• Proceedings of the KWS Conference
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• 2010.05a
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• pp.74-74
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• 2010

모바일 정보통신기기를 중심으로 전자패키지의 초소형화, 고집적화를 위해 플립칩 공법의 적용이 증가되고 있는 추세이다. 플립칩 패키징 접합소재로는 솔더, ICA(Isotropic Conductive Adhesive), ACA(Anisotropic Conductive Adhesive), NCA(Non Conductive Adhesive) 등과 같은 다양한 접합소재가 사용되고 있다. 최근에는 언더필을 사용하는 플립칩 공법보다 미세피치 대응성을 위해 NCP를 이용한 플립칩 공법에 대한 요구가 증가되고 있는데, NCP의 상용화를 위해서는 공정성과 함께 신뢰성 확보가 필요하다. 본 연구에서는 LDI(LCD drive IC) 모듈을 위한 COF(Chip-on-Film) 플립칩 패키징용 NCP 포뮬레이션을 개발하고 이를 적용한 COF 패키지의 신뢰성을 조사하였다. 테스트베드는 면적 $1.2{\times}0.9mm$, 두께 $470{\mu}m$, 접속피치 $25{\mu}m$의 Au범프가 형성된 플리칩 실리콘다이와 접속패드가 Sn으로 finish된 폴리이미드 재질의 flexible 기판을 사용하였다. NCP는 에폭시 레진과 산무수물계 경화제, 이미다졸계 촉매제를 사용하여 다양하게 포뮬레이션을 하였다. DSC(Differential Scanning Calorimeter), TGA(Thermogravimetric Analysis), DEA(Dielectric Analysis) 등의 열분석장비를 이용하여 NCP의 물성과 경화거동을 확인하였으며, 본딩 후에는 보이드를 평가하고 Peel 강도를 측정하였다. 최적의 공정으로 제작된 COF 패키지에 대한 HTS (High Temperature Stress), TC (Thermal Cycling), PCT (Pressure Cooker Test)등의 신뢰성 시험을 수행한 결과 양산 적용 가능 수준의 신뢰성을 갖는 것을 확인할 수 있었다.

• Horticultural Science & Technology
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• v.34 no.1
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• pp.32-45
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• 2016

Fruit bagging has been widely practiced in peach cultivation to produce high quality and unblemished fruit. Moreover, fruit bagging has been utilized to study the effect of shading on the quality of fruit. We conducted a proteomic analysis on peach fruit to elucidate the biochemical and physiological events that characterize the effect of bagging treatment. Comparative analysis of 2D electrophoresis (2-DE) gels showed that relative protein levels differed significantly at 125 DAFB (days after full bloom), as well as at 133 DAFB in fruit that had been bagged until 125 DAFB, followed by exposure to sunlight. Most of the proteins with altered expression were identified by MALDI TOF/TOF. Twenty-one proteins with differential expression among the groups were identified at 125 DAFB, while thirty proteins with differential expression among the groups were identified at 133 DAFB. The analysis revealed that expression of proteins involved in photosynthesis, stress responses, and biochemical processes influencing metabolism were altered during bagging treatment, suggesting that regulation of the synthesis of carbohydrates, amino acids, and proteins influenced fruit size, solid/acid ratio, and peel color. This work provides the first characterization of proteomic changes in peach in response to fruit bagging treatment. Identifying and tracking protein changes may allow us to better understand the mechanisms underlying the effects of bagging treatment.

• Journal of the Microelectronics and Packaging Society
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• v.21 no.4
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• pp.69-76
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• 2014

In this study, we developed an ultra-thin flexible printed circuit board(FPCB) using the sputtered flexible copper clad laminate. In order to enhance the adhesion between copper and polyimide substrate, a NiMoNb addition layer was applied. The mechanical durability and flexibility of the ultra-thin FPCB were characterized by stretching, twisting, bending fatigue test, and peel test. The stretching test reveals that the ultra-thin FPCB can be stretched up to 7% without failure. The twisting test shows that the ultra-thin FPCB can withstand an angle of up to $120^{\circ}$. In addition, the bending fatigue test shows that the FPCB can withstand 10,000 bending cycles. Numerical analysis of the stress and strain during stretching indicates the strain and the maximum von Mises stress of the ultra-thin FPCB are comparable to those of the conventional FPCB. Even though the ultra-thin FPCB shows slightly lower durability than the conventional FPCB, the ultra-thin FPCB has enough durability and robustness to apply in industry.

• Composites Research
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• v.32 no.1
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• pp.37-44
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• 2019

The reinforcement effect of micro-bolt for a bonded scarf joint was investigated. Three scarf ratios of 1/10, 1/20, and 1/30 were considered to examine the effect of scarf patch configuration on joint strength. To maintain the same density of micro-bolt, 16, 32, and 48 bolts were installed in the scarf joint specimens with scarf ratios of 1/10, 1/20, and 1/30, respectively. Tests were also carried out on the joints that are bonded with only adhesive and that are fastened with only micro-bolts to obtain reference values. The average failure loads of the adhesive joints with scarf ratios of 1/10, 1/20, and 1/30 were 29.7, 39.6, and 44.8 kN, respectively. In case of micro-bolt reinforcement, the failure loads at the same scarf ratios were 28.4, 37.2, and 40.1 kN, respectively, which corresponds to 96, 94, and 90% of the pure adhesive joint failure loads. In the case of using only micro-bolts, the failure loads were only 13-25% of the average failure loads of pure adhesive joints. Fatigue test was also conducted for the joints with scarf ratio of 1/10. The results show that the fatigue strength of hybrid joints using both adhesive and microbolts together slightly increased compared to the fatigue strength of adhesive joint, but the rate of increase was small to 2-3%. Through this study, it was confirmed that the reinforcement effect of micro-bolt is negligible in the scarf joints where shear stress is dominating the failure, unlike in the structure where peel stress is dominant.

