Bi-2212 Phase Research Articles

IMC growth mechanism of Sn58Bi/Cu solder joints and its effect on the coarsening of the Bi phase

IMC growth mechanism of Sn58Bi/Cu solder joints and its effect on the coarsening of the Bi phase

Microstructure of ternary Sn-Bi-xCu alloy on mechanical properties, current endurance and corrosion morphology via cycling corrosion test

Low melting temperature of Sn-58 wt.% Bi (SB) solders adding 0.5wt.% Cu (SB05C) and 1.7wt.% Cu (SB17C) concentrations were evaluated for the signal transmission in the 3D IC package. Microstructure combined with phase analysis and Pandat simulation were together with to explain the relationship among the mechanical property, electrical endurance and corrosion resistance. By Cu decoration, the presence Cu6Sn5 intermetallic compound (IMC) acts as heterogeneous nucleation sites to reduce surface free energy and generate fine Bi grain that resulted in higher hardness value. The power-law was used to explain the mechanism of interfacial IMC growth, both Cu6Sn5 and Cu3Sn formation were speculated to be volume diffusion control and surface reaction domination, respectively. The fracture morphology by shear testing indicates that earliest plastic deformation accompanied with brittle rupture were major factors due to the intergranular fracture and Cu6Sn5 compound induced bulk fracture. By cycling corrosion test (CCT), the lump shape of SnO2 by-product was found among solders at three cycling. After seven cycling, Sn phase has been completely corroded and Cu6Sn5 IMC began to be corroded forming circle shape of Cu2O but Bi phase still not be corroded among solders. In the electrical endurance, dense Cu6Sn5 dispersed in solder bulk and fine grain size were feasible to induce current crowding and joule heating, thus Cu deteriorated SB solders is easily failed.

A new aspect of the effect of fluorine doping on structural and superconducting properties in the Bi2Sr1.6La0.4CuO5+δ(O1-xFx) ceramic system

In this study, ceramic samples with the nominal composition Bi2Sr1.6La0.4CuO5+δ(O1-xFx) (where x = 0, 0.2 and 0.4) were synthesized using the solid-state reaction method to investigate the effects of fluorine anionic doping on the Bi-2201 system's structural, microstructural, and superconducting properties. X-ray diffraction analysis (XRD) confirmed the Bi-2201 phase in all samples and total incorporation of fluorine. Doping with fluorine reduced orthorhombicity, leading to an orthorhombic-tetragonal transition. Scanning electron microscopy (EDS) revealed changes in grain shape and size, while energy dispersive x-ray analysis (EDAX) confirmed fluorine incorporation. DC-electrical resistivity measurements showed that fluorine doping decreased the critical transition temperature TC (Onset), with a greater decrease observed at higher fluorine concentrations. The resistivity increase in the normal state of the sample with x = 0.4 was also noted. The conduction mechanism above TC (Onset) = 26.10 K followed the Arrhenius law, indicating thermally activated behavior due to a band gap.

Cross-sectional surface analysis of magnetic domains, microstructures, and magnetic properties of the low-temperature phase MnBi prepared by low-temperature vacuum sintering

In this work, the low-temperature phase MnBi prepared by a low-temperature vacuum sintering process at 325 °C was studied. We found a significant increase in the energy product from 2.63 MGOe in the 12-h sintered sample to 3.64 MGOe in the 48-h sintered sample. This improvement is attributed to the solid-liquid diffusion process. Cross-sectional scanning electron microscopy (SEM) reveals that MnBi forms at the external surface of Mn particles and along interior surfaces, notably within cracks. Transmission electron microscopy further demonstrates that the Mn ratio increases and Bi decreases with distance from the crack. The selected area diffraction showed variations in the Mn ratio with distance from cracks and identified both Bi and MnBi phases in the MnBi layer. Magnetic force microscopy (MFM) analysis exhibited large phase shifts indicating repulsive or attractive forces in single ferromagnetic domains. This provides valuable insight into magnetic domains in the MnBi regions near Mn cracks. The MnBi formation model, developed for the vicinity of single cracks with uniform MnBi content, partly explains the magnetic interactions and phase shifts observed near these cracks. These findings provide significant insights into the MnBi microstructural and magnetic properties, potentially useful in tailoring and engineering magnetic structures.

