High Temperature Solder Research Articles

Thermodynamic Modeling of the Au-Ge-X (X = In, Sb, Si, Zn) Ternary Systems.

In this study, the CALPHAD approach was employed to model the thermodynamics of the Au-Ge-X (X = In, Sb, Si, Zn) ternary systems, leveraging experimental phase equilibria data and previous assessments of related binary subsystems. The solution phases were modeled as substitutional solutions, and their excess Gibbs energies were expressed using the Redlich-Kister polynomial. Owing to the unavailability of experimental data, the solubility of the third elements in the Au-In, Au-Sb, and Au-Zn binary intermetallic compounds was excluded from consideration. Additionally, stable ternary intermetallic compounds were not reported in the literature and, thus, were not taken into account in the present thermodynamic calculations. Calculations of liquidus projections, isothermal sections, and vertical sections for these ternary systems have been performed, aligning with existing experimental findings. These thermodynamic parameters form a vital basis for creating a comprehensive thermodynamic database for Au-Ge-based alloys, which is essential for the design and development of new high-temperature Pb-free solders.

Synthesis and Characterization of Zn-xFe high Temperature Solder Alloy

This study aims to develop a lead-free high-temperature solder alloy using Zn and Fe, investigating how varying Fe content impacts microstructure, melting behaviour, and properties. Alloys of Zn-xFe (x = 0, 0.005, 0.01) were fabricated via melting and casting. Increasing Fe content reduced hardness and electrical conductivity, with significant microstructural changes observed. Compared to a Zn-xMo study, our results outperformed in mechanical characteristics. Zn-0.01 Fe emerged as the optimal composition, exhibiting the highest melting temperature (425.81°C), ultimate tensile strength (41.88 MPa), while displaying lower hardness and conductivity. Its microstructure boasted smaller grain boundaries, contributing to superior mechanical properties.

Electric current stressing enhanced damping properties in Sn5Sb solder

PurposeThe purpose of this paper is to investigate the effects of electric current stressing on damping properties of Sn5Sb solder.Design/methodology/approachUniformly shaped Sn5Sb solders were prepared as samples. The length, width and thickness of the samples were 60.0, 5.0 and 0.5 mm, respectively. The damping properties of the samples were tested by dynamic mechanical analyzer with a cooling system to control the test temperature in the range of −100 to 100°C. Simultaneously, electric current was imposed to the tested samples using a direct current supply. After tests, the samples were characterized using scanning electron microscope, electron backscatter diffraction and transmission electron microscope, which was aimed to figure out the damping mechanism in terms of electric current stressing induced microstructure evolution.FindingsIt is confirmed experimentally that the increase in damping properties is due to Joule heating and athermal effects of current stressing, in which Joule heating should make a higher contribution. G–L theory can be used to explain the damping properties of strain amplitude under current stressing by quantitative description of geometrically necessary dislocation density. While the critical strain amplitude and high temperature activation energy decrease with increasing electric current.Originality/valueThese results provide a new method for vibration reliability evaluation of high-temperature lead-free solders in serving electronics. Notably, this method should be also inspiring for the mechanical performance evaluation and reliability assessment of conductive materials and structures serving under electric current stressing.

Dual-cluster interpretation of Au–Sn binary eutectics and solders

Au–Sn alloy is an important high-temperature solder, but it has some disadvantages such as high cost and brittleness. Multicomponent alloying is often performed to improve performance and reduce their cost. However, due to the absence of an atomic structure model, there has been a lack of effective theory to guide their composition design. Since Au–Sn solders are typically eutectic-based, understanding the Au–Sn eutectic at the atomic level is of great significance for clarifying the composition origin of Au–Sn solders and the subsequent multi-component composition design. In the present work, the short-range order of Au–Sn eutectics is characterized using a dual-cluster model. In the dual-cluster formulism, the two eutectics Au69.6Sn30.3 and Sn94.6Au5.4 at. % are interpreted in terms of the hypoeutectic [SnAu12]Sn2Au3 + [Au–Au2Sn6]Au3 = Au70.0Sn30.0 and [Au–Sn8]Au1 + 2{[Sn–Sn10]Sn5} = Sn95.2Au4.8 alloys, respectively. The compositions of Au–Sn solders are then analyzed based on the interpreted dual-cluster formulas, which indicate that the number of atoms of the alloying elements that replace the atoms in the dual-cluster formulas is always an integer. The present method provides a quantitative approach toward developing a practical composition interpretation and design tool for Au–Sn-based solders.

