An experimental and finite element investigation of thermally induced inelastic deformation of single-level damascene copper high density interconnect structures

An atomic force microscope was used to investigate thermally induced deformation mechanisms in the areas of copper and polyimide vias in copper-polyimide interconnect structure, as a result of a thermal cycle to 350°C. The copper films exhibited evidence of copper grain boundary sliding, Coble creep, and voids formation. Cu-Ta interfacial sliding was observed in the Cu and polyimide via areas. The direction of the Cu-Ta sliding changes as the polyimide via size decreases. The polyimide experienced a residual deformation attributed to the Cu-Ta sliding and in-plane deformation of the copper vias. A finite element method was used to simulate the effect of Cu-Ta sliding on interfacial and liner plane stresses in Benzocyclobutane (BCB)-Cu and SiO2-Cu interconnect structures, heated to 400°C. A one rum thick element was used to produce a sliding effect at the Cu-Ta interface and at Cu grain boundary. The shear stresses in the SiO2-Cu system are completely relaxed by the Cu-Ta sliding. The Cu-Ta sliding increases the Ta liner plane stress in the BCB-Cu system to potentially damaging values, while the Ta stress in the SiO2-Cu system changes from tensile to compressive. Sliding at Cu grain boundary has a minor impact on Cu-Ta sliding and shear stress relaxation in the BCB-Cu system with large aspect ratio. A finite element technique was used to model the classical Nabarro-Herring creep in 1 mum square copper grain subjected to biaxial stresses of +/-10 MPa, at 800°C. A linear elastic mechanical analysis was carried out to simulate the mechanical loading and transient thermal analysis was utilized to simulate the diffusive vacancy flow process. The steady state flux components were used to predict the creep deformation of the grain and to estimate the creep strain rate at the boundaries. It was shown that the finite element procedure is capable of modeling the Nabarro-Herring creep, satisfactorily. The finite element result agrees with the analytical prediction within a factor of two

Vapor pressure development in a FR4-CU composite structure during solder reflow

This article presents a study on the development of vapor pressure a FR4-Cu composite structure when heated to a solder reflow temperature of 215 °C. Abaqus® finite element software was used to develop a representative two-dimensional model of the composite structure and to simulate moisture absorption and desorption processes. Simulation of transient moisture absorption was performed to predict moisture concentration distribution in the structure after being preconditioned in 85°C/85 % RH environment for 15 days. Simulation of transient moisture desorption was carried out at the solder reflow temperature to predict the redistribution of the moisture. Results of the moisture desorption simulation were used to compute magnitude of the vapor pressure in the structure. It was found that the moisture redistributes itself during the solder reflow process. Moisture concentration in the vicinity of the FR4-Cu interface, below the longer copper trace increases during the solder reflow. The vapor pressure in nearly 70 % of the FR4 material and close to the FR4-Cu interface, below the longer copper trace is almost equal to the saturation pressure of vapor at 215 °C. Distribution of the vapor pressure is very similar to the new distribution of moisture concentration resulting from moisture desorption process

Analysis of air and airborne particles movements in a hospital operating theater

In this study a computational fluid dynamics (CFD) method was used to develop a validated model of a hospital operating theater. The model was employed to perform simulation to predict the distribution of airflow and movement of the airborne particles inside the operating theater at a steady-state condition. The airborne particles were modeled as discrete particles which were released from the exposed body surface of the surgical staffs at a rate of 10 CFU/s. The effect of laminar inlet air flow velocity on the airborne particles concentration around the operating table was examined. It was found that the air flows straight downward from the air-conditioning diffuser towards the middle of the operating table. However, the existence of the medical lamp causes a vortex air flow condition below it. Air also penetrates the ultra-clean area on the opposite side of the operating table. The airborne particles are washed away from the vicinity of the operating table by the air flow. This is more effective when the supply air flow velocity is high. At low air flow velocity, some particles appear to penetrate into the ultra-clean area near the edges of the operating table. At higher air flow velocity, the airborne particles seem to be more effectively washed away from this region. High concentration of airborne particles occurs underneath the medical lamp due to vortices created by the air flow. Higher air flow velocity increases the level of particles concentration in this area

Computerized simulation of automotive air conditioning system: a parametric study

This paper presents results of a parametric study performed on an automotive air-conditioning (AAC) system of a passenger car. The goals are to assess the effects of varying the volumetric flow rate of supply air, number of occupants, vehicle speed, and the fractional ventilation air intake (XOA), on the dry-bulb temperature and specific humidity of the air inside the passenger’s cabin, and on the evaporator coil cooling load of the AAC system. Results of the parametric study show that increasing the supply air flow rate reduces the dry-bulb temperature of the cabin air, increases both the specific humidity of the air and the evaporator coil load. Increasing the number of occupants in the passenger cabin causes the cabin air temperature, specific humidity and the evaporator coil load to increase. Increasing the vehicle speed causes the specific humidity of the cabin air and the evaporator coil cooling load to increase but the dry-bulb temperature of the air is not significantly affected. Increasing the fractional fresh air intake (XOA) also increases the cabin air specific humidity and the evaporator coil cooling load

Field measurement of airborne particulate matters concentration in a hospital's operating room

