• Journal of the Microelectronics and Packaging Society
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• v.26 no.1
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• pp.29-33
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• 2019

With shrinking form factor and improving performance of electronic packages, high input/output (I/O) density is considered as an important factor. Fan out wafer-level packaging (FO-WLP) has been paid great attention as an alternative. However, FO-WLP is vulnerable to warpage during its manufacturing process. Minimizing warpage is essential for controlling production yield, and in turn, package reliability. While many studies investigated the effect of process and design parameters on warpage using finite element analysis, they did not take uncertainty into consideration. As parameters, including material properties, chip positions, have uncertainty from the point of manufacturing view, the uncertainty should be considered to reduce the gap between the results from the field and the finite element analysis. This paper focuses on the effect of uncertainty of Young's modulus of chip on fan-out wafer level packaging warpage using finite element analysis. It is assumed that Young's modulus of each chip follows the normal distribution. Simulation results show that the uncertainty of Young's modulus affects the maximum von Mises stress. As a result, it is necessary to control the uncertainty of Young's modulus of silicon chip since the maximum von Mises stress is a parameter related to the package reliability.

• Journal of Broadcast Engineering
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• v.26 no.5
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• pp.553-565
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• 2021

Point cloud is a set of points for representing a 3D object, and consists of geometric information, which is 3D coordinate information, and attribute information, which is information representing color, reflectance, and the like. In this way of expressing, it has a vast amount of data compared to 2D images. Therefore, a process of compressing the point cloud data in order to transmit the point cloud data or use it in various fields is required. Unlike color information corresponding to all 2D geometric information constituting a 2D image, a point cloud represents a point cloud including attribute information such as color in only a part of the 3D space. Therefore, separate processing of geometric information is also required. Based on these characteristics of point clouds, MPEG under ISO/IEC standardizes V-PCC, which imitates point cloud images and compresses them into 2D DCT-based 2D image compression codecs, as a compression method for high-density point cloud data. This has limitations in accurately representing 3D spatial information to proceed with compression by converting 3D point clouds to 2D, and difficulty in processing non-existent points when utilizing 3D DCT. Therefore, in this paper, we present 3D Discrete Cosine Transform-based Point Cloud Compression (3DCT PCC), a method to compress point cloud data, which is a 3D image by utilizing 3D DCT, and confirm the efficiency of 3D DCT compared to V-PCC based on 2D DCT.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.34 no.4
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• pp.251-255
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• 2021

a-Si is commonly considered as a primary candidate for the formation of passivation layer in heterojunction (HIT) solar cells. However, there are some problems when using this material such as significant losses due to recombination and parasitic absorption. To reduce these problems, a wide bandgap material is needed. A wide bandgap has a positive influence on effective transmittance, reduction of the parasitic absorption, and prevention of unnecessary epitaxial growth. In this paper, the adoption of a-SiO_x:H as the intrinsic layer was discussed. To increase lifetime and conductivity, oxygen concentration control is crucial because it is correlated with the thickness, bonding defect, interface density (D_it), and band offset. A thick oxygen-rich layer causes the lifetime and the implied open-circuit voltage to drop. Furthermore the thicker the layer gets, the more free hydrogen atoms are etched in thin films, which worsens the passivation quality and the efficiency of solar cells. Previous studies revealed that the lifetime and the implied voltage decreased when the a-SiOx thickness went beyond around 9 nm. In addition to this, oxygen acted as a defect in the intrinsic layer. The D_it increased up to an oxygen rate on the order of 8%. Beyond 8%, the D_it was constant. By controlling the oxygen concentration properly and achieving a thin layer, high-efficiency HIT solar cells can be fabricated.

