Myung-Do Oh

Prediction and Evaluation of Cleanliness Levels Inside a Mini-Environment by Measuring Mean Air-Age and Effective Flow Rate

Numerical and experimental studies on the evaluation and prediction of the cleanliness level in a mini-environment system were carried out. The new direct method for estimating the cleanliness of a mini-environment, which involves determining the mean air-age and effective flow rate, is developed and its performance compared with that of the previous performance index based on airflow pattern characteristics. The result shows that the airflow pattern analysis is limited in terms of estimating the real performance of the mini-environment. This is because airflow pattern characteristics, like eddy size or turbulence intensity, can qualitatively show the path of contaminants and the degree of risk, but cannot predict the quantitative variation in the contamination level according to the variation in factors such as the location of the air supply and the exhaust and ventilation rate. In contrast, the mean air-age is capable of predicting quantitative variations in contaminant concentration as well as the effect of the turbulence intensity. Also, computational fluid dynamic (CFD) calculations and experiments show that mean air-age can help predict the relative cleanliness level variation at points in the modified mini-environment when the layout of the mini-environment is changed. It is concluded that mean air-age is a more exact and effective performance index than the previous airflow pattern characteristics like the turbulence intensity or eddy size.

Thermo-fluid simulation for the thermal design of the IGBT module in the power conversion system

Abstract The junction temperature of the insulated-gate bipolar transistor (IGBT) module, which belongs to power semiconductor devices, directly impacts on the system performance of the power conversion system (PCS), and therefore, the accurate prediction of the airflow rate passing the heat sink block of the IGBT module is very important at the thermal design stage. In this paper, the thermo-fluid simulation was developed with the T–Q characteristic curve to predict the junction temperature of the IGBT module and the airflow rate of the heat sink block. The porous media model was adopted in the heat sink block with fins and the filled air between fins of the heat sink block in the PCS to remove the heavily concentrated mesh problems in the heat sink block. The proposed simulation model was compared to the experimental value for the hot spot temperature on the heat sink block and the differences were within the average 4.0% margin of error in the comparison. This simulation model can be used to evaluate the suitability of the cooling design according to various operating conditions of the fan and IGBT module with benefits of the reduction in the mesh generation and the computation time. Also, this simulation model increases the flexibility of predicting the airflow rates in the PCS due to the change of the airflow passage structure in the PCS or the capacity of the fan.

Method of Particle Contamination Control for Yield Enhancement in the Cleanroom

The practical studies on the method of particle contamination control for yield enhancement in the cleanroom were carried out. The method of the contamination control was proposed, which are composed of data collection, data analysis, improvement action, verification, and implement control. The partition check method and the composition analysis for data collection and data analysis were respectively used in the main board and the cellular phone module production lines. And these methods were evaluated by the variation of yield loss between before and after improvement action. In case that the partition check method was applied, the critical process step was selected and yield loss reduction through improvement actions was observed. While in case that the composition analysis was applied, the critical sources were selected and yield loss reduction through improvement actions was also investigated. From these results, it is concluded that the partition check and the composition analysis are effective solutions for particle contamination control in the cleanroom production lines.

Study on Thermal Comfort and Indoor Air Quality in the Classroom with System Air-conditioner and Ventilation System for Cooling Loads

The experimental and the numerical study was performed on the comparison of thermal comfort(TC) and indoor air quality(IAQ) in the lecture room for cooling loads when the operating conditions are changed. PMV value and concentration of the lecture room were measured and compared with the numerical results. The numerical results showed a good agreement with the experimental one and then the numerical tool was used to analyze thermal comfort and IAQ for a couple of operating conditions. As a result it was found that the increment of the discharge angle of system air-conditioner makes TC uniformity worse, but rarely affects IAQ. Also TC and IAQ were hardly affected by the variation of the discharge airflow. Finally it turned out that TC is merely affected by the increment of the ventilation airflow, but the average concentration can be satisfied with Japanese IAQ standards of classrooms when the ventilation airflow is more than in this study.

