Effects of process parameters on the soldering behavior of the eutectic Sn-Zn solder on Cu substrate

The effects of process parameters such as flux, dipping temperature and the heat-treatment on the soldering behaviors of the eutectic solder (composition: 91Sn-9Zn) hot-dipped on Cu substrates were investigated. The most suitable flux as tested was oleic acid for the eutectic Sn-Zn solder system hot-dipped on Cu substrate for the solder coverage. The adhesion strength obtained increased from 9.6±0.6 MPa to 11.9±0.6 MPa when the dipping temperature increased from 250 °C to 300 °C. However, it decreased from 11.9±0.6 MPa to 5.2±2.2 MPa as the sample was heated at 150 °C for 1200 h. Planar γ-Cu₅Zn₈ isolate-shaped η-Cu₆Sn₅ intermetallic layers were found in the bulk sample after heating at 150 °C for 300 h but was not found in the as-cast sample. In the plate samples, scallop-shaped γ-Cu₅Zn₈/inverted trigonal-shaped η-Cu₆Sn₅ intermetallic layers were found after heating at 150 °C for 600 h. Some pores were found at the interface between γ-Cu₅Zn₈ intermetallic compound (IMC) and the solder alloy, which might come from the formation and growth of IMCs and decreased the adhesion strength. © 2000 Kluwer Academic Publishers     

Deformation-driven formation of equilibrium phases in the Cu–Ni alloys

The homogeneous coarse-grained (CG) Cu–Ni alloys with nickel concentrations of 9, 26, 42, and 77 wt% were produced from as-cast ingots by homogenization at 850 °C followed by quenching. The subsequent high-pressure torsion (5 torsions at 5 GPa) leads to the grain refinement (grain size about 100 nm) and to the decomposition of the supersaturated solid solution in the alloys containing 42 and 77 wt% Ni. The lattice spacing of the fine Cu-rich regions in the Cu–77 wt% Ni alloy was measured by the X-ray diffraction (XRD). They contain 28 ± 5 wt% Ni. The amount of the fine Ni-rich ferromagnetic regions in the paramagnetic Cu–42 wt% Ni alloy was estimated by comparing its magnetization with that of fully ferromagnetic Cu–77 wt% Ni alloy. According to the lever rule, these Ni-rich ferromagnetic regions contain about 88 wt% Ni. It means that the high-pressure torsion of the supersaturated Cu–Ni solid solutions produces phases which correspond to the equilibrium solubility limit at 200 ± 40 °C (Cu–77 wt% Ni alloy) and 270 ± 20 °C (Cu–42 wt% Ni alloy). To explain this phenomenon, the concept of the effective temperature proposed by Martin (Phys Rev B 30:1424, 1984) for the irradiation-driven decomposition of supersaturated solid solutions was employed. It follows from this concept that the deformation-driven decomposition of supersaturated Cu–Ni solid solutions proceeds at the mean effective temperature T _eff = 235 ± 30 °C. The elevated effective temperature for the high-pressure torsion-driven decomposition of a supersaturated solid solution has been observed for the first time. Previously, only the T _eff equal to the room temperature was observed in the Al–Zn alloys.     

Phase growth competition in solid/liquid reactions between copper or Cu3Sn compound and liquid tin-based solder

Interfacial reaction between solid ?-Cu₃Sn compound and liquid Sn at 250 °C is studied for the first time. The reaction product formed at the ?-Cu₃Sn/liquid Sn interface consists of the single η-Cu₆Sn₅ phase. The growth kinetics of the η phase formed at the incremental ?/liquid Sn couple (?/η/Sn configuration) is compared to that of η phase formed at the classical Cu/liquid Sn couple (Cu/?/η/Sn configuration). The experimental method consists first in processing of intimate interfaces by dipping peaces of solid ?-Cu₃Sn compound and Cu in liquid Sn for 1 s at 250 °C. Afterwards, isothermal holding of such pre-performed couples for 10, 30, 120 and 480 min at 250 °C are performed for both couples. A theoretical analysis of the growth kinetics of η phase and comparison of its growth in both configurations are performed.     

