Preparation and characterization of nanoporous Cu6Sn5/Cu composite by chemical dealloying of Al–Cu–Sn ternary alloy

In this article, a new ternary Al–Cu–Sn alloy system has been exploited to fabricate nanoporous Cu₆Sn₅/Cu composite slices through chemical dealloying in a 20 wt% NaOH solution at an elevated temperature. The microstructure of the sliced nanoporous Cu₆Sn₅/Cu composite was characterized using x-ray diffraction, scanning electron microscopy, energy dispersive X-ray analysis, and transmission electron microscopy. The experimental results show that multi-phase precursor alloy comprises α-Al, Sn, and θ-Al₂Cu phases. The new phase Cu₆Sn₅ emerges through dealloying, and the as-dealloyed samples have three-dimensional (3D) structure composed of large-sized channels (hundreds of nanometers) and small-sized channels (tens of nanometers). Both the large- and small-sized pores are 3D, open and bicontinuous. The synergetic dealloying of α-Al and θ-Al₂Cu in the three-phase Al–Cu–Sn alloy and fast surface diffusion of Cu atoms and Sn atoms result in the formation of Cu₆Sn₅/Cu composite with bimodal channel size distributions. In addition, the dealloying duration plays a significant role in the formation of Cu₆Sn₅ and the length scales of the small-sized ligament/channels at a settled temperature.     

Solid–liquid interdiffusion bonding of Cu/In/Ni microjoints

Low-temperature solder is needed for temperature-sensitive components, step soldering and wearable devices. Low-temperature bonding is effective for reducing temperature and manufacturing costs. Indium has a low melting point, low resistance and good anticorrosion properties. Indium plays important roles in transparent conductors, the aerospace industry and flexible displays. Solid–liquid interdiffusion (SLID) bonding is one of the most reliable 3D integration technologies. The microstructure of the Cu/In/Ni bonding interface was investigated in this study. A low temperature of 180 °C was used for SLID bonding. Cu-In compounds, Cu₁₁In₉ and CuIn₂, were formed after SLID bonding at 180 °C and storing at room temperature. The reaction between Cu and In is fast, even at room temperature. The low-temperature CuIn₂ phase is undoubtedly worth investigating for solder joints.

     

Microstructure of alumina ceramic/Ag–Cu–Ti brazing alloy/Kovar alloy joint

Abstract

The microstructure of the alumina ceramic/Kovar alloy joint brazed with Ag–35·2Cu–1·8Ti (wt-%) was studied. The effects of brazing temperature on the microstructure were also discussed. It was found that the microstructure of the joint brazed at 1173 K for 5 min was TiO + TiNi₃ + TiFe/eutectic Ag–Cu/TiFe₂ + TiNi₃/TiFe₂ + Cu (s.s) +Ag (s.s). When the brazing temperature was >1193 K, there was no TiO formed on the alumina ceramic/brazing alloy interface.     

Tensile properties of Cu/Sn–58Bi/Cu soldered joints subjected to isothermal aging

The effects of isothermal aging on the tensile properties of Cu/Sn–58Bi/Cu soldered joints were investigated. Experimental results show that the scallop-shaped Cu₆Sn₅ and planar Cu₃Sn formed at the interface between solder and Cu substrate during reflowing and aging. The thickness of the intermetallic compounds (IMCs) increased almost linearly with the square root of aging time, and aging at 120 °C yielded a much faster growth of the IMCs layer than that of samples aged at 100 °C. The IMCs growth rate constants were 6.02 × 10^?18 and 1.85 × 10^?18 m² s^?1 for solder joints aged at 120 and 100 °C, respectively. The tensile strength of the Sn–58Bi/Cu soldered joints decreased slightly with the increasing aging time and temperature. The failure was dominated by the mixed fracturing in both the solder and the Cu₆Sn₅ grains irrespective of their thermal aging conditions. However, the fracture pattern tended to transform from ductile to brittle with increasing aging time and temperature. The Bi segregation and voids were observed around the Cu/Cu₃Sn interface as the long term aging at high aging temperature was carried out, which resulted in reduction of tensile strength of solder joints.     

