Effect of Rare-Earth (La,Ce, and Y) Additions on the Microstructure and Mechanical Behavior of Sn-3.9Ag-0.7Cu Solder Alloy

In this article, we report on the microstructure and mechanical properties of Ce- and Y-containing Sn-3.9Ag-0.7Cu solders. The microstructures of both as-processed solder and solder joints containing rare-earth (RE) elements (up to 0.5 wt pct) are more refined compared to conventional Sn-3.9Ag-0.7Cu, with decreases in secondary Sn dendrite size and spacing and a thinner Cu₆Sn₅ intermetallic layer at the Cu/solder interface. These results agree well with similar observations seen in La-containing solders reported previously. The monotonic shear behavior of reflowed Sn-3.9Ag-0.7Cu-X(Ce, Y)/Cu lap shear joints was studied as well as the creep behavior at 368 K (95 °C). The data were compared with results obtained for Sn-3.9Ag-0.7Cu and Sn-3.9Ag-0.7Cu-XLa alloys. All RE-containing alloys exhibited creep behavior similar to Sn-3.9Ag-0.7Cu. Alloys with Ce additions exhibited a small decrease in ultimate shear strength but higher elongations compared with Sn-Ag-Cu. Similar observations were seen in La-containing solders. The influence of the RE-containing intermetallics (CeSn₃ and YSn₃) that form in these alloys on the microstructural refinement, solidification behavior, and mechanical performance of these novel materials is discussed.     

Effects of Indium Content on Microstructural,Mechanical Properties and Melting Temperature of SAC305 Solder Alloys

The present study investigated the effects of indium (In) addition on the microstructure, mechanical properties, and melting temperature of SAC305 solder alloys. The indium formed IMC phases of Ag₃(Sn,In) and Cu₆(Sn,In)₅ in the Sn-rich matrix that increased the ultimate tensile strength (UTS) and the hardness while the ductility (% EL) decreased for all In containing solder alloys. The UTS and hardness values increased from 29.21 to 33.84 MPa and from 13.91 to 17.33 HV. Principally, the In-containing solder alloys had higher UTS and hardness than the In-free solder alloy due to the strengthening effect of solid solution and secondary phase dispersion. The eutectic melting point decreased from 223.0°C for the SAC305 solder alloy to 219.5°C for the SAC305 alloy with 2.0 wt% In. The addition of In had little effect on the solidus temperatures. In contrast, the liquidus temperature decreased with increasing In content. The optimum concentration of 2.0 wt % In improved the microstructure, UTS, hardness, and eutectic temperature of the SAC305 solder alloys.     

Dissolution and interface reactions between the 95.5Sn-3.9Ag-0.6Cu, 99.3Sn-0.7Cu, and 63Sn-37Pb solders on silver base metal

Dissolution and intermetallic compound (IMC) layer development were examined for couples formed between 99.9 silver (Ag) and molten 95.5Sn-3.9Ag-0.6Cu (wt pct), 99.3Sn-0.7Cu, and 63Sn-37Pb solders, using a range of solder temperatures and exposure times. The interface reactions that controlled Ag dissolution were sensitive to the solder composition. The Ag₃Sn IMC layer thickness and interface microstructure as a whole exhibited nonmonotonic trends and were controlled primarily by the near-interface solder composition. The kinetics of IMC layer growth were weakly dependent upon the solder composition. The processes of Ag dissolution and IMC layer growth were independent of one another.     

Microstructure and Impression Creep Characteristics of Cast Mg-5Sn-xBi Magnesium Alloys

The microstructure and creep behavior of a cast Mg-5Sn alloy with 1, 2, and 3 wt pct Bi additions were studied by impression tests in the temperature range 423 K to 523 K (150 °C to 250 °C) under punching stresses in the range 125 to 475 MPa for dwell times up to 3600 seconds. The alloy containing 3 wt pct Bi showed the lowest creep rates and, thus, the highest creep resistance among all materials tested. This is attributed to the favorable formation of the more thermally stable Mg₃Bi₂ intermetallic compound, the reduction in the volume fraction of the less stable Mg₂Sn phase, and the dissolution of Bi in the remaining Mg₂Sn particles. These particles strengthen both the matrix and grain boundaries during creep deformation of the investigated system. The creep behavior of the Mg-5Sn alloy can be divided into the low- and high-stress regimes, with the respective average stress exponents of 5.5 and 10.5 and activation energies of 98.3 and 163.5 kJ mol⁻¹. This is in contrast to the creep behavior of the Bi-containing alloys, which can be expressed by a single linear relationship over the whole stress and temperature ranges studied, yielding stress exponents in the range 7 to 8 and activation energies of 101.0 to 107.0 kJ mol⁻¹. Based on the obtained stress exponents and activation energies, it is proposed that the dominant creep mechanism in Mg-5Sn is pipe-diffusion controlled dislocation viscous glide the low-stress regime and dislocation climb creep with back stress in the high-stress regime. For the Mg-5Sn-xBi alloys, however, the controlling creep mechanism is dislocation climb with an additional particle strengthening effect, which is characterized by the higher stress exponent of 7 to 8.     

