Interface reaction between copper and molten tin–lead solders

The formation and growth of Cu–Sn intermetallic film at the interface between molten Sn–Pb solders and Cu were studied at different temperature and exposure times. The η-phase (Cu₆Sn₅) was observed to form at all conditions except at the lowest Sn level of 27 wt% and at the two highest temperatures of 290 and 310°C. The ε-phase (Cu₃Sn) was then obtained. At high Sn contents and short times, a cellular film with a rugged interface was obtained which evolved into a compact film with a scalloped interface as the Sn content decreased and exposure time increased. The ε-phase film always formed with a relatively planar interface. The intermetallic grains showed preferred crystallographic orientations. Thickness measurements showed that the net growth rate depends not only on diffusion through the film but also on the film dissolution. Precipitation of the η-phase whiskers was detected during cooling, particularly when the temperature was significantly high.     

Influence of base material properties on copper and aluminium–copper explosive welds

The influence of base material properties on the interfacial phenomena in copper and aluminium–copper explosive welds was studied. Two explosive mixtures with different detonation velocities were tested. Sound aluminium–copper joints with effective bonding were achieved by using an explosive mixture with a lower detonation velocity. High energy explosives led to extensive interfacial melting, preventing the production of consistent dissimilar welds. Unlike to the similar copper joints, the aluminium–copper welds presented very asymmetrical interfacial waves, rich in intermetallic phases and displaying a curled morphology. The interaction of the materials in dissimilar welding was found to be completely different depending on the positioning of each alloy in the joint, i.e. positioned as the flyer or as the baseplate.     

Simulation of aging process of lead frame copper alloy by an artificial neural network

1　INTRODUCTIONThefunctionsofleadframeinelectronicpackingareprovidingchannelsforelectronicsignalsbetweendevicesandcircuits ,andfixingdevicesoncircuitboards.Leadframealloysarerequiredtohavehighstrengthandgoodformabilityaswellashighelectri calandthermalconductivity .Cu basealloysarethemostpopularleadframealloysandareusedinplasticpackagingapplicationduetotheirhighthermalandelectricalconductivityaswellashighstrength[13] .Theaginghardening processinfabricationofleadframecopperalloymakesitpossi…     

Stress–temperature behavior of unpassivated thin copper films

The stress–temperature behavior of unpassivated thin (0.6–1.0 μm) copper films on silicon substrates with Si₃N₄ diffusion barriers was examined between room temperature and 600°C. Stresses were measured using a substrate curvature method and simulated using standard strain-rate equations which describe creep deformation. Simulations based on the mechanisms and data for bulk Cu could not reproduce the measured thin film data. Both the values which enter the rate equations and the rate equations themselves were modified in an attempt to obtain optimum correspondence between experiment and simulation. The best agreement was found when grain-boundary diffusional creep was neglected. The behavior could be simulated over a wide range using the rate equation for power-law creep with a stress exponent of 7 (determined from relaxation experiments), a thickness-dependent activation energy, and the temperature-dependent dislocation density (determined from X-ray peak widths). Mechanistic implications and the principal limitations of such a simulation approach are discussed.     

Anisotropic phenomena at interfaces in bismuth–saturated copper

Anisotropic Bi segregation, at surfaces of a Cu polycrystal saturated with Bi at 1223 K, changes the Cu equilibrium shape from a faceted spheroid displaying all orientations to an almost polyhedral shape with missing orientations. Surface cleaning, followed by annealing at ∼573 K, leads to Bi readsorption from some grain boundary sources.     

Lubricating behavior in chemical–mechanical polishing of copper

In this work, we simulated the Cu-chemical–mechanical polishing (Cu-CMP) using a laboratory model system. By comparing with the classic lubrication study, a “Stribeck Curve” for CMP was generated. Results indicated that the hydrodynamic lubrication regime was never reached. Based on these results, we propose a contact-polishing mode for CMP.     

Metal–metal bonding process using copper oxide nanoparticles

Abstract

This work performs metal–metal bonding using CuO nanoparticles prepared with salt base reaction in aqueous solution. A colloid solution of CuO nanoparticles was prepared by mixing Cu(NO₃)₂ aqueous solution and NaOH aqueous solution. Submicrometre sized leaf-like aggregates composed of CuO nanoparticles were produced at a Na/Cu ratio of 1·7 and at 20°C, though Cu₂(OH)₃NO₃ was also obtained. An aging process, which is a process composed of preparation of the particles at 20°C and then aging them at 80°C, provided transformation from Cu₂(OH)₃NO₃ to CuO with no damage of the leaf structure. The shear strength, which was required for separating discs bonded using the particles as a filler at 400°C in H₂ gas, was 32·5 MPa at the maximum for the particles prepared at the Na/Cu ratio of 1·7 with the aging process. These results indicated that the formation of leaf-like aggregates of CuO particles with high purity led to efficient metal–metal bonding.     