Comparison of Thermal Comfort Performance Indices for Cooling Loads in the Lecture Room - An Correlation of PMV Bnd EDT -

We performed the experimental and the numerical study on the comparison of thermal comfort performance indices for cooling loads in the lecture room for 4 cases: Fan coil unit(FCU) or 4-way cassette air-conditioner is respectively operated with the ventilation system or without. We measured the velocity, the temperature distribution and predicted mean vote(PMV) value in the lecture room for 4 different air-conditioning methods. Effective draft temperature(EDT) and PMV were investigated to analyze the characteristics of two thermal comfort indices in the lecture room and to compare their values each other. From the results we knew that there is the similarity between PMV values and EDTs when the room is air-conditioned for cooling loads. It turned out that definition of the control temperature is very important when the EDT is calculated. Finally EDT should not be used to predict the accurate thermal comfort in case that the temperature and humidity are suddenly varied and the zone affected by the solar and inner wall radiation.

A Study on the 3-D Airflow and Dynamic Cross Contamination in the Photolithography Process Cleanroom

We performed the numerical study on the characteristics of the 3-D airflow and dynamic cross contamination in the photolithography process cleanroom. The nonunifurmity, the deflection angle and the global cross contamination were used for analyzing the characteristics and performances of cleanroom. From the numerical results, we knew that the airflow characteristics of the cleanrooms are largely affected by the porosity of panel and the adjustment of dampers and the global cross contamination varies with the location of source and the passage of time through the concentration ratio.

Study on Contamination Control for Yield Enhancement in the Manufacturing Line of Cellular Phone Modules

Practical studies on the method of contamination control for yield enhancement in the cellular phone modules production line were carried out. A contamination control method was proposed, consisting of data collection, data analysis, improvement action, verification, and implementation of control. The partition check method and the composition analysis for data collection and data analysis were respectively used in the cellular phone modules manufacturing process, and these methods were evaluated by the variation of yield loss before and after implementing the actions for improvement. In the partition check method, the critical process step was selected, and yield loss reduction through improvement actions was observed, whereas in the composition analysis, critical sources were selected, and yield loss reduction through improvement actions was investigated. From the results, it is concluded that the partition check and the composition analysis are effective solutions for contamination control in cleanroom production lines.

Generation Characteristics of Ozone and NO x and Particle Removal in the Electrostatic Precipitators

We investigated the amount of the toxic gases emitted from the Electrostatic Precipitators(ESPs), which are currently used as the indoor air cleaners. The existing wire-to-plate(WTP) and neddle-to-plate(NTP) types of ESP designs are considered as the experimental corona dischargers. Using the voltage, the polarity of wire, the number of needles of NTP as the input variables, we studied the generation characteristics of ozone and and the particle removal efficiency in the ESPs. As the results, we found out that the concentration of ozone, and is increased with increasing the voltage and the number of needles, but the amount of NO is decreased. And we observed that the generation rates of ozone and are mainly related with the corona region through the photographs. Finally the experimental results showed that the particle removal efficiency of ESP with WTP type charger is more superior to that with NTP type chargers at the same voltage.

Analysis on particle deposition onto a heated, horizontal free-standing wafer with electrostatic effect

The electrostatic effect on particle deposition onto a heated, Horizontal free-standing wafer surface was investigated numerically. The deposition mechanisms considered were convection, Brownian and turbulent diffusion, sedimentation, thermophoresis and electrostatic force. The electric charge on particle needed to calculate the electrostatic migration velocity induced by the local electric field was assumed to be the Boltzmann equilibrium charge. The electrostatic forces acted upon the particle included the Coulombic, image, dielectrophoretic and dipole-dipole forces based on the assumption that the particle and wafer surface are conducting. The electric potential distribution needed to calculate the local electric field around the wafer was calculated from the Laplace equation. The averaged and local deposition velocities were obtained for a temperature difference of 0-10 K and an applied voltage of 0-1000 v.The numerical results were then compared with those of the present suggested approximate model and the available experimental data. The comparison showed relatively good agreement between them.