Sn Interface Research Articles

The effect of Sn microalloying on the selective oxidation of Fe-(6-10 at.%)Mn alloys

To evaluate the suitability of Sn microalloying as strategy to decrease the selective oxidation kinetics of Mn-alloyed advanced steels, the effects of 0.01 and 0.03 at.% Sn micro-additions on oxide morphology and oxidation kinetics for Fe-6Mn and Fe-10Mn (at.%) alloys were determined under annealing conditions characteristic of the continuous galvanizing process. Selective oxidation followed a parabolic rate law, where activation energy analysis revealed that internal oxidation is rate-determined by the grain boundary diffusion of O in Fe. The 0.01 and 0.03 at.% Sn additions significantly reduced the internal oxidation of alloys with Mn contents of 6 and 10 at.%, which was attributed to interfacial Sn segregation reducing the solubility of O in Fe, the occupation of adsorption sites for water vapour molecules, and the reduction of short-circuit diffusion of O along internal interfaces. Sn microalloying decreased the external oxidation of Fe-6Mn-(0.01,0.03)Sn, but did not significantly alter external oxide thickness of the Fe-10Mn-(0.01,0.03)Sn alloys. In this case, Sn reduced the outward diffusion of Mn along grain boundaries, but also affected the balance between the inward O flux and outward Mn flux. Incorporating the effect of Sn occupying adsorption sites into a selective oxidation model revealed that Sn microalloying is predicted to cause a transition from internal to external oxidation for Fe-10Mn. For Fe-6Mn alloys, however, a Sn micro-addition of 0.01 at.% (∼0.022 wt.%) was sufficient to significantly reduce selective oxidation kinetics and produce beneficial alterations to the external oxide morphology in order to ease reactive wetting in the continuous galvanizing process.

Exploring mechanism of suppressing void formation at Interface of Sn–9Zn and Cu

Exploring mechanism of suppressing void formation at Interface of Sn–9Zn and Cu

Interfacial Segregation of Sn during the Continuous Annealing and Selective Oxidation of Fe-Mn-Sn Alloys.

The effect of Mn on interfacial Sn segregation during the selective oxidation of Fe-(0-10)Mn-0.03Sn (at.%) alloys was determined for annealing conditions compatible with continuous galvanizing. Significant Sn enrichment was observed at the substrate free surface and metal/oxide interface for all annealing conditions and Mn levels. Sn enrichment at the free surface was insensitive to the Mn alloy concentration, which was partially attributed to the opposing effects of Mn on segregation thermodynamics and kinetics: Mn increases the driving force for Sn segregation via reducing Sn solubility in Fe but also reduces the effective Sn diffusivity by increasing the austenite volume fraction. This insensitivity was exacerbated by the depletion of solute Mn near the surface due to the selective oxidation of Mn. Thus, Sn segregation occurred in regions with a local Mn concentration lower than the nominal bulk composition of the alloys suggested. Sn enrichment at the metal/external oxide interface was reduced compared to the free surface and decreased with increasing bulk Mn content, which was attributed to changes in the external oxide morphology and metal/internal oxide interfaces acting as Sn sinks.

In situ transmission electron microscopy (TEM) study on the structural evolution behavior of nano Sn sheets under a thermal field

The pure Sn nanosheets were produced into nanospheres under the action of in-situ thermal field, and a heating experiment conducted on Sn and Cu interface samples, thereby elucidating the limitation of pure Sn as a solder material.

Research Progress of Electroplated Nanotwinned Copper in Microelectronic Packaging.

Copper is the most common interconnecting material in the field of microelectronic packaging, which is widely used in advanced electronic packaging technologies. However, with the trend of the miniaturization of electronic devices, the dimensions of interconnectors have decreased from hundreds of microns to tens of or even several microns, which has brought serious reliability issues. As a result, nanotwinned copper (nt-Cu) has been proposed as a potential candidate material and is being certified progressively. Firstly, the physical properties of nt-Cu have been widely studied. Notably, the higher thermal stability and oxidation resistance of the (111) texture causes nt-Cu to maintain excellent physical properties under high-temperature serving conditions. Secondly, recent works on the electrolyte and electroplating processes of nt-Cu on wafer substrates are summarized, focusing on how to reduce the thickness of the transition layer, improve the twin density, and achieve complicated pattern filling. Thirdly, nt-Cu can effectively eliminate Kirkendall voids when it serves as UBM or a CuP. Additionally, the high (111) texture can control the preferred orientation of interfacial intermetallic compounds (IMCs) at the Cu-Sn interface, which should be helpful to improve the reliability of solder joints. nt-Cu has superior electromigration resistance and antithermal cycling ability compared to ordinary copper RDLs and TSVs. Above all, nt-Cu has attracted much attention in the field of microelectronic packaging in recent years. The preparation-performance-reliability interrelationship of nt-Cu is summarized and displayed in this paper, which provides a solid theoretical basis for its practical applications.