Contribution of bismuth melts to gold endowment in the Baolun gold deposit, Hainan Island, South China

Bismuth (Bi) melts and related polymetallic alloys can efficiently scavenge gold (Au) from Au-unsaturated aqueous solutions, contributing to the Au endowment in many hydrothermal deposits. However, original evidence for Au–Bi melts is often poorly preserved due to post-precipitation alteration. This complicates investigation of the liquid bismuth collector model in hydrothermal Au deposits. Here we present primary evidence for the occurrence of Au–Bi melt in hydrothermal systems through an examination of the Au–Bi phases and textures in the Baolun Au deposit (Hainan Island). This study found that maldonite, native bismuth, Au–Bi symplectite and Au–Bi melt blebs appeared successively following the precipitation of native gold. Notably, large Au–Bi melt blebs were well preserved in natural systems due to the rapid cooling of fluids. The mineral assemblages and their corresponding fluid physiochemical conditions suggest that the evolution of the ore fluids at Baolun was characterized by a continuous reduction in Au and Bi concentrations and Au/Bi ratios alongside decreasing fluid temperatures and sulfur fugacity (fS2). These observations offer direct evidence for Au scavenging by Bi melts in a mesothermal (275–450 °C), low-fS2 and reduced hydrothermal system, aligning well with the Au–Bi binary phase evolution established in metallurgy. As the fluid cooled further, the Au–Bi phases were subsequently overprinted by later Te–S-rich fluids, as evidenced by the formation of bismuthinite, jonassonite, and joséite-A around the Au–Bi phases. Importantly, our study reveals that the Baolun Au deposit ischaracterizedby a Au–Bi–Te hydrothermal system and that the metamorphic country rocks at Baolun are the major source of Au, Bi, and Te.

Morphologically and Compositionally Controlled Cs2SbBr6 by Bi and Ag Substitution

AbstractMorphology‐controlled Cs2SbBr6 crystals are synthesized by Bi‐ and Ag‐substitution of the precursor solution. X‐ray diffraction (XRD) together with Raman spectroscopy confirms the lattice tilting and symmetry changes with the dominant appearance of higher index facets by Bi substitution. Ag substitution does not induce crystal symmetry changes in the Cs2BBr6 (B = Sb or Bi) phase, but results in highly defective structures hindering the formation of a smooth surface during the crystal growth. Successful substitution of Bi and limited substitution of Ag into Cs2SbBr6 is also confirmed by energy dispersive X‐ray spectroscopy (EDX). This research provides design principles and practical examples of how to control the morphology of Cs2SbBr6 crystals with structural defects and multiphase formation.

Effect of Bi content and temperature on the shear mechanical properties of Fe-Bi nanocomposites: a molecular dynamics study

In this study, the effects of Bi content and temperature on the mechanical properties of Fe–Bi nanocomposites were investigated using molecular dynamics simulation. The research reveals that the nanocomposite’s shear strength reaches a peak of 3.785 GPa at a Bi content of 0.15%, attributed to the impediment of dislocation movement by twin boundaries during shearing, resulting in a dynamic ‘Hall–Petch’ effect and exceptional shear performance of the material. The abundant twinning induced around Bi phase inclusions introduces orientational disparities within the crystal, leading to grain misalignments, with dislocations in the grains slipping near the twin boundaries. In the nanocomposites, <100> dislocations merely act as initial sites for reactions, reducing their impact on the material’s strength and fracture behavior. The maximum stress decreases with increasing temperature while the magnitude of atomic transformations increases. The proportion of atoms at grain boundaries is higher at higher temperatures, and the arrangement of atoms at grain boundaries is more complex. At a temperature of 100 K, the dislocation density is highest with the smallest variation, forming a reinforced region within the material. The above results have significant implications for the design of environmentally friendly Bi-containing free-cutting steels.

