Scaling effect of interfacial reaction on intermetallic compound formation in Sn/Cu pillar down to 1 μm diameter. (15th September 2016)

• Record Type: Journal Article
• Authors: Liu, Yingxia; Chu, Ying-Ching; Tu, K.N.
• Is Part Of: Acta materialia. Volume 117(2016)
• Page Start: 146
• Page End: 152
• Publication Date: 2016-09-15
• Subjects: Solder pillar -- Intermetallic compounds -- Diffusion mechanism -- Surface diffusion; Materials -- Periodicals; Materials science -- Periodicals; Materials -- Mechanical properties -- Periodicals; Metallurgy -- Periodicals; Chemistry, Inorganic -- Periodicals; 620.112
• DOI: 10.1016/j.actamat.2016.07.004
• Languages: English
• ISSNs: 1359-6454

Abstract

Abstract: Different diameter Sn/Cu pillars varying from 30 to 1 μm have been made by focus ion beam, and the solid state reaction to form Cu6 Sn5 in these pillars has been studied. An increased Cu-Sn reaction rate to form Cu6 Sn5 was observed as the pillar diameter decrease from 20 to 1 μm when annealed at 185 and 195 °C. With the shrinking of pillar size, surface diffusion becomes important as compared to grain boundary and lattice diffusion in the Cu-Sn interfacial reaction. Also, surface diffusion induced Kirkendall voids was observed to locate at the peripheral area just above Cu of the Cu-Sn pillars. A simple kinetic model of surface diffusion controlled intermetallic compound growth of Cu6 Sn5 is proposed for pillars with diameter below 5 μm. What is essential in the model is that we assume a rapid interstitial diffusion of Cu in Sn, and we are able to calculated surface diffusivity of Cu on Cu6 Sn5 . At 185 °C, the surface diffusivity is about 3.1 × 10 −7 cm 2 /s and the activation energy is about 0.2 ± 0.1 eV/atom. Graphical abstract: