improved BSR performance of the vehicle. Thermoplastic elastomers (TPEs), which can be recycled and have lighter weight than thermoset elastomers, are receiving much attention for weatherstrip material, but TPEs exhibit low material damping and compression set causing frictional noise and vibration between the door glass and the weatherstrip. In this study, high damping EPDM (ethylene-propylene-diene monomer)/PP (polypropylene) thermoplastic vulcanizates (TPV) were investigated by varying EPDM/PP ratio and ENB (ethylidene norbornene) fraction in EPDM. Viscoelastic properties of TPV materials were characterized by assuming that the material damping is directly related to the viscoelasticity. The optimum material damping factor (tanδ peak 0.611) was achieved with low PP ratio (14 wt%) and high ENB fraction (8.9 wt%), which was increased by 140% compared to the reference (tanδ 0.254). The improved damping is believed due to high fraction of flexible EPDM chains and higher interfacial slippage area of EPDM particles generated by increasing ENB fraction in EPDM. The stick-slip test was conducted to characterize frictional noise and vibration of the TPV weatherstrip. With improved TPV material damping, the acceleration peak of frictional vibration decreased by about 57.9%. This finding can not only improve BSR performance of electric vehicles by designing material damping of weatherstrips but also contribute to various structural applications such as urban air mobility or aircrafts, which require lightweight and high damping properties.

클라우드 SNS상에서 Proxy Re-Encryption을 이용한 사용자 모바일 인증 프로토콜

조승현 ( Seunghyun Cho ),문종호 ( Jongho Mun ),남윤호 ( Yoonho Nam ),전웅렬 ( Woongryul Jeon ),원동호 ( Dongho Won ) 한국정보처리학회 2013 한국정보처리학회 학술대회논문집 Vol.20 No.1

최근 분산 시스템의 기술이 발전하면서 소셜 네트워크 서비스(SNS)도 분산방식으로 전환해가는 추세이다. 특히, 모바일 기기 발전과 공급 확산으로 인해 모바일 기기의 분산 SNS에 대한 연구로 클라우드 컴퓨팅 기술을 응용한 모바일 클라우드 SNS가 연구되고 있다. 또한, 제 3자의 미인증 모바일 기기를 사용한 SNS 접속으로 인한 피해가 증가되고 있는 반면, 이를 방지하는 사용자 모바일 기기 인증에 대한 연구는 미흡하다. 따라서 본 논문은 Proxy Re-Encryption 기술을 응용하여 안전한 모바일 기기 인증 프로토콜을 제안한다.