Study on Ca-doping effects and structural stability in Bi2Sr2-xCaxCuO6+δ (0 ≤ x ≤ 1.2) compounds by Rietveld refinement and high-pressure Raman spectroscopy

The lattice distortion induced by element doping is regarded as an effective approach to improve the superconductivity of Bi-based superconductors. In this study, a series of Bi2Sr2-xCaxCuO6+δ (x = 0, 0.2, 0.4, 0.6, 0.8, 1.0 and 1.2) ceramic samples are prepared by Pechini sol-gel method. The Ca-doping effects, structural stability and superconductivity of Bi-2201 phase are studied by electron microscopy, high-pressure Raman spectroscopy, the standard four-probe technique, X-ray diffraction and Rietveld refinements. Results indicate that all samples are constituted by Bi-2201 main phase and Ca8.56Sr5.44Bi16O38 impurity. It can be determined that Ca atoms have entered Bi-2201 orthorhombic lattice and preferentially occupied the Sr-sites. When Ca atoms are introduced and high-pressure is exerted, the Bi-2201 lattice can present a relatively high structural stability. Meanwhile, the correlations between doping amount x, Cu–O–Cu bond angle (θ), carrier concentration of CuO2 planes and superconducting onset transition temperature (Tc,onset) are discussed particularly. It should be noted that the Bi-2201 lattice has the largest θ, the highest carrier concentration and the highest Tc,onset value of 84.98 K when x = 0.8.

Ni and Ni–P substrates inhibit Bi phase segregation and IMC overgrowth during the soldering process of Sn–Bi solder

In this paper, presents surface modification of Cu substrates by electroplating or chemical plating to obtain high-quality Ni and Ni–P coatings. The Sn58Bi solder reactions with Cu, Ni, and Ni–P UBMs at 180 °C, 250 °C, and 320 °C, respectively. Research has found that Ni and Ni–P substrates can inhibit Bi phase segregation and interfacial IMC overgrowth in Sn–Bi solder joints. Bi phase segregation occurs during the transition from Cu6Sn5 to Cu3Sn. There is Bi segregation at the interface of Sn58Bi/Cu solder joints to Cu3Sn/Cu interface, and IMC grows rapidly. However, Ni/Cu and Ni–P/Cu substrates can not only suppress the Bi phase segregation behavior of Sn58Bi solder joints during soldering, but also slow down the excessive growth of interfacial IMC; Even under the harsh soldering process of up to 320 °C for 600 s, it still has an effective blocking effect. In addition, at 320 °C, when Sn58Bi solder react with Cu, the interface directly crosses Cu6Sn5 to generate Cu3Sn, which exhibits the morphology characteristics of Cu6Sn5 due to high thermal conditions. During the soldering, Ni atoms continuously diffuse towards the interface, and Ni3Sn4 (Ni/Cu) grows from needle like in the early stage of soldering to rod like, and finally to block like; The block like appearance of Ni3Sn4 (Ni–P/Cu) occurs earlier than that of Ni3Sn4 (Ni/Cu), because the presence of columnar Ni3P layers provides a wider diffusion channel for Ni atoms, but the overall growth size is smaller than that on Ni/Cu. A higher undercooling can promote the growth of interfacial IMC, including Cu6Sn5 and Ni3Sn4. At the same time, the Bi phase inside the Sn58Bi solder joint is coarsened, and the substrate Ni/Ni–P can eliminate interfacial brittleness after eliminating Bi segregation.

