• 한국마이크로전자및패키징학회:학술대회논문집
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• 한국마이크로전자및패키징학회 2001년도 추계 기술심포지움
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• pp.67-73
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• 2001

To investigate the relationships of solder joint characteristics with solder composition and A:V ratio (solder volume per pad area), Sn-37Pb and Sn-4.0Ag-0.5Cu solder balls with 330, 400, 450 and $457{\mu}{\textrm}{m}$ size were reflowed on same substrate. Sn-37Pb and Sn-4.0Ag-0.5Cu was reflowed at $220^{\circ}C$ and $240^{\circ}C$ respectively by IR-type soldering machine. As a result of reflowed solder- ball diameter(D) and height(H) measurement, D/H was decreased with solder ball size increment in range of 330~450 ${\mu}{\textrm}{m}$. But, D/H was increased in the solder joint for 457 ${\mu}{\textrm}{m}$ size, it was caused possibly by decrement of solder ball height increment compared with solder volume increment. As a result of shear and pull test, joint strength with A:V ratio was high. Joint strength of Sn-4.0Ag-0.5Cu was higher than Sn-37Pb. However, Sn-37Pb had more stable solder joint of small standard deviation. A thick and clean scallop type Ni-Cu-Sn intermetallic compound layer was formed in high A:V ratio and Sn-4.0Ag-0.5Cu solder joint interface.

• Structural Engineering and Mechanics
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• 제68권4호
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• pp.497-505
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• 2018

Three points bending flexural test was modeled numerically to study the crack propagation in the pre-cracked beams. The pre-existing edge cracks in the beam models were considered to investigate the crack propagation and coalescence paths within the modeled samples. The effects of particle size on the single edge-notched round bar in bending test were considered too. The results show that Failure pattern is constant by increasing the ball diameter. Tensile cracks are dominant mode of failure. These crack initiates from notch tip, propagate parallel to loading axis and coalescence with upper model boundary. Number of cracks increase by decreasing the ball diameter. Also, tensile fracture toughness was decreased with increasing the particle size. In the present study, the influences of particles sizes on the cracks propagations and coalescences in the brittle materials such as rocks and concretes are numerically analyzed by using a three dimensional particle flow code (PFC3D). These analyses improve the understanding of the stability of rocks and concretes structures such as rock slopes, tunnel constructions and underground openings.

• 마이크로전자및패키징학회지
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• 제18권1호
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• pp.35-39
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• 2011

고속전단시힘의 표준화를 위한 기초 연구의 일부로 Sn-3.0wt%Ag-0.5wt%Cu 솔더 볼의 고속전단특성에 대한 연구를 수행 하였다. 고속전단 시험편 제작을 위해 직경 450 ${\mu}m$의 솔더 볼을 FR4 PCB (Printed Circuit Board) 위에 장착한 후 $245^{\circ}C$ 온도에서 리플로 솔더링을 행하였다. PCB 상의 금속 패드로는 ENIG (Electroless Nickel/mmersion Gold, i.e Cu/Ni/Au)와 OSP (Organic Solderability Preservative, Cu 패드)를 사용하였다. 고속전단 속도는 0.5~3.0 m/s 범위, 전단 팁의 높이는 10~135 ${\mu}m$ 범위에서 변화시켰다. 실험결과로서, OSP 패드의 경우 전단 팁 높이 증가에 따라 연성 파괴가 증가하였으며, 전단속도 증가에 따라 연성파괴는 감소되었다. ENIG 패드의 경우에도 전단 팁 높이 증가에 따라 연성 파괴가 증가하였다. 전단 팁 높이 10 ${\mu}m$(볼 직경의 2%)는 패드 박리 파괴가 대부분이어서 전단파면 관찰에는 부적절한 높이였다. 고속전단에너지는 OSP 및 ENIG 패드 모두 전단 팁 높이 증가에 따라 증가하는 경향을 보였다.

• 마이크로전자및패키징학회지
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• 제14권4호
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• pp.71-77
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• 2007

본 연구에서는 리플로우 횟수를 달리하여 Sn-37Pb, Sn-3.5Ag와 Sn-3.5Ag-0.75Cu (all wt.%) BGA 솔더 접합부들을 OSP가 코팅된 Cu 패드 상에 형성시킨 후, 기계적 전기적 특성을 연구하였다. 주사전자현미경 분석 결과, 접합 계면에 생성된 $Cu_6Sn_5$ 금속간화합물 층의 두께는 리플로우 횟수가 증가함에 따라 증가하였다. Sn-Pb와 Sn-Ag-Cu 솔더 접합부의 경우, 3회 리플로우 후 최대 전단 강도를 나타내었으며, Sn-Ag 솔더 접합부의 경우 4회 리플로우 후 최대 전단 강도를 나타내었다. 이후 리플로우 횟수가 10회까지 증가함에 따라 전단 강도는 점차 감소하였다. 리플로우 횟수가 증가함에 따라 전기적 특성은 점차 감소하였다.

