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Laser-induced forward transfer (LIFT) is a powerful tool for micro and nanoscale digital printing of metals for electronic packaging. In the metal LIFT process, the donor thin metal film is propelled to the receiving substrate and deposited on it. Morphology of the deposited metal varies with the thermodynamic responses of the donor thin film during and after the laser heating. Thus, the thermophysical properties of the multilayered donor sample are important to predict the LIFT process accurately. Here, we investigated thermophysical properties of a 100 nm-thick gold coated on 0.5 mm-thick sapphire and silicon substrates by means of the nanosecond time-domain thermoreflectance (ns-TDTR) analyzed by the network identification by deconvolution (NID) algorithm, which does not require numerical simulation or analytical solution. The NID algorithm enabled us to extract the thermal time constants of the sample from the nanosecond thermal decay of the sample surface. Furthermore, the cumulative and differential structure functions allowed us to investigate the heat flow path, giving the interfacial thermal resistance and the thermal conductivity of the substrate. After calibration of the NID algorithm using the thermal conductivity of the sapphire, the thermal conductivity of the silicon was determined to be 107–151 W/(m K), which is in good agreement with the widely accepted range of 110–148 W/(m K). Our study shows the feasibility of the structure function obtained from the single-shot TDTR experiments for thermal property estimation in laser processing and electronics packaging applications.

This study proposes a method for the estimation of heat generation in semiconductor devices. The proposal is based on the inverse heat transfer problem (IHTP), where the objective function is minimized using Levenberg–Marquardt regularization, and the forward problem is solved with the 3-D finite-element method (FEM). The inverse problem is divided into two types of analyses. The first is a procedure named calibration, which is the IHTP for material properties and boundary condition estimation, and the second is the inverse problem for heat source estimation. The experimental subjects are a ball grid array (BGA), quad-flat-no-leads (QFN), and a heat-sink-small-outline package (HSOP). As a first step, the calibration procedure to estimate the heat capacity and thermal conductivity of a heater is carried. Said heater is used to provide a source term for the calibration of the experimental subjects. By placing the heater on the top surface of the mold, the unknown material properties and boundary conditions of each package are determined. After model calibration, the heat generation in each respective die is successfully estimated via inverse analysis, with a maximum error of 10% relative to the HSOP.

Local oxygen transport resistances around the surface of Pt particles were examined by analyzing varying equivalent weight (EW) of ionomer in cathode catalyst layers (CCLs) of polymer electrolyte fuel cells. Traditional limiting current method was performed to estimate total oxygen transport resistances in CCLs. The local oxygen transport resistances were determined analytically from the total oxygen transport resistances in CCLs with different Pt loadings. Analysis applying a macro homogeneous model in CCLs revealed that lowering ionomer EW in CCLs caused significant increase in not only the oxygen transport resistance in thickness direction of a CCL (), but also the local oxygen transport resistance (). Additionally, the obtained oxygen transport resistances were reexamined by simple dissolution/diffusion models considering the results of measurement of water sorption isotherm. Results revealed were within the expected range. However, experimental values were much higher than values calculated by use of both the oxygen transport property of Nafion membrane and bulk PTFE/water approximated model. This indicates that unconsidered parameters related to interfacial phenomena of ionomer such as the coverage of absorbed water on the surface, oxygen dissolution rate in ionomer or blockage of Pt surface by sulfonic acid group should be employed.

We numerically investigated the temporal variation and spatial distribution of interfacial mass-transfer phase-change rate in the cathode side gas diffusion layer of a proton exchange membrane (PEM) fuel cell during startup. For this purpose, a three-dimensional transient two-phase nonisothermal model was used. A nonequilibrium evaporation-condensation interfacial mass-transfer rate is incorporated in the model, which enables us to take supersaturation and subsaturation into consideration. This helps us to investigate the most significant contribution of the phase-change rate to the transient response and thermal behavior of the cell. The effects of the operating temperature and channel inlet humidity on the phase-change rate are also investigated. It is observed that when condensation is dominant, the transient time decreases. It is also observed that the maximum temperature decreases with time due to vapor-phase diffusion and phase change.