The influence of Sm[formula omitted]O[formula omitted] nanoparticles adding on some superconducting properties of Bi[formula omitted]Pb[formula omitted]Sr[formula omitted]Ca[formula omitted]Cu[formula omitted]O[formula omitted] ceramics

High-Temperature Superconductors Bi1.6Pb0.4Sr2Ca2Cu3O10+δ samples doped with Sm2O3 nanoparticles in different quantities (0.00, 0.02, 0.04 and 0.06), were synthesised. Solid state feedback technique was used to prepare the samples and then characterised. The morphology and structure of the specimens were deployed by scanning electron microscopy (SEM) and X-ray diffraction (XRD) examination. The spectroscopy of the energy dispersive X-ray (EDX) experiment was utilised to obtain the elemental composition of the samples. Resistivity versus temperature measurement in DC mode was employed to estimate the critical transition temperature of each sample. XRD with the Rietveld refinement process revealed that Bi2223 and Bi2212 stages exist mutually in specimens with orthorhombic crystal systems. The lowest percentage of volume fraction associated with the Bi2223 phase belonged to the sample with x=0.06 nanoparticle samarium doped. It was detected that with rising samarium content the volume division of the Bi2223 phase decreases but the Bi2212 stage increases compared with the pristine specimen. SEM showed that the shrinkage of grain size occurs when the amount of nano-sized Sm was added to x=0.02 sample with lower inter-coupling among superconducting granules. This effect might be verified by SEM and TEM images. EDX exhibited some peaks related to Sm and other elements of the Bi2223 structure. These patterns confirm that all elements associated with the compounds were introduced into the Bi2223 matrix. The critical temperatures such as Tconset, TcPeak and Tczero decreased for Sm doped samples compared with the pure sample. Adding Sm2O3 nanoparticles causes rising calculated density and hole carrier concentration. These outcomes can be interpreted as the allocation of additional positive charges to the CuO2 planes. It is worth mentioning that the superb properties such as high-Tc, high Jc, strong flux pinning, and good thermal stability, for Bi2223 and high breakdown electric field, high dielectric constant, and large bandgap for Sm2O3 are the issues to motivate the author to dope Bi2223 with Sm2O3 NPs. In brief, the electrical, mechanical and structural properties of Sm2O3 NPs doped Bi2223 play the main role in the applications, which drive the investigations to emphasise the synthesis of superconducting samples.

Mechanical properties and microstructure evolution of Sn–Bi-based solder joints by microalloying regulation mechanism

Sn–Bi based solders are used in electronic packaging for interconnection processes. However, the rate of research on the comprehensive performance of solders is difficult to match the rapid development of advanced manufacturing of integrated circuits, resulting in the inability to obtain interconnect structures with excellent reliability for electronic devices. To demand a more effective modification method, we chose to dope 1.0 wt % In element in Sn58Bi–1Sb alloy. The strength, micromechanical properties and creep resistance of the solder were improved due to the combined effect of solid solution strengthening and diffusely distributed second phase strengthening. Furthermore, the addition of In element dramatically improved the thermal properties and wettability due to the generation of Bi3In5 intermetallic compounds (88.9 °C) and the activation energy of the solder wettability reaction was reduced to 247.36 J/mol. Notably, the addition of In element increased the amount of β-Sn phase deviation and decreased the Schmid factor value of β-Sn phase, resulting in a significant increase in the strength and micro-zone creep resistance. Under the action of current, a large amount of uniform Bi particle deviations and sub-crystalline structures persist in the β-Sn phase of the Sn58Bi–1Sb1In solder matrix. In the Cu/Sn58Bi–1Sb1In/Cu joints, many Bi particles are staggered in the β-Sn phase. Since the resistivity of the β-Sn phase is smaller than that of the Bi phase, the energization process leads to a possible further increase of the local currents at certain locations in the β-Sn phase, which reduces the electromigration resistance of the β-Sn phase. After energization, the biphasic twin structure with excellent electromigration resistance starts to degrade. The results show that the doping of In element comprehensively improves the performance of Sn58Bi–1Sb solder. It opens up a new idea for the design of alloying modification of tin-bismuth based solder.

