Antti Salo

Reliability study of flexible display module by experiments

Flexible display module reliability were investigated herein with experiments, such as bending, twisting and ball drop. The pretests of all the three experiments were carried out firstly to primarily understand the flexibility and mechanical behavior of the display. Based on the pretest results, the corresponding fatigue test setup method and process were put forward. Then, the fatigue tests were executed. At last, through the failure analysis, the flexibility and reliability of the flexible display in different use cases were evaluated. Suggestions about how to use the display and improve the reliability through change the design were given also.

The Use of Murata Ceramic Bluetooth Antenna for Wrist Device Based on Flexible Printed Circuit Boards

In this paper, the Murata ceramic Bluetooth antenna, which has been successfully used on rigid printed circuit boards, is now applied to flexible printed circuit boards. Based on this Bluetooth antenna, a novel wrist device that can be wirelessly connected to mobile phones is developed. In particular, to reduce the height of the wrist device, the ground-clearance type Murata Bluetooth antenna is adopted. It is demonstrated that the wrist device works very well in real environments.

Bandwidth potential analysis of GSM antennas based on oval-shaped mobile terminals

In this paper, the effect of long-axis length of oval-shaped chassis on the bandwidth potential of GSM antennas is analyzed for the first time. The optimal long-axis lengths for oval-shaped chassis to achieve the maximum antenna bandwidth at 900MHz and 1800MHz are obtained. Simulation results show that the optimal long-axis length of oval chassis at 900MHz is about 155mm, and at 1800MHz the optimal lengths are about 80mm and 165mm. In addition, a comparison in optimal length between rectangular and oval-shaped chassis is also discussed.

Rigid-Flexible Printed Circuit structure optimization by simulations

Rigid-Flexible Printed Circuit Boards (RFPCB) has the advantages of providing not only the flexibility and bendability required by many electronic products, but also the reliability required by the key electronic components. In this study, based on one kind of RFPCB which would be used for a wearable device prototype, the structure optimization was performed by simulations. Through the structural analysis, it is found that there are some risk places for potential failures, such as the corners of the connecting part of the RFPCB. Normally, the stress concentrations would locate on these places if the circuit boards encounter the bending, twisting or tension conditions during the assembly process or usages. Hence the three load conditions are simultaneously considered in the optimization. To reduce the stress concentration in the corners of connecting part, the structure of the FPC cross section were optimized. The various optimization proposals are presented firstly. Then the simulations were executed. At last, by comparing the maximum Von Mises stress of different simulation cases, the optimized structure was attained. Appending substrate layers on top and bottom layer of FPC and setting air gap between the appending substrate and FPC is suggested using tension and twisting cases. The original design is better used under the loading condition of bending.

Reliability of Flexible Display by Simulation and Strain Gauge Test

With the requirements of miniaturization of the portable consumer electronic products, more and more new materials, fabricating process and technologies are used to make the electronic components flexible, bendable and wearable. Flexible display, as one of the most important components, recently attracts an enormous research interest in industry and university. With the application of these technologies, the reliability issue has been coming forth with the different designs, fabrication processes and substrate material applications. In this paper, simulations including three points bending and twisting in different ways are investigated. In order to verify the simulation model, a special simulation model that contains the strain gauge is built. Through the comparison of the simulation results and strain gauge test results, the initial right model was given. Based on this model, the impact of different bending setup parameters to the display flexibility were studied, such as the bending roller radius, the span of support roller, bending height and etc. And the flexibility and reliability of the display were evaluated by the comparisons.

Thermal analysis based on the environmental tests of STN display

Environmental test is widely used to verify the adaptability and reliability of various electronic products in the last decades. The sharp change of temperature and humidity in certain situations could pose a serious reliability issue on the electronic components. This paper presents an experimental study of one kind of plastic substrate based flexible display called STN(Super-Twisted Nematic). The study focuses on the reliability of display under various temperature and humidity conditions. Considering the range of temperature and humidity changed in applications, the experiments are divided into four subgroups: cold test, cyclic damp heat test, the steady state damp heat test and dry heat test. Through all the tests, the STN display reliability was evaluated and the failure modes were obtained. Based on these tests, the thermal-structural simulation model was built. By the simulation, part of the experiment phenomenon were explained. It provides a solid foundation for further reliability study of the STN display in the practical applications.