Contact angles by the solid-phase grain boundary wetting (coverage) in the Co–Cu system

The microstructure of binary Co–13.6 wt% Cu and Cu–4.9 wt% Co alloys after long anneals (930–2,100 h) was studied between 880 and 1,085 °C. The contact angles between (Co) particles and (Cu)/(Cu) grain boundaries (GBs) in the Cu–4.9 wt% Co alloy are between 50° and 70°. In the Co–13.6 wt% Cu alloy, the transition from incomplete to complete wetting (coverage) of (Co)/(Co) GBs by the second solid phase (Cu) has been observed. The portion of completely wetted (Co)/(Co) GBs increases with increasing temperature beginning from T _wss = 970 ± 10 °C and reaches a maximum of 15% at 1,040 °C. This temperature is very close to the Curie point in the Co–Cu alloys (1,050 °C). Above 1,040 °C, the amount of completely wetted (Co)/(Co) GBs decreases with increasing temperature and reaches zero at T _wsf = 1,075 ± 5 °C. Such reversible transition from incomplete to complete wetting (coverage) of a GB by a second solid phase is observed for the first time.     

Thermoanalytical study of the polymorphism and melting behavior of Cu<Subscript>2</Subscript>V<Subscript>2</Subscript>O<Subscript>7</Subscript>

We have developed a procedure for the synthesis of phase-pure α- and β-Cu₂V₂O₇. Thermal analysis and X-ray diffraction demonstrate that the β-phase (monoclinic structure) exists at low temperatures (stability range 25–610°C), while α-Cu₂V₂O₇ (orthorhombic structure) is stable in the range 610–704°C. The α-phase observed during cooling, in particular at room temperature, is in a metastable state. The melting of the high-temperature phase γ-Cu₂V₂O₇, which forms between 704 and 716°C, has the highest rate in the range 770–785°S and is accompanied by peritectic decomposition and oxygen gas release. Subsequent cooling gives rise to four exothermic peaks, one of which (780.9°C) is attributable to the crystallization of the peritectic melt, one (620.1°C) is due to the γ → α → β phase transformations of Cu₂V₂O₇, and the other two arise from the crystallization of multicomponent low-melting-point eutectics containing α- and β-Cu₂V₂O₇, CuVO₃, and other compounds.     

Characterization of the alumina oxide,copper and nickel powders and their processing intended for fabrication of the novel hybrid composite: A comparative study

The aim of this study was the fabrication and characterization of the novel hybrid composite from the Al₂O₃/Cu/Ni system. The research included the production of composite specimens by uniaxial pressing and their further sintering. The influence of the ceramic and metallic powders and their sintering temperature on the microstructure of composites was investigated. The firing process was conducted in reducing the atmosphere at three different temperatures, selected on the basis of the copper-nickel phase diagram: 1100 °C, 1260 °C, 1400 °C. Reference samples of Al₂O₃/Cu were also produced in the same way for comparative purposes. The addition of the third component, which together with copper will form a Ni−Cu solid solution, was intended to improve the wettability of ceramic matrix through a liquid metallic phase, and thus to reduce the phenomenon of the liquid metal flow on samples surface during sintering. However, it had an impact on physical and mechanical properties.     

