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Abstract The growth kinetics of the intermetallic compound layer formed between Sn-8Zn-3Bi solder and a bare Cu substrate by solid-state isothermal aging were examined at temperatures between 343 and 423 K for periods ranging from 0 to 100 days. A quantitative analysis was performed of the intermetallic compound layer thickness as a function of the aging time and aging temperature. For the identification of the intermetallic compounds, both Energy Dispersive X-ray and X-Ray Diffraction were employed. [ABSTRACT FROM AUTHOR]

The morphological and compositional evolutions of intermetallic compounds (IMCs) formed at three Pb-free solder/electroless Ni-P interface were investigated with respect to the solder compositions and reflow times. The three Pb-free solder alloys were Sn3.5Ag, Sn3.5Ag0.75Cu, and Sn3Ag6Bi2In (in wt.%). After reflow reaction, three distinctive layers, Ni3Sn4 (or Ni-Cu-Sn for Sn3.5Ag0.75Cu solder), NiSnP, and Ni3P, were formed on the electroless Ni-P layer in all the solder alloys. For the Sn3.5Ag0.75Cu solder, with increasing reflow time, the interfacial intermetallics switched from (Cu,Ni)6Sn5 to (Cu,Ni)6Sn5 + (Ni,Cu)3Sn4, and then to (Ni,Cu)3Sn4 IMCs. The degree of IMC spalling for the Sn3.5Ag0.75Cu solder joint was more than that of other solders. In the cases of the Sn3.5Ag and Sn3Ag6Bi2In solder joints, the growth rate of the Ni3P layer was similar because these two type solder joints had a similar interfacial reaction. On the other hand, for the Sn3.5Ag0.75Cu solder, the thickness of the Ni3P and Ni-Sn-P layers depended on the degree of IMC spalling. Also, the shear strength showed various characteristics depending on the solder alloys and reflow times. The fractures mainly occurred at the interfaces of Ni3Sn4/Ni-Sn-P and solder/Ni3Sn4. [ABSTRACT FROM AUTHOR]

The interracial reactions between two Sn-Cu (Sn-0.7Cu and Sn-3Cu, wt.%) ball-grid-array (BGA) solders and the Au/Ni/Cu substrate by solid-state isothermal aging were examined at temperatures between 70°C and 170°C for 0 to 100 days. For the Sn-0.7Cu solder, a (Cu,Ni)6Sn5 layer was observed in the samples aged at 70-150°C. After isothermal aging at 170°C for 50 days, the solder/Ni interface exhibited a duplex structure of (Cu,Ni)6Sn5 and (Ni,Cu)3Sn4. For the Sn-3Cu solder, only the (Cu,Ni)6Sn5 layer was formed in all aged samples. Compared to these two Sn-Cu solders, the Cu content in the (Cu,Ni)6Sn5 layer formed at the interface increased with the Cu concentration in the Sn-xCu solders. And, the shear strength was measured to evaluate the effect of the interracial reactions on the mechanical reliability as a function of aging conditions. The shear strength significantly decreased after aging for 1 day and then remained nearly unchanged by further prolonged aging. In all the samples, the fracture always occurred in the bulk solder. Also, we studied the electrical property of Cu/Sn-3Cu/Cu BGA packages with the number of reflows. The electrical resistivity increased with the number of reflows because of an increase of intermetallic compound (IMC) thickness. [ABSTRACT FROM AUTHOR]

The growth kinetics of intermetallic compound layers formed between eutectic Sn–3.5Ag BGA (ball grid array) solder and (Cu, immersion Au/electroless Ni–P/Cu) substrate by solid-state isothermal aging were examined at temperatures between 343 and 443 K for 0–100 days. In the solder joints between the Sn–Ag eutectic solder ball and Cu pads, the intermetallic compound layer was composed of two phases: Cu6Sn5 (η-phase) adjacent to the solder and Cu3Sn (ε-phase) adjacent to the copper. The layer of intermetallic on the immersion Au/electroless Ni–P/Cu substrate was composed of Ni3Sn4. As a whole, because the values of the time exponent (n) are approximately 0.5, the layer growth of the intermetallic compound was mainly controlled by a diffusion-controlled mechanism over the temperature range studied. The growth rate of Ni3Sn4 intermetallic compound was slower than that of the total Cu–Sn(Cu6Sn5+Cn3Sn). The apparent activation energy for growth of total Cu–Sn(Cu6Sn5+Cu3Sn) and Ni3Sn4 intermetallic compound were 64.82 and 72.54 kJ mol−1, respectively. [ABSTRACT FROM AUTHOR]

Characterizes the thermal conductivity and mechanical properties of sheath alloy materials for Bi-2223 superconductor tapes. Thermal diffusivity of sheath alloy materials for Bi-2223 superconductors; Variation of yield strength, ultimate tensile strength, elongation, and grain size for silver and silver alloy.

