Interfacial reactions between Ni substrate and the component Bi in solders

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Title:	Interfacial reactions between Ni substrate and the component Bi in solders
Authors:	Lee,MS;Liu,CM;Kao,CR
Contributors:	化學工程與材料工程學系
Keywords:	DIFFUSION
Date:	1999
Issue Date:	2010-06-29 17:28:54 (UTC+8)
Publisher:	中央大學
Abstract:	The reactions between Ni and liquid Bi at 300, 360, 420, and 480 degrees C were studied. Bismuth is an important element in many electronic solders, while Ni is used in many printed circuit board surface finishes. It was found that the only intermetallic compound formed was NiBi3. The other intermetallic compound NiBi, which is thermodynamically stable at these temperatures, did not form. Reaction at 300 degrees C produced a thick reaction zone, which is a two-phase mixture of NiBi3 needles dispersed in Bi matrix. The thickness of the reaction zone increase;i rapidly with reaction time, reaching 400 mu m after 360 min. Reactions at 360 and 420 degrees C produced very thin reaction zones, and the major interaction was the dissolution of Ni into liquid Bi. Reaction at 480 degrees C produced extremely thin reaction zone, and the dissolution of Ni into liquid Bi was very fast and was the major interaction. It is proposed that the formation of the reaction zone is controlled by two factors: the solubility limit and the diffusivity of Ni in Liquid Bi. Small diffusivity and small solubility limit, i.e., lower temperature, tend to favor the formation of a thick reaction zone. In addition to the NiBi3 formed within the reaction zone, NiBi, also formed outside the reaction zone in the form of long needles with hexagonal cross section. The dissolution rate of Ni into Bi is comparable to that of Ni into Sn at the same temperature, and is much slower than the dissolution rates for Au, Ag, Cu, and Pd into Sn.
Relation:	JOURNAL OF ELECTRONIC MATERIALS
Appears in Collections:	[National Central University Department of Chemical & Materials Engineering] journal & Dissertation

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