Interface between Sn-Sb-Cu solder and copper substrate

Influence of antimony and copper in Sn-Sb-Cu solder on the melting and solidification temperatures and on the microstructure of the interface between the solder and copper substrate after wetting the substrate at 623 K for 1800 s were studied. Microstructure of the interface between the solder and copper substrates in Cu-solder-Cu joints prepared at the same temperature for 1800 s was observed and shear strength of the joints was measured. Influence of the atmosphere - air with the flux and deoxidising N₂ + 10H₂ gas - was taken into account. Thermal stability and microstructure were studied by differential scanning calorimetry (DSC), light microscopy, scanning electron microscopy (SEM) with energy-dispersive spectrometry (EDS) and X-ray diffraction (XRD). Melting and solidification temperatures of the solders were determined. An interfacial transition zone was formed by diffusion reaction between solid copper and liquid solder. At the interface Cu₃Sn and Cu₆Sn₅ phases arise. Cu₃Sn is adjacent to the Cu substrate and its thickness decreases with increasing the amount of copper in solder. Scallop Cu₆Sn₅ phase is formed also inside the solder drop. The solid solution Sn(Sb) and SbSn phase compose the interior of the solder drop. Shear strength of the joints measured by push-off method decreases with increasing Sb concentration. Copper in the solder shows even bigger negative effect on the strength.     

Orientation relationships, interfaces, and microstructure of η-Cu6Sn5 formed in the early-stage reaction between Cu and molten Sn

A very thin η-Cu₆Sn₅ layer has been formed by dipping thin Cu foil into molten Sn at 240 °C for 1 s and quenching in ice water. After removing electrolytically the Sn on the surface, the η-Cu₆Sn₅ grains on the Sn side are shown to have a worm-type shape 0.3-0.5 μm wide and up to 2 μm long. Transmission electron microscopy (TEM) analysis shows that the η-Cu₆Sn₅ grains on the Cu side can be as small as 5 nm, indicating that the η-Cu₆Sn₅ /Cu interface is the nucleation side.The orientation relationships between η-Cu₆Sn₅ and Cu are determined by TEM. The η-Cu₆Sn₅ (112?0) surface is the interface with both the Cu (001) and (1?11) surfaces, and a common orientation relationship of (0001)_η//(110)_Cu is present on both interfaces. The match of atoms between η-Cu₆Sn₅ and Cu on the interfaces is analyzed.     

The microstructure of η′-Cu6Sn5 and its orientation relationships with Cu in the early stage of growth

The microstructure of η′-Cu₆Sn₅ during the early stage of growth was studied. Sn was electroplated onto thin Cu foil at room temperature and the specimen was annealed at 150 °C for 30 s. The Cu and Sn on the η′-Cu₆Sn₅ surfaces were removed electrolytically and the specimens were analyzed by scanning and transmission electron microscopy. The η′-Cu₆Sn₅ grains on the Cu side were as small as 5 nm but grew rapidly to 0.3 to 0.5 μm on the Sn side.The orientation relationships between η′-Cu₆Sn₅ and Cu were studied by a thin-film technique. Cu was evaporated onto the NaCl (001) and (111) surfaces to form epitaxial Cu thin films and Sn was then evaporated onto the Cu films to form η′-Cu₆Sn₅. Two types of orientation relationships were found, i.e., (1) [204]_η′//[001]_Cu (zone axis), (402?)_η′//(110)_Cu, and (020)_η′//(11?0)_Cu, and (2) [204]_η′//[111]_Cu (zone axis), (402?)_η′//(11?0)_Cu, and (020)_η′//(1?1?2)_Cu. The interfaces were analyzed.     

