In this study, in order to investigate the effect of the heterogeneity of the laminated structure in a FR-4 on the thermal fatigue life of the Interstitial Via Hole (IVH) in a Printed Wiring Board (PWB), we suggest a practical technique for investigating the variation factors that affect thermal fatigue life. On the basis of the technique, the variation factors were investigated using a thermal cycling test and Finite Element Analysis (FEA). The FEA was conducted with detailed modeling of the plain fabric glass cloth in a PWB, and the analysis results agreed well with the crack conditions and order of fatigue fractures which were observed in the thermal cycling test. We found that differences in the laminating conditions of the glass cloth and differences in the IVH position relative to the glass cloth at certain laminating conditions affect the thermal fatigue life of the IVH. These differences are the variation factors of the thermal fatigue life of an IVH, and combinations of the variation factors will affect the thermal fatigue life of an IVH.

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The influence of the crystalline texture on the etching rate of copper was studied in a sulfuric acid/hydrogen peroxide etching solution using a scanning probe microscope (SPM), electron back scatter diffraction patterns (EBSD), and polarization techniques. The results clearly showed that the crystal faces oriented around the {101} and {111} faces etched at a slower rate than those oriented around the {001} face. The {001} oriented polycrystalline copper showed a relatively noble corrosion potential and depolarization of the cathodic partial reaction. It was suggested that the etching rate of polycrystalline copper is controlled by the mean value of the reduction rate of the hydrogen peroxide on each of the grain surfaces. The {001} face has the highest reduction rate of hydrogen peroxide on the grain. The addition of 1-propanol to the etching solution could reduce the difference for the etching rate of each crystal orientation.

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Previous studies of the macroscopic (the resistance after mounting) and microscopic (the contact resistance between fillers) measurements of conductive adhesives have made progress. However, the conduction mechanism between the electrodes of devices and circuit boards has not been clarified. This is because flat (2D) observations are usually used, though the acutual conductive behavior is three dimensional (3D). In this report, we observed the 3D-conductive line using FIB-SEM, with repeated polishing and observation. Our results show that we successfully analyzed an accurate model.

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In this work, we introduce a novel method for in-plane thermal diffusion applied to a 3D System in Package (SiP). An evaluation device consisting of a micro-heater was fabricated on a 100 μm-thick Si substrate. A high thermal conductivity (HTC) 10 μm thick multilayer film is deposited directly on the back of the Si substrate. The hotspot temperature time response is measured by supplying a pulse power of 0.1 J in 8.5 ms to the heater. The peak temperature rise in the hotspot is confirmed to be 27% lower than that of a device without the HTC film. Furthermore, the temperature difference between the center of the hotspot and a point 1,000 µm away from the hotspot is decreased 20% by changing the pulse width of heating from 16.6 ms to 100 ms. In conclusion, the use of HTC film evens the temperature distribution over the entire substrate simultaneously and reduces the hotspot peak temperature.

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In this study, adhesive strength is newly considered in terms of the singular stress appearing at the end of the interface between the adhesive and the adherent. Here the critical intensity of the singular stress is examined as the debonding criterion for all types of single lap joints having different adhesive thickness and overlap length. The intensity of the singular stress can be evaluated by the application of the finite element method focusing on the stress value at the end element of the interface. It should be noted that, except for the case of small overlap length, the separation always occurs at the edge of the interface causing unstable growth and final brittle fracture. In this type of fracture, it is found that the critical intensity of the stress singular field is constant independent of the adhesive thickness and overlap length.

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We studied electroless copper plating with a nanodispersion of polypyrrole using the loss of oxidation-reduction ability of polypyrrole by UV irradiation as a method of pattern plating on PET film. Using this method, palladium catalysts are only adsorbed onto the polypyrrole sites where there is no UV irradiation, resulting in the formation of pattern plating. Examining the irradiation conditions indicates that UV irradiation with wavelengths shorter than 300 nm is effective for the degradation of polypyrrole and copper was not deposited when the polypyrrole surface resistivity is higher than 10¹² Ω/□. In pattern UV-irradiation for polypyrrole, the introduction of a reduction process where palladium ions (Pd²⁺) are reduced to zero-valent palladium (Pd) after catalyzing removed a small amount of residual palladium at the UV-irradiation sites and then allowed suitable pattern plating. In summary, this method can easily accomplish direct pattern plating on PET films.

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In flip chip technology, electromigration affects the reliability of the solder interconnections. When investigating electromigration in the solder joint, it is essential to examine the effective charge number (Z*) of the atoms involved in the electromigration. In this study, first, a solder joint with almost equivalent current crowding on electromigration was produced by using 1mm thick Cu plates. After that, nine markers were formed on the cross-sectioned solder joint. Then, the migration length of each marker was systematically measured under two conditions. The Z* of each marker was examined by the marker's migration length.

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