Cold test and cyclic damp heat test of plastic substrate based displays

The plastic substrate based displays have attracted a lot of interest in recent years because of their potential applications in portable electronic devices. Many of them have high brightness, high contrast, and large angle of view, with the flexibility for accommodating different form factors. However, their reliability in practical applications has not been systematically studied. For many plastic materials, the temperature and humidity reliability are among the biggest concerns. This paper presents an experimental study of the plastic substrate based liquid crystal display with the focus on its reliability under varying temperature and humidity conditions. In this study, the cold test and the cyclic damp heat tests were conducted with visual inspections and electro-optical properties measurement during each test procedure. These provide a solid foundation for further studies on the reliability of displays based on plastic substrate technology in practical applications.

The steady state damp heat test and dry heat test of plastic substrate based displays

The plastic substrate based display has many advantages in practical applications of electronics, such as portable, flexible, super thin etc. However, its reliability may significantly impact its performance under the specific environmental conditions. Among the environmental factors, the temperature and humidity are two of the most important factors which may affect the performance of the displays dramatically. In this study, to evaluate the reliability and adaptability under the high temperature and the high humidity, the new environmental testing process for the plastic substrate based displays is presented. It consists of the damp heat under steady state test and the dry heat test, together with visual inspections and electro-optical property measurement. Based on the test, the analysis and assessment of the reliability and adaptability of the plastic substrate based displays under high temperature and high humidity were further performed.

FEA based design optimization of exciting sensitivity for micromachined piezoelectric transducer

This paper is to perform a design optimization of Micromachined piezoelectric transducer by maximizing the system exciting sensitivity. The tranducer is a membrane-based micromachined transducer with the piezoelectric film to excite the membrane vibrating. In this study, the exciting sensitivity is taken as the optimization objectibve. Specifically, when fixing the exciting signal, the transducer structure is optimized to maximize the vibrating magnitude of the membrane. The shape and size of the piezoelectric film are selected as the design parameters to optimize the structure of the transducer. Through analysis, four different piezoelectric structure designs were proposed and explored for optimizing the exciting sensitivity of the transducer. To perform the analysis and the subsequent optimization, finite element simulation was taken and all the FEA models were built on ANSYS software. The optimal design and sensitivity analysis are performed from the results of simulations on ANSYS; the corresponding structural parameters of the piezoelectric film for optimal design are identified. Finally, the optimization results of the exciting sensitivity for the transducers of these different piezoelectric film structures are compared; the design method to improve the exciting sensitivity of the transducer is provided.

Drop test simulation study of flexible devices

In this paper, a wrist device conception was selected to study the reliability of flexible devices by drop test simulation. In the conception device, all of the components cannot be made flexible immediately. Some of them are still rigid, such as the Ball Grid Array (BGA), the connector, and some other big components like the vibrator. The reliability of the device, where such rigid components are mounted on a flexible plastic substrate, is anything but guaranteed. In this study, a system level simulation model of a drop test was developed. In this simulation model, there are some challenges, such as the uncertain initial shape of the assembled products, the long impact time, and the unknown mechanical behaviours of new materials. To solve these problems, some manual work and some model simplification were performed. For the flexible device, the reliability study focussed on the electrical connection and the assembly processes. Before building the model, structural analysis of this device had been carried out first. Based on this analysis, some points of potential concern were identified. Based on these points, several submodels were refined such as the display, the BGA solder joint, and the Flexible Printed Circuit (FPC) copper trace. Seven drop simulations had been executed with different drop directions. There were six basic orthogonal drop directions and one additional drop direction, that was anticipated to have a serious impact on the reliability of the device. Through the simulations, some weak locations were pointed out by the observation of the stress level of Von Mises in the drop test. The results were delivered to the electronical and mechanical designer for reference in the new design and some actions were taken to optimize the design.