Kazumichi Machida

Fundamental Investigation of Design and Performance of Substrates. Design and Assembly Process of Substrates System for Power Semiconductor. (Report 1).

Power-control semiconductors are widely used in industrial applications. The development of power semiconductor such as insulated-gate bipolar transister enables much faster switching, higher current and higher voltage rating. While high-performance of the semiconductor is accompanied by an evolution of heat. A substrate system, therefore, is very important part to dissipate heat from the semiconductor.Design and assembling process substrates system for the semiconductor have been researched and developed. In this report, especially, a conceptual design and performance of the substrate is discussed through a calculation of thermal stress by finite element method and an analysis of its function. It was clarified that the design accepted region of initial performance of the substrate was bounded by a dielectric breakdown voltage, a current capacity and a thermal conductivity. The substrate is consisted of conductors and an insulator. The dielectric breakdown voltage is determined by thickness of ceramics insulator. The current capacity is determined by thickness of copper conductor. The thermal conductivity is determined by materials and thickness between conductor and insulator. Furthermore, it was found that maximum principal stress is generated at a corner of ceramics and copper conductor at the lowest temperature, and the stress occurence crack at the ceramics. A reliability of the substrate was dominated by thermal stress generated in ceramics under temperature cycles.

Design and Assembly Process of Substrates System for Power Semiconductor. (Report 3). Investigation of New Assembly Prcess of Substrates System with High Performance.

New assembly process of the substrates system with high performance has been establised by adopting the same bonding condition of both Cu sheet-Mo sheet by vaccum diffusion bonding process and Cu sheet-alumina by the adjusting Ti content in active brazing metal. The substrates system has been consisted by the conductors with three layered structure of Cu and Mo sheets, and 96% alumina as insulator, as already reported.The bond with high reliability of Cu and Mo sheets has made by vacuum diffusion bonding process under the condition of 1, 300K for 2, 400s under the pressure of 10-2 Pa. Furthermore, in order to assemble the substrates system with high performance by one processing stage, the bonding condition of Cu sheet and alumina requires to coincide with that of Cu and Mo sheets. It was shown experimen-tally that the bond of Cu sheet-alumina with high reliabilty was obtained by selecting nearly 30 wt% Ti powder mixed with Cu powder as active brazing metal. As the results, the assemly process of the both the conductor and the insulator-Mo sheet, Cu sheet and alumina-has been able to be achieved with bonding of one processing stage by adopting the bonding condition of 1, 300 K for 2, 400 s. In addition, it was also confirmed that voids or other defects are not observed in the bond interface by the inspection of SEM etc.

Study on vapor-shielded pressure bonding process of nonferrous metals by resistance heating and its inprocess quality control. (Report-6). Improvement of properties of contact-bars by applying new bonding process.

The bonds in mass-produced electric devices are recently required high reliability in precision and in quality.For the purposes, new bonding process for dissimilar metals by resistance heating is successfully developed.To control the material deformation, the optimum electrode constitution of materials, sizes and their arrangement is established as described in Report-1 and Report-2.To get high quality at bonds, the vapor shield process available to clean the material interface while bonding is developed as described in Report-3 and Report-4.Moreover, inprocess control system for getting high quality bonds stably is newly developed and automatic bonder for mass-production line of contact-bars is successfully manufactured as described in Report-5.In this study, main properties of contact-bars bonded by the new process which is operated in massproduction line are examined in comparison with the conventional one by brazing.The main results obtained are as follows;1) Bond strength increases of 40% as compared with the conventional one.2) Temperature rise at bond by arcing heat input to the contact-top is sharply suppressed.3) Bond strength at high temperature of 973 K is three times as high as the conventional one.4) Hardness of carrier bar required spring property is kept at higher value.5) Noticeable longer life of electromagnetic switchgears is confirmed by JEM-standard test.

Study on vapor shielded pressure bonding process of nonferrous metals by resistance heating and its inprocess quality control. (Report 4). Shielding mechanism by vapor and constitution of vapor shielded pressure bonding process.

Contact-bars of electromagnetic switchgears are required high precision and high quality at bonds. For the purposes, the Vapor Shielded Pressure Bonding (V.S.P.B) process and its inprocess control system are successfully developed.To control the material deformation, thermo-characteristics by resistance heating while bonding are examined, and the optimum electrode materials and their constitution are selected as described in the report-1 and -2Then, the examination of bonding quality and its improvement by vapor shield process are described in the report-3.In this study, the mechanism of vapor shielding on cleaning action at the bonding interface and the fundamental properties of bonds are investigated.Moreover, the basic constitution of Vapor Shielded Pressure Bonding Process are examined and the each optimum condition is clarified.The main results obtained are as follows;1) The follow facts about surface oxidation of materials are clarified by AES.a) Material heating in air atmosphere accelerates the striking oxidation.b) Vapor shield can effectively control the oxidation while heating.2) The essential factors of vapor shield process and the typical features of bonds are clarified.a) Liquid composed by 15%-ethanol solution in water is good for vapor shield.b) Compounds both at bonds and expelled metal obtained under vapor shield are of eutectic of Ag and Cu.c) Vapor shield can raise the bond strength of 28% comparing with the one in air atmosphere.3) V.S.P.B process for high precision and high quality of bonds consists of the suitable vapor shielding condition and the optimum resistance heating conditions