[in Japanese]

View full abstract

Near-ternary eutectic Sn–Ag–Cu alloys are leading candidates for Pb-free solders. However, the mechanism responsible for the nucleation of each morphology is still unclear. The solidification process and the volume fraction of each morphology in the specimen were investigated in order to clarify the solidification mechanism. In this study, Sn–3.5Ag–0.5Cu and Sn–3.5Ag–1.5Cu (mass%) were prepared. Each phase nucleated at a lower temperature than the equilibrium value because of the undercooling for nucleation. The structure and the order for solidification obtained in this study were different from that predicted from the phase diagram generated using the software Pandat.

View full abstract

To investigate electrochemical migration (ECM), a relatively new test method has been developed by the authors, which enables real time monitoring of the migration process using microscope observation and insulation resistance measurement under the micro dew condensation environment. This research has focused on studying the dew drop changes and the ECM growth process under micro dew condensation. In addition, we investigated the ECM accceleration factor of each type of test condition using this new method. The results show that the greater the number of test cycles, the more conducive to wetting the surface of the substrate board becomes. When the gap between the electrodes is covered with dew water, the ECM grows into the dew water.

View full abstract

In order to obtain Cu-to-Cu joints with high strength and ionic migration resistance, low temperature bonding processes (250°C~400°C) using three kinds of Cu nanoparticles (mean particle sizes: d=7.2 nm, 64.8 nm, and 498 nm) or mixed Ag–Cu nanoparticles were studied. With Cu nanoparticles, the Cu-to-Cu joints using 64.8 nm diameter Cu nanoparticles showed the highest strength. With mixed Ag–Cu nanoparticles comprised of Cu nanoparticles (d=498 nm) and Ag nanoparticles (d=7.9 nm), the strength of Cu-to-Cu joints using 50%Ag–50%Cu nanoparticles was higher than that of any other joints using mixed Ag–Cu nanoparticles. The electrodes prepared using mixed 50%Ag–50%Cu nanoparticles showed higher ionic migration resistance than that prepared using Ag nanoparticles only.

View full abstract

The development of PKG-substrates with lower coefficients of thermal expansion (CTE) is desired, since the warpage introduced by the difference between the coefficients of the substrates and that of the silicon chips is a serious obstacle in the practical application of FC-PKG technology. Simulation and experimental studies were conducted in the present study in order to reduce the CTE-values of the PKG-substrates by using nanosilica particles. The FEM simulation revealed that the reduction of the CTE of the substrates was important to suppress the warpage. 25 nm-diameter nanosilica induced deteriorations in the properties of the substrates; i.e., a reduction in T_g and an increase in CTE. A thermo-gravimetrical study showed incomplete cross-linking due to inhibition by the acidic protons from the unreacted free silanol groups on the nanosilica surface. Curing at higher temperatures and for longer duration led to an increase in T_g and a reduction of α₂. Finally, by employing a newly developed polyimide with lower CTE and higher silica content of 45 vol%, we succeeded in preparing a PKG-substrate with a 5 ppm/K lower CTE compared to the conventional one.

View full abstract

In recent years, Ultra Wideband (UWB) radio technologies have been gaining a lot of attention for high-speed, large-capacity communication at close range. Small dimensions which allow these technologies to be built into electronic devices, broadband VSWR characteristics, and omni-directional radiation patterns in the horizontal plane are required for UWB antennas. In this paper, an UWB antenna with omni-directional radiation patterns in the horizontal plane, which can be built into a USB memory case, is proposed. The characteristics of the antenna formed on a printed circuit board are investigated. It was found that the proposed antenna performed with good VSWR characteristics and radiation patterns at the UWB frequencies.

View full abstract

Research on the inspection and defect repair process for improving the production yield is becoming more important in the flat panel production process which has expanded remarkably in recent years. In this research, a new non-contact inspection method for the fast and accurate detection of electrical defects subject to repair in a-Si TFT circuits is proposed. The proposed method enables much faster inspection in comparison with the conventional Pin Probe inspection method which has been used for years. In addition, since it cannot only detect defects in the target circuit but also specify the location of each defect, a more efficient process management can be realized by having such information in common with the repair system. Further, this non-contact method can eliminate a running cost which has been the most serious problem in the test process by removing the need to replace the pin probing fixtures which vary depending on the circuit type.

View full abstract