Interfacial reactions in Sn–20In–2.8Ag/Cu couples

Interfacial reactions between Sn–20 wt.%In–2.8 wt.%Ag (Sn–20In–2.8Ag) Pb-free solder and Cu substrate at 250, 150, and 100 °C were investigated. A scallop-type η-Cu₆Sn₅ phase layer and a planar ε-Cu₃Sn phase layer formed at the interface at 250 °C. The indium content in the molten solder near the interface was increased with the formation of the η-Cu₆Sn₅ phase; and the η-Cu₆Sn₅, Ag₂In, Cu₂In₃Sn, and γ-InSn₄ phases formed from the solidification of the remaining solder. At 100 and 150 °C, only the η-Cu₆Sn₅ phase was found at the interface. However, unusual liquid/solid reaction-like interfacial morphologies, such as irregular elongated intermetallic layers and isolated intermetallic grains, were observed in the solid-state reactions. These η phase layers had less Sn content than the Sn–20In–2.8Ag alloy, resulting in an excess Sn-rich γ-InSn₄ phase accumulating at the interface and forming porous η layers on top of the initially formed dense η layers at 150 °C. At 100 °C, large elongated η grains were formed, whereas the interfacial layers remained almost unchanged after prolonged reaction. Based on the experimental evidence, the growth of the η phase was proposed to follow a diffusion-controlled mechanism at 250, 150 and 100 °C, while that of the ε phase was probably controlled by the reaction.     

Comparative study of ITO and FTO thin films grown by spray pyrolysis

Tin doped indium oxide (ITO) and fluorine doped tin oxide (FTO) thin films have been prepared by one step spray pyrolysis. Both film types grown at 400 °C present a single phase, ITO has cubic structure and preferred orientation (4 0 0) while FTO exhibits a tetragonal structure. Scanning electron micrographs showed homogeneous surfaces with average grain size around 257 and 190 nm for ITO and FTO respectively.The optical properties have been studied in several ITO and FTO samples by transmittance and reflectance measurements. The transmittance in the visible zone is higher in ITO than in FTO layers with a comparable thickness, while the reflectance in the infrared zone is higher in FTO in comparison with ITO. The best electrical resistivity values, deduced from optical measurements, were 8 × 10⁻⁴ and 6 × 10⁻⁴ Ω cm for ITO (6% of Sn) and FTO (2.5% of F) respectively. The figure of merit reached a maximum value of 2.15 × 10⁻³ Ω⁻¹ for ITO higher than 0.55 × 10⁻³ Ω⁻¹ for FTO.     

Physical properties of Sn58Bi–xNi lead-free solder and its interfacial reaction with copper substrate

The aims of this research are to investigate the effects of Ni on the physical properties of Sn58Bi–xNi lead-free solder, and to examine its interfacial reaction with the copper substrate. In the experiments, four concentrations of Ni (i.e. 0.05, 0.1, 0.5 and 1.0 wt.%) were individually added into Sn58Bi and their respective microstructure, tensile strength, elongation, melting temperature, wettability and electrical resistivity of Sn58Bi–xNi were subsequently measured. The results indicated that Ni refined the microstructure of the solder matrix and induced the formation of Ni₃Sn₄ intermetallic phase, and that the size and volume fraction of Ni₃Sn₄ were positively correlated to the Ni content. The optimal concentration of Ni to enhance the tensile strength of the alloy was 0.1 wt.%, but the elongation of the alloy was inversely correlated to the Ni content. The addition of Ni contributed positively to the melting temperature and wetting behavior of the alloy, whereas no significant change in the electrical resistivity of Sn58Bi–xNi was detected. In addition, Ni increased the thickness of the intermetallic layer at the interface, and only monoclinic η′-Cu₆Sn₅ phase was present at the intermetallic layer. Nevertheless, the intermetallic phase of this research was dissimilar from the findings of existing literature.     

Microstructure and mechanical properties of Sn–Bi solder joints reinforced with Zn@Sn core–shell particles

We proposed Zn@Sn particles to improve the mechanical properties of the Sn–58 wt% Bi (Sn58Bi) solder. The effects of 3, 6, and 9 wt% Zn@Sn particles on the microstructure and mechanical properties of Sn58Bi were investigated. The addition of Zn@Sn to Sn58Bi solder inhibited microstructural coarsening, which mitigated the brittleness of Sn58Bi solder joints during aging. The zinc-rich phases dispersively distributed in the solder joints effectively inhibited the coarsening of the Bi-riched phase. At the same time, Cu₅Zn₈ instead of Cu₆Sn₅ formed at the composite solder/Cu interface. After 21 days of aging, the shear strengths of solder joints doped with 6 wt% Zn@Sn decreased from 54.06 to 36.41 MPa. Compared with the undoped solder joints before and after aging, the shear strengths increased by 34% and 173.1%, respectively. Thus, the composite solder paste has great potential to be used as a low-temperature lead-free solder in the electronic packaging industry.