An analytical review on interfacial reactions in high-temperature die-attach: The insights into the effect of surface metallization and filler materials

This review aims for a comprehensive insight into the interfacial reactions and the effects of surface metallization in high temperature die-attach, which is critical in governing the reliability of resultant interconnects of power electronic modules. With the emerging high-temperature filler materials, the interfacial interactions and microstructural evolutions exhibit various distinctive features, which demands detailed examination in order to identify suitable surface finishes. The metallization is not always beneficial to improving the quality and reliability of the interconnects, and consideration should also be given to the cost-effectiveness and manufacturability. The intermetallic compounds (IMCs) formed during interfacial reactions are of prime concerns for an extended discussion, together with the formation of solid solution at interfaces which can also be an important topic to explore. In this work, five commonly-encountered high temperature solder fillers are examined, including high-Pb, Au-based, Bi-Ag, Zn-Al solders and nano Ag paste, the emphasises are put on the interactions with different metallized surfaces in die-attach. The effects of metallization on interfacial reactions and formation of interfaces are discussed. Finally, the recommendations of suitable metallization are outlined to enable cost-effective and reliable interconnects for the related applications.

Controlling Pore Position during Transient Liquid Phase Bonding for High-temperature Soldering Processes

Controlling Pore Position during Transient Liquid Phase Bonding for High-temperature Soldering Processes

Effect of Minor Sb Additions on Thermal Properties, Microstructure and Microhardness of Sn–Ag–Cu High-Temperature Solder Alloys

Effect of Minor Sb Additions on Thermal Properties, Microstructure and Microhardness of Sn–Ag–Cu High-Temperature Solder Alloys

Fabrication of High-Temperature Solder by Zn Plating Films Containing Al Particles

This study investigated the microstructure and melting point of the Zn–Al composite electroplating film. The cross-sectional microstructure and shear strength of the joints made from the plating films were also evaluated. Zn and Al were confirmed in the plating films from initial microstructure observation. The plating film prepared by a plating bath without cationic surfactant melted near the melting point of Zn and the eutectic point of Zn–Al. When jointed at a joining temperature of 443°C, joining pressure of 5 MPa, and holding time of 5 min, multiple intermetallic compounds, Zn–Al eutectic layers, and unreacted Al particles were observed in the joint layer. From quantitative analysis, the multiple intermetallic compounds were estimated to be Zn–Ni and Zn–Al–Ni intermetallic compounds. The shear strength of the joints increased with increasing joining pressure but was lower than that of Sn–5Sb solder. Fracture after the shear test was observed at the interface between unreacted Al particles and Zn–Al–Ni intermetallic compounds, and inside unreacted Al particles.

A Drop-in High-Temperature Pb-Free Solder Paste that Outperforms High-Pb Pastes in Power Discrete Applications

Sn-based high-temperature lead-free (HTLF) solder pastes have been developed as a drop-in solution to replace the high-Pb solder pastes in power discrete applications. The pastes were designed to combine the merits of two constituent powders. A SnSbCuAg powder, with the melting temperature above 320°C, was designed to maintain a high-temperature performance. A SnAgCuSb powder, with a melting temperature around 228°C, was added to the paste to enhance wetting and improve joint ductility. In the design, the final joint will have the low-melting phase (the melting temperature >228oC) in a controllable quantity embedded into the high-melting SnSbCuAg matrix. HTLF-1, one of the designs, maintained the bond shear strength up to 15MPa, even around 290°C. Another design, HTLF-2, has a similar bond shear strength as Pb92.5/Sn5/Ag2.5 around 290°C, but exceeds substantially below 250°C. The power discrete components had been built with both HTLF solder pastes for both die-attach and clip-bond through the traditional high-Pb process, which demonstrated the drop-in processing compatibility. The components survived three additional SMT reflows (peak temperature of 260°C) and passed moisture sensitivity level 1. This confirmed that the maintained joint strength (comparable to or stronger than high-lead), helped to keep the joint integrity within the encapsulated components, even with melting phases in a controllable quantity existing above 228°C. Both HTLF solder pastes outperformed Pb92.5/Sn5/Ag2.5 in RDS(on) even after 1000cycles of TCT (-55/175oC), which is attributed to the intrinsic lower electrical resistivity of Sn of both HTLF pastes. Microstructural observation had shown no corner cracks for both die-attach and clip-bond joints after TCT.

