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신기훈(Ki-Hoon Shin) (사)한국CDE학회 2017 한국CDE학회 논문집 Vol.22 No.4
This paper presents a method for surface to surface development between 3D sculptured surfaces. This technique can be used as a way of confirming in advance the contour shape of the original surface on the target surface that can minimize the geometric changes while the original surface is developed on a specific portion of the target surface of the human body. For this purpose, both the original and target surfaces were first tessellated and roughly flattened on a 2D plane. Next, the facet models were optimally developed onto a 2D plane by geometry-based method, minimizing geometric errors (e.g., area change ratio). Finally, the 3D point on the target surface corresponding to the 2D nodal point of the original facet model were obtained by calculating barycentric coordinates on the 2D plane. An example was presented to validate the proposed surface to surface development method.
기능성 경사 복합재를 이용한 사출금형의 냉각회로 모델링
신기훈(Ki-Hoon Shin) 대한기계학회 2011 大韓機械學會論文集A Vol.35 No.12
일반적으로 사출금형의 사출주기는 플라스틱 제품의 냉각 시간에 크게 좌우되는 데, 냉각회로를 적용하여 조절할 수 있다. 금형의 냉각회로는 전통적으로 기계가공을 통하여, 직선형상만을 생성할 수 있었지만, 최근 적층조형 방법의 개발로 코어 형상을 따라가는 형상적응형 냉각회로를 생성할 수 있게 되었다. 한편 금형의 다이 재질로 열저항력이 크고, 치수변화가 적은 H13 스틸이 널리 사용되고 있지만, 열전도율이 낮기 때문에 냉각효율은 높지 않다. 이러한 점에서 열전달 효율을 극대화 시킬 수 있는 방법으로 H13 스틸과 구리(Cu)를 기능적으로 혼합한 기능성 경사 복합재(FGM)를 적층조형을 이용하여 냉각회로에 적용하는 방안이 검토되고 있다. 이러한 시도로서 본 논문에서는 H13 스틸과 Cu 간의 FGM 을 이용한 형상적응형 냉각회로의 모델링 방법을 제안하고자 한다. The cycle time in injection moulding greatly depends on the cooling time of the plastic part that is controlled by cooling channels. Cooling channels are required to facilitate the heat transfer rate from the die to the coolant without reducing the strength of the die. Employing layered manufacturing techniques (LMT), a die embedding conformal cooling channels can be fabricated directly while conventional cooling channels are usually made of straight drilled hole. Meanwhile, H13 tool steel is widely used as the die material because of its high thermal resistance and dimensional stability. However, H13 with a low thermal conductivity is not efficient for certain part geometries. In this context, the use of functionally graded materials (FGMs) between H13 and copper may circumvent a tradeoff between the strength and the heat transfer rate. This paper presents a method for modeling of conformal cooling channels made of FGMs.
플립칩 패키지에서 무연 솔더 조인트 및 UBM의 열충격 특성 해석
신기훈(Ki-Hoon Shin),김형태(Hyoung-Tae Kim),장동영(Dong-Young Jang) 한국생산제조학회 2007 한국생산제조학회지 Vol.16 No.5
This paper presents a computer-based analysis on the thermal shock characteristics of Pb-free solder joints and UBM in flip chip assemblies. Among four types of popular UBM systems, TiW/Cu system with 95.5Sn-3.9Ag-0.6Cu solder joints was chosen for simulation. A simple 3D finite element model was first created only including silicon die, mixture between underfill and solder joints, and substrate. The displacements due to CTE mismatch between silicon die and substrate was then obtained through FE analysis. Finally, the obtained displacements were applied as mechanical loads to the whole 2D FE model and the characteristics of flip chip assemblies were analyzed. In addition, based on the hyperbolic sine law, the accumulated creep strain of Pb-free solder joints was calculated to predict the fatigue life of flip chip assemblies under thermal shock environments. The proposed method for fatigue life prediction will be evaluated through the cross check of the test results in the future work.
신기훈(Ki-Hoon Shin),김주한(Joo-Han Kim) 한국생산제조학회 2007 한국생산제조학회지 Vol.16 No.6
UBM (Under Bump Metallurgy) of flip chip assemblies consists of several layers such as the solder wetting, the diffusion barrier, and the adhesion layers. In addition, IMC layers are formed between the solder wetting layers (e.g. Cu, Ni) and the solder. The primary failure mechanism of the solder joints in flip chips is widely known as the fatigue failure caused by thermal fatigues or electromigration damages. Sometimes, the premature brittle failure occurs in the IMC layers. However, these phenomena have thus far been viewed from only experimental investigations. In this sense, this paper presents a method for solid modeling of IMC layers in flip chip assemblies, thus providing a pre-processing tool for finite element analysis to simulate the IMC failure mechanism. The proposed modeling method is CSG-based and can also be applied to the modeling of UBM structure in flip chip assemblies. This is done by performing Boolean operations according to the actual sequences of fabrication processes.