Collapse of interconnected open

The closing behavior of interconnected open pores has been investigated in W-Ni systems where the dominant sintering mechanism is grain boundary diffusion. The samples were prepared by conventional powder metallurgy technique with large W particles containing Ni contents of 0.03 to 0.1 wt pct. The microstructure analysis indicated that pore collapse predominantly occurs at the three grain junction midpoints and produces closed pores at the four grain corners. The observed critical porosity, below which all the pores exist in isolated form, was found to be about twice as great as the critical porosity predicted by morphological perturbation theory. From these results, it is concluded that the grain boundary diffusion flux across the pore surface, as well as the capillary force, plays an important role in the closing behavior of interconnected open pores.     

Characterization of 2:1 type layered aluminosilicate via intercalation reaction

The stable intercalation compounds were synthesized by ion exchange reaction of the cations (Ca²⁺, Mg²⁺, etc.) existing in the interlayer of the 2:1 type layered natural aluminosilicate with n-decylammonium ion and by successive molecular intercalation reaction of the primary n-alcanol (ROH, R = C₁₀H₂₁, C₁₂ H₂₅, C₁₄H₂₉). The charge densities were calculated from the basal spacings of n-decylammonium derivatives under primary n-alcanol. As the result, the aluminosilicates used in this study have the charge density of 0.25, 0.34 per formula unit and interlayer cation exchange capacity of 69.3, 92.4 meg./l00g, respectively.     

Matrix penetration of w/w grain

The matrix phase of 93W-5.6Ni-l.4Fe heavy alloy has penetrated into W/W grain boundaries during a newly developed heat treatment which consists of repeated isothermal holdings at 1150 °C and water quenching between them. With the matrix penetration, the impact energy increases from 57 to 170 J, whereas the ultimate tensile strength and elongation remain un- changed. The tensile fracture surface of specimens appears similar regardless of the matrix penetration: predominant cleavage of W grains and dimple fracture of matrix. The fracture sur- face by impact, on the other hand, reveals a change of W/W interface failure toward ductile failure of penetrated matrix with many dimples by increasing the matrix penetration. The in- crease in the fraction of ductile failure and observed crack blunting is attributed to the increase in impact energy with the matrix penetration.     

Reconfigurable Optical Add‐Drop Multiplexer Using a Polymer Integrated Photonic Lightwave Circuit

We have developed a fully functional reconfigurable optical add‐drop multiplexer (ROADM) switch module using a polymer integrated photonic lightwave circuit technology. The polymer variable optical attenuator (VOA) array and digital optical switch array are integrated into one polymer PLC chip and packaged to form a 10‐channel VOA integrated optical switch module. Four of these optical switch modules are used in the ROADM switch module to execute 40‐channel switching and power equalization. As a wavelength division multiplexer (WDM) filter device, two C‐band 40‐channel athermal arrayed waveguide grating WDMs are used in the ROADM module. Optical power monitoring of each channel is carried out using a 5% tap PD. A controller and firmware having the functions of a 40‐channel switch and VOA control, optical power monitoring, as well as TEC temperature control, and data communication interfaces are also developed in this study.     

Designing a Stable Cathode with Multiple Layers to Improve the Operational Lifetime of Polymer Light‐Emitting Diodes

The short device lifetime of blue polymer light‐emitting diodes (PLEDs) is still a bottleneck for commercialization of self‐emissive full‐color displays. Since the cathode in the device has a dominant influence on the device lifetime, a systematic design of the cathode structure is necessary. The operational lifetime of blue PLEDs can be greatly improved by introducing a three‐layer (BaF₂/Ca/Al) cathode compared with conventional two‐layer cathodes (BaF₂/Al and Ba/Al). Therefore, the roles of the BaF₂ and Ca layers in terms of electron injection, luminous efficiency, and device lifetime are here investigated. For efficient electron injection, the BaF₂ layer should be deposited to the thickness of at least one monolayer (～3 nm). However, it is found that the device lifetime does not show a strong relation with the electron injection or luminous efficiency. In order to prolong the device lifetime, sufficient reaction between BaF₂ and the overlying Ca layer should take place during the deposition where the thickness of each layer is around that of a monolayer.     

Reliability of Au bump flip chip packages with adhesive materials using four-point bending test

In this study, the bending fatigue reliability of Au bump flip chip packages with anisotropic conductive film (ACF) and non-conductive film (NCF) as adhesive materials was evaluated using a four-point bending test. Differential bending between the substrate and the Si chip was the dominant failure driver for the Au bump flip chip packages subjected to the bending test. The bending fatigue life of the NCF joint was longer than that of the ACF joint, regardless of the bending frequency. The main reason for the increased electrical resistance of the packages with ACF and NCF was the delamination between the adhesive material and the electroless Ni-immersion Au (ENIG) pad and between the Au bump and ENIG pad, respectively. For the ACF package, the bending stress was concentrated at the conductive particles between the Au bump and the ENIG pad during the bending fatigue test, resulting in a low bending fatigue strength. The delamination in the packages propagated with increasing bending fatigue cycles and frequency. The Au bump flip chip package with NCF was mechanically robust due to the higher initial strength and the larger bonding area between the Au bump and the ENIG pad.     

Effects of isothermal aging and temperature–humidity treatment of substrate on joint reliability of Sn–3.0Ag–0.5Cu/OSP-finished Cu CSP solder joint

This study examined the effects of isothermal aging and temperature–humidity (TH) treatment of substrate on the joint reliability of a Sn–3.0Ag–0.5Cu (wt.%)/organic solderability preservative (OSP)-finished Cu solder joint. Two types of OSP-finished chip-scale-package (CSP) substrates were used, those subjected and not subjected to the TH test. This study revealed an association between the interfacial reaction behaviors, void formation and mechanical reliability of the solder joint. Many voids were formed at the interface of the OSP-finished Cu joint subjected to the TH test. These voids were caused by the oxidation of the OSP-finished Cu substrate during the TH test. In the shear tests, the shear force of the joint with the substrate not subjected to the TH test was slightly higher than that with the TH test. The mechanical reliability of the solder joint was degraded by voids at the interface.     

Mechanical reliability of Sn-rich Au–Sn/Ni flip chip solder joints fabricated by sequential electroplating method

In this study, we evaluated the mechanical reliability of Sn-rich, Au–Sn/Ni flip chip solder bumps by using a sequential electroplating method with Sn and Au. After reflowing, the average diameter of the solder bump was approximately 80 μm and only a (Ni,Au)₃Sn₄ intermetallic compound (IMC) layer was formed at the interface. Due to the preferential consumption of Sn atoms within the solder matrix during aging, the solder matrix was transformed sequentially in the following order: β-Sn and η-phase, η-phase, and η-phase and ε-phase. In the bump shear test, the shear force was not significantly changed despite aging at 150 °C for 1000 h and most of the fractures occurred at the interfaces. The interfacial fracture was significantly related to the formation of brittle IMCs at the interface. The Sn-rich, Au–Sn/Ni flip chip joint was mechanically much weaker than the Au-rich, Au–Sn/Ni flip chip joint. The study results demonstrated that the combination of Sn-rich, Au–Sn solder and Ni under bump metallization (UBM) is not a viable option for the replacement of the conventional, Au-rich, Au–20Sn solder.