Composite soldering materials for high-temperature stable solder joints

The thermal load on electronic assemblies is constantly increasing. The reasons for this increase are, on the one hand, the integration of power electronic components in an ever smaller space and thus an increasing power density and, on the other hand, the increasingly harsh environmental conditions with high temperature load. In addition to electronic components and substrate materials, the soldered connections are also exposed to this stress and must withstand it. The thermal stability is primarily determined by the melting temperature of the solder material or by the remelting temperature of the final solder interconnection. The remelting temperature can be purposefully increased through diffusion soldering. The advantage of diffusion soldering is that the operating temperature of the final solder joint can exceed the joining process temperatures. By using the composite soldering materials and diffusion soldering process it is possible to produce the solder interconnections that can withstand the high thermal and thermomechanical stress [1]. In this work, the composite solder material, consisting of the base solder alloy BiSnAg in eutectic composition with a melting point of 139 °C and added copper particles, was examined. The added copper particles have a direct influence on the dynamics of the diffusion process. Diffusion can also be influenced by adjusting the soldering process parameters, such as maximum temperature and time above liquidus of the base solder alloy, with the aim of achieving isothermal solidification. The solidification can take place through the parallel reactions: the reaction between tin and copper with the formation of high-melting intermetallic phases Cu3Sn and Cu6Sn5 and the growth of bismuth crystals through coarsening of the structure and tin depletion in the original eutectic solder alloy [2].

Controlling the thermal aging and Kirkendall void diffusion speed of sputtered silver interlayers in GaN power semiconductor packaging interfaces for in-wheel motor system integrations

We investigate the role of an Ag interlayer to suppress Kirkendall void formation in Ti/Ni surface finishes on the die-attached joints during harsh thermal aging tests at 250 °C. GaN dies were attached to the Ti/Ag/Ni sputtered direct bonded aluminum (DBA) and Ti/Ni sputtered DBA substrate using a high-temperature soldering, respectively. Without the Ag interlayer, void size increased to 0.69 µm after 1000 h of aging, but with the Ag interlayer, it reduced to 0.0794 µm. The Ag interlayer retards the development of cracks and void coalescing by controlling the diffusion rate between Ni/Sn at the bonding interface during thermal aging.

Reaction wetting behaviour of improved Ti-based brazing fillers on carbon/carbon composites at 1423–1573 K

Ti-based brazing fillers for carbon/carbon composite (C/C) connections are very promising; however, there is a lack of research on this topic. The wetting behaviour and mechanism of Ti-Cu-Si fillers on C/C at 1423–1573 K were investigated in this study. When the temperature was less than 1473 K, the contact angle decreased with time because of TiC layer formation, which exhibited a large interfacial ideal adhesion work (Wad) of 9.815 J/m2. However, the contact angle increased abnormally over time when the temperature exceeded 1473 K. This nonwetting behaviour can be attributed to the formation of SiC and Ti3SiC2 phases, which naturally increased the interfacial energy and surface roughness and decreased Wad (Wad of TiCu/SiC was reduced to 3.669 J/m2), and this hinders the spread of the liquid on the C/C substrate. These results suggest that increasing the temperature does not necessarily imply an improvement in wettability, thereby providing a new idea for developing high-temperature solders for C/C welding.

Wetting behavior and mechanical properties of Sn-10Sb solder/Ni-plated Cu system with different surface structures

The Sn-10Sb alloy is a high-temperature lead-free solder for soldering with Cu substrates. It often causes brittle solder joints and poor reliability due to the generation of an over-thick interfacial layer. Adding Ni plating to Cu substrates can suppress the generation of an excessively thick interfacial layer. This paper investigated the wettability and bonding strength of two different surface structures of Ni-plated Cu substrates with Sn-10Sb solder. Sn-10Sb solder exhibited a contact angle of 69° on the rough Ni-plated Cu substrate and 80° on the smooth one. TEM and XPS analyses demonstrated that the interfacial reaction product between the Ni-plated Cu substrate and the solder was (Cu, Ni)6Sn5. The finer grains on the smooth Ni-plated surface inhibit the diffusion of Cu atoms into the solder and the slower the interfacial reaction rate, which is more conducive to the generation of stable (Cu, Ni)6Sn5 phase. Therefore, the bonding strength ratio between the Ni-plated Cu substrate with a smooth surface and the solder is better.

