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The Kirkendall effect is the motion of the boundary layer between two metals that occurs as a consequence of the difference in diffusion rates of the metal atoms. The effect can be observed for example by placing insoluble markers at the interface between a pure metal and an alloy containing that metal, and heating to a temperature where atomic diffusion is possible; the boundary will move relative to the markers. This process was named after Ernest Kirkendall (1914–2005) assistant professor of chemical engineering at Wayne State University from 1941 to 1946. He discovered the effect in 1947. The Kirkendall effect has important practical consequences. One of these is the prevention or suppression of voids formed at the boundary interface in various kinds of alloy to metal bonding. These are referred to as Kirkendall voids. In 1972, C.W. Horsting of the RCA Corporation published a paper which reported test results on the reliability of semiconductor devices in which the connections were made using aluminium wires bonded ultrasonically to gold plated posts. His paper demonstrated the importance of the Kirkendall effect in wire bonding technology, but also showed the significant contribution of any impurities present to the rate at which precipitation occurred at the wire bonds. Two of the important contaminants that have this effect, known as Horsting effect (Horsting voids) are fluorine and chlorine. Both Kirkendall voids and Horsting voids are known causes of wire bond fractures, though historically this cause is often confused with the purple colored appearance of one of the five different gold-aluminium intermetallics, commonly referred to as "purple plague" and less often "white plague".〔(【引用サイトリンク】url=https://nepp.nasa.gov/index.cfm/20987 )〕 ==History== The Kirkendall effect was discovered by Ernest Kirkendall and Alice Smigelskas in 1947, in the course of Kirkendall’s ongoing research into diffusion in brass. The paper in which he discovered the famous effect was the third in his series of papers on brass diffusion, the first being his thesis. His second paper revealed that zinc diffused more quickly than copper in alpha-brass, which led to the research producing his revolutionary theory. Until this point, substitutional and ring methods were the dominant ideas for diffusional motion. Kirkendall’s experiment produced evidence of a vacancy diffusion mechanism, which is the accepted mechanism to this day. At the time it was submitted, the paper and Kirkendall’s ideas were rejected from publication by Robert Franklin Mehl, director of the Metals Research Laboratory at Carnegie Institute of Technology. Mehl refused to accept Kirkendall’s evidence of this new diffusion mechanism, and denied publication for over six months, only relenting after a conference was held and several other researchers confirmed Kirkendall’s results.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Kirkendall effect」の詳細全文を読む スポンサード リンク
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