Physicochemical and environmental properties of arsenic sulfide sludge from copper and lead−zinc smelter

Physicochemical properties of arsenic sulfide sludge (ASS) from copper smelter (ASS-I) and lead−zinc smelter (ASS-II) were examined by XRD, Raman spectroscopy, SEM−EDS, TG−DTA, XPS and chemical phase analysis method. The toxicity characteristic leaching procedure (TCLP), Chinese standard leaching tests (CSLT), three-stage sequential extraction procedure (BCR) and batch leaching experiments (BLE) were used to investigate the environmental stability. The ASSs from different smelters had obviously different physicochemical and environmental properties. The phase composition and micrograph analysis indicate that ASS-I mainly consists of super refined flocculent particles including amorphous arsenic sulfide adhered with amorphous sulfur and that ASS-II mainly consists of amorphous arsenic sulfide. The valence state of arsenic in both sludges is trivalent, but the valence composition of sulfur is quite different. The ASSs have thermal instability properties. The results of TCLP and CSLT indicate that the concentrations of As and Pd in the leaching solution exceed the standard limits. More than 5% and 90% of arsenic are in the form of acid soluble and oxidizable fractions, respectively, which explains the high arsenic leaching toxicity and environmental activity of ASS. This research provides comprehensive information for the disposal of ASS from copper and lead−zinc smelter.     

Electrodeposition of copper–tin alloys using deep eutectic solvents

While alloy deposition is a frequently studied topic analysis of the alloy phases formed is a complex and often destructive process. In the current study the complex copper–tin alloy system has been studied in deep eutectic solvents using a variety of electrochemical and surface analysis techniques to determine the mechanism of alloy deposition and composition of deposits. The use of electrochemical quartz crystal microbalance is shown to enable real-time monitoring of alloy composition and the latter is shown to be very dependent upon the concentration of ions in solution. For this system X-ray diffraction was also used to study the phase behaviour of the deposits as a function of solution composition and current density. Finally it was shown for the first time that brighteners used for copper deposition in aqueous solutions also work in ionic liquids.     

Sustainable copper extraction from mixed chalcopyrite–chalcocite using biomass

This paper elaborated on the sustainability of the copper extraction process. In fact, an alternative copper extraction route from mixed sulphide ores, chalcopyrite and chalcocite using mesophilic biomass consortium at 33.3 °C and ferric leaching process were attempted. Bioleaching experiments were settled with a fraction size of −75+53 µm. Bacteria were used as the catalyst. A copper yield of 65.50% was obtained. On the other hand, in ferric leaching process, with a fraction size of −53+38 µm, when the temperature was increased to 70 °C, the copper leaching rate increased to 78.52%. Thus, comparatively, the mesophilic bioleaching process showed a more obvious advantage in copper extraction than leaching process with a high temperature. However, it has been resolved from the characterization performed using SEM−EDS, FTIR and XRD observations coupled with different thermodynamic approaches that, the indirect mechanism is the main leaching mechanism, with three transitory mechanisms (polysulphide, thiosulphate and elemental sulphur mechanisms) for the mixed chalcopyrite−chalcocite ore. Meanwhile, the speciation turns into Cu₂S−CuS−Cu₅FeS₄−Cu₂S before turning into CuSO₄. While ferrous oxidation and the formation of ferric sulphate occur, and there is a formation of strong acid as bacteria digest sulphide minerals into copper sulphate at low temperature, which is why this copper production scenario requires a redox potential more than 550 mV at room temperature for high copper leaching rate.     

Deformation induced phase rearrangement in near eutectic tin–lead alloy

Deformation induced microstructural changes in the near eutectic tin (Sn)–lead (Pb) alloy are investigated. This study is motivated by the thermomechanical reliability of solder materials used in microelectronic packages, with the primary objective of gaining fundamental understandings of pure mechanical effects without the influence of diffusion related phenomena. Bulk specimens, having an initial microstructure of equiaxed Pb-rich particles within the Sn-rich matrix, are subject to relatively fast deformations of tension, compression and bending. Microhardness indentation is employed to characterize the sliding behavior along grain boundaries and interphase boundaries. It is observed that phase rearrangement induced by boundary sliding commences when the overall strain is still relatively small, giving rise to the gradual development of aligned regions free of the Pb-rich phase. These Pb-free zones, or equivalently Sn grain clusters, are aligned in the direction of macroscopic normal stresses. A micromechanical model, supported by further experimental evidences, is proposed to explain the observed microstructural changes. This study also illustrates the possibility of mechanically induced phase coarsening in Sn–Pb solder alloys.     