Comparison of interfacial reactions and isothermal aging of cone Ni-P and flat Ni-P with Sn3.5Ag solders

Electroless Ni-P plating has good prospects for application as a diffusion barrier layer for interfacial reactions. In this study, the interfacial reaction between the microcone-structured Ni-3.5%P coating with high crystallinity and the Sn3.5Ag solder was investigated and compared with Sn3.5Ag/flat-Ni-(2%, 5%, 10%)P couples. Wettability experiments of Sn3.5Ag on four types of Ni-P coatings were carried out. Reflow at 250 °C for various minutes was performed, as well as isothermal aging experiments at 175 °C for various durations. The results showed that the Sn3.5Ag achieved the best wettability on cone Ni-3.5%P due to the pyramidal morphology that provides an additional driving force for wetting. During isothermal aging, the growth of intermetallics (IMCs) in the Sn3.5Ag/cone-Ni-3.5%P couple was attributed to the contribution of boundary diffusion mechanism to the rate control process, while that in the remaining three couples was a grain boundary diffusion-limited process. After reflow and isothermal aging, fewer microvoids and no harmful Ni-Sn-P layers were detected in the interface of Sn3.5Ag/cone-Ni-3.5%P couples, while they were detected in the other three couples, indicating that the cone Ni-3.5%P couple could inhibit the formation of Ni-Sn-P layer and microvoids. As a result, Sn3.5Ag/cone Ni-3.5% couples exhibited better shear resistance.

Designed 2D/2D/2D Bi2WO6/Ti3C2/SnNb2O6 Z-scheme heterojunction via interfacial chemical bond with enhanced photocatalytic activity

2D/2D/2D materials are widely used in photocatalysis owing to the advantages of high specific surface area, large contact interface, numerous charge transfer channels and ultrashort charge transfer distance. In this work, 2D/2D/2D Bi2WO6/Ti3C2/SnNb2O6 catalysts were successfully constructed via an anaerobic hydrothermal method. Due to ultrathin 2D Ti3C2 MXene served as an electron mediator and combined with 2D SnNb2O6 and 2D Bi2WO6 by Ti−O−Sn interface bond or Ti–O–Bi interface bond to form Z-scheme heterojunction, which could afford charge transfer channels and increase reactive sites. As a result, the Bi2WO6/Ti3C2/SnNb2O6 composites significantly improved the photodegradation efficiency of tetracycline hydrochloride due to the high redox ability, and its degradation rate in 90 min was 10.22 times that of SnNb2O6. This work provides an effective method to construct 2D/2D/2D Z-scheme heterojunction by tight chemical bond.

Effect of Al Bronze Interlayer on Liquid–Solid Compound Interface of Sn Bronze/Steel

To address the challenges of liquid metal embrittlement (LME) cracks and low bonding strength at the Sn bronze/steel liquid–solid compound interface, an innovative Sn bronze/Al bronze/steel laminated composite is fabricated using a wire arc additive manufacturing (WAAM) process, which involved introducing an Al bronze interlayer. The microstructure of interlayer and its related interfaces, as well as the mechanical properties of the composites, are investigated. Results show that the microstructure of Al bronze is mainly composed of α‐Cu and β‐Cu3Al. An interdiffused layer with a maximum thickness of 5 μm exists at the Al bronze/steel interface, which plays an important role in interface adaptation. The Sn bronze/Al bronze interface possesses a 30 μm α(Cu–Al–Fe) transition layer, and the continuous transition of α + β → α(Cu–Al–Fe) → α(Cu–Sn) from the base material to the clad layer is realized. No LME cracks are found in the steel after the Al bronze and Sn bronze deposition. The Al bronze/steel and Sn bronze/Al bronze interfaces exhibit strong bonding strengths of 395 and 361 MPa, respectively.