Counter-intuitive mechanical performance variation in aged low-temperature interconnections in electronic packaging

Different from the conventional aging induced continuous mechanical performance deterioration in solder joints, a counter-intuitive “decrease-increase-decrease” variation in shear strength with a peak value 12 MPa higher than the initial state was captured in aged low-temperature BGA structure Cu/Sn–58Bi/Cu solder joints. The first decrease in shear strength was dominated by the coarsening of Sn and Bi phases. The following increase in shear strength was rooted in the concurrent Bi subgrain strengthening, solid solution strengthening of Bi element in Sn-rich phase and precipitation strengthening induced by the Bi-rich phase particles. The eventual decrease in shear strength was ascribed to severely deteriorated interface between the solder matrix and intermetallic compound layer being the weaker site in the long time aged solder joint. This aging induced strengthening phenomenon is inspiring in mechanical performance optimization and reliability elevation of SnBi-based solder joints for the coming chiplet and heterogeneous integration packaging.

Floquet engineering of axion and high-Chern number phases in a topological insulator under illumination

Quantum anomalous Hall, high-Chern number, and axion phases in topological insulators are characterized by its Chern invariant C (respectively, C=1, integer C&gt;1, and C=0 with half-quantized Hall conductance of opposite signs on top and bottom surfaces). They are of recent interest because of novel fundamental physics and prospective applications, but identifying and controlling these phases has been challenging in practice. Here we show that these states can be created and switched between in thin films of Bi_22Se_33 by Floquet engineering, using irradiation by circularly polarized light. We present the calculated phase diagrams of encountered topological phases in Bi_22Se_33, as a function of wavelength and amplitude of light, as well as sample thickness, after properly taking into account the penetration depth of light and the variation of the gap in the surface states. These findings open pathways towards energy-efficient optoelectronics, advanced sensing, quantum information processing and metrology.

Distinctive Effects between Hydrothermal and Ultrasound Synthesized SnO2 Nanoparticles on Ceramic Bi1.6Pb0.4Sr2Ca2Cu3O10+δ Superconductor

The effect of additions of two series of SnO2 nanoparticles synthesized using two different methods on crystal structure and superconductivity of Bi1.6Pb0.4Sr2Ca2Cu3O10+δ (BPSCCO) superconductors was investigated. Two series of spherical SnO2 nanoparticles were synthesized independently by using ultra-sonication (US-SnO2) and hydrothermal (HT-SnO2) methods. Polycrystalline samples of (Bi1.6Pb0.4Sr2Ca2Cu3O10+δ)1−x(SnO2)x, where x ranged between 0, 0.002 and 0.004, were fabricated by the solid-state reaction method. X-ray diffraction patterns showed a decrease in the volume fraction of the Bi-2223 and an increase in that of the Bi-2212 phases. Scanning electron microscopy images presented the “needle-like blossom” on the surface of the US-SnO2 doped samples, while the phenomenon was not found on the HT-SnO2 doped samples. The Tc was decreased extremely with US-SnO2 doping while slightly HT-SnO2 nanoparticle-doped samples. The field dependence of Jc, Jc(B), showed the opposite tendencies on two series of samples: Jc(B) was enhanced on the HT-SnO2 nanoparticle-doped samples, and that was decreased on UT-SnO2 nanoparticle-doped samples. The application of the Dew-Hughes model to explore the flux pinning mechanism exhibited that the point-like pinning centers were dominant on the HT-SnO2 doped samples. On US-SnO2 doped samples, however, the additional pinning center type was not found and could be explained by the observed over-sized SnO2 nano-needle.&#x0D; &#x0D; &#x0D;

Reducing anisotropy of rhombohedral Bi-rich phase for high-performance Ag-alloyed Sn–Bi low-temperature solders

The rhombohedral structure is with anisotropic properties, leading to brittle mechanical properties. However, it is one of the major constituent phases, the (Bi) phase, in the Sn–Bi-based low-temperature solders, which is demanding in the electronic industry for reducing the soldering temperature and alleviating the warpage in high-density fine-pitch electronic packaging. Herein, we proposed a high-performance Ag-alloyed Sn–Bi (SBA) low-temperature solder by reducing the fraction and, more importantly, the anisotropy of the (Bi) phase. We found that the (Bi) phase exhibited considerable solubility for Ag and Sn, even after thermal aging, without any nanoprecipitates as confirmed with both CALPHAD-type thermodynamic modeling and high-resolution TEM. The solution effects of Ag and Sn in the (Bi) phase is elaborated based on in situ nano-indentation, EPMA compositional analyses, EBSD characterizations, and ab initio calculations. The presence of Ag and Sn in the (Bi) phases resulted in both solid solution hardening and softening effects, depending on the Schmid factor of the grain. As a result, in (Bi) polycrystals, alloying could effectively mitigate the anisotropic mechanical properties of the (Bi) phase and facilitated a more uniform dispersion of forces exerted among (Bi) grains in all orientations. Consequently, the designed SBA solder exhibited superior mechanical properties, e.g., an ultimate tensile strength (UTS) of 55 MPa, elongation of 46%, and toughness of 20.6 × 106 J/m3 at a strain rate of 0.0005 s−1. This understanding opens the door for enhanced rhombohedral phase in alloy design for various applications.