Reliability studies of Sn–9Zn/Cu and Sn–9Zn–0.3Ag/Cu soldered joints with aging treatment

In this study, the interfacial reactions and joint reliabilities of Sn–9Zn/Cu and Sn–9Zn–0.3Ag/Cu were investigated during isothermal aging at 150 °C for aging times of up to 1,000 h. Cu₅Zn₈ IMCs layer is formed at the as-soldered Sn–9Zn/Cu interface. Adding 0.3wt.% Ag results in the adsorption of AgZn₃ on the Cu₅Zn₈ IMCs layer. The as-soldered Sn–9Zn/Cu and Sn–9Zn–0.3Ag/Cu joints have sufficient pull strength. The thickness of the IMCs layer formed at the interface of Sn–9Zn/Cu and Sn–9Zn–0.3Ag/Cu both increase with increasing aging time. Correspondingly, both the pull forces of the Sn–9Zn and Sn–9Zn–0.3Ag soldered joints gradually decrease as the aging time prolonged. However, the thickness of the IMCs layer of Sn–9Zn–0.3Ag/Cu increases much slower than that of Sn–9Zn/Cu and the pull force of Sn–9Zn–0.3Ag soldered joint decreases much slower than that of Sn–9Zn soldered joint. After aging for 1,000 h, some Cu–Sn IMCs form between the Cu₅Zn₈ IMC and the Cu substrate, many voids form at the interface between the Cu₅Zn₈ layer and solder alloy, and some cracks form in the Cu₅Zn₈ IMCs layer of Sn–9Zn/Cu. The pull force Sn–9Zn soldered joint decreases by 53.1% compared to the pull force measured after as-soldered. Fracture of Sn–9Zn/Cu occurred on the IMCs layer on the whole and the fracture micrograph implies a brittle fracture. While the pull force of Sn–9Zn–0.3Ag soldered joint decreases by 51.7% after aging at 150 °C for 1,000 h. The fracture mode of Sn–9Zn–0.3Ag soldered joint is partially brittle at the IMCs layer, and partially ductile at the outer ring of the solder.     

Effects of Si and Cu contents on grain size of Al–Si–Cu alloys

The influence of the silicon and copper contents on the grain size of high-purity Al–Si, Al–Cu, and Al–Si–Cu alloys was investigated. In the Al–Si alloys, a poisoning effect was observed and a poor correlation between the grain size and growth restriction factor was obtained. A possible cause of the poisoning effect in these alloys is the formation of a TiSi₂ monolayer on the particles acting as nucleation sites or another poisoning mechanism not associated with TiSi₂ phase formation. In the Al–Cu alloys, a good correlation between the grain size and growth restriction factor was found, whereas in the Al–Si–Cu alloys, the correlation between these two parameters was inferior.     

Extrusion of AI–Zn–Mg–Cu–Zr alloys

Abstract

Four aluminium alloys of different zinc/magnesium ratio have been studied under various extrusion conditions. The alloys were cast in steel book moulds and subjected to initial thermomechanical treatments. Studies were made of hot extrusions and cold hydrostatic extrusions and in each case the changes in the extrusion parameters were analysed. An attempt has been made to explain some of the extrusion defects which appeared in various extruded sections. The extrusion speed was found to be crucial, since sections developed surface cracks at higher speeds. The extrusion speed was also found to vary inversely with the extrusion ratio, with higher speeds at low ratios. A well defined solute–depleted weld zone was observed on each of the four faces of a square tube extruded using a porthole die. Thermal treatment was not found to improve this weak weld zone. Tubes extruded using a floating-mandrel die withstood pressure testing up to 550 MPa.