Microstructure and morphology of the soldering interface of Sn–2.0Ag–1.5Zn low Ag content lead-free solder ball and different substrates

Eutectic Sn–Ag–Cu lead-free solder has limited applications due to cost and reliability issues. Sn–Ag–Zn solder has the advantages of low melting point, good mechanical properties and reliable welding interface. However, the research system of low silver content Sn–Ag–Zn solder is incomplete. In this paper, Sn–2.0Ag–1.5Zn low silver content alloy solder is soldered to different substrates. The interfacial reaction after soldering and the microstructure and reliability under different aging treatment conditions are studied. Sn–2.0Ag–1.5Zn solder is made into solder balls by direct melting method. The solder balls are placed in a solder strength tester to be heated and welded to the substrate, and then the solder joints are placed in a heating furnace for aging treatment. The results show that the solder is soldered to the bare Cu substrate, and a dense double-layer Intermetallic Compound (IMC) structure of Cu5Zn8 and Ag3Sn is formed at the interface after aging treatment. The double-layer structure blocks each other, limiting the development of copper-tin IMCs. The solder is soldered with the Cu substrate electroplated with Ni barrier layer, and the soldering interface forms a thin layer of Ni3Sn4 metal compound. After aging for 1000 h, the thickness of Ni3Sn4 is about 1 μm, the thickness of Ni barrier layer is kept at 2–3 μm, and the barrier effect of Ni barrier layer is stable. Sn–2.0Ag–1.5Zn solder has excellent loss performance in long aging treatment. It has good heat-resistance aging treatment, good quality of solder connection, high interface reliability and less environmental pollution. The low silver content in Sn–2.0Ag–1.5Zn solder results in a significant cost reduction. Coarse IMC Ag3Sn is not easily formed. The optimized ratio of Ag and Zn in Sn–2.0Ag–1.5Zn solder improves the strength and toughness of the solder joint. The performance has been improved, and it is a very promising alloy solder.

Peculiarities of the density of states in SN junctions

We study the density of states (DoS) ν(E) in a normal-metallic (N) film contacted by a bulk superconductor (S). We assume that the system is diffusive and the SN interface is transparent. In the limit of thin N layer (compared to the coherence length), we analytically find three different types of the DoS peculiarity at energy equal to the bulk superconducting order parameter Δ0. (i) In the absence of the inverse proximity effect, the peculiarity has the check-mark form with ν(Δ0)=0 as long as the thickness of the N layer is smaller than a critical value. (ii) When the inverse proximity effect comes into play, the check-mark is immediately elevated so that ν(Δ0)>0. (iii) Upon further increasing of the inverse proximity effect, ν(E) gradually evolves to the vertical peculiarity (with an infinite-derivative inflection point at E=Δ0). This crossover is controlled by a materials-matching parameter which depends on the relative degree of disorder in the S and N materials.

Forming mechanism and growth of Kirkendall voids of Sn/Cu joints for electronic packaging: A recent review

For the common Cu-Sn interconnection system in microelectronics packaging, a significant concern is the sporadic interfacial void formation within the Cu–Sn interface and intermetallic compound (IMC) layer during the service. The existence of these voids affects the electrical and mechanical properties of the joint and thus deteriorates reliability. Most scholars simply attribute the Kirkendall voids problem to the Kirkendall effect caused by the difference in Cu/Sn inter-diffusion coefficients. However, Kirkendall voids are formed for a combination of many reasons. The plating additives, current density, surface roughness, coating thickness, and substrate types affect the formation of Kirkendall voids. We believe that among the many factors affecting the formation of voids, the unbalanced diffusion of elements (Kirkendall effect) is the root cause, and impurities and Cu microstructure are the dominant factors. The addition of alloying elements to the solder affects the formation of voids by changing the unbalanced diffusion of elements. This paper releases the possible mechanism of Kirkendall voids and gives the perspective summary from three steps of void formation, and the available suppression method is given based on the final solution.

