• Proceedings of the International Microelectronics And Packaging Society Conference
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• 2000.04a
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• pp.43-55
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• 2000

In traditional electronic packages the die and the substrate are interconnected with fine wire. Wire bonding technology is limited to bond pads around the peripheral of the die. As the demand for I/O increases, there will be limitations with wire bonding technology. Flip chip technology eliminates the need for wire bonding by redistributing the bond pads over the entire surface of the die. Instead of wires, the die is attached to the substrate utilizing a direct solder connection. Although several steps and processes are eliminated when utilizing flip chip technology, there are several new problems that must be overcome. The main issue is the mismatch in the coefficient of thermal expansion (CTE) of the silicon die and the substrate. This mismatch will cause premature solder Joint failure. This issue can be compensated for by the use of an underfill material between the die and the substrate. Underfill helps to extend the working life of the device by providing environmental protection and structural integrity. Flux residues may interfere with the flow of underfill encapsulants causing gross solder voids and premature failure of the solder connection. Furthermore, flux residues may chemically react with the underfill polymer causing a change in its mechanical and thermal properties. As flip chip packages decrease in size, cleaning becomes more challenging. While package size continues to decrease, the total number of 1/0 continue to increase. As the I/O increases, the array density of the package increases and as the array density increases, the pitch decreases. If the pitch is decreasing, the standoff is also decreasing. This paper will present the keys to successful flip chip cleaning processes. Process parameters such as time, temperature, solvency, and impingement energy required for successful cleaning will be addressed. Flip chip packages will be cleaned and subjected to JEDEC level 3 testing, followed by accelerated stress testing. The devices will then be analyzed using acoustic microscopy and the results and conclusions reported.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.21 no.4
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• pp.340-351
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• 2010

This paper presented compact CW sub-THz imaging system using the terahertz transmitter(Tx) that generates 0.34 THz electromagnetic wave based on electronic device. Using 0.34 THz electromagnetic wave generated by Tx, we measured transmitting terahertz wave magnitude and phase information respectively with terahertz receiver(Rx) based on sub harmonic mixer. This paper measured and compared images of several samples to obtain better imaging results by changing time delay and step distance of scanning stage which affect image resolution. Also, through the imaging measurement of various samples, we were able to assure possibility of application of terahertz wave.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.19 no.5
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• pp.556-561
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• 2008

The characteristics of microwave reflectometry, which is based on the technologies of FM radar and is applied as a non-invasive method to examine the properties including density distribution of inhomogeneous media, is investigated. The microwave reflectometry system requires not only an optimized system hardware but as well as the understanding of system response from the media under test in order to provide the system solution describing the object under test quantitatively. The introduction of microwave reflectometry especially in the area of applied plasma physics has been relatively new and the number of usage is found to be increasing gradually. The experimental method to characterize the microwave system as a device to examine the properties of plasma is explained. The microwave reflectometry signals consist of the cutoff signals which originate from the region where most of the reflected power comes from and the scattered signals which result as an interaction of the microwave and the density perturbations. This paper describes the experimental results of the scattered signal from the microwave reflectometry, such as the wavenumber dependence and the sensitivity on density perturbation, and the comparison of the characteristics with those from the numerical simulations and those from the cutoff signals.

• Coupled systems mechanics
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• v.5 no.2
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• pp.191-201
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• 2016

Coupled structures are widely seen in civil and mechanical engineering. In coupled structures, monitoring the translational motion of its key components is of great importance. For instance, some coupled arms are equipped with a hydraulic piston to provide the stiffness along the piston axial direction. The piston moves back and forth and a distance sensing system is necessary to make sure that the piston is within its stroke limit. The measured motion data also give us insight into how the coupled structure works and provides information for the design optimization. This paper develops two distance sensing systems for coupled structures. The first system measures distance with ultrasonic sensor. It consists of an ultrasonic sensing module, an Arduino interface board and a control computer. The system is then further upgraded to a three-sensor version, which can measure three different sets of distance data at the same time. The three modules are synchronized by the Arduino interface board as well as the self-developed software. Each ultrasonic sensor transmits high frequency ultrasonic waves from its transmitting unit and evaluates the echo received back by the receiving unit. From the measured time interval between sending the signal and receiving the echo, the distance to an object is determined. The second distance sensing system consists of a wire draw encoder, a data collection board and the control computer. Wire draw encoder is an electromechanical device to monitor linear motion by converting a central shaft rotation into electronic pulses of the encoder. Encoder can measure displacement, velocity and acceleration simultaneously and send the measured data to the control computer via the data acquisition board. From experimental results, it is concluded that both the ultrasonic and the wire draw encoder systems can obtain the linear motion of structures in real-time.