Characterisation of Ag–Sn–Cu Dental Amalgam Powder and Its Amalgam Triturated with Nominal and Higher Pressure

Ag–Sn–Cu lathe cut particles of dental amalgam powders are mixed with mercury with an approximate 1:1 ratio. Mercury and amalgam powder mixtures are triturated at nominal pressure and at higher pressure applied intermittently, and then condensed into an acrylic mould with reasonably higher condensation pressure as well, followed by setting at room temperature for different time period. The microstructural features of the amalgam alloy powders and its amalgams of various states are studied by FESEM, X-ray elemental mapping, X-ray diffraction, differential scanning calorimetry and by hardness measurement as well. Results showed that the amalgams triturated with higher pressure have yielded finer matrix γ₁ (Ag₂Hg₃), presence of Ag-rich β₁ and finer unreacted γ (Ag₃Sn) phases with reduced porosity and higher hardness.     

Thermal properties and interfacial reaction between the Sn-9Zn-<Emphasis Type="Italic">x</Emphasis>Ag lead-free solders and Cu substrate

The thermal properties and interfacial reaction between the Sn-9Zn-xAg lead-free solders and Cu substrate, such as solidus and liquidus temperatures, heat of fusion, intermetallic compounds, and adhesion strength, have been investigated. Two endothermic peaks appear in the DSC curve when the Ag content in the Sn-9Zn-xAg solder alloy is above 1.5 wt pct. The solidus temperatures of the Sn-9Zn-xAg solder alloys are around 197 °C, but the liquidus temperatures decrease from 225.3 °C to 221.7 °C and 223.6 °C with increasing the Ag content in the solder alloy from 1.5 to 2.5 and 3.5 wt pct, respectively. Three intermetallic compounds, namely, Cu₆Sn₅, Cu₅Zn₈, and Ag₃Sn are observed at the Sn-9Zn-xAg/Cu interface. The Cu₅Zn₈ is formed close to the Cu substrate, Ag₃Sn is adjacent to it, and Cu₆Sn₅ is nearest the Sn-9Zn-1.5Ag solder alloys. A bi-structural Cu₆Sn₅ layer with hexagonal η-Cu₆Sn₅ and monoclinic η′-Cu₆Sn₅ is found at the Sn-9Zn-1.5Ag/Cu interface due to Ag dissolution. A maximum adhesion strength of 10.7±0.8 MPa is obtained at the Sn-9Zn-2.5Ag/Cu interface as soldered at 250 °C for 30 seconds.     

Thermal analysis of the compositional shift in a transient liquid phase during sintering of a ternary Cu-Sn-Bi powder mixture

In this work, differential scanning calorimetry (DSC) and microstructural analysis were used to study the transient-liquid-phase sintering (TLPS) of a Cu-Sn-Bi powder mixture. During sintering, the liquid phase shifts from a Sn-rich (i.e., ∼90 wt pct Sn) to a Bi-rich (i.e., >78 wt pct Bi) composition. In addition, the presence of Bi creates two melting events: a Sn:Bi eutectic reaction at 139 °C and a reaction involving the melting of (Bi) at 191 °C. The Sn:Bi eutectic melting event was fully transient. The melting event at 191 °C was consistent with the formation of a terminal Bi-rich liquid phase. The rate of compositional shift toward this terminal liquid phase at 260 °C was dependent on the rate of the reaction of the Sn with the Cu powder to form intermetallic phases. For mixtures made with medium and fine Cu powder, the terminal Bi-rich composition was reached after isothermal hold times of 20 and 15 minutes, respectively. This resulted in a new melting point for the mixture of 191 °C. For coarse Cu powders, the rate of the compositional shift toward a Bi-rich composition was much slower. The liquid phase remained at a hypoeutectic Sn-Bi composition estimated at 80 wt pct Sn, while the mixture maintained a melting point of 139 °C.     