MST/43     

Influence of POSS nano-particles on Sn–3.0Ag–0.5Cu–xPOSS/Cu composite solder joints during isothermal aging

Polyhedral oligomeric silsesquioxanes (POSS) nano-particles reinforced Sn–3.0Ag–0.5Cu–xPOSS (x = 1, 3, 5) composite solders were prepared and were reflowed on Cu substrates at 543 K. Then, the solder joints were isothermal aged at 393 K for 24 and 48 h, respectively. Microstructural evolution of the solder joints were observed by scanning electron microscopy and the influence of POSS nano-particles on the solder joint were investigated. The results showed that β-Sn primary phase was refined and the number of grain boundary increased with the addition of POSS nano-particles. The growth rates of intermetallic compounds (IMCs) layer were suppressed by the adsorption affection of POSS nano-particles to the IMCs layer during isothermal aging. Moreover, the dissolution process of the IMCs layer, which was accompanied by with the growth of the IMCs layer, changed the morphology of the IMCs layer. The growth rate and the dissolution rate of the IMCs layer in Sn–3.0Ag–0.5Cu–3POSS/Cu composite solder joint were the lowest.     

Investigation of mechanical properties of advanced Al–Zn–Mg–Cu alloy

Abstract

The mechanical properties of the rapidly solidified 7000 series powder alloy CW 67 were investigated for various extrusion and heat treatment conditions. The principal aim of the work was to ascertain the optimum processing route for peak aged (T6) material. The highest proof stress in the T6 condition was found to be 572 MN m^?2 for material extruded at 325°C and aged for 13·5 h at 120°C after solutionising. The ductility of this material was found to be 13·5%. The fracture toughness was measured in two orientations and found to be approximately 21 MN m^?3/2 in the short transverse direction and 44 MN m^?3/2 in the longitudinal direction. Degassing and hot compaction was found to improve the fracture toughness of the material substantially.

MST/1504     

Mechanical properties of intermetallic compounds at the Sn–3.0Ag–0.5Cu/Cu joint interface using nanoindentation

Intermetallic compounds (IMCs) at the Sn–3.0Ag–0.5Cu/Cu joint interface were prepared through reflow soldering and isothermal aging in a QHL360 SMT fully automatic reflow soldering system and a high-temperature test chamber, respectively. The mechanical properties of IMCs were then studied and characterized by nanoindentation. The mechanical responses of both Cu₆Sn₅ and Cu₃Sn (IMCs) show large dependence on the strain rate during loading. In addition, multiple pop-in events are observed in Cu₆Sn₅ but not evident in Cu₃Sn. During loading, the contact stiffness of IMCs increases almost linearly with the indentation depth under each strain rate. In total, the hardness and elastic modulus of Cu₃Sn are larger than those of Cu₆Sn₅, and the hardness of both Cu₆Sn₅ and Cu₃Sn increase with increasing strain rate. During the holding stage, creep deformations of IMCs increase as loading strain rate increases. Indentation creep displacement–time curves for Cu₆Sn₅ and Cu₃Sn can be well described by the generalized Kelvin model. The lower creep rate sensitivity exponent of Cu₃Sn implies its relatively higher creep resistance.     

Phase transformation and fracture behavior of Cu/In/Cu joints formed by solid–liquid interdiffusion bonding

In this paper, microstructure evolution and phase transformation of Cu–In intermetallic compounds in Cu/In/Cu joints formed by solid–liquid interdiffusion bonding at 260 and 360 °C were investigated respectively. The shearing properties and fracture behaviors of the Cu/In/Cu joints formed under different bonding conditions were also studied. For Cu/In/Cu joints bonded at 260 °C, Cu₁₁In₉ phase firstly generated and then Cu₂In phase formed between Cu₁₁In₉ layer and Cu substrate. For Cu/In/Cu joints bonded at 360 °C, Cu₂In phase firstly formed and then parts of Cu₂In grains transformed to Cu₇In₃ phase, and this transition from incomplete to complete coverage of Cu₂In/Cu₂In grain boundaries by Cu₇In₃ phases was observed with the bonding time increasing. The shear test results show that Cu₂In was high-quality phase which could improve the mechanical properties of Cu/In/Cu joints. After shear test, the fractures in Cu/In/Cu joints bonded at 260 °C were found at Cu₁₁In₉ layers and the fracture mode was cleavage fracture. In the case of the joints bonded at 360 °C, the intergranular fractures were found at the interface between Cu₂In layer and Cu₇In₃ layer while the cleavage fractures were found at Cu₇In₃ layer.     

