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레이저 간섭계 ( ESPI ) 를 이용한 폴립칩 패키지의 열변형 평가
장우순(Woo Soon Jang),이백우(Baik Woo Lee),김동원(Dong Won Kim),정증현(Jeung Hyun Jeong),백경욱(Kyung Wook Paik),권동일(Dong Il Kwon),나전웅(Jae Woong Nah) 대한금속재료학회 ( 구 대한금속학회 ) 2002 대한금속·재료학회지 Vol.40 No.9
In this study, electronic speckle pattern interferometry (ESPI) was applied to a non-destructive and real-time evaluation of the thermal deformation in a flip-chip package. The displacement resolution of ESPI was improved with magnifying lenses, and ESPI was modified to measure the deformation of micro systems. The flip-chip package thermally deforms with increasing temperature, and the difference in the thermal expansion between the chip and the PCB induces the micro-failure at the solder joint. To evaluate the level of thermal deformation precisely, the horizontal and vertical deformations were measured in the temperature range of 25℃ to 125℃ in situ using the resolution-enhanced ESPI to a sub-micrometer scale. From the experimental results, it was found that the CTE (coefficient of thermal expansion) difference between the chip and the PCB leads to shear strain at the solder joint. In addition, the shear strain could be evaluated at each solder joint. To verify these experimental results, the finite element analysis(FEA) results were compared with the ESPI results. The FEA results were similar to the ESPI results, which confirmed the adequacy of our application.
ESPI를 이용한 플립칩 솔더접합부의 열응력 인가에 따른 전단변형률 평가
장우순(Woosoon Jang),이백우(Baik-Woo Lee),김동원(Dong-Won Kim),권동일(Dongil Kwon) 대한기계학회 2001 대한기계학회 춘추학술대회 Vol.2001 No.8
In this study, we measure the thermal deformation of flip-chip solder joint by ESPI (Electronic Speckle Pattern Interferometry) system that has some advantages such as non-contact, non-destructive, real-time and full-field measurement. The ESPI system has been applied to bulk materials, but we try to apply it to micro material such as flip-chip package by improving its resolution with long working-distance microscope, zoom lens and iris. The sub-micrometer scale thermal deformation of flip-chip solder joint is measured from 25℃ to 125℃. Local shear strain in solder ball is also calculated from the measured thermal displacement. In addition, the experimental result from ESPI is compared with the predicted result from FEA(Finite Element Analysis). It is shown that shear strain from the experiment are similar to the predicted result from FEA.
레이저 간섭계(ESPI)에 의해 측정된 플립칩 열변형의 유한요소해석 모델링을 통한 솔더볼의 유동곡선 평가
이백우,김주영,나재웅,백경욱,권동일 대한금속재료학회 2003 대한금속·재료학회지 Vol.41 No.6
The goal of this study was to determine the uniaxial flow curve for solder balls in a flip-chip from experimental-computational algorithms based on finite element modeling (FEM) of in-plane thermal displacement data measured by electronic speckle pattern interferometry (ESPI). In order to measure the deformation of such tiny components as the solder balls in the flip-chip, the spatial resolution of ESPI was increased to submicron scale by magnifying the areas studied. The flow curve for solder balls in the flip-chip was determined by the algorithm, which effectively matches the simulated solder deformation by FEM to the measured deformation by ESPI. The algorithms were applied to Sn-36Pb-2Ag flip-chip solder balls. The flow curve obtained for flip-chip solder was compared with those for bulk solder. The microstructure was also studied to clarify the flow curve results.
김주영,이백우,권동일 대한금속재료학회 2004 대한금속·재료학회지 Vol.42 No.12
Bluntness is inevitable at the tip of a sharp indenter such as the Berkovich indenter used in nanoindentation experiments; this bluntness causes the hardness values observed at low contact depths (<~100 nm) to fall below the Nix and Gao model curve. We present an indentation size effect (ISE) model that extends the available contact depth for ISE application down to several tens of nanometers by considering the tip bluntness effect. The present model reflects the effect of tip bluntness on the distribution of geometrically necessary dislocations needed to accommodate the blunted tip, and the change in the ratio of plastic to total contact depth with contact depth. We applied the present model to nanoindentation results for annealed and strain-hardened Cu, and to previously reported nanoindentation results for surface-nanocrystallized Al-alloy. Good fit was observed between the present model and the hardness results over the full contact depth range. (Received July 22, 2004)
기상 증착된 비정질 실리콘 카바이드 박막질의 기판 온도 의존성
김주영,이백우,남호석,권동일 대한금속재료학회 2004 대한금속·재료학회지 Vol.42 No.3
The dramatic variations in structure and internal stress in an amorphous silicon carbide film (a-SiC) induced by forming process have been reported extensively. Vapor-depositions of a-SiC film were simulated by molecular dynamics simulation employing the Tersoff potential. To understand effect of substrate temperature that is one of the most important factors involved in the changes in structure and intrinsic stress, the vapor-depositions at various substrate temperatures (500-2500 K) were performed. Then, the MD simulations of cooling to 298 K were carried out. For both cooled and as-deposited a-SiC films, the analyses of structure and internal stress with deposition process parameters entailed the calculation of density, chemical order, and in-plane stress [(σ_(xx)+σ_(yy))/2].