     

Low temperature processing of hybrid nanoparticulate Indium Tin Oxide (ITO) polymer layers and application in large scale lighting devices

We report on transparent conductive indium tin oxide (In₂O₃:Sn; ITO) nanoparticle films processed at a low temperature of 130 °C for the application in lighting devices using spin coating and doctor blading techniques. Major emphasis is put on the beneficial application of the particular transparent electrode material for the fabrication of patterned large area electroluminescence lamps. In order to improve film properties like adhesion and conductivity, hybrid nanoparticle-polymer blends out of ITO particles and organic film-forming agent polyvinylpyrrolidone (PVP) and the organofunctional coupling agent 3-methacryloxypropyltrimethoxysilane (MPTS) have been developed. The layers were cured by UV-irradiation, which was also used for lateral structuring of the transparent, conductive electrode. Additional low-temperature heat treatment (T = 130 °C) in air and forming gas improved the electronic properties. While pure ITO nanoparticulate layers processed at 130 °C exhibited conductance of up to 3.1 Ω^− 1 cm^− 1, the nanocomposite coatings showed a conductance of up to 9.8 Ω^− 1 cm^− 1. Corresponding layers with a sheet resistance of 750 Ω/□ were applied in electroluminescent lamps.     

Suppression effect of Cu and Ag on Cu3Sn layer in solder joints

Cu₃Sn intermetallic compound (IMC) layer is usually formed in solder joints. Since the formation of Cu₃Sn could induce large volume shrinkage, and further cause a lot of reliability issues, many works focused on suppressing the formation or growth of the Cu₃Sn layer. This work explored that Cu and Ag alloying elements also have benefit in suppressing the Cu₃Sn growth during isothermal aging stage. The Cu₆Sn₅ IMC layer seems to be much stable in the Sn/Cu solder joint during aged at 150 and 180 °C, its thickness changed little, while the Cu₃Sn IMC layer grew much quickly. After about 300 h, the thickness of Cu₃Sn layer exceeds that of Cu₆Sn₅ layer. For the Sn-3.5Ag/Cu and Sn-0.7Cu/Cu solder joints, the thickness of Cu₃Sn layer is near half of that of Cu₆Sn₅ layer. According to the relation between interface location and aging time, the reaction generated at the Cu₆Sn₅/Cu₃Sn interface, which is governed by atom fluxes, controls the growth of Cu₃Sn IMC layer. Since Ag and Cu alloying elements suppress the coarsening of Cu₆Sn₅ IMC grains, the diffusion paths for Cu atoms toward the solder are more for Ag or Cu containing solder joints. Therefore, the growth of the Cu₃Sn layer by consuming Cu₆Sn₅ layer is slower in the SnAg/Cu and SnCu/Cu solder joints than that in the Sn/Cu joints.     

Low temperature formation of Si1 − x − yGexSny-on-insulator structures by using solid-phase mixing of Ge1 − zSnz/Si-on-insulator substrates

We proposed the low temperature formation technique of strain-relaxed Si_{1 − x − y}Ge_xSn_y-on-insulator (SGTOI) structures. We found that the solid-phase reaction and the formation of single and uniform Si_{1 − x − y}Ge_xSn_y layer on an insulator after annealing SiO₂/Ge_1 − zSn_z/SOI structures even at a temperature as low as 400 °C. We characterized the crystalline structure of SGTOI, and investigated the effects of annealing, Sn incorporation, and a SiO₂ cap layer on the solid-phase reaction between Ge_1 − zSn_z and SOI layers. The solid-phase reaction is enhanced with a higher Sn content and a thicker SiO₂ cap layer, and then Si_{1 − x − y}Ge_xSn_y layers are more rapidly formed. The SGTOI layer exhibits very low mosaicity and have good crystallinity.     

Interfacial reaction and growth behavior of IMCs layer between Sn–58Bi solders and a Cu substrate

This paper reports on the interfacial reaction and growth behavior of intermetallic compounds (IMCs) layer (η-Cu₆Sn₅ + ε-Cu₃Sn) between molten Sn–58Bi solder and Cu substrate for various liquid–solid soldering temperatures and times. In addition, the Bi segregation at the Cu₃Sn/Cu interface was also discussed, too. It was found that the Cu₆Sn₅ IMC could be observed as long as the molten solder contacted with the Cu substrate, while the Cu₃Sn IMC was formed at the interface between Cu₆Sn₅ and Cu substrate as the higher soldering temperature and/or longer soldering time were applied. Both thickness of total IMCs layer and Cu₆Sn₅ grains size increased with increased soldering temperature or time. The growth of the Cu-Sn IMCs layer during soldering exhibited a linear function of the soldering temperature and 0.27 power of soldering time. With soldering temperature increasing (above 280 °C in this present study), Bi was accumulated at the Cu₃Sn/Cu interface and resulted in some isolated Bi particles were formed.     