• Journal of the Economic Geographical Society of Korea
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• v.25 no.3
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• pp.281-298
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• 2022

The COVID-19 pandemic has so far given the world a great shock and fear that cannot be compared to other infectious diseases, and local economies are experiencing a serious economic crisis accordingly. This paper examines the regional characteristics of economic recession and resilience due to the COVID-19 pandemic, focusing on the employment fluctuations in 85 cities nationwide. Although the overall trend is in line with national employment indicators, there are some differences in the shock response and the recovery of employment in individual cities. The difference between cities is somewhat greater in the resilience of the recovery stage than the resistance, which is the shock-response stage. In terms of resilience, cities in the capital area have relatively good condition compared to cities in the non-capital area. The weak resilience of large cities such as Seoul, which has a high population density, can be explained to be the effect of the COVID-19 pandemic of infectious diseases. Regarding the economic structure of the city, the ratio of service and sales workers, wholesalers and retailers, and food and lodging businesses are analyzed as valid explanatory variables for the resilience of cities.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.30 no.2D
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• pp.127-134
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• 2010

Tunnel sections on the highway are different from rest of sections on the highway in terms of velocity, the number of passing cars, and vehicle density which, in particular, affect drivers' behavior before and after drivers pass through the tunnel. However, literature review reveals that former studies are too focused on quantitative indicator to consider qualitative aspects. Therefore, this paper conducts survey questionnaire and IPA (Importance Performance Analysis) to find out qualitative improvements on velocity drop on the tunnel sections. The results show as follows: First, drivers require improvements of tunnel form (length and curved form inside tunnel) which is derived from long distance tunnel. Second, experts primarily ask for amendment of geometric characteristics. With comparison of requirements of both drivers and experts, there are many differences in length of tunnel and form of curved tunnel. This also presents that drivers don't satisfy with both length of tunnel and form of curved tunnel that are provided as a part of highway design factors.

• Journal of the Korea institute for structural maintenance and inspection
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• v.17 no.3
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• pp.118-125
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• 2013

The synthetic fibers including Polyvinyl alcohol and Polyethylene fibers have been successfully used in the manufacture of high ductile fiber reinforced cementitious composites. Polypropylene (PP) fiber has also been used in composites, not for the purpose of achieving a high level of tensile ductility but to improve the fire resistance performance of concrete exposed to high temperatures. This paper discusses the method for enhancing the performance of composites supplemented with PP fiber. Five types of mixture proportions were designed with high volume fly ash for testing the performance of composites. Type I cement and fly ash F were used as binding materials. The water-to-binder ratio was 0.23~0.25, and the amount of PP fiber used was 2 vol%. Polystyrene bead were also used to increase the tensile ductility of composites. A series of experiments including slump, density, compression and uniaxial tension tests were performed to evaluate the performance of cementitious composites supplemented with PP fiber. From the test results, it was exhibited that the performance of composites supplemented with PP fiber can be enhanced by adopting the mechanics and statistics theory.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.11a
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• pp.55-55
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• 2009

Silicon Carbide (SiC) is a material with a wide bandgap (3.26eV), a high critical electric field (~2.3MV/cm), a and a high bulk electron mobility (${\sim}900cm^2/Vs$). These electronic properties allow high breakdown voltage, high frequency, and high temperature operation compared to Silicon devices. Although various SiC DMOSFET structures have been reported so far for optimizing performances. the effect of channel dimension on the switching performance of SiC DMOSFETs has not been extensively examined. In this paper, we report the effect of the interface states ($Q_s$) on the transient characteristics of SiC DMOSFETs. The key design parameters for SiC DMOSFETs have been optimized and a physics-based two-dimensional (2-D) mixed device and circuit simulator by Silvaco Inc. has been used to understand the relationship with the switching characteristics. To investigate transient characteristic of the device, mixed-mode simulation has been performed, where the solution of the basic transport equations for the 2-D device structures is directly embedded into the solution procedure for the circuit equations. The result is a low-loss transient characteristic at low $Q_s$. Based on the simulation results, the DMOSFETs exhibit the turn-on time of 10ns at short channel and 9ns at without the interface charges. By reducing $SiO_2/SiC$ interface charge, power losses and switching time also decreases, primarily due to the lowered channel mobilities. As high density interface states can result in increased carrier trapping, or recombination centers or scattering sites. Therefore, the quality of $SiO_2/SiC$ interfaces is important for both static and transient properties of SiC MOSFET devices.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.47 no.6
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• pp.57-65
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• 2010

In this paper, we present a universal steganalysis scheme. The proposed method extract features of two types. First feature set is extracted from histogram characteristic of the wavelet subbands. Second feature set is determined by statistical moments of wavelet characteristic functions. 3-level wavelet decomposition is performed for stego image and cover image using the Haar wavelet basis. We extract one features from 9 high frequency subbands of 12 subbands. The number of second features is 39. We use total 48 features for steganalysis. Multi layer perceptron(MLP) is applied as classifier to distinguish between cover images and stego images. To evaluate the proposed steganalysis method, we use the CorelDraw image database. We test the performance of our proposed steganalysis method over LSB method, spread spectrum data hiding method, blind spread spectrum data hiding method and F5 data hiding method. The proposed method outperforms the previous methods in sensitivity, specificity, error rate and area under ROC curve, etc.