Reactive surface-exposed anatase TiO2 (a-TiO2) is highly desirable for applications requiring superior photocatalytic activity. In order to obtain a favorable surface, morphology control of the a-TiO2 using capping agents has been widely investigated. Herein, we systematically study the effects of different F sources (HF, TiF4, and NH4F) as the capping agent on the morphology control and photocatalytic activities of a-TiO2 in a hydrothermal process. When either HF or TiF4 was added, large truncated bipyramids formed with the photocatalytically active {001} facet, whereas the NH4F was not effective for facet control, yielding nanospheres similar to the pure a-TiO2. The morphology changes were related to the decomposition behaviors of the F sources in the solvent material: HF and TiF4 decomposed and supplied F− ions before a-TiO2 nucleation, which changed the nucleation rate and growth direction, leading to the resultant a-TiO2 morphology. On the other hand, NH4F supplied F− ions after a-TiO2 nucleation and could not change the growth behavior. In terms of the photocatalytic effect, the HF- and TiF4-treated a-TiO2 effectively decomposed ∼90% and ∼80% of methylene blue, respectively, in 1 h, while ∼60% was decomposed for the NH4F-treated a-TiO2. Note that pure a-TiO2 photocatalytically decomposed only ∼10% of methylene blue over the same time. These results pave the way to precise control of the facet of TiO2 through using different capping agents. [ABSTRACT FROM AUTHOR]

A novel method of carbonaceous coating on the surface of copper particles was developed through a chemical vapor deposition (CVD) process to prevent the oxidation of copper nanoparticles (CNPs). The types of poly(vinyl pyrrolidone) (PVP) used were K-12 (MW 3,500) and K-30 (MW 45,000). The amounts of PVP used ranged from 10 to 50 wt %. Additionally, processing temperatures of 900 and 875 °C were tested and compared. The optimum CVD process conditions for the carbonaceous coating were as follows: 875 °C processing temperature, 50 wt % K12 PVP solution, and gas conditions of . The resistivity change in the fabricated copper pattern was confirmed that the initial resistivity value of the ink with a mixing ratio of carbonaceous-coated CNPs to 1-octanethiol-coated CNPs of (w/w) maintained its initial resistivity value of 2.93 × 10−7 Ω·m for more than 210 days. [ABSTRACT FROM AUTHOR]

Analytical electron microscopy (AEM) was used to examine the initial interfacial reaction layers between a eutectic Sn-3.5Ag solder and an electroless nickel-immersion gold-plated (ENIG) Cu substrate during reflow at 255 °C for 1 s. AEM confirmed that a thick upper (Au,Ni)Sn2 layer and a thin Ni3Sn4 layer had formed through the reaction between the solder and ENIG. The amorphous electroless Ni(P) plated layer transformed into two P-rich Ni layers. One is a crystallized P-rich Ni layer, and the other is an intermediate state P-rich Ni layer before the crystallization. The crystallized P-rich layer consisted of Ni2P and Ni12P5. A thin Ni2P layer had formed underneath the Ni3Sn4 layer and is believed to be a predecessor of the Ni2SnP ternary phase. A Ni12P5 phase was observed beneath the Ni2P thin layer. In addition, nanocrystalline Ni was found to coexist with the amorphous Ni(P) phase in the intermediate state P-rich Ni layer. [ABSTRACT FROM AUTHOR]

The interfacial reactions and ball shear properties of an In-48wt%Sn solder joint with an electroplated Au/Ni ball grid array substrate were investigated with increasing numbers of reflows using scanning electron microscopy, transmission electron microscopy, energy dispersive x-ray spectrometry, inductively coupled plasma-atomic emission spectroscopy, x-ray diffractometry, and bonding testing. After one reflow, two different intermetallic compound (IMC) layers, AuIn and AuIn2, were formed at the solder-substrate interface. The AuIn was completely transformed into the AuIn2 after three reflows. The AuIn2 IMC layer broke off, and a thin continuous Ni3(SnxIn1-x)4 IMC layer was formed between the molten solder and the exposed Ni substrate after four reflows. After 10 reflows, the AuIn2 IMC layer completely spalled off the substrate and the Ni3(SnxIn1-x)4 IMC layer was dissolved into the molten solder. These interfacial reactions greatly affected the shear properties of the solder joint. [ABSTRACT FROM AUTHOR]

The microstructural evolution and interfacial reactions of fluxless-bonded, Au-20wt%Sn/Cu solder joint were investigated during reflow and aging. After reflowing at 310 °C, only one thick and irregularly shaped ?(Cu) layer was formed at the interface. After the prolonged reflow reaction, the AuCu layer was formed between the ?(Cu) layer and the Cu substrate. During reflowing, the Cu substrate reacted primarily with the ?-phase in the solder matrix. The solid-state interfacial reaction was much faster at 250 °C than at 150 °C. After aging at 250 °C for 100 h, thick ?(Cu), AuCu and AuCu3 IMC layers were formed at the interface. The formation of the AuCu3 intermetallic compound (IMC) was caused by Cu enrichment at the AuCu/Cu layer interface. After aging for 500 h, cracks were observed inside the interfacial AuCu layer. The study results clearly demonstrate the need for an alternative surface finish on Cu, to ensure the high temperature reliability of the Au-20Sn/Cu solder joint. [ABSTRACT FROM AUTHOR]