Key Engineering Materials Vols. 326-328

Abstract: Reliability of automotive parts has been one of the most interesting fields in the automotive industry. Especially wiper motor for automobiles is important part because of improving visual comfort for the driver and the passengers. Therefore, we have dealt with the reliability test procedure of wiper motor. The failures such as wear-out of brush, bearing damage, motor coil burnout are caused by the electrical and mechanical operating for low and high actions of wiper motor. In this research, we have qualitatively selected the efficient test items through the analysis of the life and potential failures of wiper motor. So, wiper motor itself requires an estimation of life causing failure of brush wear out in order to operate the system safely. We have tested six wiper motors. The result is established by employing the weibull plot. We validated the life of wiper motor to the experimental result.

Abstract: In this paper, a low temperature hermetic wafer level packaging scheme for the RFMEMS devices is presented. For hermetic sealing, Au-Sn multilayer metallization with a square loop of 70 %m in width is performed. The size of the MEMS package is 1mm × 1mm × 700 %m. The shear strength and hermeticity of the package satisfy the requirements of MIL-STD-883F. The total insertion loss for the packaging is 0.075 dB at 2 GHz.

Abstract: Lead zirconate titanate (Pb(Zr0.48Ti0.52)O3 or PZT) films were grown on platinized silicon wafers (Pt/SiO2/Si) by d.c. reactive sputtering method with multi targets. The Pb content of PZT films has been widely recognized as affecting not only the phase formation and microstructure but also the dielectric and ferroelectric properties. Pb content of PZT films was controlled by the variation of Pb target current. The relation between Pb content and Pb target current was expressed as y=0.89x-11.09. The x and y are Pb target current and Pb content, respectively. The pyrochlore phase was transformed to perovskite phase as Pb content was increased. This phase transformation improved the ferroelectric properties of PZT films. In PZT films with perovskite phase, fatigue properties were not improved with excess Pb content. Fatigue properties of PZT films began to be fatigued after 106 switching cycles and coincided with the typical PZT fatigue behavior. Excess Pb content (Pb vacancy) did not affect the fatigue properties of PZT films.

Abstract: Thermocompression bonding of electroplated gold is a promising technique for achieving low temperature, wafer level hermetic bonding without the application of an electric field or high temperature. Silicon wafers were completely bonded at 320
at a pressure of 2.5. The interconnection between the packaged devices and external terminal did not need metal filling and was made by gold films deposited on the sidewall of the via-hole. In the hermeticity test, packaged wafers had the leak rate of 2.74 ± 0.61 × 10-11 Pa m3/s. In the result of application in packaging of FBAR filter, the insertion loss is increased from -0.75dB to -1.09dB at 1.9.

Abstract: The differences in the coefficient of thermal expansion (CTE) between the chip and the FR-4 board generate the shear strains and the bending moment in the solder joint. It seems to be a main cause of failure in the solder joint when the chip and the FR-4 board are heated repeatedly. Thus, the fatigue loading induced by thermal cycling is a major concern in the reliability of the solder joint. The magnitude of shear strain and the final failure are known to be influenced by varying boundary conditions such as the difference of CTE, the height of solder, the distance of the solder joint from the neutral point (DNP) and the temperature variation. In this paper, the effects of boundary conditions on the failure probability of the solder joint are studied by using the failure probability models such as the First Order Reliability Method (FORM) and the Monte Carlo Simulation (MCS). Furthermore, the stiffness of the solder joint is considered to investigate the influence at the failure probability.

Abstract: This paper deals with the hygrothermal stress induced in a polymeric thin film deposited on Si wafer subjected to the combined influence of temperature change and moisture absorption. The laser scanning method and the boundary element method (BEM) are employed to investigate the residual stresses. The film/wafer system is assumed to be linearly elastic. The film/substrate system is assumed to be stress-free at a temperature of C o 300 and is cooled from a cure temperature down to room temperature. Then the moisture concentration in the film is increased to the saturation level. The normal stress across thickness of the thin film is estimated from wafer curvature measurements. The boundary element method is employed to investigate the whole stresses in the film. The numerical results for the normal stress across thickness of the film show good agreement with experimental results obtained by using the laser scanning method. The singular stress is observed near the interface corner. Such residual stresses are large enough to initiate interface delamination to relieve the residual stresses.

Abstract: This paper includes a study on the surface treatments of the barrel of small arms with an aim at improving resistance of corrosion and wear. The inner surface of the barrel is Cr plated or nitrided to improve the performance under the firing. The endurance test was conducted to compare the wear resistance of standard barrel (the non surface treatment barrel), the Cr plating barrel and the nitriding barrel. The wear resistance is evaluated by inner diameter of the barrel, muzzle velocity and dispersion during the firing. And the salt water immersion test was conducted to estimate the corrosion resistance. As the results of the tests, the Cr plating barrel is superior to the NST barrel and the nitriding barrel in a view of corrosion and wear.

Abstract: Railways are a mass transportation system with high safety and punctuality. These strengths have been well proved by tests and evaluations. Railways are an integrated system with cars, power, signal, communication, line structures and operation. Among many safety standards of these systems, contact force between wheels and lines can be chosen since a derailment coefficient evaluated by contract force is the most important fact that decides the safety of railways. Especially regarding express trains, since they run twice faster than conventional ones, the evaluation of a derailment coefficient is more important than any other criteria. Currently, Korean express trains between Seoul and Pusan use the same stations as conventional trains in Daejeon and Dong-Daegu; therefore, express trains run on conventional lines from express lines. This paper describes test results acquired by increasing the train speed where express lines and conventional lines are connected. Test results tell that it is safe with under 0.8 derailment coefficient and running time is reduced by 10~30 seconds in each section.

Abstract: As there are many wear parts in the bogie of freight car, the cost of maintenance is high. Also there are many problems to change the wear plates. In case of welded structure bogie, wear plates are attached 30 positions. Especially, the occurrence of the wear quantity at the side of axle box is higher than any other wear plates. Wear parts needs the low wear and high strength. But the repeated load of carbody has acted on wear parts up down direction continually, the friction force defects at their surfaces. At present, the life of wear plates at the side of axle box is about 3~4 years. So we need the new development of wear plate over ten years life to improve the durability and find the new composite material for maintenance free.

Abstract: Power plant weldments are composed of various microstructures. Due to welding and PWHT processes, the microstructure of the base metal adjacent to fusion line is transformed into entirely different microstructures, collectively known as heat affected zone (HAZ). Creep, on the other hand, is considered as the most important deterioration mechanism of heat resistant components found in power plants. Therefore it is essential to evaluate creep properties of HAZ, which is considered to be very hazardous in weldment. Recently, most of the creep tests for HAZ are conducted using cross weld type specimen. However there are some problems with this type of creep test due to the results being largely varied according to the volume fraction of HAZ. In this paper, SP-Creep test, which has confirmed the availability for creep properties evaluation, has been conducted on each of the weldment microstructures. The results showed that each microstructure has a different creep behavior. The overall creep properties of HAZ are worse than those of the weld metal. Among the HAZ structures, fine grained HAZ has the worst creep properties.