• Advances in aircraft and spacecraft science
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• v.11 no.1
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• pp.83-103
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• 2024

Adhesive bonding is currently widely used in many industrial fields, particularly in the aeronautics sector. Despite its advantages over mechanical joints such as riveting and welding, adhesive bonding is mostly used for secondary structures due to its low peel strength; especially if it is simultaneously exposed to temperature and humidity; and often presence of bonding defects. In fact, during joint preparation, several types of defects can be introduced into the adhesive layer such as air bubbles, cavities, or cracks, which induce stress concentrations potentially leading to premature failure. Indeed, the presence of defects in the adhesive joint has a significant effect on adhesive stresses, which emphasizes the need for a good surface treatment. The research in this field is aimed at minimizing the stresses in the adhesive joint at its free edges by geometric modifications of the ovelapping part and/or by changing the nature of the substrates. In this study, the finite element method is used to describe the mechanical behavior of bonded joints. Thus, a three-dimensional model is made to analyze the effect of defects in the adhesive joint at areas of high stress concentrations. The analysis consists of estimating the different stresses in an adhesive joint between two 2024-T3 aluminum plates. Two types of single lap joints(SLJ) were analyzed: a standard SLJ and another modified by removing 0.2 mm of material from the thickness of one plate along the overlap length, taking into account several factors such as the applied load, shape, size and position of the defect. The obtained results clearly show that the presence of a bonding defect significantly affects stresses in the adhesive joint, which become important if the joint is subjected to a higher applied load. On the other hand, the geometric modification made to the plate considerably reduces the various stresses in the adhesive joint even in the presence of a bonding defect.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.144.2-144.2
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• 2016

Diamond-like carbon (DLC) coatings have been widely applied to the mechanical components, cutting tools due to properties of high hardness and wear resistance. Among them, hydrogenated amorphous carbon (a-C:H) coatings are well-known for their low friction properties, stable production of thin and thick film, they were reported to be easily worn away under high temperature. Non-hydrogenated tetrahedral amorphous carbon (ta-C) is an ideal for industrial applicability due to good thermal stability from high $sp^3$-bonding fraction ranging from 70 to 80 %. However, the large compressive stress of ta-C coating limits to apply thick ta-C coating. In this study, the thick ta-C coating was deposited onto Inconel alloy disk by the FCVA technique. The thickness of the ta-C coating was about $3.5{\mu}m$. The tribological behaviors of ta-C coated disks sliding against $Si_3N_4$ balls were examined under elevated temperature divided into 23, 100, 200 and $300^{\circ}C$. The range of temperature was setting up until peel off observed. The experimental results showed that the friction coefficient was decreased from 0.14 to 0.05 with increasing temperature up to $200^{\circ}C$. At $300^{\circ}C$, the friction coefficient was dramatically increased over 5,000 cycles and then delaminated. These phenomenon was summarized two kinds of reasons: (1) Thermal degradation and (2) graphitization of ta-C coating. At first, the reason of thermal degradation was demonstrated by wear rate calculation. The wear rate of ta-C coatings showed an increasing trend with elevated temperature. For investigation of relationship between hardness and graphitization, thick ta-C coatings(2, 3 and $5{\mu}m$) were additionally deposited. As the thickness of ta-C coating was increased, hardness decreased from 58 to 49 GPa, which means that graphitization was accelerated. Therefore, now we are trying to increase $sp^3$ fraction of ta-C coating and control the coating parameters for thermal stability of thick ta-C at high temperatures.

• Journal of the Korean Society of Food Science and Nutrition
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• v.45 no.4
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• pp.562-568
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• 2016

This study investigated the effects of Yuza pectin extract (0, 0.1, 0.15, and 0.2%, w/v) on the physicochemical, microbial, rheological, and sensory properties of yogurt. Pectin extract was extracted from Yuza peel by using citrate after juicing the flesh. The total sugar content of Yuza pectin was 89.07%. The pH of Yuza pectin extract-added yogurt was 4.43. All Yuza pectin extract-added yogurt samples showed shear-thinning flow behaviors (n=0.33~0.44). The values for apparent viscosity ($0.34{\sim}0.47Pa{\cdot}s$), consistency index ($4.48{\sim}10.25Pa{\cdot}s^n$), yield stress (6.56~17.61 Pa), storage modulus (47.96~75.21 Pa), and loss modulus (19.79~26.06 Pa) for 0.1~0.2% (w/v) Yuza pectin extract-added yogurt were considerably higher than those of the control. These result indicated that Yuza pectin extract could enhance steady and dynamic shear rheological properties of yogurt. The sensory scores of Yuza pectin extract-added yogurt were higher than those of the control.