Wearable products or biosensors require conformability to a complex curved surface or stretching and moving shapes such as parts of the human body. However, it is difficult to apply conventional printed wiring boards (PWBs) or flexible printed circuits (FPCs) to these applications. This situation prompted us to develop a novel wiring structure suitable for 3D-conformable devices. Our structure is composed of spiral-shaped metal wiring and a polymeric insulating layer that has a similar shape. This wiring structure has the following key features: (1) 3D conformability that combines deformability with robustness, (2) low and unchanged electrical resistance during stretching, and (3) a process applicability that allows solder mounting processes or photo processes to be employed to manufacture this device. In this paper, we show the advantages of this structure compared to other conventional types. We also demonstrate a conformable LED matrix display in which LED chips are mounted at the center of each spiral in the array.

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We studied the effects of adding various amounts of Sb to Sn-3.5Ag-0.5Bi-6.0In-0.8Cu (SABIC) solder in terms of the phase transformation temperature for the β-Sn and γ(InSn₄) transformation, mechanical properties such as strength and ductility, and thermal fatigue properties under thermal cycling (−40°C/175°C). With increasing amounts of added Sb, the temperature at which the phase transformation occurred increased. At 150 and 175°C, breaking elongation values of solders as a measure of ductility became the highest for an Sb content of 0.5 wt.%. As the phase transformation temperature increased, deformations of the solder joints after the thermal fatigue test were suppressed. The thermal fatigue properties were best at an Sb content of 1.0 wt.%, at which the phase transformation temperature was greater than 175°C. It is considered that raising the phase transformation temperature to a temperature higher than the maximum operating temperature of electronic devices should be the topmost priority to improve crack extension behavior.

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This paper describes the prediction method of the bottom temperature of power Si MOSFET by using CFD (Computational Fluid Dynamics) analysis. For accurate thermal design of electronics, nano-micro scale hot spot temperature in semiconductor devices should be considered. Electro-Thermal Analysis is attractive method to calculate accurate temperature distribution of semiconductor devices. In our previous results, we proposed simple estimation method of nano-micro scale hot spot temperature from the results of Electro-Thermal Analysis. In the method, accurate estimation of temperature at the bottom side of the device is required. In this study, power Si MOSFET is focused as a semiconductor device, which is widely used in power electronics area. Then, in this paper, appropriate CFD modeling for detecting the bottom temperature of power Si MOSFET is discussed. To verify the appropriate CFD modeling, the analysis results are compared with the experimental results, and the suitable assumption of heat generation in CFD analysis is discussed. From the results, it is investigated that not only heat generation from silicone die but also other factor should be considered in the CFD modeling to detect accurate temperature of power Si MOSFET.

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In recent years, the circuit (printed board) designers play an increasingly important role in the thermal design of electronic devices. Generally, small chip type components generate but a very low level of heat. Lately, however, the heat generation density of small chip type components is rising along with the downsizing of electronics. Small chip type components have no cooling devices, and heat dissipation from the components occurs mainly through the copper pattern on the board. Therefore, if the design of copper pattern on the board is inadequate, generated heat from the components cannot be dissipated, thus running a risk of excessive temperature rise.
This paper discusses the relationship between the mounting pad shape and the temperature rise of the board, which can be significant in the thermal management of small surface mount components. Using the concept of constriction thermal resistance, the temperature of the component can be estimated easily without taking complex copper patterns into consideration.

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The increasing sophistication of information in society and the impending ‘Internet of Things’ will require smaller and higher-performance electronic devices, and faster also signal transmission, Particularly printed circuit board materials, such as cyclo-olefin polymers (COP) and liquid-crystal polymers (LCP), have been drawn attention for their low dielectric properties. Circuitry formation on these materials need plating treatment. Plating techniques on surface-modification using UV irradiation have been reported, but irradiation times of approximately 5 and 10 min, respectively, to achieve sufficient adhesion strength. However, these long treatment times present a challenge to productivity. To address this problem, we performed experiments using an improved, high-power UV lamp, with the aim of reducing the time required for surface modification treatment. We achieved significant reductions in UV-irradiation processing time, achieving an adhesion strength comparable to that obtained by a conventional method by irradiating COP plates for 45 seconds and LCP plates for 75 seconds.