Preferential growth of intermetallics under temperature gradient at Cu–Sn interface during transient liquid phase bonding: insights from phase field simulation

Transient liquid phase bonding under temperature gradient in electronics interconnections yields intermetallic grains at the bonding interface with different morphological features compared with conventional soldering process. However, the interfacial reactions due to the thermal gradient that result in the preferential growth of intermetallics are yet to be fully understood. In this study, incorporating with the thermotransport effect a multiphase field model is developed to elaborate the fundamental growth mechanism of Cu6Sn5 intermetallic in the Sn/Cu solder interconnect under temperature gradient. We particularly account for the effect of orientation and anisotropic thermal conductivity of Cu6Sn5 intermetallic grains in relation to the temperature gradient during their growth, as observed thermal conductivity with the c-axis of Cu6Sn5 intermetallic parallel to the gradient can be 1.6 times of those perpendicular to the gradient. Simulation results show that the temperature gradient can accelerate the growth of the Cu6Sn5 phase, as reported in the experiments. The heat flux is mainly conducted through the intermetallic grain with c-axis parallel to the temperature gradient, causing faster growth of the grain than the grain with c-axis perpendicular to the temperature gradient; the growth rate difference of the two types of grains becomes more pronounced under high temperature gradient. It is revealed that the faster and preferential growth of this type of intermetallic grain is attributed to the higher thermomigration induced diffusion flux and accompanying faster atomic interdiffusion process, especially near the solder/intermetallic interface.

Stress modulation on photodegradation of tetracycline by Sn-doped BiOBr

Stress modulation is an effective method to improve the performance of photocatalysts. In this paper, the stress modulated photocatalytic performance was achieved by constructing lateral pseudo-heterogeneous interface of Sn(IV)-doped BiOBr nanosheets, which were synthesized by a simple one-pot hydrothermal method. The stress value was calculated by W-H plot method based on the XRD results. The modulated photocatalytic performance was demonstrated by the photocatalytic degradation of tetracycline (TC) under visible light irradiation. The presence of tensile stress makes that 16% Sn(IV)-doped BiOBr has the strongest photo-generated current, and exhibits a p-n type electrochemical performance from the M-S plots, which results in the best photocatalytic degradation ability of ~ 16% Sn(IV)-doped BiOBr. Pure BiOBr is a n type semiconductor, Sn(IV)-doping makes BiOBr to be a p-n type semiconductor. It is found that the internal stress changes from compress force to stretch force with the increase of Sn(IV) content from 1% to 20%. Different radical sacrificial agents were added to clarify the photocatalytic mechanism. The relationship between internal stress and the photocatalytic performance has great potential to design new photocatalysts for the treatment of environmental pollutants.

Achieving a high dielectric constant and low dielectric loss of polymer composites filled with an interface-bonded g-C3N4@PbS narrow-bandgap semiconductor

Scattering medium-bandgap semiconductors into polymers cannot remarkably improve the dielectric constant in composites. Nanoscale ceramic leads to a high interface leakage current. To obtain a high dielectric constant and low loss, in this work, graphitic carbon nitride (g-C3N4)@PbS microparticles were prepared for fabricating polymer-based ternary composites. Polymer/PbS binary composites were also fabricated. In terms of electric properties, ternary composites show more advantages than binary composites. In ternary composites, the improved dielectric constant is ascribed to SN bonding at the g-C3N4/PbS interface. Decreased dielectric loss is rooted in the reduced interface leakage current (from the large size of the hybrid filler) between the polymer and PbS. Under high fields, the reduced breakdown strength is attributed to the reduced bandgap in the hybrid filler compared with PbS and g-C3N4. The innovation of this work is the high-efficiency collaboration between microsized and interfacial SN bonding in g-C3N4@PbS filler. The ternary composite with 15 wt% hybrid filler has a high dielectric constant of ~ 39 and a low dielectric loss of ~ 0.04 at 100 Hz (low field) as well as a high breakdown strength of ~ 202 MV m−1 under a direct-current field. This work might enlighten the fabrication of polymer composites with great promise in energy storage.

