Aulis Tuominen

Characterization of resolution cycle times of corrective actions in mobile terminals

Resolution cycle times for resolving issues raised by customers is one of the essential factors for indication of the customers satisfaction. The fact that there are many mobile terminals manufacturers implies that competition to grab and hold market share for a sustainable time is very strong. A forecasting model, based on a selected statistical distribution, is built up to give an estimation of the resolution time in three different category products. In this paper the model does not specify different failure symptoms reported by customers. Uncertainties and the reliability of the model buildup are discussed and example of an optimized correction action is given. Copyright

Interference Colors of TiO2 Nanotube Arrays Grown by Anodic Oxidation

The study describes the interference color of anodic TiO2 nanotube arrays on titanium foil. TiO2 nanotube arrays are prepared by oxidizing titanium foil in an aqueous electrolyte solution of hydrofluoric acid (HF, 0.5 wt.%). The morphologies of the oxide film are characterized by FESEM. The empirical color properties are obtained using the L*a*b* system. The different interference colors of oxidized Ti samples are obtained depending on the anodization time. The anodization time clearly indicates a strong effect on the reflectance at the visible wavelength region, thus confirming the observed color differences. Consequently, the interference colors can be controlled by the anodization time. By observing the coloration of Ti during the anodization, the interference colors can be utilized to identify the thickness of oxide layer and the formation of nanotubes on Ti sheet.

Forecasting a change in technology: Are Dye-sensitised Solar Cells a source of ubiquitous energy?

The purpose of this paper is to review developments in Dye-sensitised Solar Cells (DSC) and discuss the feasibility of the technology as a future source of ubiquitous energy. Rapid technological developments have made the technology a viable future photovoltaic technology, but its overall impact is still unclear. This review on recent developments strives, based on historical developments, to forecast the future for sensitised solar cells as a source of ubiquitous energy.

The safety assessment of wind-photovoltaic hybrid power system for afforestation in desertification area

In this paper, we introduce the wind-photovoltaic hybrid power system (WPHPS) installed in Mongolia and the safety assessment for the WPHPS, which was implemented to prevent the failure mode. In order to prevent desertification and build afforestation, two groups of photovoltaic systems were installed in the Gobi desert. One of the generators, which produces 70kW of the power, operates as the power plant for cultivation in this area and another one works with wind power generator. To operate these installed systems effectively, must be implemented the safety assessment. Failure Mode and Effect Analysis (FMEA) was used as a safety assessment method in this study. The 28 of important assemblies of WPHPS were evaluated by FMEA and the results carried out 47 failure modes.

Increasing placement capacity with area based optimization and line balancing

Printed wiring board placement optimization of high‐speed placement machines in a high volume surface mount line was studied based on more careful analysis of the board layout beforehand. In this method, the target is to get the board area to be assembled as small as possible in each successive placement machine, paying the most attention on component coordinates already during preliminary line balancing phase. Optimization and line balancing principles, that had showed promising results already in the first studies when compared to globally used well‐known commercial optimization systems, were now further developed. Results presented and illustrated in this paper show remarkable, comparable, improvement in both cycle time reduction and in balance of the whole surface mount line. The main difference between this method and the advanced commercial solutions is explained in detail. Board layout, feeder arrangement, sequence of fiducial registration, and XY‐table movement were taken into deeper consideration in the method.

A Two-Dimensional Model for CO2/Fuel Multiphase Flow on the Anode Side of a DMFC

Increasing the efficiency of passive fuel cells is a significant hurdle in commercializing small fuel cells. By understanding the interactions within a single cell, possibilities for further performance increases in fuel cell structures overall are uncovered. To investigate the multiphase flows and the interactions between the layers on the anode side of a direct methanol fuel cell (DMFC), a single cell was studied using a two-dimensional model. This multiphase model focuses on the flow mechanism of a single CO2 gas bubble. The model describes the mass transfer in a single cell by using the physical properties of a single bubble and by tracing its movement. The simulation results indicate that the thickness of a gas diffusion layer (GDL) has an effect on the CO2 bubble size at a low power output level. When the power output is increased, the porosity and the GDL’s contact angle with CO2 play a significant role in determining the size of the CO2 bubbles. The final bubble size and the time it takes for the bubbles to penetrate the layers of the DMFC are controlled by the physical properties of the GDL and by the power output. The model suggests that, to achieve optimal performance, the GDL in passive DMFCs should be thick enough to allow bubbles grow to their maximum size. The thickness of the GDL can be calculated by estimating the maximum size of the bubble.

Hydrogen sensing performance of TiO 2 nanotubes at room temperature

We report the hydrogen sensing properties of a sensor using TiO2 nanotube arrays. The TiO2 nanotube arrays were fabricated by anodization on titanium foil, in an electrolyte containing 0.5 wt% hydrofluoric acid mixed with water, the electric potential being 15V. TiO2 nanotube arrays were annealed at 600 Celsius for 1 h. The sensors were equipped with platinum electrodes. These two were connected with a metal wire using silver paste. The measurements of the sensors electrical resistance were performed in NTP. The hydrogen sensor using TiO2 nanotube arrays shows a linear sensitivity with various hydrogen concentrations. After repeating exposure to hydrogen at room temperature, the sensors resistance indicated a stable recovery to its initial resistance. The reproducibility of this exam is reliable.

Evaluation of Reflow Ovens for Lead-Free Soldering

A set of different reflow ovens were evaluated in order to determine their capabilities to produce lead-free solder joints. Thermal profiles of different reflow ovens were measured using profile equipment and the heat transfer capabilities for all of the investigated reflow ovens were evaluated by determining the time constants for heating. Thermal model used is presented. It was shown that the smaller the time constant for a reflow oven the better the heat transfer capability, and thus the smaller variation in the peak soldering temperatures. The order of superiority of investigated reflow ovens is presented

Available thermal budget in lead-free reflow process

The electronics industry will have to implement lead-free soldering in the near future. Lead-free technology implementation phases are divided into lead-free processes and leadfree product. The prime issue is the component availability and component heat tolerance with the higher soldering temperatures. There is concern about the stability and heat resistance of a range of plastic encapsulated devices, capacitors, filters, connectors and even printed circuit boards. In this study the process window size of the lead-free soldering process is compared for the current tin-lead process. Parameters affecting the soldering process, e.g. the temperature difference between a components top and bottom surface during the soldering, are discussed. Optimization of the reflow oven for lead-free technology is also discussed. Experiments are presented showing in some cases more variation in the normal reflow oven capability than what is the measured temperature difference between the top and bottom surfaces of the component, clearly highlighting the complexity of the problem in practice.