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The displacement and stress-strain distribution of a device-embedded substrate under bending stress was simulated using the finite element method (FEM). In addition, the capacitance change of embedded devices was measured experimentally using an actual TEG substrate under bending stress. The results of the FEM analysis indicated that tensile stress at the surface of an embedded device may be a cause of electrical property changes. They may be affected by the substrate construction, especially the existence of a surface-mounted device. From the results of measuring the capacitance of an embedded chip capacitor with applied bending stress, the capacitance value increased relative to the stress. It was presumed that the distance between the electrodes of a laminated ceramic capacitor was narrowed slightly by the bending stress, which caused the capacitance increase.

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In this paper, as a result of reviewing the conventional mold design process from the viewpoint of the design architecture, it was found that the design of the antennas can be familiar to mold designers because both the die design and the antenna design adopt integral design process, where the design is studied and a feed back is given back to the design. Therefore, decoration molding technology which is one of the applications of die designing technology is very effective for antenna design.

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Additions of 1.5wt%Bi to Sn-0.7wt%Cu-0.05wt%Ni (SN100C) were investigated for their influence on mechanical properties and the intermetallic (IMC) layer formed between the solder and Cu substrates. Solder balls of Sn-0.7wt%Cu (Sn07Cu), SN100C, Sn-0.7wt%Cu-0.05wt%Ni-1.5wt%Bi (SN100CV) and Sn-3wt%Ag-0.5wt%Cu (SAC) were reflowed onto Cu ball grid arrays (BGAs). They were examined in the as reflowed condition and after a heat treatment of annealing at 150°C up to 1,500 hours. The mechanical properties of SN100C, SN100CV and SAC solder balls were investigated by nano-indentation, and cross-sections of the interfacial IMC layer were observed by SEM to determine the morphology and average interfacial IMC layer thickness. It was found that the effect of Bi additions was to increase the lattice parameters and alter the mechanical properties. The near-eutectic microstructure and suppression of Cu₃Sn at the IMC layer that are associated with Ni additions are not altered by the presence of 1.5wt%Bi.

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We proposed a novel fabrication method of a self-standing curved film with pillar-shaped hole patterns using spherical soft ultraviolet (UV) imprint lithography. Spherical soft UV imprint lithography was performed using a patterned polydimethylsiloxane (PDMS) mold and a convex mold. The mother molds were prepared using a unique three-dimensional (3D) printer system and replicated by PDMS molding method. By exploiting the low surface free energy and elasticity of the PDMS molds, a patterned thin curved film with a curvature radius of 40 mm was realized without any significant cracks, and the hole pattern size was obtained with an error of less than 5%. Moreover, by applying appropriate force, a zero-residual-layer imprint was successfully achieved maintaining the accuracy of the hole pattern. These results indicate that the proposed spherical soft UV imprint lithography is applicable for fabrication of 3D structures and 3D functional devices.

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Electrovibration is one of promising methods for tactile feedback in mobile devices because of its simplicity of the structure and principle. In order to increase the capability of tactile presentation with the electrovibration, we developed an electrovibration tactile display with 1 mm electrode resolution. Voltage to each electrode is controlled separately and the tactile display can present electrovibration stimulus distribution. We designed the tactile display and optimized the voltage waveform to avoid destruction of an insulator. We fabricated the proposed tactile display with micro-fabrication process. We experimentally evaluated the relationships between stimulation condition and perception in subjects. The obtained results indicated that the multi- electrode design had a potential to enhance tactile rendering performance of electrovibration stimulation.

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