Toshihide Takahashi

Development of Ag3Sn Intermetallic Compound Joint for Power Semiconductor Devices

Pb-based solders are used as high temperature solders in power semiconductor devices. Although use of Pb is globally restricted, alternative materials are inadequate to replace Pb-based solder. This study aims to replace Pb-based solder with an intermetallic compound (IMC). Samples were produced to join a Si chip with evaporated Ag and Sn films onto a Ag-plated Cu substrate at 523 K for 10 s. As a result, the evaporated films were completely transformed into a Ag 3 Sn IMC. The IMC joint showed higher strength until 543 K and good heat-aging resistance at 423 K. Therefore, this joint would be promising in replacing Pb-based solders.

Bulk nanocomposite using self-forming core/shell nanoparticles and its magnetic properties for high-frequency applications

A bulk nanocomposite composed of tightly packed self-forming core/shell nanoparticles of metal/oxide was fabricated. The crystalline grain size of the nanoparticles, the packing ratio, and the composition were controlled in the nanocomposite, and their effects on the magnetic properties were investigated. The crystalline grain size of the nanoparticles, the packing ratio, and the composition strongly influenced the magnetic anisotropy field, magnetic coercivity, relative permeability, and loss factor at GHz bands. High permeability with a low loss factor of less than 1.5% at up to 1 GHz was obtained in the nanocomposite in which the nanoparticles with a crystalline grain size of approximately 15 nm were tightly packed.

Dual-port technique in navigation-guided endoscopic resection for intraparenchymal brain tumor

Background: In navigation-guided endoscopic surgery performed via a single port, the interference of surgical instruments often disturbs the resection and hemostasis. Case Description: With regard to this, we designed a dual-port technique for navigation-guided endoscopic surgery in a 62-year-old man, with intraparenchymal anaplastic astrocytoma. Two transparent sheaths with Nelaton tubes were inserted in the front of the target lesion via an infinity-shaped burr hole, under the control of the navigation system. The lesion was removed partially using a rigid endoscope and several surgical tools through the bilateral ports. Using the new method, it was convenient to perform hemostasis with bipolar coagulation and aspiration, without any interference from the surgical instruments during the surgery. Conclusion: The offered dual-port technique may be included in surgery planning for elderly patients or patients in particular conditions, with intraparenchymal brain tumors.

Mixed Germ Cell Tumor with Extensive Yolk Sac Tumor Elements in the Frontal Lobe of an Adult

Intracranial nongerminomatous germ cell tumors (NGGCTs) in unusual locations are extremely rare. Here, we report a case of a yolk sac tumor in the frontal lobe in a middle-aged patient. A 42-year-old man was admitted to our hospital for headache and nausea. Magnetic resonance imaging (MRI) showed an enhanced mass lesion with a marked cyst component. The serum alpha-fetoprotein (αFP) level was extremely high. Histological examination of specimens after subtotal removal revealed a primary mixed germ cell tumor with extensive yolk sac tumor elements, often referred to as an intracranial “yolk sac tumor.” The preoperative diagnosis of NGGCTs in unusual age and locations is extremely difficult. Clinicians should consider the possibility of NGGCTs, including yolk sac tumors, when intracranial tumors with unusual MRI findings are encountered.

Study on temperature dependence of viscosity of halogen-free dispensing solder paste

A dispensing process has been used to apply solder paste in surface mount technology (SMT) production. To stabilize the dispensing process, it is necessary to understand the influence of storage conditions on the viscosity of solder paste as one of various factors. In this paper, halogen-free dispensing solder paste is treated at a constant temperature and the variation of its viscosity is examined using a cone-plate-type viscometer, which can measure the viscosity of even a small amount of solder paste. Also, the tin salt is extracted from the solder paste after thermal treatment and the amount of tin in the tin salt is measured, from which the mechanism of increasing viscosity is discussed. In addition, the activation energy for increasing the viscosity of the halogen-free dispensing solder paste is calculated from an Arrhenius equation, and a predictive formula for the viscosity of solder paste is derived. Using this formula, it is possible to prevent dispensing failures by optimizing the storage conditions of halogen-free dispensing solder paste.