Effects of endogenous Al and Zn phases on mechanical properties of Sn58Bi eutectic alloy

Sn58-xBi-xAl-xZn were prepared by adding different addition (x = 0, 1.0, 2.0, and 3.0 wt%) of Al and Zn, and their response to melting point, microstructure, phase structure and mechanical properties were investigated. The presence of Sn-Bi-Zn eutectic significantly reduces the melting point of the alloy, but the heat fusion is increased with the increase of Zn and Al addition. The Al element is dispersed in the SnBi eutectic matrix in the form of dendritic Al-rich phase, and the Zn element is dispersed in the form of needle-like Zn-rich phase. Besides, the addition of Al and Zn leads to the refinement of the eutectic structure and the reduction of the interlaminar spacing. The Al, Zn, and Bi can be dissolved in Sn to form β-Sn phase. The competition of Al, Zn, and Bi solubilizes in Sn results in the diffraction peak of the alloy to shift. The doping of Al and Zn in Sn causes the diffraction peak of the alloy to shift to the right, but when the proportion of Bi solubilizes in Sn increases, the diffraction peak of the alloy shifts to the left. The phase interface of Sn and Bi is the non-coherent interface. The mismatch degrees between (200) Sn and (102¯) Bi is 27.5%. The liquid metal induced embrittlement (LMIE) phenomenon can be observed between Al grain and Sn phase, which leads to brittle fracture of Al grains. With the increase of Al and Zn content, the mechanical properties are significantly improved. When the Al and Zn addition reaches 2 wt%, the ultimate tensile strength (UTS) of Sn56Bi2Al2Zn reaches 68.5 MPa, while the elongation reaches 49.04%, which is 22.76% and 46.34% higher than that of Sn58Bi. However, when the Al and Zn addition reaches 3 wt%, the Sn56Bi3Al3Zn possess the best UTS (70.5 MPa), but the plasticity is reduced to 26.80%. Moreover, the macroscopic hardness of Sn55Bi3Al3Zn is 25.3 HV, which is 22.2% higher than that of Sn58Bi (20.7 HV). Results show that the endogenous Al and Zn phases plays an important role in the mechanical properties of Sn58Bi.

Interface behavior and electrical properties of Zn–Sn–Cu (CTZ) stacking layer films with thermal diffusion and electrically induced crystallization

In this study, a Zn–Sn–Cu sandwich structure was heated and electrically crystallized. The morphology, phase structure, diffusion behavior, and interface electrical properties of the sandwich structure and the microstructure changes in Zn, Sn, and Cu driven by heat and electricity were investigated. The experimental results revealed that thermal effects caused marked diffusion of Cu atoms. Cu6Sn5 IMC was formed at the Cu–Sn interface, and Cu5Sn8 was formed at the Zn–Sn interface. The electron flow drove Sn atoms into Cu with directional diffusion and inhibited Cu6Sn5 formation. Moreover, the overall electrical properties, interlayer thickness, and microstructure differences varied with the diffusion behavior and interface composition caused by thermal and electrical effects.

Investigation of microstructure and wetting behavior of Sn–3.0Ag–0.5Cu (SAC305) lead-free solder with additions of 1.0 wt % SiC on copper substrate

The current investigation was conducted to understand the effect of 1wt. % silicon carbide (SiC) in the Sn–3.5Ag–0.5Cu (SAC305) lead-free solder alloy which was produced by the powder metallurgy method. A systematic investigation of the microstructure of the solidified composite solder along with its wetting behavior was carried out at different reflow temperatures (230°C–290°C). From microstructure investigation, it was clear that SiC ceramic particles influence the development of IMCs at the Cu–Sn interface and refine microstructure in the bulk solder region. Micro-cracks were detected at Cu/SAC interface and also in the Cu6Sn5 layer. This is due to the development of extremely (brittle) intermetallic layer and ductile nature of Sn–3.0Ag–0.5Cu solder. The intermetallic layer thickness increased substantially with the increase of reflow temperatures (230°C–290°C). A uniform distribution of SiC, Ag3Sn, and Cu6Sn5 IMCs were found in the bulk b-Sn matrix. The result shows that the SiC particles promote the extra nucleation sites for the development of b-Sn phase and IMCs in the solidified structure. In addition to this, SiC particles, b-Sn dendrites and IMCs can prevent dislocation slippage which helps in attaining a strong solder joint due to strong strengthening effect. The results showed that the spread ratio, spread factor, and the relative spread area (RSA) increased while the equilibrium contact angle decreased with an increase in reflow temperature. This can be attributed to the strong adsorption effect and high surface free energy of the SiC particles.

