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Die Attachment Method on a Cu Finish by Pressure-Assisted Sinter Bonding in Air Using Cu Formate Paste

Jo Kyeong Hwan, Lee Jong-Hyun

Archives of Metallurgy and Materials

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2020

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Vol. 65, iss. 3

1057--1061

EN

A paste containing Cu(II) formate rods was prepared, and characteristics of sinter bonding at 250°C under a pressure of 10 MPa were investigated to accomplish a high-speed die attachment for wide-bandgap power chips on Cu finish in air. Synthesisn of the plate-type Cu formate particles from CuO was accomplished through a wet reaction for 180 min. Cu, formed in situ in the bondline by pyrolysis of the formate during heating for the attachment, was sufficiently active to lead high-speed sintering within a carbon dioxide-hydrogen atmosphere derived from the pyrolysis, and the oxide layer on the Cu finish was reduced by the hydrogen. As a result, sinter bonding for 10 min formed a robust bonding with a shear strength approaching 27 MPa.

2

Adaptive Differential Evolution with Elite Opposition-Based Learning and its Application to Training Artificial Neural Networks

Choi Tae Jong, Lee Jong-Hyun, Youn Hee Yong, Ahn Chang Wook

Fundamenta Informaticae

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2019

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Vol. 164, nr 2-3

227--242

EN

Differential Evolution (DE) algorithm is one of the popular evolutionary algorithms that is designed to find a global optimum on multi-dimensional continuous problems. In this paper, we propose a new variant of DE algorithm by combining a self-adaptive DE algorithm called dynNP-DE with Elite Opposition-Based Learning (EOBL) scheme. Since dynNP-DE algorithm uses a small number of population size in the later of the search process, the population diversity becomes low, and therefore premature convergence may occur. We have therefore extended an OBL scheme to dynNP-DE algorithm to overcome this shortcoming and improve the optimization performance. By combining EOBL scheme to dynNP-DE algorithm, the population diversity can be supplemented because not only the information of individuals but also their opposition information can be utilized. We measured the optimization performance of the proposed algorithm on CEC 2005 benchmark problems and breast cancer detection, which is a research field that has recently attracted a lot of attention. It was verified that the proposed algorithm could find better solutions than five state-of-the-art DE algorithms.

3

Characteristics of Die-Attach Method by Sinter Bonding Using Ag-40Cu Mechanically Alloyed Particles

Choi Woo Lim, Lee Jong-Hyun

Archives of Metallurgy and Materials

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2019

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Vol. 64, iss. 2

507--512

EN

Ag and Cu powders were mechanically alloyed using high-energy planetary milling to evaluate the sinter-bonding characteristics of a die-attach paste containing particles of these two representative conductive metals mixed at atomic scale. This resulted in the formation of completely alloyed Ag-40Cu particles of 9.5 μm average size after 3 h. The alloyed particles exhibited antioxidation properties during heating to 225°C in air; the combination of high pressure and long bonding time at 225°C enhanced the shear strength of the chip bonded using the particles. Consequently, the chips sinter-bonded at 225°C and 10 MPa for 10 min exhibited a sufficient strength of 15.3 MPa. However, an increase in bonding temperature to 250°C was detrimental to the strength, due to excessive oxidation of the alloyed particles. The mechanically alloyed phase in the particle began to decompose into nanoscale Ag and Cu phases above a bonding temperature of 225°C during heating.