Current stressing-induced growth of Cu3Sn in Cu/Sn/Cu solder joints

We investigated the influence of current stressing on a crystallographic microstructure of intermetallics in Cu/Sn/Cu solder joints using electron backscatter diffraction (EBSD). After direct current (DC) stressing at 150 °C for 10 d, the total Sn of the Cu/Sn/Cu was converted into a tri-layer structure of Cu₃Sn/Cu₆Sn₅/Cu₃Sn. The Cu₃Sn layers that grew on the cathode and anode are asymmetrical during DC stressing. A preferred direction < 010> Cu₃Sn along the current direction on the anode was found after current stressing.     

Nitrogen doped p-type SnO thin films deposited via sputtering

p-Type SnO thin films were fabricated via reactive RF magnetron sputtering on borosilicate substrates with an Sn target and Ar/O₂/N₂ gas mixture. The undoped SnO thin film consisted of a polycrystalline SnO phase with a preferred (1 0 1) orientation; however, with nitrogen doping, the preferred orientation was suppressed and the grain size decreased. The electrical conductivity of the undoped SnO thin films demonstrated a relatively low p-type conductivity of 0.05 Ω⁻¹ cm⁻¹ and it was lowered slightly with nitrogen doping to 0.039 Ω⁻¹ cm⁻¹. The results of the X-ray photoelectron spectroscopy suggested that the nitrogen doping created donor defects in the SnO thin films causing lower electrical conductivity. Lastly, both the undoped and doped SnO thin films had poor optical transmittance in the visible range.     

High temperature thermopower and electrical resistivity studies in the transparent conducting oxide Sn doped MgIn2O4

Sn doping in an n-type transparent conducting oxide MgIn₂O₄ is carried out and its effect on the high temperature transport properties viz. thermopower and electrical resistivity is studied. A solid solution exists in the composition window Mg_1+xIn_2−2xSn_xO₄ for 0 < x ≤ 0.4. The band gap as well as the transport properties increases with increasing Sn concentration. The high temperature resistivity properties indicate degenerate semiconducting behavior for all the compositions. The highest figure of merit obtained is 0.12 × 10⁻⁴ K⁻¹ for the parent compound at 600 K.     

Effects of rare earth additions on the microstructural evolution and microhardness of Sn30Bi0.5Cu and Sn35Bi1Ag solder alloys

The effects of trace amounts of rare earth (RE) additions on the melting property, microstructural evolution and microhardness of SnBiCu and SnBiAg solder alloys were studied by differential scanning calorimetric tester, Vickers hardness tester and microstructural observation. The results indicated that with the additions of RE, the melting property of the SnBiCu–xRE and SnBiAg–xRE (x = 0, 0.25 and 0.5) solder alloys changed slightly. The microstructures of the β-Sn phase, Cu₆Sn₅ and Ag₃Sn intermetallic compounds (IMCs) in the solder matrices were refined due to the surface adsorption effect of RE. In addition, the microhardness of the solder alloys increased remarkably with the additions of RE because of the refined microstructures. Moreover, the formed Cu₆Sn₅ IMC layers in SnBiCu–xRE/Cu and SnBiAg–xRE/Cu solder joints were much thinner than those in the undoped-RE SnBiCu/Cu and SnBiAg/Cu solder joints after reflowing and aging tests. This is because the RE decreased the interfacial energy of Cu₆Sn₅ IMC layer and then suppressed the Cu atoms to react with Sn atoms to form Cu₆Sn₅ IMC layer.     