The feasibility of an optical technique is examined for the measurement of the membrane water content in polymer electrolyte fuel cells (PEFCs). Transmission of the infrared light of 1.92 μm wavelength is used to measure the water content in the polymer electrolyte membrane. A calibration procedure is examined, and the technique is applied for the transient measurement of a Nafion membrane that gives the value of water diffusion coefficient, consistent with previous reports. The technique is then applied to an operating PEFC to show its applicability for in situ measurement.

The feasibility of an optical technique is examined for the measurement of the membrane water content in polymer electrolyte fuel cells (PEFCs). Transmission of the infrared light of 1.92 μm wavelength is used to measure the water content in the polymer electrolyte membrane. A calibration procedure is examined, and the technique is applied for the transient measurement of a Nafion membrane that gives the value of water diffusion coefficient, consistent with previous reports. The technique is then applied to an operating PEFC to show its applicability for in situ measurement.

Ultrashort-pulse lasers are able to recover stiction-failed microelectromechanical systems (MEMS) structures. A possible physical mechanism for this process is an electronic disruption of the bonding between the structure and the substrate, which depends strongly on the peak carrier temperatures. This article presents predicted carrier temperatures for polycrystalline silicon microcantilevers irradiated with ultrashort-pulse lasers. The effects of increased carrier-phonon coupling, reduced thermal conductivity, and increased absorption for polycrystalline silicon as compared to crystalline silicon are determined. An expression for the optimal absorption coefficient is derived for processes in which the excitation is desired at a specified depth into the material.

•A two-phase model developed using an open source software FreeFem++.•The numerical model was built to investigate the crossover characteristics of hydrogen and oxygen across the membrane.•The higher EW of Nafion® is required to significantly decrease gas crossover phenomenon while the cell performance was reduced negligibly.•The increase in the stoichiometric flow ratio and channel length, the gas crossover decreased and the cell performance improved.

Local oxygen transport resistances around the surface of Pt particles were examined by analyzing varying equivalent weight (EW) of ionomer in cathode catalyst layers (CCLs) of polymer electrolyte fuel cells. Traditional limiting current method was performed to estimate total oxygen transport resistances in CCLs. The local oxygen transport resistances were determined analytically from the total oxygen transport resistances in CCLs with different Pt loadings. Analysis applying a macro homogeneous model in CCLs revealed that lowering ionomer EW in CCLs caused significant increase in not only the oxygen transport resistance in thickness direction of a CCL (rO2,macro), but also the local oxygen transport resistance (RO2,local). Additionally, the obtained oxygen transport resistances were reexamined by simple dissolution/diffusion models considering the results of measurement of water sorption isotherm. Results revealed rO2,macrowere within the expected range. However, experimental RO2,localvalues were much higher than values calculated by use of both the oxygen transport property of Nafion membrane and bulk PTFE/water approximated model. This indicates that unconsidered parameters related to interfacial phenomena of ionomer such as the coverage of absorbed water on the surface, oxygen dissolution rate in ionomer or blockage of Pt surface by sulfonic acid group should be employed.

We numerically investigated the temporal variation and spatial distribution of interfacial mass-transfer phase-change rate in the cathode side gas diffusion layer of a proton exchange membrane (PEM) fuel cell during startup. For this purpose, a three-dimensional transient two-phase nonisothermal model was used. A nonequilibrium evaporation–condensation interfacial mass-transfer rate is incorporated in the model, which enables us to take supersaturation and subsaturation into consideration. This helps us to investigate the most significant contribution of the phase-change rate to the transient response and thermal behavior of the cell. The effects of the operating temperature and channel inlet humidity on the phase-change rate are also investigated. It is observed that when condensation is dominant, the transient time decreases. It is also observed that the maximum temperature decreases with time due to vapor-phase diffusion and phase change.