scispace - formally typeset
Search or ask a question
Author

Katsuya Watanabe

Bio: Katsuya Watanabe is an academic researcher from Hokkaido University. The author has contributed to research in topics: Alloy & Phase (matter). The author has an hindex of 6, co-authored 14 publications receiving 223 citations.


Cited by
More filters
Journal ArticleDOI
TL;DR: In this article, copper has been cold sprayed onto aluminium alloy substrates, the surfaces of which had been prepared in a variety of ways, including grit-blasting, and the bond strength was assessed via a novel intermetallic growth method along with adhesive pull-off testing.
Abstract: The mechanism of bonding in cold spraying is still a matter of some debate. In this work, copper has been cold sprayed onto aluminium alloy substrates, the surfaces of which had been prepared in a variety of ways. The coating-substrate bonding was assessed via a novel intermetallic growth method along with adhesive pull-off testing, and related to the substrate preparation method. The bond strength has been rationalized in terms of a modified composite strength model, with two operative bonding mechanisms, namely (i) metallurgical bonding and (ii) mechanical interlocking of substrate material into the coating. In most cases, mechanical interlocking is able to account for a large proportion of the total bond strength, with metallurgical bonding only contributing significantly when the substrate had been polished and annealed prior to spraying. In addition, grit-blasting has been shown to significantly reduce the bond strength compared to other substrate preparation methods.

292 citations

Journal ArticleDOI
TL;DR: High temperature aging at 250 °C for up to 196 h has been used to accelerate the aging process of the bonds and the results of micro-XRD analysis confirmed that Cu 9 Al 4 , and CuAl 2 were the main IMC products, while a third phase is found which possibly is CuAl.

222 citations

Journal ArticleDOI
TL;DR: In this paper, the formation of Cu/Al IMC was observed and the activation energy was obtained from an Arrhenius plot (ln (growth rate) versus 1/T).
Abstract: Copper wire bonding is an alternative interconnection technology that serves as a viable, and cost saving alternative to gold wire bonding. Its excellent mechanical and electrical characteristics attract the high-speed, power management devices and fine-pitch applications. Copper wire bonding can be a potentially alternative interconnection technology along with flip chip interconnection. However, the growth of Cu/Al intermetallic compound (IMC) at the copper wire and aluminum interface can induce a mechanical failure and increase a potential contact resistance. In this study, the copper wire bonded chip samples were annealed at the temperature range from 150/spl deg/C to 300/spl deg/C for 2 to 250 h, respectively. The formation of Cu/Al IMC was observed and the activation energy of Cu/Al IMC growth was obtained from an Arrhenius plot (ln (growth rate) versus 1/T). The obtained activation energy was 26Kcal/mol and the behavior of IMC growth was very sensitive to the annealing temperature. To investigate the effects of IMC formation on the copper wire bondability on Al pad, ball shear tests were performed on annealed samples. For as-bonded samples, ball shear strength ranged from 240-260gf, and ball shear strength changed as a function of annealing times. For annealed samples, fracture mode changed from adhesive failure at Cu/Al interface to IMC layer or Cu wire itself. The IMC growth and the diffusion rate of aluminum and copper were closely related to failure mode changes. Micro-XRD was performed on fractured pads and balls to identify the phases of IMC and their effects on the ball bonding strength. From XRD results, it was confirmed that the major IMC was /spl gamma/-Cu/sub 9/Al/sub 4/ and it provided a strong bondability.

201 citations