Microstructural development in a rapidly cooled eutectic Sn-3.5% Ag solder reinforced with copper powder

Experiments using eutectic Sn-3.5% Ag solder paste were conducted with the objective of examining the conjoint influence of copper particles addition and rapid cooling on microstructural development. The composite solder mixture was made by thoroughly mixing a pre-weighed amount of copper particles with a commercial Sn-3.5% Ag solder paste. The experiments were quite similar to the heating and cooling cycle of an industrial reflow soldering process. Heating of the samples was conducted in a furnace whose temperature was carefully controlled. The cooling process was conducted on a chilled aluminum block through which coolant was circulated at 0.5 °C. When the solder temperature reached 250 °C, the circulating system would turn on automatically and the sample, which is still molten, is forced to cool rapidly. Temperature records of the solder samples revealed that addition of copper particles to the eutectic Sn-3.5% Ag did not appreciably affect the heating and melting properties when compared to the unreinforced Sn-3.5% Ag counterpart. However, copper particles did change the solidification temperature of the composite solder. Detailed observations for varying amounts of copper particle addition revealed that copper particles less than 1.0 wt.% lowered the solidification temperature of the composite solder. For copper particles greater than 1.0 wt.%, the solidification temperature increased a few degrees Celsius, indicating that some of the copper particles did not completely dissolve in the Sn-dominant solder during the melting process. Results reveal that as-solidified microstructures of the eutectic Sn-3.5% Ag solder contain columnar type dendrites of the Sn-rich phase and a eutectic mixture of the Sn₃Ag and Sn-rich phase located between the dendrite columns. The addition of copper particles to the eutectic Sn-3.5% Ag solder does refine the morphology of the primary phase, which is attributed to the presence and distribution of the Cu₆Sn₅ intermetallic in the solder matrix.     

Effect of TiO2 nanoparticles on the horizontal hardness properties of Sn-3.0Ag-0.5Cu-1.0TiO2 composite solder

The improvement in the hardness of Sn-3.0Ag-0.5Cu solder alloy reinforced with 1.0 wt % TiO₂ nanoparticles was evaluated by nanoindentation. A specific indentation array was performed on four different horizontal cross sections of the composite solder with different heights and diameters, in order to verify the mixing homogeneity of TiO₂ nanoparticles within the Sn-3.0Ag-0.5Cu solder paste during the ball milling process. The phase analysis indicated successful blending of the Sn-3.0Ag-0.5Cu with the TiO₂ nanoparticles. According the scanning electron microscopy micrographs, presence of the TiO₂ nanoparticles reduced the size of the Cu₆Sn₅ and Ag₃Sn intermetallic compound phases. Incorporation of the 1.0 wt % TiO₂ nanoparticles improved the hardness values up to 26.2% than that of pure SAC305. The hardness values increased gradually from the top cross sections towards adjacent to the solder/substrate interface. The mechanism of the hardness improvement attained by the TiO₂ nanoparticles addition were also investigated on the horizontal cross sections of the samples.     

Microstructure evolution and interfacial bonding mechanisms of ultrasonically soldered sapphire/Al dissimilar joints using Sn-based solders

Sapphire and 5A06 Al were ultrasonically soldered with Sn9Zn, SAC305 alloy solders and NiCu alloy foam added Sn-based composite solders, respectively. The microstructure and mechanical properties of joints were investigated and the interfacial bonding mechanism was analyzed. Cracks were observed at the sapphire/Sn matrix interface in joints soldered with alloy solders, which were disappeared in the joints soldered with composite solders. In the joint using NiCu–Sn9Zn composite solder, the solder seam was uneven and Al₃Ni intermetallic compound (IMC) layer was formed on the surface of NiCu alloy skeletons. While in the joint using NiCu-SAC305 composite solder, fine particles of (Ni,Zn)₃Sn₄ were largely formed and homogeneously distributed in the solder seam. An amorphous Al₂O₃ transition layer was formed at the sapphire/Sn matrix interface, and Zn enrichment was found at the Sn matrix/amorphous Al₂O₃ interface. The action mechanism of Zn was analyzed by first-principles calculation. The joints soldered with NiCu-SAC305 composite solder exhibited the highest shear strength of 74.42 MPa, the shearing failure mainly happened in the soldering seam.     