Study of rapidly solidified Cu–Cr–RE alloys

Electrical engineering materials of Cu–Cr–RE have been made using the technology of rapid solidification, composite green compacts, extrusion and so on. By means of the analysis of optical metallographs, electron microscopy, physical and mechanical properties as well as electrical properties, and the examining of the hardness, softening temperature, etc. the authors selected Cu–Cr–Y alloy, which has excellent comprehensive properties. The authors have also made a deep study of the chromium and yttrium elements, which affect the structure, the recrystallization temperature, the strength at room and high temperature, the resistivity and contact resistance, and have also compared the properties of the Cu–Cr and Cu–Cr–Y alloy. The results show that rapidly solidified technology and added rare–earth elements not only enhance the fine grain boundary strengthening, but also the second phase strengthening. Cu/Cu–Cr–Y composite material improves the thermal stability and thermal endurance, and also maintains a better electrical conductivity and thermal conductivity.     

Study of rapidly solidified Cu–Cr–RE alloys

Electrical engineering materials of Cu–Cr–RE have been made using the technology of rapid solidification, composite green compacts, extrusion and so on. By means of the analysis of optical metallographs, electron microscopy, physical and mechanical properties as well as electrical properties, and the examining of the hardness, softening temperature, etc. the authors selected Cu–Cr–Y alloy, which has excellent comprehensive properties. The authors have also made a deep study of the chromium and yttrium elements, which affect the structure, the recrystallization temperature, the strength at room and high temperature, the resistivity and contact resistance, and have also compared the properties of the Cu–Cr and Cu–Cr–Y alloy. The results show that rapidly solidified technology and added rare-earth elements not only enhance the fine grain boundary strengthening, but also the second phase strengthening. Cu/Cu–Cr–Y composite material improves the thermal stability and thermal endurance, and also maintains a better electrical conductivity and thermal conductivity.     

Investigation on the intermetallic compound layer growth of Sn–0.5Ag–0.7Cu–xGa/Cu solder joints during isothermal aging

This work was focused on the influence of Ga on the thermal properties, microstructural evolution and interfacial morphology with aging treatment at 150 °C of low-silver Sn–0.5Ag–0.7Cu (SAC) lead-free solder. The melting temperature of the SAC–Ga solder was decreased owing to the low melting point element Ga and the formations of intermetallic compound (IMC) and growth at the interfaces of SAC/Cu and SAC–0.5Ga/Cu were studied for different aging time ranging from 0 to 720 h. The results indicated that for both solders, the thickness of the IMC increased with aging time prolonging. However, compared with the interface of SAC/Cu, the thickness of the interface of SAC–Ga/Cu was obviously suppressed and the growing speed was slowed down, which may be attributed to the decreased activity of copper atoms by Ga addition, so that the SAC–Ga solder showed relatively planar-like IMC instead of scallop-like at the interface.     

Formation of composite Cu–graphite and Cu–PTFE coatings and their tribological characterization

The Dynamic Chemical Plating (DCP) technique allows production of 2-μm copper films containing particles of graphite or PTFE in 18 and 15 min, respectively, at ambient temperature. DCP yields composites with particle-incorporation fractions of 12% for graphite micro-particles and 22% for PTFE nano-particles. The composite films show excellent tribological properties, acting as self-lubricating coatings with friction coefficients as low as 0.18.     

