Commercial solder alloys with Bi additions are increasingly used in electronics manufacturing due to their low melting point and strengthening effects. However, the solubility of Bi in Sn is highly temperature-dependent, and partial or complete dissolution of Bi precipitates at elevated temperatures may impact solder joint reliability. To investigate the thermal stability and mechanical response of Bi-containing solders at service temperatures, two alloys—Sn-1.5wt%Bi-0.7wt%Cu-0.05wt%Ni (S1) and Sn-3.5wt%Ag-3wt%Bi-2wt%Sb-0.8wt%Cu (S2)—were characterized by in-situ scanning electron microscopy (SEM), in-situ synchrotron powder X-ray diffraction (PXRD), and tensile testing over a range of temperatures. During heating, Bi phase dissolution was observed in the alloy with higher Bi content, leaving voids that remained upon cooling. Consequently, the alloy with the higher Bi concentration exhibited a pronounced decrease in ultimate tensile strength after heating. In contrast, the alloy with lower Bi concentration maintained a relatively stable microstructure and ultimate tensile strength (UTS) throughout the heating cycle. The effect of the changing concentration of Bi on the Sn phase crystal lattice was examined using synchrotron PXRD.

The common Electro-Optical (EO) waveguide used an integrated electrode design that embedded the electrode in the metal layer of the waveguide. This design has its own disadvantage since post-fabrication customization of the electrode and waveguide structure is impossible. This research proposes a solution for applying the modular design concept to the EO waveguide. The device is separated into three major components: the electrode, the EO waveguide, and the retention unit. This allowed customization in post-fabrication and improved the simplicity of the fabrication. The proposed Long Period Grating (LPG) EO waveguide has an operating wavelength range of 1,510–1,531 nm, with alternative post-customization to alter its operating wavelength to 1,466–1,483 nm. The device can be fabricated with much simpler machinery and could be done in parallel.

This study introduces a device that uses dielectric heating with a 50-Hz AC voltage to cook food at low temperatures. Moreover, the number of microorganisms that adhere to food before and after heating, as well as the effectiveness of low-temperature heating using electric current in inactivating bacteria, is examined. The proposed low-temperature cooking method involves placing the food in a parallel plate capacitor, applying an alternating current, and heating the food through its resistance. This system reduces the capacitive reactance of the impedance expected from the power supply by placing an inductor in series. However, it is important to control the inductance because the electrical properties of the food change during the heating process. In this study, we developed a device that eliminated the inductor by reducing the frequency from approximately 800 kHz in previous research to 50 Hz, and we confirmed that the device heats the sample. We also investigated the effect of 50-Hz alternating current on the inactivation of bacteria in commercial salmon. We found that more than 99 % of viable bacteria were killed compared with that before heating, indicating the satisfactory bacterial inactivation capability of dielectric heating.

Silicon carbide (SiC) power devices exhibit superior thermal stability, higher breakdown voltages, and enhanced efficiency, making them ideal for electric vehicle (EV) applications. However, current packaging technologies, especially die bonding and wire bonding, remain inadequate for operation beyond 250°C. This study explores the use of a Ni-Al composite paste for die bonding and Ag wire bonding to enhance high-temperature reliability and performance of SiC devices. SiC Schottky barrier diode (SiC-SBD) samples were tested under varying thermal conditions and after high-temperature storage. The Ni-Al paste demonstrated exceptional thermal stability without voids or cracks during testing. By contrast, when Ag wire was bonded to Al pads, the bond strength declined and resistivity increased due to the formation of intermetallic compounds (IMCs). Conversely, Ag wire bonded on Ag/Ni-Al pads retained its structural integrity and exhibited stable electrical performance. These results highlight the potential of the proposed materials to optimize SiC device packaging for high-temperature applications, and thereby advance power electronics in demanding environments.

The power cycling (PC) test is one of the important methods to assess the reliability performance of power modules under the actual switching operation of power semiconductor devices. The actual operation of silicon carbide metal-oxide-semiconductor field-effect transistors (SiC-MOSFETs) require positive and negative gate-voltage switching. This study investigated the effects of positive and negative gate-voltage switching on the characteristics of SiC-MOSFETs during PC tests. Two types of test circuits were used: a traditional circuit with a fixed positive gate-voltage and a new circuit with positive and negative gate-voltage switching. The traditional test circuit led to degradation in SiC-MOSFETs, including gate threshold-voltage shifts and on-state voltage fluctuations. The degradation of SiC-MOSFETs was improved by applying a positive and negative gate-voltage switching every cycle during the PC test. The new test circuit led to the accuracy improvement of PC lifetime estimations. The results demonstrated that the positive and negative gate-voltage switching were essential for the PC tests of the SiC-MOSFET power module.

The minimum pitch for flip-chip bonding is limited by the difference in the thermal expansion coefficient between the chip and the substrate, it is approximately 40 µm when solder is used for the bumps. This constraint can be significantly alleviated by applying a conductive paste to the bumps and bonding the chips together at low temperatures. Bumps made of conductive paste are typically formed via screen printing. By using the imprinting method, bumps and wirings can be formed with a narrow pitch and high aspect ratio. In addition, replica molds can be used repeatedly to reduce processing costs. To use the replica mold repeatedly, the silver paste embedded in the recessed pattern of the replica mold during imprinting must be completely transferred to the substrate and the initial state of the replica mold must be kept constant. Therefore, we investigated the transferability of the imprint technology by changing the process conditions during imprinting. Using a UV-curable silver paste as an imprinting process, we confirmed that UV-curing the silver paste before separating the replica mold from the substrate improved the transferability.