Volatility–volume relationship of Chinese copper and aluminum futures market

Following Bessembinder and Seguins, trading volume is separated into expected and unexpected components. Meanwhile, realized volatility is divided into continuous and discontinuous jump components. We make the empirical research to investigate the relationship between trading volume components and various realized volatility using 1 min high frequency data of Shanghai copper and aluminum futures. Moreover, the asymmetry of volatility–volume relationship is investigated. The results show that there is strong positive correlation between volatility and trading volume when realized volatility and its continuous component are considered. The relationship between trading volume and discontinuous jump component is ambiguous. The expected and unexpected trading volumes have positive influence on volatility. Furthermore, the unexpected trading volume, which is caused by arrival of new information, has a larger influence on price volatility. The findings also show that an asymmetric volatility–volume relationship indeed exists, which can be interpreted by the fact that trading volume has more explanatory power in positive realized semi-variance than negative realized semi-variance. The influence of positive trading volume shock on volatility is larger than that of negative trading volume shock, which reflects strong arbitrage in Chinese copper and aluminum futures markets.     

Stress corrosion in copper–nickel alloys: influence of ammonia

Abstract

The test results from an earlier investigation by the author on the mechanical behaviour of a low nickel nickel-copper alloy exposed to a solution of 3·5%NaCl + 10%MgCl₂ with and without ammonia indicated that the presence of 1% ammonia alters the failure mode and affects the load bearing capacity of the material. In the present investigation, further tests have been conducted on the same alloy to study its mechanical/corrosion behaviour on exposure to an aqueous solution of ammonia in comparison with exposure to a similar solution of ammonia containing 3·5%NaCl + 10%MgCl₂. A constant displacement rate of 9·6 × 10^-3 μ m s^-1 was used and the concentration of ammonia was maintained at 5%. On exposure to the 5% aqueous ammonia solution, the mechanical properties of the alloy were degraded significantly and the material exhibited a brittle stress corrosion type of failure. However, on exposure to 5% ammonia in the presence of 3·5%NaCl + 10%MgCl₂, there was less change in failure mode relative to that in air and a significant improvement in the mechanical properties of the material compared with those in aqueous ammonia. This indicates that the presence of MgCl₂ and/or NaCl can be beneficial when low nickel copper alloys are exposed to ammonia. This paper presents the experimental results and observations from the recent tests, and discusses the relative roles of ammonia and NaCl/MgCl₂ in determining the mechanical properties and modes of failure in a low nickel content copper-nickel alloy.     

Cold metal transfer welding–brazing of magnesium to pure copper

Magnesium alloy AZ31B and pure copper T2 were lapped and joined by cold metal transfer (CMT) welding–brazing method by AZ61A magnesium alloy wire with a 1·2 mm diameter. Results indicated that a satisfied Mg/Cu CMT welding–brazing joint was obtained in the stable welding processes with no spatter. The joint was composed of Mg–Mg welding joint formed between the Mg weld metal and the Mg base metal, and Mg–Cu brazing joint formed between the Mg weld metal and the local molten Cu base metal. The microstructure and the intermetallic compound (IMC) distribution were inspected and analysed in detail. The interfacial reaction layers of the brazing joint consisted of Mg₂Cu, Al₆Cu₄Mg₅, MgCu₂ and Mg₁₇Al₁₂ IMCs. The tensile shear strength of the Mg/Cu CMT welding–brazing joint could reach 172·5 N mm^?1. In addition, two different fracture modes were observed: at the fusion zone and at the brazing interface.     

Electrodeposition of lead–tin alloy from methanesulphonate bath containing organic surfactants

The article discusses the process of electrodeposition of lead-tin alloy (tin content in the deposit up to 10–12 wt %) from methanesulfonate electrolytes. A composition was proposed of organic additives to the electrolyte providing attainment of high quality microcrystalline coatings with the alloy of predetermined composition at relatively low content of Sn²⁺ in the solution. It has been shown that the tin content in the deposit increases at an increase in current density and decrease in the electrolyte temperature. For production of anti-frictional Pb-Sn alloys with the tin content of about 10% the electrolysis should be performed at a current density of about 4 A/dm² and the temperature not exceeding 25°C. The effect of a decrease in the discharge rate of the Sn²⁺ ions into the alloy at deposition from electrolyte without organic additives was discovered, that is stipulated by deceleration of crystallization stage of tin on foreign substrate. When the alloy is deposited from electrolyte containing a composition of organic additives, the effect of super-polarization of discharge of Sn²⁺ ions is reduced.     