Influence of minor additions on characteristics of Cu–Al–Ni alloy

Abstract

The aluminium and nickel contents of Cu–Al–Ni alloy are varied to relate the parent phase chemistry to its shape memory behaviour. Rare earth and grain refining elements (titanium, zirconium, boron, etc.) are added in minor quantities to assess their effects on the grain refinement of the alloy and also on its shape recovery behaviour. It is observed that increasing the aluminium and nickel contents decreases the shape recovery temperature whereas minor additions are found to increase it. The alloys have been aged in the parent as well as the martensitic phase to investigate the influence of minor additions on their aging response. It is observed that precipitation of γ₂ phase occurs during the initial stage of aging of the ternary alloy. The aging behaviour is monitored via changes in resistivity and hardness of the alloys during aging. Minor additions are found to retard the precipitation of γ₂ phase during aging. Titanium and rare earths particularly reduce the tendency for grain coarsening in the alloy. It is further observed that two types of martensite, β′₁ and γ′₁, are produced in the alloys under investigation. The transformation temperatures of these martensites are also related to the aluminium content of the alloy.

MST/1744     

Growth behavior of interfacial Cu–Sn intermetallic compounds of Sn/Cu reaction couples during dip soldering and aging

The formation and growth of intermetallic compound (IMC) layer at the interface between pure Sn and a Cu substrate during dip soldering and aging were studied. The soldering was conducted at 250 °C using dipping method, followed by aging treatment at 150 °C for up to 10 days. The results showed that the IMC layer flattened with aging duration because the grooves in scallop-like IMC provide a more convenient access for Cu atoms to dissolve and react with solders and previous IMCs. And when isothermal aging was subjected, the growth rate of Cu₆Sn₅ was lower than that of Cu₃Sn due to Cu₃Sn growing rapidly with aging time by consuming Cu₆Sn₅ at the interface of Cu₃Sn/Cu₆Sn₅. Kirkendall voids were observed at Cu₃Sn/Cu interface as well as inside the Cu₃Sn layer as the Sn/Cu couple was aged at 150 °C for prolonged time, with which the Cu₃Sn IMC dominates the interfacial IMCs growth. During solid-state aging, the mean diameter (d) of interfacial Cu₆Sn₅ grains increased dramatically with the increasing time (t). The relationships between d and t were given to be d = 1.22 t ^0.291 for samples formed at 250 °C for 1 min and d = 1.53 t ^0.259 for samples formed at 250 °C for 5 min, respectively.     

The effects of the decreasing joint size on interfacial microstructure and shear behavior of micro-scale BGA structure Cu/Sn–3.0Ag–0.5Cu/Cu joints under coupled electromechanical loads

Journal of Materials Science: Materials in Electronics - Joint size effects on interfacial intermetallic compound (IMC) morphology, shear performance, and fracture behavior of micro-scale ball grid...     

An investigation on microwave sintering of Fe, Fe–Cu and Fe–Cu–C alloys

The powder characteristics of metallic powders play a key role during sintering. Densification and mechanical properties were also influenced by it. The current study examines the effect of heating mode on densification, microstructure, phase compositions and properties of Fe, Fe–2Cu and Fe–2Cu–0·8C systems. The compacts were heated in 2·45 GHz microwave sintering furnaces under forming gas (95%N₂–5%H₂) at 1120 °C for 60 min. Results of densification, mechanical properties and microstructural development of the microwave-sintered samples were reported and critically analysed in terms of various powder processing steps.     

Effects of Al–8.5Si–25Cu–xY filler metal foils on vacuum brazing of SiCp/Al composites

Rapidly solidified Al–8.5Si–25Cu–xY (wt-%, x?=?0, 0.05, 0.1, 0.2, 0.3, 0.4, and 0.5) foils were used as filler metal to braze Al matrix composites with high SiC particle content (SiCp/Al-MMCs), and the filler presented fine microstructure and good wettability on the composites. The joint shear strength first increased, then decreased and a sound joint with a maximum shear strength of 135.32?MPa was achieved using Al–8.5Si–25Cu–0.3Y as the filler metal. After Y exceeded 0.3%, a needle-like intermetallic compound, Al3Y, was found in the brazing seam, resulting in a dramatic decline in the shear strength of the brazed joints. In this research, the Al–8.5Si–25Cu–0.3Y filler metal foil was found to be suitable for the brazing of SiCp/Al-MMCs with high SiC particle content.