Synthesis, crystal stability, and electrical behaviors of La0.7Sr0.3Cr0.4Mn0.6O3?δ–XCu0.75Ni0.25 for its possible application as SOFC anode

La_0.7Sr_0.3Cr_0.4Mn_0.6O_3−δ (perovskite-type) nanocomposites impregnated with XCu_0.75Ni_0.25 have been synthesized by sol–gel method. Crystal structure of LSCM–Cu_0.75Ni_0.25 composites were refined by the Rietveld method. Crystal symmetry of CuO and NiO nanoparticles have monoclinic and cubic symmetry, respectively, but after sintering at 1,200 °C and reducing the temperature to 600 °C, it’s transformed into a new Cu_0.75Ni_0.25 intermetallic solid solution without secondary phase. We have detected a cationic inter-diffusion in Cu ↔ Ni interphase crystals during this reduction process; however, when sintering time exceeds 2 h at 1,200 °C this reaction mechanism is interrupted by a sublimation phenomenon; which causes Cu₂O cubic structure segregation from monoclinic CuO structure. This leads to Cu precipitation from the Cu_1−x Ni _x solid solution. Cu_0.75Ni_0.25 inhibits the LSCM perovskite-type grain growth (t ≈ 220 nm). Electrical conductivity indicates the presence of semiconductor and metallic-type behaviors with a maximum electrical conductivity (800 °C) >4.5 (log σ, Sm cm⁻¹). When Cu_0.75Ni_0.25 concentration was 25 and 35 %, semiconductor behavior were dominated. Thermal expansion coefficients showed a linear dependence inversely proportional to Cu_0.75Ni_0.25 concentration. Electrical conductivity, Rietveld analysis, Porosity, TEC, and E _a behaviors lead to the conclusion that the anodes between 25 and 35 % (Cu_0.75Ni_0.25) are closer to applications at SOFC.     

Die attach properties of Zn–Al–Mg–Ga based high-temperature lead-free solder on Cu lead-frame

Several candidate alloys have been suggested as high-temperature lead-free solder for Si die attachment by different researchers. Among them, Zn–Al based alloys have proper melting range and excellent thermal/electrical properties. In this study, Zn–Al–Mg–Ga solder wire was used to attach Ti/Ni/Ag metallized Si die on Cu lead-frame in an automatic die attach machine. Die attachment was performed in a forming gas environment at temperature ranging from 370 to 400 °C. At the interface with Cu lead-frame, CuZn₄, Cu₅Zn₈ and CuZn intermetallic compound (IMC) layers were formed. At the interface with Si, Al₃Ni₂ IMC formed when 200 nm Ag layer was used at the die back and AgZn and AgZn₃ IMC layers when the Ag layer was 2,000 nm thick. Microstructure of the bulk solder consists of mainly two phases: one with a brighter contrast (about 80.9 wt% Zn) and the other one is a mixture of light (about 73.7 wt% Zn) and dark phases (about 45 wt% Al). Zn–Al–Mg–Ga solder wetted well on Cu lead-frame, covered entire die area and flowed in all directions under the Si die. Less than 10% voids were found in the die attach samples at die attach temperatures of 380 and 390 °C. Die shear strength was found within the acceptable limit (21.8–29.4 MPa) for all the die attach temperatures. Die shear strength of standard Pb–Sn solder was also measured for comparison and was found to be 29.3 MPa. In electrical test, maximum deviation of output voltage after 1,000 thermal cycles was found 12.1%.     

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.     

Effect of Firing Temperature on the Structure and Superconducting Properties of YBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>7−<Emphasis Type="Italic">x</Emphasis></Subscript> Films

YBa₂Cu₃O_7−x (YBCO) films were prepared on LaAlO₃ single crystal substrate under various firing temperatures (750–800 °C) in the crystallization process by metalorganic deposition (MOD) method. The coating solution was made by mixing the fluorine-free precursor solution containing Y and Cu with Ba–fluorine precursor solution (Ba-TFA). The effect of firing temperature on the structure and superconducting properties of YBCO films was systematically investigated. The results indicated that YBCO-films were smooth, crack-free, exhibited good textures and retain high oxygen content according to the XRD and SEM images. Sample of YBCO-film fired at 780 °C showed highest superconducting properties including high critical transition temperature T _c=89 K, sharp transition temperature ΔT _c<1 K, and critical current density J _c=2.8 MA cm⁻², which are attributable to excellent in-plane textures and dense microstructures with good connectivity between the grains.     