Effect of Active Al on the Microstructure and Mechanical Properties of a Mo/Sn-Based Solder Interface: First-Principles Calculation and Experimental Study

In this work, Sn-based active alloys were used to solder a Mo electrode and Al together, and the effect of active Al on the Mo/solder interface was studied with methods of first-principles calculation and experiments. The Mo(110)/Sn(001) interface with bridge site was found to have the largest work of adhesion (Wad). The heat of segregation (ΔGseg) results reveal that Al atoms prefer to diffuse to the interface and form bonds with Mo, resulting in the Al-Mo intermetallic compound (IMC) layer. When two Al atoms appear at the interface, the value of Wad increases to 3.02 J/m2 dramatically, which indicates that Al strengthens the Mo/Sn interface. Then pure Sn, Sn-9Zn, Sn-9Zn-2Al, and Sn-13.5Zn-10Al alloys were prepared to solder Mo and Al assisted by ultrasound. Pure Sn and Sn-Zn solders have weak bonding with Mo, and the joints fractured from the interface with very low strength. When the Sn-9Zn-2Al and Sn-13.5Zn-10Al solders were used, the active Al segregated to the interface and reacted with Mo. The interface was strengthened by the Al-Mo IMC layer. The joints fractured inside the solder layer, and the shear strength of joints using Sn-13.5Zn-10Al reached 35 MPa.

Combining multi-phase field simulation with neural network analysis to unravel thermomigration accelerated growth behavior of Cu6Sn5 IMC at cold side Cu–Sn interface

In Pb-free solder alloys used in solder balls of diameter of 50 µm or smaller, larger proportion of Cu6Sn5 intermetallics formation is a major reliability concern, and this is aggravated in presence of external thermal gradient. A complete understanding of the mechanism for intermetallics compound (IMC) growth under thermomigration is essential for devising solder materials resistant to degradation under thermal gradient. This work integrates neural network analysis with multi-phase field method to quantify the mechanism of thermomigration at the cold side of a solder-substrate system. At hot side temperature of 523.15 K, 1D multi-phase field model is built for a combined driving force of bulk diffusion and thermomigration, and is solved using finite element method (FEM). The free energy density function for the thermomigration driving force is introduced, and coupled with the functions for bulk and interfacial free energy density of each phase. Data of heats of transport, temperature difference and growth rate constant of IMC are obtained from multiple FEM simulations, and the FEM-generated dataset is employed in the neural network. The machine learning predicted growth rate constant is tallied with experimental value, and heat of transport of Cu in IMC phase (QCuimc) is determined from the inverse method. The obtained value of optimized QCuimc is +35.10 kJ/mol. 2D IMC grain growth simulations are performed with hot-side at 523.15 K and the cold side lowered to 523.0817 K and 522.0 K respectively, thereby revealing that the accelerated grain growth for larger temperature difference is noticed within the first 20 s of the simulations.

The Evolution of Microstructures and Mechanical Properties of SnAgCu/Cu Weld Interface during Isothermal Aging

Based on the model of the diffusion flux ratio of Cu and Sn at the Cu/Cu3Sn/Cu6Sn5/Sn interface, the evolution of microstructures, the behavior of formation and growth of intermetallic compound (IMC) for Sn95.5Ag3.8Cu0.7 solder aged at 150 °C were studied. The nano indentation was applied to measure the hardness and elastic modulus of the IMC. The tensile strength and the low cyclic fatigue properties of the weld joint were also measured. The results showed that the thickness increments of Cu3Sn and Cu6Sn5 phases of IMC are mainly controlled by diffusion mechanism. The growth rates of Cu3Sn and Cu6Sn5 are 7.86×10-19 m2/s and 7.80×10-17 m2/s, respectively. The hardness and elastic modulus of IMC enhance with increasing aging time. For 24h aging time, the microstructure of the Cu6Sn5 keeps scalloped shape and the elastic modulus of IMC layer are similar to the copper substrate, which result in high fatigue resistance of the welded joint and its tensile strength of 69.50 MPa. With the mechanical hardening cumulative effects resulting from aging and cyclic strain, the fatigue performance and tensile strength of the welded joint gradually worse with the further increase of the aging time.