电子部件封装用无铅焊接材料的研究动态

介绍了无铅焊接材料的研究背景，并以发展前景良好的候选材料Sn-Ag，Sn-Bi，Sn-Zn系共晶合金为例，介绍了无铅焊接材料的研究现状和存在的问题。研究表明，Sn-3．5％Ag基合金具有良好的力学性能，但熔点偏高；Sn-58％Bi基合金的机械性能略差，并且熔点太低；Sn-8％Z。基合金虽然有合适的熔点，但润湿性差。本文还简略地介绍了由日本开发的材料设计系统以及在无铅材料开发中的作用，并指出该材料设计系统将是开发无铅焊接材料中不可缺少的工具。     

Interfacial reactions in molten Sn/Cu and molten In/Cu couples

The interfacial reactions of molten Sn and molten In with solid Cu substrate were determined by studying their reaction couples. The annealing temperature was 300 °C. The phases formed at the interface were examined by optical microscopy, scanning electron microscopy, and electron probe microscopy analysis (EPMA). The thickness of the reaction layers was measured using an image analyzer. For Cu/Sn couples, two phases, ε and η, were found. Only the Cu₁₁In₉ phase was observed at the interface of the Cu/In couples. In comparison with the results of couples of solid Sn and solid In with solid Cu substrate, their phase formation sequences were similar; however, the interfacial morphology and the reaction rates were different. For the liquid/solid couples, the reaction rate was much faster and the interface was nonplanar. A mathematic model was also proposed to describe the dissolution of the Cu substrate and the growth of the intermetallic compounds. Fast dissolution of the substrate was observed in the beginning of the reaction and was followed by a relatively slow growth of the intermetallic compounds at the interface.     

Interfacial Reactions,Microstructure, and Strength of Sn-8Zn-3Bi and Sn-9Zn-Al Solder on Cu and Au/Ni (P) Pads

The Sn-8Zn-3Bi and Sn-9Zn-Al Pb-free solders were used to mount passive components onto printed circuit boards (PCBs) with electroless Ni immersed Au (ENIG) finishing layers using a reflow soldering process. The component mounted boards were aged at 150 °C for 200 to 1100 hours. The interfacial reactions and microstructure of the interfaces between the solders and the pads were observed using scanning electron microscopy and energy-dispersive spectrometry (EDS). Both solder joints on the two pads had similar interfacial microstructures; i.e., a very thin γ ₂-AuZn₃ layer was formed at the interface of the solder and Ni-P layer. The γ ₂-AuZn₃ layer transformed to an ε-AuZn₈ intermetallic compounds (IMC) with a consistent thickness during aging. Zinc atoms redeposited onto the IMC layer increased with increasing aging time. After aging at 150 °C for various times, the shear strengths of the ENIG and organic solderability preservative (OSP) joints were evaluated. The shear strength of the Sn-8Zn-3Bi solder joint was better than that of the Sn-9Zn-Al solder joint. All of the solder joints deteriorated after aging; however, the degradations of the OSP solder joints were more evident than those of the ENIG solder joints.     

A thermodynamic model of nickel smelting and direct high-grade nickel matte smelting processes: Part II. distribution behaviors of Ni, Cu, Co, Fe, As, Sb, and Bi

A thermodynamic model has been developed to predict the distribution behavior of Ni, Cu, Co, Fe, S, As, Sb, and Bi in nickel smelting and direct high-grade nickel matte smelting processes. The model has been validated by numerous experimental data and industrial data with a wide range of operating conditions. The effect of operating conditions on the distributions of Ni, Cu, Co, As, Sb, and Bi among the gas, matte, and slag phases has been investigated. It was found that the distribution behavior of Ni, Co, Cu, As, Sb, and Bi in the nickel smelting furnace depends on process parameters such as the smelting temperature, matte grade, oxygen enrichment, Fe/SiO₂ ratio in the slag, Cu/Ni ratio in charge, and oil/air ratio. The parameters also have an influence on the behavior of Fe₃O₄ in the slag.     

