In order to improve the creep resistance of Sn based solder alloys, it is effective to strengthen the primary β-Sn phase by solidsolution hardening through solute atoms. Focusing on Ga, which has high solid solubility limit over a wide range of temperatures, the effect of Ga addition on the creep properties of Sn was investigated. The stress exponent and activation energy demonstrated that the creep deformation mechanism of Sn was a climb-controlled dislocation creep controlled by pipe diffusion. Moreover, assuming no temperature dependence of the segregation of Ga to stacking faults, the creep deformation mechanisms of Sn-Ga alloys were considered to be a climb-controlled dislocation creep controlled by pipe diffusion. A comparison of the creep resistance of Sn-based binary alloys, such as Sn-Ga, Sn-Bi, Sn-Sb, and Sn-Zn, revealed that Ga was the most effective element for improving the creep resistance of Sn, followed by Bi, Zn, and Sb.

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A probe pin to inspect the operation of semiconductor chips is damaged by repetition of inserting it to a Sn-Bi solder ball of the semiconductor package and conducting due to the low melting temperature of the Sn-Bi solder. The purpose of this study was to clarify the growth behavior of the reaction layer formed at the interface between the probe pin and the Sn-Bi solder. A Pd-30Cu-29.5Ag-0.5Zn （mass%） probe pin and a Sn-58Bi （mass%） alloy were prepared. The interfacial reaction between the probe pin and Sn-58Bi was investigated by aging at 120℃ for up to 1000 h. It was found that the PdSn₃ + PdSn₄ + Cu₆Sn₅ + Ag₃Sn layer is formed at the joint interface and grows toward the solder side in the early stage in aging. Then, Ag which diffuses fast in Sn gathered at the solder side in the reaction layer and formed the aggregate layer of Ag₃Sn. With the progress of aging, the PdSn₂ + PdSn + Cu₃Sn + Ag₃Sn layer formed at the probe side in the reaction layer. Finally, the reaction layer, which consists of the aggregate layer of Ag₃Sn, the PdSn₃ + PdSn₄ + Cu₆Sn₅ layer and the PdSn₂ + PdSn + Cu₃Sn + Ag₃Sn layer from the solder side to the probe pin side, forms at the interface between the probe pin and the solder.

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In this study, the crack initiation and propagation behaviors in Si/Cu joints with Sn-6.4Sb-3.9Ag （mass%）, Sn-6.4Sb-3.9Ag-0.25Ni-0.003Ge （mass%） and Sn-3.0Ag-0.5Cu （mass%） lead free solder were investigated using an electrolytic Cu plated substrate. The Si chip which surface is coated with Ti/Ni/Au thin layers was prepared. （Cu,Ni）₆Sn₅ layers formed at both Si/solder and Cu/solder interfaces in the joints with Sn-6.4Sb-3.9Ag based solder. In contrast, Cu₆Sn₅ layers formed at both the interfaces in the joints with Sn-3.0Ag-0.5Cu, although very thin discontinuous Cu₆Sn₅ layer formed at the Si/solder interface. It was found that a crack growth occurs at the （Cu,Ni）₆Sn₅/β-Sn interface in the Sn-6.4Sb-3.9Ag based solder joints by the pseudo power cycle test. The electron backscattered diffraction analysis result shows that fine recrystallized grains generate in the cracked area in Sn-6.4Sb-3.9Ag based solder joints, and crack propagation occurs in the high-angle grain boundaries of their recrystallized grains. In the joint with Sn-6.4Sb-3.9Ag-0.25Ni-0.003Ge, many fine IMCs such as SbSn, Ag₃Sn and （Cu,Ni）₆Sn₅ were formed. Their IMCs can suppress the recrystallization of β-Sn and the crack propagation. Thus, heat cycle resistance of the joint with Sn-6.4Sb-3.9Ag-0.25Ni-0.003Ge was improved. In contrast, the heat cycle resistance of the joint with Sn-3.0Ag-0.5Cu was inferior to that with Sn-6.4Sb-3.9Ag based solder, due to rapid interfacial cracking between the Ti layer and solder.

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The purpose of this study is to clarify the joint behavior during ultrasonic flip chip bonding using the in-situ bonding monitoring method with the semiconductor strain sensor. Some characteristic tendencies related with the bonding strength ware extracted from the strain waves below the joint region. The higher the bonding strength was, the bigger reduction of the vertical compression strain during applying ultrasonic vibration was. Furthermore, the joint status was found to be correlated with the change in the amplitude and harmonic components of the horizontal strain with time. Especially, the difference in harmonic components of each wave was very useful as the future value of the machine learning algorithms for judging bonding qualities.

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We have been targeting “Silicon anisotropic wet etching in alkaline solution”, which is one of the key processing technologies for silicon MEMS. In the future, it is necessary to develop environment-friendly wet etching process. However, the etching with a low-concentration alkaline solution is difficult because the etched surface became rough when a low-concentration （about 20 wt% or less） alkaline aqueous solution is used. In this study, the wet etching method using droplets of 5 wt%KOH solution was investigated. The droplet is　heated locally and the moisture in the droplet evaporates just before etching, then the droplet turns to high-concentration. As a result, it was found that a smooth etching surface, which cannot be generally obtained with a 5 wt% KOH aqueous solution, can be obtained under appropriate conditions of the amount of droplets and the heating temperature. This etching method has the advantage of localized etching, and it can be applied not only to single crystal silicon etching but also to etching of new materials for micro devices.