• Progress in Medical Physics
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• v.29 no.2
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• pp.66-72
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• 2018

The proper position of a multi-leaf collimator (MLC) is essential for the quality of intensity-modulated radiation therapy (IMRT) and volumetric modulated arc radiotherapy (VMAT) dose delivery. Task Group (TG) 142 provides a quality assurance (QA) procedure for MLC position. Our study investigated the QA validation of the mechanical leaf gap measurement and the maintenance procedure. Two $VitalBeam^{TM}$ systems were evaluated to validate the acceptance of an MLC position. The dosimetric leaf gaps (DLGs) were measured for 6 MV, 6 MVFFF, 10 MV, and 15 MV photon beams. A solid water phantom was irradiated using $10{\times}10cm^2$ field size at source-to-surface distance (SSD) of 90 cm and depth of 10 cm. The portal dose image prediction (PDIP) calculation was implemented on a treatment planning system (TPS) called $Eclipse^{TM}$. A total of 20 VMAT plans were used to confirm the accuracy of dose distribution measured by an electronic portal imaging device (EPID) and those predicted by VMAT plans. The measured leaf gaps were 0.30 mm and 0.35 mm for VitalBeam 1 and 2, respectively. The DLG values decreased by an average of 6.9% and 5.9% after mechanical MLC adjustment. Although the passing rates increased slightly, by 1.5% (relative) and 1.2% (absolute) in arc 1, the average passing rates were still within the good dose delivery level (>95%). Our study shows the existence of a mechanical leaf gap error caused by a degenerated MLC motor. This can be recovered by reinitialization of MLC position on the machine control panel. Consequently, the QA procedure should be performed regularly to protect the MLC system.

• The Journal of the Korea Contents Association
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• v.11 no.8
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• pp.33-42
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• 2011

In this paper we designed and implemented a wireless communication circuit which can control the remote devices integrating RFID and ZigBee. This system unifies transmit part and receive part. And this system recognizes RFID tag data, then the recognized information is controlled by MCU, and transmitted to a remote device through the ZigBee. This is operated on TinyOS. If this system is applied to a entrance security system, it can permit/deny one's entrance as well as control the personal computer or other electronic devices. Our experiment shows the result of the recognized data transmission is very different according to a opened playground and a closed place. The data transmission time is stable in the indoor and the data transmission distance is long in the outdoor. We anticipate that our system be applied the various office oriented domains by connecting to the Wired LAN or the WLAN of IEEE 802.11x category.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2007.10a
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• pp.449-452
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• 2007

An intelligent robot with RSSI based indoor location estimation function was designed and implemented. A wireless sensor node was attached to the robot to received the location data from the indoor location estimation function. Spartan III was used as the main control device in the mobile robot. The current location data collected from the indoor location estimation system was transferred to the mobile robot and server through Zigbee/IEEE 802.15.4 wireless communication of the sensor node. Once the location data is received, the sensor node senses the direction of the robot head and directs the robot to move to its destination. Indoor location estimation intelligent robot is able to move efficiently and actively to the user appointed location by implementing the proposed obstacles avoidance algorithm. This system is able to monitor real-time environmental data and location of the robot using PC program. Indoor location estimation intelligent robot also can be controlled by executing the instructions sent from the PC program.