Growth of Ge1 − xSnx heteroepitaxial layers with very high Sn contents on InP(001) substrates

We investigated the crystalline structures of Ge_1 − xSn_x heteroepitaxial layers with Sn contents greater than 20% grown on InP and Ge substrates. Considering the lattice mismatch between the Ge_1 − xSn_x layers and the substrates, we achieved epitaxial growth of Ge_1−xSn_x layers with very high Sn content by suppressing the Sn precipitation; in addition, we improved upon the crystalline quality of Ge_1 − xSn_x heteroepitaxial layers. As a result, we could successfully form a 130 nm-thick Ge_1 − xSn_x heteroepitaxial layer on an InP substrate with a Sn content as high as 27% without Sn precipitation. We also improved the crystalline quality of Ge_1 − xSn_x layers by annealing at a temperature as low as 290 °C.     

Effect of intermetallic compounds on fracture behaviors of Sn3.0Ag0.5Cu lead-free solder joints during in situ tensile test

In this paper, in situ tensile tests under various amounts of deformation were performed on Sn3.0Ag0.5Cu lead-free solder joints subjected to multi-reflow and isothermal aging processes by using a scanning electron microscope. Microstructure evolution and deformation behavior of the solder joints were observed. Effects of the intermetallic compound (IMC) Cu₆Sn₅ on fracture behaviors of the solder joints were investigated. Results showed that the Sn3.0Ag0.5Cu lead-free solder joints contained only a few Sn grains, and the sequence and degree of plastic deformation varied for the different grains in the same solder joint due to the strong anisotropic properties of Sn grains. Further experiments revealed that plastic deformation occured primarily in the form of slip bands in the solder joints during the in situ tensile test. Various fracture modes including intergranular and phase boundary fractures were observed. The fracture behaviors of solder joints were significantly affected by morphologies and distributions of the Cu₆Sn₅ IMCs. It was found that Cu₆Sn₅ particles located at the grain boundaries are apt to become crack sources, and that the long rod shaped Cu₆Sn₅ were easily broken. However, spherical Cu₆Sn₅ hardly deformed during the tensile test, resulting in dynamic recrystallization. In this case, fracture occured at the sub-grain boundaries.     

Interfacial reaction in bimetallic Sn/Cu thin films

Interfacial reaction in electroplated bimetallic Sn/Cu (the layer grown last is given first) thin films was studied by Auger depth profiling and X-ray diffraction measurements. Direct experimental evidence was found for the formation of intermetallic compounds in the SnCu interface, i.e. η'-Cu₆Sn₅ at room temperature and both η'-Cu₆Sn₅ and ε-Cu₃Sn at 150°C. The results of a quantitative analysis of the film composition and sputtering-induced effects are also discussed.     

Structural,optical and electrical properties of In4Sn3O12 films prepared by pulsed laser deposition

Highly conducting (σ ∼ 2.6 × 10³ Ω⁻¹ cm⁻¹) In₄Sn₃O₁₂ films have been deposited using pulsed laser deposition (PLD) on glass and quartz substrates held at temperatures between 350 and 550 °C under chamber pressures of between 2.5 and 15 mTorr O₂. The crystallinity and the surface roughness of the films were found to increase with increasing substrate temperature. Electron concentrations of the order of 5 × 10²⁰ cm⁻³ and mobilities as high as 30 cm² V⁻¹ s⁻¹ were determined from Hall effect measurements performed on the films. Fitting of the transmission spectral profiles in the ultra-violet–visible spectrum has allowed the determination of the refractive index and extinction coefficient for the films. A red-shift in the frequency of plasmon resonance is observed with both increasing substrate temperature and oxygen pressure. Effective masses have been derived from the plasma frequencies and have been found to increase with carrier concentration indicating a non-parabolic conduction band in the material In₄Sn₃O₁₂. The optical band-gap has been determined as 3.8 eV from the analysis of the absorption edge in the UV. These results highlight the potential of these films as lower In-content functional transparent conducting materials.     

Growth behavior of Cu6Sn5 grains formed at an Sn3.5Ag/Cu interface

The growth behavior of Cu₆Sn₅ grains formed at an Sn3.5Ag/Cu interface was investigated. During soldering, Cu₆Sn₅ grains formed at the interface, showing a flattened ovoid shape. During solidification, Cu precipitated from molten solder in the form of Cu₆Sn₅, forming faceted surfaces on existing interfacial grains. The interfacial Cu₆Sn₅ morphology was unrelated to its crystal orientation, which was primarily dependent on reaction temperature. A reaction temperature of 240 °C led to an increase in (002) growth and a decrease in (101) growth with time. However, the (002) plane peak was not detected in the interfacial grains formed at a higher reaction temperature (280 °C).