Hemocompatibility and anti-endothelialization of copper–titanium coating for vena cava filters

The deposition of coatings or films is an acceptable surface modification method for implanted cardiovascular devices. Cu/Ti coatings of various ratios of Cu and Ti atoms were prepared using the vacuum arc plasma deposition method. The phase composition and concentration of elements were investigated via X-ray diffraction and X-photoelectron energy spectrum, respectively. The hemolysis ratio, lactate dehydrogenase (LDH), clotting time, and platelet adhesion of different coatings were characterized to evaluate blood compatibility. The growth of endothelial cells on various coatings was also investigated by observing the morphous and amount of human umbilical vein endothelial cells (HUVECs) under a scanning electron microscope. The Cu/Ti coatings present good blood compatibility. However, with increasing quality ratio of Cu/Ti, the hemolysis ratio increases, and some platelets begin to break slightly. The activated partial thromboplastin times (APTTs) of various coatings are similar to the TiNi substrate, the coatings can also inhibit platelet adhesion, and the amount of platelets of TiNi is more than the Cu/Ti coating from the LDH assay. The adhesion of HUVECs illustrates that endothelial cell adhesion and proliferation are significantly inhibited with > 10 wt.% Cu concentration. A Cu/Ti coating with good compatibility and anti-endothelialization has potential applications for special cardiovascular devices.     

Anticorrosion properties of textured substrates made of copper–nickel-based ternary alloys

The tendency of some copper–nickel-based ternary alloys with additions of 3d transition metals, such as Cr, V, and Fe, to oxidation has been studied. The resistance to the oxidation was evaluated by the thermogravimetry method. It has been established that the strengthened textured tapes made of the Cu–40% Ni–1.2% Cr and Cu–40% Ni–1.4% Fe alloys have significantly better anticorrosive properties at 700°C than tapes made of pure copper and other investigated alloys, and can be used as substrates for epitaxial deposition of buffer and superconducting layers at elevated temperatures.     

Electrochemical behaviour of copper–silver alloys in sodium carbonate aqueous solution

Abstract

The electrochemical behaviour of Cu–20 wt-%Ag and Cu–80 wt-%Ag alloys was studied in aerated Na₂ CO₃ solutions using cyclic voltammetry, potentiodynamic anodic polarisation, and current transient techniques. The microstructure of the compounds formed on the surface of the alloy during the anodic potential sweep was obtained using XRD analysis. The dissolution behaviour of either of the two constituents from the alloys resembles that of the pure state. The galvanic coupling effect enhances the dissolution of the less noble metal, copper, on alloying with silver. The anodic sweep potential exhibited seven anodic peaks A₁ , A₂ , A₃ , A₄ , A₅ , A₆ , and A₇ prior to the oxygen evolution reaction. These peaks are assigned to the formation of Cu₂O, Cu(OH)₂ , CuO, Ag₂O, Ag₂ CO₃ , and Ag₂O₂ respectively. Potentiostatic current/time transients showed that the formation of Cu₂O, CuO, Ag₂O, and Ag₂ CO₃ layers involves a nucleation and growth mechanism under diffusion control.     

The structure of molten zones in explosion welding (aluminium–tantalum,copper–titanium)

Investigations were carried out into the relief of the flat- and wave-shaped interfaces for explosion-welded aluminium–tantalum and copper–titanium welded joints. For these systems, characterized by a relatively high mutual solubility of the initial elements, the results show a typical set of the structures of the interfaces replacing each other with the intensification of the welding conditions. The unusual shape of the projections on the flat interfaces was found. They are similar to splashes, which form on the surface of the liquid, although they are solid-phase splashes. The vortex structure of the zones of local melting was also detected. The unusual shape of the waves was found: in the presence of mutual solubility they consist of the specially ordered set of projections. It may be assumed that this is caused by the formation of intermetallic compounds on the surface of the projections. The processes of self-organization, ensuring the evolution of the relief of the interface in the intensification of the welding conditions, have been investigated. The role of intermetallic compounds in these self-organization processes is clarified.