• Journal of Sasang Constitutional Medicine
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• v.9 no.2
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• pp.227-243
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• 1997

The experimental study used in this paper was done to examine the clinical effects of Taeumchowetang for the gastric ulcer and the function of gastrointestinal tract using rats and mice which were administered orally the water extraction from Taeumchowetang. Then, the counter-action of the water extraction on the isolated ileum and gastric fundus, the inhibitory effects of pylorus-ligated ulcer and indomethacin-induced ulcer, the associations with gastric juice secretion, total acidity, pepsin output, the transportability in the small and large intestine, were studied with administering acetylcholine chloride and barium chloride. In addition, it was investigated whether the central nervous system related to pain control and sleeping time was influenced by Taeumchowetang. The following results have been obtained; 1. As resulting from injection of acetylcholine chloride and barium chloride into the isolated ileum of rats and mice, Taeumchowetang led to have an inhibitory effect on the muscle contraction of the ileum. Then, acetylcholine chloride was measured as lower effect than barium chloride 2. For the inhibitory effect on contraction for the gastric fundus strip in rats by either acetylcholine chloride or barium chloride, the one showed low inhibitory effect, on the other hand the other showed density-dependent effect. 3. The water extraction was given on the pylorus ligated ulcer with using two different administration groups of 1,300mg/kg and 2,600mg/kg, each result was measured as 22.9% and 36.5% for an ulcerous inhibitory effect (p<0.05). 4. According to the two administration groups, the preventive effect was tabulated 18.1% and 29.3% for indomethacin-induced ulcer (p<0.05, P<0.01). 5. For associations with gastric juice secretion, total acidity, pepsin output in the administration group 2,600mg/kg, Taeumchowetang was recognized as having an inhibitory effects related to suppressive actions involving gastric juice secretion(p<0.05), and free acidity(p<0.01), but there was no significant association with total acidity and pepsin output. 6. To know the transportability in the intestine, BaSO4 solution was used. The transportability of the small intestine in the administration group 2,600mg/kg was 22.2% which was statistically significant compared with the large intestine's transportability(P<0.01). 7. In the administration group 1,300mg/kg and 2,600mg/kg, analgesic effect with against acetic acid was measured as being 16.8% and 24.4% which was shown as statistically siginificant(p<0.01). 8. No statistically significant association between Taeumchowetang and sleeping time was found in both 1,300mg/kg and 2,600mg/kg by administering phenobarbital-Na. According to the results of this study, Taeumchowetang has agreed with the effects of literature review. Further more in this study, Taeumchowetang also has preventive effects on pylorus-ligated ulcer. Hence, Teaumchowetang can be significant effect such as both anti ulcer agent and increasing gastric activity for the patients who suffer from gastric ulcer.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.45 no.6
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• pp.498-507
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• 2017

Electronic equipments comprised of high density components with various packaging types have been recently applied to a satellite. Therefore, to guarantee high reliability of electrical equipment, a design approach, which can reduce the development period and cost through an early diagnosis in potential risks of failure, should be established. In the previous research, the reliability assesment of the electronic equipments have based on Steinberg's fatigue failure theory. However, this theory was not enough for further investigation of life prediction and reliability of the electronic equipments comprised of various sizes and packaging types due to its theoretical limitations and analysis results sensitivity with regard to different modeling technic. In that case, if detailed finite element model is established, aforementioned problems can be readily solved. However, this approach might arise disadvantage of spending much time. In this paper, to establish strategy for high reliability design of electronic equipment, we performed mechanical reliability evaluation of CCB (Camera Controller Box) at qualification level based on the approach using Sherlock unlike design techniques applied to existing business.