Effect of electroactive nickel on the low-temperature annealing behavior of silicon

We have studied the effect of low-temperature annealing on the behavior of electroactive nickel in silicon. The results demonstrate that the state of electroactive nickel centers in silicon is stable up to 200°C. Starting at 300°C, the SiNi solid solution decomposes and the electroactive nickel concentration decreases. From low-temperature (t > 200°C) annealing kinetics, the activation energy for the annealing of a deep center at E _c − 0.41 eV is estimated at 1.2–1.5 eV. The decomposition rate of the SiNi solid solution increases with temperature.     

Precipitation hardening of Cu – Ti – Zr alloys

Abstract

The influence of age hardening temperature and time on the hardness, tensile properties, electrical conductivity, and microstructure of Cu – 4Ti – 0.1Zr and Cu – 3Ti – 0.1Zr alloys has been investigated. The resulting microstructure of these alloys suggests that zirconium addition prohibited the formation of compositional modulations in the solution treated condition. These alloys exhibited maximum hardness and strength on peak aging at 450°C for 24 h by the formation of a coherent and metastable Cu₄Ti phase (β') in modulated structure while overaging occurred by the formation of equilibrium phase β-Cu₃Ti. The electrical conductivity of both the alloys increased moderately on aging. Unlike in an earlier study of binary Cu – Ti and some ternary Cu – Ti – X alloys, overaging did not cause any discontinuous precipitation in the Cu – Ti – Zr alloys investigated. Modulated structure formed on peak aging persisted on prolonged aging at 450°C for 80 h or at 500°C for 8 h.     

Synthesis and characterization of nano-sized BaxSr1?xSO4 (0 ≤ x ≤ 1) solid solution by a simple surfactant-free aqueous solution route

A facile aqueous solution route has been employed to synthesize Ba _x Sr_1−x SO₄ (0 ≤ x ≤ 1) solid solution nanocrystals at room temperature without using any surfactants or templates. The as-synthesized products were characterized by means of X-ray diffraction (XRD), X-ray fluorescence spectrometer (XRF), scanning electron microscopy (SEM), and differential scanning calorimetry-thermogravimetry (DSC-TG). The Ba _x Sr_1−x SO₄ solid solution nanocrystals exhibit an orthorhombic structure and an ellipsoidal-shaped morphology with an average size of 80–100 nm. The lattice parameters of Ba _x Sr_1−x SO₄ solid solution crystals increase with increasing x value. However, they are not strictly coincident with the Vegard’s law, which indicates that the as-obtained products are non-ideal solid solutions. The Ba _x Sr_1−x SO₄ solid solution nanocrystals have an excellent thermal stability from ambient temperature to 1300°C with a structural transition from orthorhombic to cubic phase at about 1111°C.     

Role of aluminum distribution on the growth of CuIn0.75Al0.25Se2 films and numerical simulation of p-CuIn0.75Al0.25Se2/n-CuAlSe2 heterojunction solar cell