Microstructure, electrochemical and mechanical properties of novel Zn–Sn–Cu–Ni high-temperature solder containing a small amount of Al

Microstructure, electrochemical and mechanical properties of novel Zn–Sn–Cu–Ni high-temperature solder containing a small amount of Al

Growth behavior of intermetallic layers at the interface between Cu and eutectic Sn–Bi by grain boundary diffusion with the grain growth at solid-state temperatures

The growth kinetics and rate-controlling processes of intermetallic layers formed in Cu/(Sn-58 wt% Bi) diffusion couples were investigated. Isothermal annealing of diffusion couples was conducted in the temperature range of 363–393 K for various times up to 384 h. In the diffusion couple, an intermetallic layer composed of Cu6Sn5 with irregular scallop shapes and Cu3Sn with relatively uniform thickness forms at the Cu/(Sn–Bi) interface. Isothermal sections of the equilibrium phase diagram in the ternary Bi–Cu–Sn system were calculated at the isothermal annealing temperatures and the peak temperature of the reflow process by a CALPHAD (calculation of phase diagrams) method. The diffusion path passes through the three-phase tie-triangle, including Cu6Sn5 and Cu3Sn. The obtained thicknesses were plotted against the annealing time, and a power function equation was found to describe their relationship. The values of the exponent in the power function were close to 0.25, indicating that the layer growth was predominantly controlled by boundary diffusion with the grain growth. Furthermore, the exponent values were relatively insensitive to the annealing temperature. The relationship between the exponent and the annealing temperature was analyzed, and it was concluded that the grain growth in the intermetallic layer followed a parabolic law. The growth and morphology evolution of the intermetallic compound and Sn–Bi eutectic microstructure at the interface were depicted, shedding light on the widening of the eutectic microstructure. Additionally, the activation enthalpy for the rate-controlling process of intermetallic layer growth at solid-state temperatures was evaluated using a least-squares method, providing insights into the energy barrier for the diffusion or transport of atoms across the interface. This study contributes to a better understanding of intermetallic layer formation and growth in Cu/(eutectic Sn–Bi) diffusion couples, offering valuable information for developing reliable solder joints and high-temperature solders.

Influence of CrFeCoNiCu high-entropy alloy and ultrasonic stirring on the thermal, electrochemical and mechanical properties of Zn-30Sn high-temperature solder alloy

In this study, the thermal, electrochemical and mechanical properties of Zn-30Sn solder alloy with different contents of CrFeCoNiCu high-entropy alloy (HEA) (0, 0.5 and 1 wt%) were investigated. At the same time, ultrasonic stirring was introduced into the melting process. The results suggested that the addition of HEA could refine the microstructure and the Zn matrix phases accelerated to dissolve to form more precipitation phases with the increase of HEA content from 0 to 1.0 wt%. The application of ultrasound could make the distribution of the phases disperse and facilitate the formation of dense and uniform corrosion products during the corrosion process. The electrochemical corrosion test and tensile test results showed that the ultrasonically treated Zn-30Sn solder alloy containing 1.0 wt% HEA had the lowest corrosion current density (Icorr = 1.11 μA·cm−2), the highest ultimate tensile strength (101.13 MPa) and yield strength (25.55 MPa), indicating that the corrosion resistance and mechanical properties were most outstanding. Moreover, the melting temperature of the composite solder alloys was slightly decreased from 379.5 °C to 377.5 °C.

Thermodynamic Description of the Au-Sb-Sn Ternary System

Phase equilibria and thermodynamic properties of the Au-Sb-Sn ternary system are important for the design of Au-based alloys as high-temperature lead-free solders to replace high-Pb solders. In this work, phase transition temperatures of five Sb-Sn alloys were measured using differential thermal analysis (DTA), and the temperatures of three invariant reactions were determined. Based on the measured experimental results in this work and the reported results, the Sb-Sn binary system was re-optimized using the CALPHAD method. The calculated results were in good agreement with available phase equilibria and thermodynamic data. This work was further combined with the previous assessments of the Au-Sn and Au-Sb binary systems and the present optimization of the Sb-Sn binary system to calculate the phase equilibria and thermodynamic properties of the Au-Sb-Sn ternary system, according to the reported experimental results, including thermodynamic properties and phase equilibria. The calculated liquidus projection, isothermal sections, vertical sections, as well as enthalpy of mixing and activity of Sn in liquid alloys are consistent well with the reported experimental results. A self-consistent set of thermodynamic parameters was obtained to accurately describe Gibbs energies of various phases in the Au-Sb-Sn ternary system, which would serve as a sound basis for developing a thermodynamic database of multicomponent Au-Sn-based alloy systems.