김우식,권동일,장재일,이백우 대한금속재료학회(대한금속학회) 2000 대한금속·재료학회지 Vol.38 No.8
It is well known that the crack tip opening displacement (CTOD) test, widely used for heat-affected zone (HAZ) toughness evaluation, is very sensitive to complex distribution of microstructures in HAZ. So, as the second step of the researches on metallurgical analyses of fracture characteristics in HAZ of improved 9% Ni steel, this study aimed to investigate the microstructure distribution including local brittle zone (LBZ) and its influences on CTOD toughness. To study the correlation between microstructures and actual HAZ toughness in more systematic way, K-grooved HAZ specimens were prepared for the CTOD tests. To figure out the microstructure influence, the microstructure-distribution maps were constructed by semi-empirical method including the process of sectioning and observation of tested specimens. In the regions near fusion line, it was found that the crack initiations were ruled by weakest-link-typed failure, which resulted in relatively low toughness of the regions. In the regions of fusion line (F.L.) +2 ㎜ and +3 ㎜, i.e. relatively high toughness regions, the failure was ruled by rule-of-mixture type. It was also revealed that the minimum fraction of LBZs showing the weakest-link-typed failure was 17% in crack tip front of actual HAZ specimens. From the results obtained, the mechanism of toughness change based on metallurgical analyses was proposed and discussed.
鄭아람,李柏雨,鄭增鉉,張宰溢,權東一 대한금속재료학회 2002 대한금속·재료학회지 Vol.40 No.1
The fracture of eutectic Sn-Ag solder joint by thermal aging was investigated through a pull test and microstructural observation. The joint strength in the pull test decreased with increasing aging time and was saturated for aging time more than 25 hours. The change in joint strength was explained not only by such metallurgical factors as grain growth and intermetallics formation, but also by the mechanical factor of strength mismatch between solder and intermetallics. For aging time less than 25 hours, Cu_6Sn_5 intermetallics formed. Strength mismatch between solder and Cu_6Sn_5 intermetallics reduces joint strength by causing stress concentrations around the intermetallics. Joint strength decreased with the Hall-Petch relationship as solder grains become coarsened with increasing aging time. For aging time above 25 hours, Cu_3Sn intermetallics formation was confirmed. During Cu_3Sn intermetallics formation, voids generally formed. They play an important role in determining the primary failure site. The present study shows that an extended aging time reduces the joint strength and then saturates because all solder joint failure is more strongly determined by local stress concentration around voids than by the stress concentration caused by strength mismatch.
노치 효과와 하중 속도 효과를 고려한 소형 노치 시편의 파괴인성 평가
권동일,장재일,이백우 대한금속재료학회(대한금속학회) 2000 대한금속·재료학회지 Vol.38 No.12
Notch effect and loading rate dependency on fracture toughness were considered when evaluating fracture toughness of small notched specimens using the instrumented impact test. Notch effect was analyzed into stress redistribution effect and stress relaxation with a viewpoint of stress triaxiality. Stress redistribution effect was corrected by introducing effective crack length, which was the sum of actual crack length and plastic zone size. Stress relaxation effect was also corrected using elastic stress concentration factor, which would decrease if plastic deformation occurred. As a result, corrected fracture toughness of the notched specimen was very consistent with the reference fracture toughness obtained using precracked specimen. In addition, limiting notch root radius, below which fracture toughness was independent of notch radius, was observed and discussed. Loading rate dependency on fracture toughness, which was obtained from the static three point bending test and the instrumented impact test, was also discussed with stress field in plastic zone ahead of a notch and fracture based on stress control mechanism.
소형펀치 시험의 선형탄성 파괴역학적 분석을 통한 파괴이성 평가
권동일,장재일,주장복,이백우 대한금속재료학회(대한금속학회) 2001 대한금속·재료학회지 Vol.39 No.1
Small punch test is used to assess the reliability of industrial facilities such as fusion reactor structures and power generation systems. Conventional small punch tests evaluate transition temperature and fracture strain by analyzing the load-deflection curves and deformation behaviors, respectively. However, previous research did not consider fracture mechanical concepts such as flaw, stress analysis and fracture toughness. In this study, to obtain more reliable fracture characteristics based on linear elastic fracture mechanics in small punch tests, a pre-crack was introduced to small punch specimen. Stress and deformation behaviors near the crack tip were analyzed and the stress intensity factor was derived. Using the load at crack initiation point, the fracture toughness of SA 508 Cl.3 steel was successfully evaluated.