Chalcopyrite thin films of CuIn_0.75Al_0.25Se₂ have been grown by a two-stage process containing e-beam evaporation of a threefold (In/Cu/Al/Se) precursor deposition onto glass substrates in a high vacuum followed by post selenization at various temperatures (300–550 °C) using a horizontal tubular furnace. The X-ray diffraction pattern of precursor layers selenized at?≤?525 °C shows the formation of co-existence of CuInSe₂ and Cu(In,Al)Se₂ phases, as well as a mixture of two Cu(In,Al)Se₂ phases with different Al content. The precursor layers selenized at 550 °C results in the formation of single-phase Cu(In,Al)Se₂ thin films. The presence of an intense A₁ mode at 174.7 cm^?1 in the Raman spectra of selenized films at 550 °C confirms the growth of Cu(In,Al)Se₂ phase. The energy-dispersive spectra of stacked layers selenized at 550 °C shows a Cu-poor and (In?+?Al)-rich composition with atomic ratios of Cu/(In?+?Al)?=?0.79, Al/(In?+?Al)?=?0.25, and Se/(Cu?+?In?+?Al)?=?0.98. The secondary ion mass spectra depth study reveals a shift in Al distribution from graded to uniform with an increase in selenization temperature to 550 °C. The stacked layers selenized at 550 °C reveal a uniform distribution of void-free dense grains (~?0.7 μm). Optical and electrical studies of selenized Cu(In,Al)Se₂ films at 550 °C show a direct band gap of 1.22 eV with a higher hole mobility of 14.0 cm²/V-s. The heterojunction solar cell of p-Cu(In,Al)Se₂/n-CuAlSe₂ was numerically simulated using SCAPS-1D software, yielding a high power conversion efficiency (η) of 21.01%.

     

A new chemical route for the preparation of fine ferrite powders

Precursors to MFe₂O₄ [spinels ferrites; where M = Ni(II), Co(II) and Zn(II)] have been prepared by the evaporation of polyvinyl alcohol added mixed metal nitratesolution, in presence and absence of urea. Theprecursor materials have low ignition temperature and are spontaneously combustible at low temperatures (250°C to 400°C). The heat liberated through the process is sufficient for the crystallization of the desired ferrite phase. The urea added process resulted in finer, superparamagnetic particles (12–17 nm) compared to the process without urea (particle size 25–30 nm). The ultrafine ferrite powders obtained have been characterized by X-ray powder diffraction (XRD), thermal gravimetry (TG), differential scanning calorimetry (DSC), infrared spectroscopy (IR), transmission electron microscopy (TEM) and room temperature magnetic measurement studies.     

In situ X-ray diffraction study of the effects of germanium and nickel concentrations on melting in gold-based contacts to gallium arsenide

Using X-ray diffraction in situ at 1 atm, the melting of the as-deposited film and the formation of the reaction product was investigated for gold, Au-Ge and Au-Ge-Ni contacts with various germanium and nickel concentrations. For the Au-Ge contact, the melting temperature of the as-deposited film was found to be 512±12 °C, 486±13 °C, 363±12 °C, and 363±12 °C with germanium concentrations of 0 wt.%, about 0.6 wt.%, 3 wt.% and 12 wt.% respectively. For the Au-Ge-Ni contacts, the melting temperature of the as-deposited film was 363±12 °C, 363±12 °C and 413±11 °C with germanium concentrations in the range 10–12 wt.% and nickel concentrations of 0 wt.%, 4 wt.% and 17 wt.% respectively. On subsequent cooling after the melting of the contact film, Au₇Ga₂ formed in Au-Ge contacts with 0–3 wt.% Ge and it melted on second heating at 405±5 °C, 387±18 °C and 337±12 °C for germanium concentrations of 0 wt.%, about 0.6 wt.% and 3 wt.% respectively. On subsequent cooling after the melting of the contact film, Au₂Ga formed in Au-Ge contacts with 12 wt.% Ge and Au-Ge-Ni contacts; Au₂Ga melted on second heating at 363±12 °C for Au-Ge-Ni contacts with 12 wt.% Ge and 4 wt.% Ni, and at 413±11 °C for Au-Ge-Ni contacts with 10 wt.% Ge and 17 wt.% Ni. Hence germanium decreased the melting temperatures of α-AuGa (gold-rich solid solution) and Au₇Ga₂ because of the presence of dissolved germanium in these phases. In addition, nickel increased the melting temperature of α-AuGa (gold-rich solid solution) and Au₂Ga owing to the presence of dissolved nickel in these phases.     