• 대한기계학회논문집A
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• 제26권5호
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• pp.932-938
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• 2002

In structural applications, brittle materials such as soda-lime glasses and ceramics are usually subjected to multiaxial stress state. Brittle materials with cracks or damage by foreign object impacts are apt to fracture abruptly from cracks, because of their properities of very high strength and low fracture toughness. But in most cases, the residual strength of structural members with damage has been tested under uniaxial stress condition such as the 4-point bend test. Depending upon the crack pattern developed, the strength under multiaxial stress state might be different from the one under uniaxial. A comparative study was carried out to investigate the influence of stress state on the residual strength evaluation. In comparable tests, the residual strength under biaxial stress state by the ball-on-ring test was greater than that under the uniaxial one by the 4-point bend test, when a small size indendation crack was introduced. In the case that crack having an angle of 90deg. to the applied stress direction, the ratio of biaxial to uniaxial flexure strength was about 1.12. The residual strength was different from crack angles to loading direction when it was evaluated by the 4-point bend test. The ratio of residual strength of 45deg. crack to 90deg. one was about 1.20. In the case of specimen cracked by a spherical impact, it was shown that an overall decrease in flexure strength with increasing impact velocity, and the critical impact velocity for formation of a radial and/or cone crack was about 30m/s. In those cases that relatively large cracks were developed as compared with the case of indented cracks, the ratio of residual strength under biaxial stress state to one uniaxial became small.

• 한국산학기술학회논문지
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• 제20권7호
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• pp.8-15
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• 2019

본 연구에서는 칼슘 술폰산염 컴플렉스 그리스와 리튬 컴플렉스 그리스를 합성하고, 그리스의 일반 물성, 유변학적 특성 및 윤활성능을 비교하였다. 내열성 시험인 적점 시험에서 칼슘 술폰산염 컴플렉스 그리스의 열 안정성은 섭씨 300도 이상, 리튬 컴플렉스 그리스는 섭씨 245도로 측정되었다. 점도시험에서 칼슘 술폰산염 컴플렉스 그리스는 7.0 파스칼 초, 리튬 컴플렉스 그리스는 4.5 파스칼 초로 측정되었다. 따라서 칼슘 술폰산염 컴플렉스 그리스가 리튬 컴플렉스 그리스보다 내열성 및 점착성면에서 우수함을 확인하였다. 4-ball 내마모시험에서 칼슘 술폰산염 컴플럭스 그리스는 0.43 밀리미터, 리튬 컴플럭스 그리스는 0.85 밀리미터로 측정되었고, 4-ball 내하중성 시험에서 칼슘 술폰산염 컴플렉스 그리스는 620 킬로그램중, 리튬 컴플렉스 그리스는 125 킬로그램중 으로 측정되었다. 따라서, 칼슘 술폰산염 컴플렉스 그리스가 리튬 컴플렉스 그리스보다 내마모성 및 내하중성에서 우수하였다. 위 시험결과로 고온 및 고하중의 윤활에서는 칼슘 술폰산염 컴플렉스 그리스가 리튬 컴플렉스 그리스보다 더 효과적인 것을 알 수 있었다.

• 대한기계학회논문집A
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• 제33권4호
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• pp.440-446
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• 2009

This paper was designed to fabricate the miniature spur gear with pitch circle of 2.25mm using extrusion process of a mechanically alloyed Al-78wt%Zn powder. The mechanical alloying of the powder particles were performed for ball milled times of 4h, 8h, 16 and 32h by the planetary ball milling. The mechanical properties of these alloyed powders, which were compacted and sintered-cylindrical preforms, were estimated using compression test. The results showed that the alloyed powder with average particle size of $10{\mu}m$ milled for 32h has the highest compressive(fractured) strength(288MPa). Extrusions of the miniature spur gear using the alloyed powder were carried out at different extrusion temperatures. Extrusion temperature of $300^{\circ}C$ provided the spur gear with the highest relative density and Vickers hardness and without any surface defects.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2000년도 추계학술대회 논문집
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• pp.15-18
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• 2000

We developed a human-sized BWR(biped walking robot) driven by a new actuator based on the ball screw which has high strength and high gear ratio. The robot overcomes the limit of the driving torque of conventional BWRs. Each leg of the robot is composed of three pitch joints and one roll joint. In all, a 10 degree-of-freedom robot with two balancing joints was developed. The BWR was developed to walk autonomously such that it is actuated by small torque motors and is boarded with DC battery and controllers. In the performance test, the BWR performed nice motions of sitting-up and sitting-down. Through the test, we could find capability of high performance in biped-walking.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2000년도 제15차 학술회의논문집
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• pp.267-267
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• 2000

We developed a human-sized BWR(biped walking robot) driven by a new actuator based on the ball screw which has high strength and high gear ratio. The robot overcomes the limit of the driving torque of conventional BWRs. Each leg of the robot is composed of three pitch joints and one roll joint. In all, a 10 degree-of-freedom robot with two balancing joints was developed. The BWR was developed to walk autonomously such that it is actuated by small torque motors and is boarded with DC battery and controllers. In the performance test, the BWR peformed nice motions of sitting-up and sitting-down. Through the test, we could find capability of high performance in biped-walking.

• 한국기계가공학회지
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• 제18권3호
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• pp.103-108
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• 2019

The results of the measurement of the flow-rate coefficient (Cv-value) and the analysis of a small ball valve are summarized follows. The Cv-values of 1/2-, 3/4- and 1-inch ball valves were measured using a flow-rate measurement test. The manufacturer obtained the Cv-value using a theoretical calculation method. The new experimental measurement and analysis method yielded more reliable results. In addition, the Cv value obtained through numerical analysis was almost identical the value provided by the manufacturer, which was based on experimental results. A Study on Flow Analysis results are all similar appearances as the reliability of the results.