Influences of oxygen partial pressure on the phase composition of the (Bi, Pb)-2212 precursor powder

Bi-2223 tapes, synthesized through the two-powder method, exhibit distinctive features such as high current density and a controllable secondary phase. Traditionally, the two-powder method involves the separate preparation of Bi-2212 and CaCuO powders followed by their mixing. However, during this process, it is necessary to dope the Bi-2212 powder with an appropriate Pb content to achieve a stable lattice structure in the Bi-2223 phase. The alteration of ion valences between Pb2+ and Pb4+ influences the oxygen content, thereby affecting the phase formation of (Bi, Pb)-2212 and, consequently, the final properties of Bi-2223 tapes. Surprisingly, limited research has explored the impact of the heat treatment process on (Bi, Pb)-2212. Consequently, this study investigates the phase composition and microstructure of (Bi, Pb)-2212 under various oxygen partial pressures to deepen our understanding of the effect of Pb on the composition of (Bi, Pb)-2212. Simultaneously, the behavior of Pb in the lattice of Bi-2212 is analyzed. Ultimately, the findings reveal that low oxygen conditions are advantageous for fabricating (Bi, Pb)-2212 powder with a high main phase content and a reduced secondary phase, thereby demonstrating excellent current-carrying performance in Bi-2223 tapes.

Fabrication and characterization of Sn-57 wt% Bi film by pulse DC current co-electrodeposition and reflow

The electrodeposited Sn-Bi eutectic alloys can satisfy the need for micro-bumps with low melting point in 3D packaging. We deposited Sn-Bi film by pulse DC current in electroplating solutions based on methane sulfonic acid (MSA). The effects of MSA concentrations and pulse frequencies on morphology and composition of deposits were investigated. As the MSA concentration increased from 120 ml/L to 160 ml/L, the hydrogen evolution reaction weakened resulting in smoother deposited surfaces, and the Bi content decreased. In the use of pulses allowing deposits to become more uniform and denser, the Sn-56.73 wt% Bi film with smooth surfaces were fabricated at a pulse frequency of 4 Hz and an MSA concentration of 120 ml/L, of which melting point was 134.35 °C. By using transmission electron microscopy (TEM) and electron backscattered diffraction (EBSD), the structures were characterized more microscopically, which are essential for diffusion and electromigration of micro-bumps. The near-eutectic deposits, both before and after reflowing, consisted of uniformly distributed tetragonal β-Sn phases and hexagonal Bi phases, and the most preferred orientations after reflowing were the same as before reflowing, that were (220)//ND for β-Sn and (1̅012)//ND for Bi. The average grain sizes of Sn and Bi in the deposits after reflowing were 1.44 µm and 0.64 µm, respectively, which were much smaller than those of Sn58Bi alloy obtained by rapid solidification. Dislocations were observed in Sn grains and misorientation values in β-Sn phases were larger, which illustrated that the β-Sn phase carried larger strains. As evaluated by constant loading rate (CLR) nanoindentation tests, the hardness and modulus were significantly improved after reflowing, and creep stress indices of the deposits before and after reflowing were 51.74 and 7.07, respectively.