• Korean Journal of Materials Research
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• v.27 no.2
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• pp.107-112
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• 2017

The BCBJ (Back Contact and Back Junction) or back-lit solar cell design eliminates shading loss by placing the pn junction and metal electrode contacts all on one side that faces away from the sun. However, as the electron-hole generation sites now are located very far from the pn junction, loss by minority-carrier recombination can be a significant issue. Utilizing Medici, a 2-dimensional semiconductor device simulation tool, the interdependency between the substrate thickness and the minority-carrier recombination lifetime was studied in terms of how these factors affect the solar cell power output. Qualitatively speaking, the results indicate that a very high quality substrate with a long recombination lifetime is needed to maintain the maximum power generation. The quantitative value of the recombination lifetime of minority-carriers, i.e., electrons in p-type substrates, required in the BCBJ cell is about one order of magnitude longer than that in the front-lit cell, i.e., $5{\times}10^{-4}sec$ vs. $5{\times}10^{-5}sec$. Regardless of substrate thickness up to $150{\mu}m$, the power output in the BCBJ cell stays at nearly the maximum value of about $1.8{\times}10^{-2}W{\cdot}cm^{-2}$, or $18mW{\cdot}cm^{-2}$, as long as the recombination lifetime is $5{\times}10^{-4}s$ or longer. The output power, however, declines steeply to as low as $10mW{\cdot}cm^{-2}$ when the recombination lifetime becomes significantly shorter than $5{\times}10^{-4}sec$. Substrate thinning is found to be not as effective as in the front-lit case in stemming the decline in the output power. In view of these results, for BCBJ applications, the substrate needs to be only mono-crystalline Si of very high quality. This bars the use of poly-crystalline Si, which is gaining wider acceptance in standard front-lit solar cells.

• Korean Journal of Materials Research
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• v.28 no.1
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• pp.38-42
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• 2018

Continuous efforts are being made to improve the efficiency of Si solar cells, which is the prevailing technology at this time. As opposed to the standard front-lit solar cell design, the back-lit design suffers no shading loss because all the metal electrodes are placed on one side close to the pn junction, which is referred to as the front side, and the incoming light enters the denuded back side. In this study, a systematic comparison between the two designs was conducted by means of computer simulation. Medici, a two-dimensional semiconductor device simulation tool, was utilized for this purpose. The $0.6{\mu}m$ wavelength, the peak value for the AM-1.5 illumination, was chosen for the incident photons, and the minority-carrier recombination lifetime (${\tau}$), a key indicator of the Si substrate quality, was the main variable in the simulation on a p-type $150{\mu}m$ thick Si substrate. Qualitatively, minority-carrier recombination affected the short circuit current (Isc) but not the opencircuit voltage (Voc). The latter was most affected by series resistance associated with the electrode locations. Quantitatively, when ${\tau}{\leq}500{\mu}s$, the simulation yielded the solar cell power outputs of $20.7mW{\cdot}cm^{-2}$ and $18.6mW{\cdot}cm^{-2}$, respectively, for the front-lit and back-lit cells, a reasonable 10 % difference. However, when ${\tau}$ < $500{\mu}s$, the difference was 20 % or more, making the back-lit design less than competitive. We concluded that the back-lit design, despite its inherent benefits, is not suitable for a broad range of Si solar cells but may only be applicable in the high-end cells where float-zone (FZ) or magnetic Czochralski (MCZ) Si crystals of the highest quality are used as the substrate.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.13 no.1
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• pp.329-332
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• 2012

LEDs are using widely in a field of illumination, LCD LED backlight, mobile signals because they have several merits, such as low power consumption, long lifetime, high brightness, fast response, environment friendly. To achieve high performance LEDs, one needs to enhance output power, reduce operation voltage, and improve device reliability. In this paper, we have proposed that the optimum design and specialized process could improve the performance of LED chip. It was showed an output power of 7cd and input supplied voltage of 3.2V by the insertion technique of current blocking layer. In this paper, GaN-based LED chip which is built on the sapphire epi-wafer by selective MOCVD were designed and developed. After that, their performances were measured. It showed the output power of 7cd more than conventional GaN-based chip. It will be used the lighting source of a medical equipment and LCD LED TV with GaN-based LED chip.