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High-temperature enclosed electrochemical migration （ECM） is one of the new defects in the board assembly that occurs at the sealed bottom electrode when the device gets heated with running for a long period of time. This defect can also occur in the dry conditions unlike ordinary ECM. We have developed a novel method that can easily reproduce this phenomenon so that the migration behavior can be observed. The formation of high-temp enclosed ECM is caused by movement of the metal ions, when the flux residue underneath the electrode is soft and has high fluidity. Therefore, it can be prevented by optimizing the elastic modulus of the flux residue at the component operating temp. This approach is effective even if the flux residue contains a large amount of activators such as organic acids.

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A master mold which defines the final wiring configuration is firstly fabricated, then transferred to a replica mold to form an inverted shape of the master mold, succeeded with the filling of recesses of the replica mold with conductive paste, and finally the conductive paste will be transferred to a substrate. We report on the development of a technology for forming wirings with a relatively simple process using imprinting technology. Thanks to a soft replica mold, wirings have been successfully transferred across the substrate wiring steps with 10-micron high. This imprinting technology keeps it possible to form fine and high aspect substrate wirings with low temperature process.

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The objective of this study is to consider candidate materials for Cu-Cu direct bonding as advanced interconnect technology using Nanoporous Cu materials. Nanoporous Cu structure can be obtained by two kinds of electroplating process. One is the direct porous plating process by additive which can form Nanoporous structure directly. The other is de-alloying process which can form Nanoporous structure by de-alloying of Cu-X alloy. By using electroplated Nanoporous Cu structure, we compared the property of Nanoporous structure and carried out the bonding test. Nanoporous structure shows higher bonding strength because of its unique properties. The possibility that Nanoporous Cu is promising materials for advanced bonding technology was confirmed.

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Paste roll state is an important factor for the robust printing process, but there are only few reports related to it. In this study, we investigated a squeegee shape to improve the continuous printability by stabilizing the paste roll behavior. Against this goal, we estimated that the issue is the weak paste flow and the decrease in the paste amount. Using fluid analysis, we developed the squeegee shape that can suppress the decrease in the paste amount with keeping the paste flow strong. As a result, we achieved to improve the continuous printability 5 times higher than a general flat squeegee.

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We have developed a novel microfabrication technology applying Metal Assisted Chemical Etching. This technology makes it possible to chemically process the entire surface of Si wafer simultaneously with high productivity. When processing high aspect ratio trenches with this technology, it is important to suppress the generation of the fine-hole-shaped defects on the walls of trenches that reduce the strength of trenches. In this study, we estimated the model that the fine hole-shaped defects were caused by the Au atoms, and as a countermeasure, we added polymer additive that could inactivate Au diffusion region to the etching solution. As a result, polymer additive inhibited the dissolution of Si in Au diffusion region and suppressed the development of fine hole-shaped defects.

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Sintered bonding using Ag particles is one of the bonding materials that enables high-temperature operation of power modules. This bonding has begun to be applied as a die bonding material under SiC chip for getting both low heat resistance and high heat dissipation. This research report focuses on the effect of voids in the sintered Ag layer on bonding reliability. The void geometry observed with SEM（Scanning Electron Microscope） and EBSD（Electron Back Scatter Diffraction）. The mechanical properties of each void ratio were got by tensile test and stress relaxation test, and compared with the bonding reliability. As a result, it was found that the dense sintered Ag layer is superior to the sparse sintered Ag layer in terms of bonding reliability, because the shear strain and creep strain of the dense sintered Ag layer are suppressed in heat cycle test. Furthermore, comparing shear Strain and creep strain, it was found that creep strain is the dominant factor in bonding reliability in heat cycle test.

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A method of forming convex structure on the metal surface by attaching particles using the cold spray method is suggested to improve the bonding strength of the resin/metal interface due to the anchor effect. In this paper, titanium particles are sprayed on copper substrates. The relationship between the cold spray conditions and the convex structure formed on the substrate surface as well as the shear strength of particle/substrate, were evaluated. Higher gas temperature caused the increase of particle adhesion rate and the particle adhesion height. As the gas pressure increased, the adhesion height is decreased. The shear strength of particle substrate was increased with higher gas temperature and higher gas pressure. The improving effect of cold spray process on the bonding strength of epoxy resin was also confirmed. Especially, the particle adhesive strength and the adhesion rate showed a good correlation with the bonding strength of the epoxy resin on copper substrates.

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The effect of the chemical factors on electrical resistivity and interfacial electrical resistivity between silver-plated aluminum filled electrically conductive adhesives composed of polyhydroxyurethane-based binders and metal electrodes was investigated. Three types of polyhydroxyurethanes having different average molecular weights were used for the adhesives. The effect of the isocyanate cross-linker on the electrical resistivity differs depending on the difference in the average molecular weight in the binders. The interfacial electrical resistivity was increased by decreasing the molecular weight of the polyurethane binder. In addition, the isocyanate cross-linker was found to affect the interfacial electrical resistivity with copper electrodes. These results suggest that the binder chemistry of flexible electrically conductive adhesives influence both of electrical resistivity and interfacial electrical resistivity with metal electrodes.

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