Interfacial IMC Layer and Tensile Properties of Ni-Reinforced Cu/Sn–0.7Cu–0.05Ni/Cu Solder Joint: Effect of Aging Temperature

Thermal aging behavior on the intermetallic compounds (IMCs) layer and mechanical properties of Cu/Sn–0.7Cu/Cu and Cu/Sn–0.7Cu–0.05Ni/Cu joints has been investigated from aging temperature of 60–180 °C for 100 h. Layer thickness increases as aging temperature rose for both the joints. Mechanical properties deteriorates with increase in aging temperature. After aging at 180 °C, any signs of ductile fracture surface with a large amount of dimples are absent. Instead, an intergranular fracture surface is obtained for both the joints, indicating that the process transformes from ductile to brittle behavior. However, brittle Cu₃Sn layer is observed between Cu₆Sn₅ layer and Cu substrate for Cu/Sn–0.7Cu/Cu joint after aging at 60 °C, while (Cu, Ni)₃Sn IMC layer is detected until aged at 140 °C for Cu/Sn–0.7Cu–0.05Ni/Cu. Compared with Cu/Sn–0.7Cu/Cu joint, the interfacial morphology directly changes from scallop-shaped into layer-shaped structure with lower Gibbs free energy, and the layer thickness is obviously suppressed after addition of Ni particle. Excellent mechanical properties, including UTS, elongation, and hardness, are obtained for Cu/Sn–0.7Cu–0.05Ni/Cu because of the slight increase in layer thickness and dense layer-shaped interfacial morphology. Thermal aging reliability is enhanced for the Cu/Sn–0.7Cu–0.05Ni/Cu solder joint after doping with 0.05 wt% Ni particle.     

Microstructural aspects of the dissolution and melting of Al2Cu phase in Al-Si alloys during solution heat treatment

The dissolution and melting of Al₂Cu phase in solution heat-treated samples of unmodified Al-Si 319.2 alloy solidified at ≈10 °C were studied using optical microscopy, image analysis, electron probe microanalysis (EPMA), and differential scanning calorimetry (DSC). The solution heat treat-ment was carried out in the temperature range 480 °C to 545 °C for solution times of up to 24 hours. Of the two forms of Al₂Cu found to exist,i.e., blocky and eutectic-like, the latter type is more pronounced in the unmodified alloy (at ≈10 °C) and was observed either as separate eutectic pockets or precipitated on preexisting Si particles, β-iron phase needles, or the blocky Al₂Cu phase. Dissolution of the (Al + Al₂Cu) eutectic takes place at temperatures close to 480 °C through frag-mentation of the phase and its dissolution into the surrounding Al matrix. The dissolution is seen to accelerate with increasing solution temperature (505 °C to 515 °C). The ultimate tensile strength (UTS) and fracture elongation (EL) show a linear increase when plotted against the amount of dissolved copper in the matrix, whereas the yield strength (YS) is not affected by the dissolution of the Al₂Cu phase. Melting of the copper phase is observed at 540 °C solution temperature; the molten copper-phase particles transform to a shiny, structureless phase upon quenching. Coarsening of the copper eutectic can occur prior to melting and give rise to massive eutectic regions of (Al + Al₂Cu). Unlike the eutectic, fragments of the blocky Al₂Cu phase are still observed in the matrix, even after 24 hours at 540 °C.     

Development and characterisation of direct laser sintering multicomponent Cu based metal powder

Abstract

Recent advances in direct metal laser sintering (DMLS) have improved this technique considerably; however, it still remains limited in terms of material versatility and controllability of laser processing. In the present work, a multicomponent Cu based metal powder, which consisted of a mixture of Cu, Cu–10Sn and Cu–8·4P powder, was developed for DMLS. Sound sintering activities and high densification response were obtained by optimising the powder characteristics and manipulating the processing conditions. Investigations on the microstructural evolution in the laser sintered powder show that liquid phase sintering with partial or complete melting of the binder (Cu–10Sn), but non-melting of the cores of structural metal (Cu) acts as the feasible mechanism of particle bonding. The additive phosphorus acts as a fluxing agent to protect the Cu particles from oxidation and shows a concentration along grain boundaries owing to the low solubility of P in Cu and the short thermal cycle of laser sintering. A directionally solidified microstructure consisting of significantly refined grains is formed, which may be ascribed to laser induced non-equilibrium effects such as high temperature gradient and rapid solidification.     

Solid solution creep behavior of Sn-xBi alloys

This study details the steady-state creep properties of Sn-1 wt pct Bi, Sn-2 wt pct Bi, and Sn-5 wt pct Bi as a function of stress and temperature. All data, including previous work on pure Sn, are described by the following empirical equation: