Papers by Author: Ikuo Shohji

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Authors: Takehiko Takahashi, Susumu Hioki, Ikuo Shohji, Osamu Kamiya
Abstract: The low-cycle fatigue behavior and the relationship between the surface features in the low-cycle fatigue testing and the fatigue life of Sn-3.5Ag and Sn-0.7Cu lead-free solders were investigated at strain rate of 0.1%/s at room temperature, 80 and 120oC. In addition, the fatigue life was estimated by using the surface deformation of the solders, and image processing. And also, it was compared with Coffin-Manson type of fatigue behavior. The fatigue life of Sn-3.5Ag solder was superior to that of Sn-0.7Cu solder at temperatures, 80 and 120oC. The fatigue life determined by surface deformation indicated a close behavior to Coffin-Manson type fatigue behavior in those solders. Therefore the low-cycle fatigue life of solders could be estimated by the surface deformation.
Authors: Ikuo Shohji, Tatsuya Kobayashi, Tomotake Tohei
Abstract: The aim of this study is to investigate the relationship between the inelastic strain range and the thermal fatigue lives of chip size package solder joints with Sn-Pb and Sn-Ag-Cu solder balls. The inelastic strain range was examined by finite element analysis. In both solder joints, the exponential terms in the inelastic strain range term in the Coffin-Manson equation were evaluated as 1.8 - 2.3. These values are very close to the conventional one used in Sn-Pb and the Pb containing solders. The inelastic strain range is almost proportional to the temperature range in the Sn-Pb solder joint. On the contrary, the inelastic strain range is proportional to approximately the square root of the temperature range in the Sn-Ag-Cu solder joint. The deference depends on the change of the stress-strain hysteresis curve in the thermal cycle.
Authors: Ikuo Shohji, Satoshi Shimoyama, Hisao Ishikawa, Masao Kojima
Abstract: Impact properties of solder ball joints with Sn-9mass%Zn and Sn-3mass%Ag- 0.5mass%Cu lead-free solders were investigated under aging at 423 K. In the case of the joints with Cu electrodes, both Sn-9Zn and Sn-3Ag-0.5Cu joints have similar impact forces before aging. For the Sn-3Ag-0.5Cu joint, fracture occurred in an intermetallic compound (IMC) layer formed in a joint interface regardless of aging, and thus the impact force was stable upon aging at 423 K for 500 h. For the Sn-9Zn joint, fracture mode changed from solder fracture to other fracture upon aging and thus this change led a decrease in the impact force. In the Sn-9Zn joint with an electroless Ni/Au plated electrode, fracture occurred in the solder regardless of aging, and thus impact properties improved compared with the joint using the Cu electrode. The impact properties are superior to those of the Sn-3Ag-0.5Cu joints with the Cu and the electroless Ni/Au electrodes.
Authors: Hayashi Yumi, Ikuo Shohji, Hiroshi Miyazawa
Abstract: Self-annealing behaviors of the electrodeposited silver films which preferentially orient in (001) and (111) directions were investigated by in situ EBSP analysis. In the (001)-oriented film, self-annealing starts in storage for a few hours at R. T. and is almost complete after storage for 6 h at R. T. (001)- and (212)-oriented recrystallized grains mainly nucleate, and (001)-oriented grains mainly grow up. In the (111)-oriented film, self-annealing starts in storage for 15 min at R. T. and is almost complete after storage for 1 h at R. T. (111)-, (001)- and (212)-oriented recrystallized grains mainly nucleate, and (111)-oriented grains mainly grow up. The size of recrystallized grains induced in the (111)-oriented film by self-annealing is approximately half that in the (001)-oriented film although the rate of recrystallization in the (111)-oriented film is faster than that in the (001)-oriented one. The area fraction of the preferential orientation after completion of recrystallization saturates in approximately 70% and 50% in the (001)- and (111)-oriented films, respectively.
Authors: Ikuo Shohji, Susumu Arai, Naoki Kano, Noboru Otomo, Masahisa Uenishi
Abstract: A Cu brazing sheet has been developed using a Cu-P composite plating method. A Cu-P composite plating layer, which contains 7mass%P, was formed on a Cu plate with a copper sulfate solution including P particles. The melting start temperature of the Cu-P composite layer was determined to be approximately 765°C. Microstructure and joint strength of a brazed joint with the Cu-P composite layer were investigated and compared with those of the joint with a conventional Cu-7P filler foil. As the results of the study, it was clarified that the Cu-P composite layer developed is feasible to use as a brazing material for Cu and Cu alloys.