Effect of sulfurization in hydrogen sulfide on the properties of Cu(In,Ga)Se2 thin-film absorbers

In this research Cu(In,Ga)Se₂ thin films were sulfurized in H₂S–Ar gas mixture with processing temperatures ranging from 400 to 550 °C and time ranging from 10 to 60 min. The change in crystal phases, microstructure and chemical compositions of the absorber layers after sulfurization were investigated by X-ray diffraction, high resolution TEM, scanning electron microscopy, Raman scattering spectrum, energy dispersive X-ray spectrometer. In the process of sulfurization, the crystallinity and sulfurization degree of the Cu(In,Ga)(S,Se)₂ films depend strongly on the sulfurization temperature. The ‘Cu–Au’ phase was found for samples grown at low sulfurization temperature and transformed to chalcopyrite-type phase at high sulfurization temperature. The Se–S vibration mode of Cu(S,Se) alloy was also observed in the Raman spectra.     

Kinetics of intermetallic compound layer growth and interfacial reactions between Sn–8Zn–5In solder and bare copper substrate

Abstract

The growth kinetics of the intermetallic compound layer formed between Sn–8Zn–5In solder and bare Cu substrate by solid-state isothermal aging were examined at temperatures between 70 and 150°C for times up to 100 days. Experimental results showed that the intermetallic compound observed on the bare copper substrate was γ-Cu₅Zn₈ and its thickness increased with ageing temperature and time. The layer growth of the intermetallic compound in the couple of the Cu/Zn satisfied the parabolic law at the given temperature range. As a whole, because the values of time exponent (n) were approximately 0·5, the layer growth of the intermetallic compound was considered to be mainly controlled by diffusion mechanism over the temperature range studied. The apparent activation energy for growth of the γ-Cu₅Zn₈ intermetallic compound was 62 kJ mol^?1.     

High-temperature electrical conductivity and thermal expansion of SmBa2(Cu1-xFex 3O6+δ (x = 0–0.2)

The electrical conductivity and thermal expansion of SmBa₂(Cu_1-xFe_{x 3}O_6+δ (x = 0-0.2) were measured in air in the temperature range from 20 to 900°C. The linear thermal expansion coefficient was determined to be (12.8–13.5) × 10^-6 K^-1 in the temperature range from 20 to 350°C and (16.2–17.8) × 10^-6 K^-1 in the range from 350 to 800°C. Between 400 and 900°C, the conductivity of SmBa₂(Cu_1-xFe_x)₃O_6+δ was found to decrease with increasingx, mainly in the rangex = 0–0.1. This finding was interpreted in terms of the Fe occupancies on the Cu(1) and Cu(2) sites.     

Enhancement of MgAl<Subscript>2</Subscript>O<Subscript>4</Subscript> spinel formation from coprecipitated precursor by powder processing

Although low temperature fast coprecipitation technique has been used to synthesize stoichiometric (MgO-nAl₂O₃, n = 1) MgAl₂O₄ spinel forming precursor, delayed spinellization has always been the concern in this process. In this article, the precursor of this ‘fast technique’ has been used for bulk production by further processing by high speed mixing with solvents and mechanical activation by attrition milling in terms of superior spinellization. At 1000°C, MgAl₂O₄ — γ-Al₂O₃ solid solution and MgO phases are formed (spinel formed by 1000°C is regarded as primary spinel). At higher temperatures, due to large agglomerate size, MgO can not properly interact with the exsolved α-Al₂O₃ from spinel solid solution to form secondary spinel; and consequently spinellization gets affected. Solvent treatment and attrition milling of the coprecipitated precursor disintegrate the larger agglomerates into smaller size (effect is more in attrition). Then MgO comes in proper contact with exsolved alumina, and therefore total spinel formation (primary + secondary) is enhanced. Extent of spinellization, for processed calcined samples where some alumina exists as solid solution with spinel, can be determined from the percentage conversion of MgO. Analysis of the processed powders suggests that the 4 h attrited precursor is most effective in terms of nano size (< 25 nm) stoichiometric spinel crystallite formation at ≤ 1100°C.