A Drop-in High-Temperature Pb-Free Solder Paste that Outperforms High-Pb Pastes in Power Discrete Applications

Sn-based high-temperature lead-free (HTLF) solder pastes have been developed as a drop-in solution to replace the high-Pb solder pastes in power discrete applications. The pastes were designed to combine the merits of two constituent powders. A SnSb-based Ag/Cu-containing high temperature powder, with the melting temperature above 320° C, was designed to maintain a high-temperature performance. A Sn-rich SnAgCu-Sb powder, with a melting temperature around 228° C, was added to the paste to enhance wetting and improve joint ductility. In the design, the final joint will have the low-melting phase (the melting temperature >228o C) in a controllable quantity embedded into the high-melting SnSb matrix. HTLF-1, one of the designs, maintained the bond shear strength up to 15MPa, even around 290° C. Another design, HTLF-2, has a similar bond shear strength as Pb92.5/Sn5/Ag2.5 around 290° C, but exceeds substantially below 250° C. The power discrete components had been built with both HTLF solder pastes for both die-attach and clip-bond through the traditional high-Pb process, which demonstrated the drop-in processing compatibility. The components survived three additional SMT reflows (peak temperature of 260° C) and passed moisture sensitivity level 1. This confirmed that the maintained joint strength (comparable to or stronger than high-lead), helped to keep the joint integrity within the encapsulated components in the following SMT process, even with the controlled quantity of the melting phases above 228° C. Both HTLF solder pastes outperformed Pb92.5/Sn5/Ag2.5 in the resistance from drain to source when power is on (RDS(on)), even after 1000cycles of TCT (-55/175o C), which is attributed to the intrinsic lower electrical resistivity of Sn of both HTLF pastes. Microstructural observation had shown no corner cracks for both die-attach and clip-bond joints after TCT.

Структура и свойства паяных соединений высоколегированных никелевых сплавов, полученных с помощью дугового нагрева в вакууме

Repair of blades made of the cast high-temperature nickel alloys with the volume content of γ’-phase of 50...65% and more by fusion and built-up welding practically leads to no results. Only introduction of special methods in certain cases provides restoration of a section satisfying the blade operation conditions. Therefore, the leading foreign and domestic enterprises mainly use high-temperature soldering in vacuum with general heating to repair blades of the nozzle unit, flaps of the adjustable nozzle and other parts of the gas turbine hot pass. It becomes possible to increase performance of the permanent joints (especially the small ones) by high-temperature soldering with the lowest acceptable thermal effect on the base metal through local heating in vacuum by the arc discharge with the hollow cathode. Arc soldering in vacuum with supply of the powder composite solders to the greatest extent combines advantages of built-up welding and high-temperature soldering with the general heating. Results of metallographic studies and mechanical tests of the solder joints obtained by arc soldering in vacuum with powder composite solders on samples with imitation of the surface defects showed higher performance compared to that for joints created by high-temperature soldering in vacuum with general heating.

Combination of enhanced strength-ductility trade-off and stress relaxation resistance of MWCNTs reinforced Sn–5Sb-0.3Cu matrix composite

In this study, the strength-ductility trade-off and stress relaxation (SR) behavior of Sn–5Sb-0.3Cu (SSC503) alloy reinforced with (0, 0.05and 0.1 wt%) multi-walled carbon nanotubes (MWCNT) have been investigated under different pre-strains and initial stress levels. The results show that the pre-deformation can extend the duration of initial SR stage and significantly promote the stress reduction rate. The SSC503–0.05MWCNT composite alloy exhibits the optimum increase in SR resistance, yield strength (σy), ductility, and creep threshold stresses with the values of 75.8%, 17.3%, 77.9% and 10.6%, respectively. The scanning transmission electron microscopy (STEM) images and electron probe microanalyzer (EPMA) revealed that the distribution of MWCNT in SSC503 alloy was concentration dependent. 0.05MWCNT concentration induced a dendritic/cellular transition of β-Sn grains and restrained the growth of β-Sn, Cu6Sn5, SnSb, Sn3Sb2 and Cu2Sb IMC compositions, whereas 0.1MWCNT led to the partial agglomeration of MWCNT into β-Sn grain surfaces. MWCNTs are adsorbed at the surface-active atoms of Sb metalloid to form Sb-coated MWCNTs (Sb/C) in situ, which act as a bridge between MWCNT and Cu6Sn5 particles. The modified composites represent a vital technological progress for utilization in high temperature solder applications.