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The microvoids formation and morphology of intermetallic compounds formed at the Sn–9Zn/Cu interface with and without Ag addition have been investigated by scanning electron microscopy and energy dispersive spectrometry and pull-off test. The microvoids are formed at the Sn–9Zn/Cu interface after aging at 180°C for 100 h and at the Sn–9Zn–3.5 Ag/Cu interface after aging at the same temperature for 1000 h. The formation of the microvoids is inhibited by Ag addition. After aging at 180°C for 1000 h, the planar Cu6Sn5 and scallop-shaped Cu6Sn5 are observed at the Sn–9Zn/Cu and Sn–9Zn–3.5 Ag/Cu interfaces, respectively. The decomposition rate of the Cu5Zn8 and the growth rate of the Cu6Sn5 at 180°C at the Sn–9Zn/Cu interface are determined as 2.22 × 10−9 and 6.80 × 10−10 m s−1/2, respectively, and those at the Sn–9Zn–3.5Ag/Cu interface are determined as 8.61 × 10−10 and 5.40 × 10−9 m s−1/2, respectively. The adhesion strength of the Sn–9Zn–3.5 Ag/Cu interface increases from 5.76 ± 0.77 to 14.19 ± 0.75 MPa when aging time increases from 0 to 1000 h and shows a better solder joint reliability than the Sn–9Zn solder alloy. [Copyright &y& Elsevier]

The crystal growth, morphology and structure of the intermetallic compounds (IMCs) at the Sn–9Zn–xAg/Cu interface have been investigated. During isothermal aging, the local strain and crystallite size of the IMCs vary with aging time due to the growth and decomposition of the IMCs. The Kirkendall voids form at the Sn–9Zn/Cu interface after aging at 180°C for 250 h but are not observed at the Sn–9Zn–xAg/Cu interface at the same aging parameters. Ag is repelled from the monoclinic η′-Cu6Sn5 which transforms to the hexagonal η-Cu6Sn5 and reacts with Sn to promote the growth of the Ag3Sn. The diffusion coefficients of Sn in Cu6Sn5 are determined 5.76×10−10 and 2.82×10−10 cm2/s at 250°C when the Ag contents in the solders are 0.5 and 1.5 wt%, respectively. [Copyright &y& Elsevier]

The effect of Ag addition on the structures of the intermetallic compounds (IMCs) and the adhesion strength of the Sn–9Zn–xAg solder alloy/Cu interface has been investigated by X-ray diffraction, scanning electron microscopy, energy dispersive spectrometry, transmission electron microscopy and electron diffraction. The XRD patterns show that the η-Cu6Sn5, η′-Cu6Sn5 and Cu5Zn8 are found at the Sn–9Zn–xAg/Cu interface. The Ag3Sn formed at the interface when Ag addition is above 2.5 wt%. Monoclinic and hexagonal Cu6Sn5 intermetallic compounds (IMCs) are formed at the interface close to the solder alloy. A high-resolution lattice image also shows the same result and the bi-structural Cu6Sn5 grows as a twin-like crystallite along the boundaries. The adhesion strength has an opposite relationship to the crystallite size of the Cu6Sn5 layer. [Copyright &y& Elsevier]

The crystal growth of intermetallic compounds at the interface of Sn–9Zn–xAg/Cu (x=0, 0.5, 1.5, 2.5 and 3.5 wt%) lead-free solders has been investigated by optical microscope, X-ray diffractometer, scanning electron microscope, and energy dispersive spectrometer. The results show that the more Ag is added to the Sn–9Zn alloy, the more Ag–Zn compounds form in the solder matrix in which Zn reacts with Ag and hinders the diffusion of Ag. Ag dissolves in Cu6Sn5 and changes the lattice constant of Cu6Sn5 as formed in the liquid–solid reaction. After long-term aging, the dissolved Ag is repelled from Cu6Sn5 and forms Ag3Sn with Sn at the interface, but the crystallite size of Cu6Sn5 decreases from 301.2 to 189.5 nm when the Ag content increases from 0 to 3.5 wt%. [Copyright &y& Elsevier]

Abstract: The microstructures of double-clad Cr4+:YAG crystal fibers grown using a co-drawing laser-heated pedestal growth method were studied by high-resolution transmission electron microscopy and photoluminescence spectroscopy. The core is single-crystalline garnet elongated in [111] direction, whereas inner cladding a composite of Cr3+:γ-Al2O3 nanocrystals in Cr4+: silicate glass due to YAG/SiO2 inter-diffusion and a high crystal-field-stabilization energy of Cr3+ attained in close packed oxide. Cr4+ fluorescence intensity decreases and shifts to lower wavelength for the inner cladding in comparison with the core. [Copyright &y& Elsevier]