Effect of ball–material ratio on Cu-Bi mixed powder and self-lubricating material properties

Purpose This study aims to investigate the effects of ball–material ratio on the properties of mixed powders and Cu-Bi self-lubricating alloy materials. Design/methodology/approach Cu-Bi mixed powder was ball milled at different ball–material ratios, and the preparation of Cu-Bi alloy materials was achieved through powder metallurgy technology. Scanning electron microscopy, X-ray diffraction and Raman spectroscopy were conducted to study the microstructure and phase composition of the mixed powder. The apparent density and flow characteristics of mixed powders were investigated using a Hall flowmeter. Tests on the crushing strength, impact toughness and tribological properties of self-lubricating alloy materials were conducted using a universal electronic testing machine, 300 J pendulum impact testing machine and M200 ring-block tribometer, respectively. Findings With the increase in ball–material ratio, the spherical copper matrix particles in the mixed powder became lamellar, the mechanical properties of the material gradually reduced, the friction coefficient of the material first decreased and then stabilized and the wear rate decreased initially and then increased. The increase in the ball–material ratio resulted in the fine network distribution of the Bi phase in the copper alloy matrix, which benefitted its enrichment on the worn surface for the formation a lubricating film and improvement of the material’s tribological performance. However, a large ball–material ratio can excessively weaken the mechanical properties of the material and reduce its wear resistance. Originality/value The effects of ball–material ratio on Cu-Bi mixed powder and material properties were clarified. This work provides a reference for the mechanical alloying process and its engineering applications.

Effect of co on the morphology and mechanical properties of the Sn-3.0Ag-0.5Cu/Sn-58Bi composite solder joints on ENEPIG surface

Microelectronic devices have demonstrated advanced capabilities, including multifunctionality and high input-output density, rendering them widely used in significant fields such as big data, data centers, and supercomputing. The reliability of microelectronics packages is contingent on the integrity of welded joints under diverse operating conditions for these applications. This research aims to examine the effects of 0.5 wt% Co element on the microstructure and properties of Sn-3.0Ag-0.5Cu/Sn-58Bi composite solder joints fabricated on the ENEPIG pads. The solder joints were exposed to a peak temperature of 220 °C and maintained at this level for different periods of time. The research included conducting a comparative examination on samples with and without additional Co to investigate the influence of Co inside solder joints on their microstructure and mechanical properties. The results show that the IMC changed from needle rod (Cu, Ni, Pd)6Sn5 to granular (Cu, Ni, Co, Pd)6Sn5 with the increase of holding time. The IMC at the solder joint interface added by Co changes from (Cu, Ni, Co, Pd)6Sn5 to (Ni, Cu, Co, Pd)3Sn4. The added Co element mainly exists in the form of a solid solution inside the solder joint, resulting in enhanced hardness of the Sn and Bi phases in the solder joint and a reduction in modulus.

Intermetallic compound growth behavior and mechanical performance in Sn58Bi/Cu solder joint bearing Mg particles incorporation during thermal aging

The microstructure and intermetallic compound (IMC) growth in Sn58Bi/Cu and Sn58Bi-0.4 Mg/Cu solder joints were examined in this study under varied thermal aging time (6, 12, 18, 24, and 30 h) at 120 °C. The Shear test was conducted to assess the solder joint mechanical performance. The results indicated that the precipitation of the Bi phase in Sn58Bi/Cu and Sn58Bi-0.4 Mg/Cu solder joints was not significantly inhibited by adding Mg as aging time increased. The IMC layer thickness of both solder joints increased as the aging time increased, but the Cu3Sn IMC thickness in Sn58Bi-0.4 Mg/Cu solder joint was consistently thinner than that in Sn58Bi/Cu joint. The temporal evolution of the Cu3Sn IMC layer was investigated, and it was found that the inclusion of Mg particles reduced the diffusion coefficient of Cu3Sn IMC. Furthermore, the shear test revealed that throughout the initial phases of thermal aging, fractures occurred within the solder matrix for both joints. As thermal aging time increased, fractures extended into the IMC layer, accompanied by transgranular and intergranular fractures. Simultaneously, adding Mg particles delayed brittle fracture in the solder joints, enhancing their mechanical properties.