In a hospital operating room, adequate air flow and cleanliness are crucial to protect the patient from surgical site infection (SSI) during a procedure. The probability of the patient to get the infection is related to the concentration of bacteria carrying particles inside the room. This paper presents a field measurement study to quantify the concentration of particulate matters (PM) in a hospital operating room which complies with the ISO Class 7 requirements. The operating room was equipped with High Efficiency Particulate Air (HEPA) filters and a vertical laminar air flow (LAF) system. The measurements were conducted at three height levels from the floor namely 1.2 m, 1.8 m and 2.4 m. The data was logged at a rest condition, in accordance to the ISO 14644-1 requirements. A HPC300 particle counter was used to measure the concentrations of particulate matters namely PM0.5, PM1 and PM5. The results show that the concentrations of all particulate matters were higher at the height level of 1.2 m compared to other height levels. The concentration of PM0.5 was relatively higher than PM1 and PM5 in the vicinity of operating table

Experimental study on a cold storage system with a variable speed compressor

Selection of a compressor for a refrigeration system is generally done based on a peak load operating condition. The energy consumed by the compressor can potentially be reduced by regulating the compressor speed using an inverter. This experimental study investigates energy saving and performance enhancement potentials in an experimental cold-storage system when the electric frequency supply is reduced from 45 to 25 Hz, with a 5 Hz interval. The system is equipped with a compressor with a power rating of 3 HP (2.25 kW) and R22 was used as the refrigerant. The cooling load of the system was provided using an electric heater placed at the bottom of the cold storage chamber. Results show that the power input to the compressor was reduced when the electric frequency supply was decreased. The highest reduction in the compressor power input occurred when the electric frequency was decreased from 45Hz to 40Hz. The results also show that the coefficient of performance (COP) of the cold storage system was improved when the electric frequency supply was decreased. The largest COP improvement occurred when the frequency was decreased from 30 Hz to 25 Hz

Improvement of thermal comfort inside a mosque building

A combined natural ventilation and mechanical fans are commonly used to cool the interior space inside the mosques in Malaysia. This article presents a study on thermal comfort in the Al-Jawahir Mosque, located in Johor Bahru, Malaysia. The objective is to assess the thermal comfort inside the mosque under the present ventilation system by determining the Predicted Mean Vote (PMV) and the Predicted Percentage of Dissatisfied (PPD). These values were then compared to the limits stated in the ASHRAE Standard-55. It was found that the PMV varies from 1.68 to 2.26 while the PPD varies from 61 to 87. These show that the condition inside the mosque is quite warm. Computational fluid dynamics (CFD) method was used to carry out flow simulations, to identify a suitable strategy to improve the thermal comfort inside the mosque. Results of CFD simulations show that installing four exhaust fans above the windows on the west-side wall of the mosque is the most effective strategy to improve the thermal comfort inside the mosque. Both the PMV and PPD values can potentially be reduced by more than 60

Effectiveness of blade tip on low speed horizontal axis wind turbine performance

There has been an increasing demand for renewable energy in order to create a sustainable society as the non-renewable energies such as fossil fuel resources are limited. Modern wind turbines claim that they have a high efficiency in term of wind energy extraction. However, there are still having losses due to tip vortex causing to a reduction in performance. Motivated by this reason, this research aims at exploring the possibility to increase the performance of low speed small-scaled horizontal axis wind turbine with various tip devices using Computational Fluid Dynamics (CFD). Four wind turbine blades with different tip devices which consist of sword tip, swept tip, upwind winglet and downwind winglet are compared with wind turbine blade without tip device in term of CP. The application of tip device can significantly reduce induced tip vortex and improve wind turbine performance. For TSR below than 4, adding a sword tip increases CP about 7.3%, swept tip increases CP about 9.1%, upwind winglet increases CP about 1.8% and downwind winglet increases CP about 3.2%. It is observed that the best tip device for low wind speed application is swept tip as it give the highest performance increment compared to without tip device

Reducing soak air temperature inside a car compartment using ventilation fans

This article presents an investigation on the effects of using ventilation fans on the air temperature inside a car passenger compartment when the car is parked under the sun. It was found from a measurement that the air temperature inside the passenger compartment could raise up to 48°C. Computational fluid dynamics method was used to develop model of the compartment and carry out flow simulations to predict the air temperature distribution at 1 pm for two conditions: without ventilation fans and with ventilation fans. The effects of fan location, number of fans used and fan airflow velocity were examined. Results of flow simulations show that a 17% temperature reduction was achieved when two ventilation fans with airflow velocity of 2.84 m/s were placed at the rear deck. When three fans were used, an additional 3.4% temperature reduction was attained. Placing two ventilation fans at the middle of the roof also reduced the air temperature by 17%. When four fans were used a further 4.8% temperature reduction was achieved. Increasing the airflow velocity at the four fans placed at the roof, from 2.84 m/s to 15.67 m/s, caused only a small reduction in the air temperature inside the passenger compartment

Effect of Regeneration Air Temperature on Desiccant Wheel Performance

Desiccant wheels are used as an air dehumidifier in air-conditioning and industrial applications. Desiccant wheel performance determines the size and cost of the whole system. A good desiccant wheel is one that saves energy usage. This article presents an experimental investigation on the effects of varying the regeneration air temperature, viz., 50, 60 and 70oC, on desiccant wheel performance. Three performance criteria were considered, namely condition of process outlet air, dehumidifier efficiencies and dehumidification rate. Two kinds of efficiency of the desiccant wheel dehumidifier were examined, namely thermal and dehumidification efficiency. Results of the experiments show that increasing the regeneration air temperature increases the dry bulb temperature of the process outlet air. However the moisture content of the process outlet air is reduced. The dehumidification efficiency of the desiccant wheel decreases with increasing regeneration air temperature, i.e., 46.7, 45.8 and 45.3 % for 50, 60 and 70oC, respectively. In contrast, the dehumidification rate increases with an increase in the regeneration air temperature, namely 32.6, 37.1 and 40.2 g/h for 50, 60 and 70oC, respectively