Authors: Yawara Hayashi, Ikuo Shohji, Yusuke Nakata, Tomihito Hashimoto
Abstract: To create a high reliability solder joint using IMCs dispersed in the joint, the joints with four types of lead-free solder were investigated. The joint with Sn-3.0Ag-0.7Cu-5.0In (mass%) has high die shear force compared to other joints investigated, and the joint with the Ni-electroplated Cu bonded at 300 oC for 30 min showed the maximum die shear force due to formation of a large number of fine IMCs. In the joint with Sn-0.7Cu-0.05Ni (mass%), uniform dispersion of a large number of IMCs was achieved, although the die shear force of the joint is lower than that of the joint with Sn-3.0Ag-0.7Cu-5.0In. In the joint with Sn-5.0Sb (mass%), a solder area was remained in the center of the joint although a large number of columnar IMCs form at the joint interface. The die shear force of the joint with Sn-5.0Sb increased with increasing the bonding time due to formation and growth of IMCs. In the joint with Sn-3.0Ag-0.5Cu (mass%), IMCs formed at the joint interface and did not disperse in the entire joint.
Authors: Ikuo Shohji, Ryohei Arai, Hisao Ishikawa, Masao Kojima
Abstract: The tensile properties of Sn-x(x=1, 2, 3)Ag-0.5Cu-0.05Ni-0.005Ge (mass%) alloys were investigated. In addition, the ball shear force was investigated with solder balls and two types electrodes, Cu and electroless Ni/Au plated Cu, to examine joint reliability under heat exposure conditions. Tensile strength of the alloy decreases with decreasing the Ag content. On the contrary, elongation increases with decreasing the Ag content. When the Ag content reduces, primary β-Sn phases are coarsened and eutectic microstructures diminish. The decrease of the eutectic microstructures causes a reduction of the tensile strength. In as-soldered joints with Sn-Ag-Cu-Ni-Ge solder balls and Cu electrodes, the ball shear force increases with increasing the Ag content. However, the ball shear force decreases with increasing heat exposure time. After heat exposure treatment at 423 K for 500 h, the ball shear force is relatively stable at lower values regardless of the Ag content. In the joints with electroless Ni/Au plated Cu electrodes, the ball shear force slightly increases with increasing heat exposure time. Even after heat exposure treatment at 423 K for 500 h, hierarchy of the ball shear force is maintained. The ball shear force becomes high with increasing the Ag content.
Authors: Hirohiko Watanabe, Masayoshi Shimoda, Noboru Hidaka, Ikuo Shohji
Abstract: Sn-Ag-Cu-Ni-Ge solder alloy has been developed to improve the mechanical properties of the Sn-Ag-Cu base solders and prevent oxidation of those solders. In this paper, an interfacial reaction and microstructure between the solder and a Cu electrode were investigated under heat exposure conditions. It was found that intermetallic compounds growth at the interface of the solder and the Cu electrode was greatly affected by amounts of added elements. Adding Ni in the solder can suppress the formation and growth of intermetallic compounds (IMCs) such as Cu-Sn and decreasing the amount of adding Ag in the solder can prevent the formation and growth of Ag3Sn. Moreover, it was found that there was an effect of suppress the growth of the Cu3Sn formed on the interface of Cu and (Cu,Ni)6Sn5 by adding Ni from analysis results of EDX and TEM.
Authors: Chiko Yorita, Tatsuya Kobayashi, Ikuo Shohji
Abstract: Semiconductor packages that use metallization and lead-free solders are increasingly being used in electronic products. In this study, interface reactions and joint-strength reliability were investigated for Sn-3W%Ag-0.5W%Cu solder ball joints joined to Cr/Cu and Cr/Ni-40W% metallization layers that were heat treated at 260°C. The strength of the joint with the Cr/Cu metallization layer decreased as the duration of the heat treatment increased. Sn and Cr interface reactive layers were generated after the loss of Cu in the Cr/Cu metallization layer, but the connection was maintained. By contrast, the connection of the joint to the Cr/Ni-40W metallization layer was relatively stable under the heat treatment conditions investigated.
Authors: Hirohiko Watanabe, Marie Nagai, Tsutomu Osawa, Ikuo Shohji
Abstract: Dissolution properties of Cu in molten Sn-Ag-Cu-Ni-Ge alloys have been investigated. In particular, the effect of the Ni content in the alloys on the dissolution properties has been examined. Moreover, the dissolution properties have been compared with those of Sn-Ag and Sn-Ag-Cu alloys. To investigate the dissolution rate of Cu in molten alloys, Cu wires were dipped in molten alloys heated at 250, 270 and 290°C. Dissolution thickness of Cu wire is proportional to dipping time regardless of alloy type. The dissolution rates of Cu follow the order Sn-Ag > Sn-Ag-Cu > Sn-Ag-Cu-Ni-Ge. In Sn-Ag-Cu-Ni-Ge alloys, the dissolution rate of Cu decreases with increasing the Ni content. In cases of Sn-Ag and Sn-Ag-Cu alloys, a thin Cu-Sn compounds layer forms at the interface between Cu and the alloy and dissolution of Cu does not proceed uniformly. On the contrary, a thick reaction layer, which consists of granular Cu-Ni-Sn compounds, forms at the interface between Cu and the Sn-Ag-Cu-Ni-Ge alloy. Since the reaction layer inhibits dissolution of Cu in molten alloy, the dissolution rate slows down and dissolution of Cu proceeds uniformly in the Sn-Ag-Cu-Ni-Ge alloys.
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