Electrodeposition of eutectic Sn96.5Ag3.5 films from iodide–pyrophosphate solution

Electrodeposition of SnAg alloy films and the effect of additives like PEG-600 and hydrazine hydrochloride on the same were studied in KI–K₄P₂O₇ solutions. PEG-600 was found to adsorb on the electrode surface, resulting in strong reduction inhibition of tin pyrophosphate complex ions, but it does not affect the reduction of silver iodide complex. It was found that hydrazine hydrochloride acted as a reducing agent for Sn⁴⁺ species and greatly improved surface morphology and roughness of the films by preventing the formation of Sn dendrites during electrodeposition. Eutectic Sn_96.5Ag_3.5 was obtained from a plating solution that contained both PEG-600 and hydrazine hydrochloride as additives, at the deposition current density of 40 mA cm⁻². Stress measurements of the SnAg films showed that it was tensile. X-ray analysis of the deposit showed the presence of β-Sn and ?-Ag₃Sn phases in the eutectic SnAg film. The DSC profile of SnAg film gave the melting point as 222 °C.     

Electroless Co-P for diffusion barrier in Pb-free soldering

Lead-free solders with high tin content and high melting temperature limit the reliability of electroless nickel/immersion gold finish on copper as diffusion barrier. Autocatalytic cobalt-phosphorus is proposed as a barrier metallization for copper in lead-free soldering. Autocatalytic deposition of cobalt is carried out in hypophosphite containing electrolytes at 95 °C and pH 8. Autocatalytic Co-P/Au finish with about 4 wt% P content strongly limits interdiffusion and intermetallic compounds formation with respect to the Ni-P/Au finish with Sn-Pb and Sn-Ag-Cu solder alloys. Contact angle of Sn-Pb solder alloy with Ni-P/Au and Co-P/Au layers is comparable, while in the case of Sn-Ag-Cu alloy contact angle is much lower for Co-P/Au than for Ni-P/Au layers. Mechanical strength of lead-free joints for Ni-P/Au and Co-P/Au finishes is evaluated with shear test on BGA coupons, obtaining higher joint strength values for autocatalytic cobalt.     

Electrodeposition and characterisation of Sn-Ag-Cu solder alloys for flip-chip interconnection

A pyrophosphate and iodide based bath was investigated for the electrodeposition of near-eutectic Sn-Ag-Cu alloys, which are promising lead-free solder candidates for electronics interconnection. Near-eutectic Sn-Ag-Cu electrodeposits (2.5-4.2 wt.% Ag and 0.7-1.5 wt.% Cu) were achieved from the system as measured by wavelength dispersive X-ray spectroscopy (WDS). Electroplating such near-eutectic ternary alloys at higher deposition rates was possible with the application of electrolyte agitation. Different morphologies of deposited Sn-Ag-Cu films were analysed using scanning electron microscopy (SEM). X-ray diffraction (XRD) data indicated that Sn, Ag₃Sn and Cu₆Sn₅ were present in the “as-electrodeposited” Sn-Ag-Cu film. The microstructure of the deposits and the morphology of Ag₃Sn and Cu₆Sn₅ intermetallics were characterised from cross-sectional images produced from a focused ion beam scanning electron microscopy and then imaged from transmission electron microscopy (TEM) micrographs. The proposed bath proved capable of producing fine pitch near-eutectic Sn-Ag-Cu solder bumps as demonstrated on a glass test wafer.     

Synthesis and characterization of ceramic nanoparticles reinforced lead-free solder

Sn-0.7Cu is among the least expensive types of lead-free solders available. However, its poor mechanical properties have limited its application. In this study, Sn-Cu lead-free solder reinforced with amorphous silica (SiO₂) nanoparticles was synthesized through powder metallurgy route. Desired mixtures of raw materials was mechanically milled, compressed, sintered and extruded to prepare bulk solder samples. The samples were characterized by optical and electron microscopy as well as mechanical tests. The results showed that mechanical properties were increased by addition of SiO₂ nanoparticles to the solder matrix. Addition of 1.5 wt% ceramic reinforcement to the composite increased tensile, yield and compressive strengths up to 27%, 23% and 41%, respectively, compared to those of the monolithic sample. In addition, the ceramic nanoparticles caused an up to 50% decrease in the wetting angle between the substrate and the nanocomposite solder.     

The effects of Cu and Al on dry sliding wear properties of eutectic Sn-9Zn lead-free solder alloy

The present study investigates the influence of Cu and Al on microstructure and wear behavior of a eutectic Sn-9Zn solder alloy. The Sn-9Zn–X alloy was produced by adding various amounts of Cu and Al through investment casting method. The produced Sn-9Zn–X alloys were characterized by a scanning electron microscope, X-ray diffraction, and hardness measurements. In wear tests at 1 ms^?1 sliding speed, 10 N load and 5 different sliding distances (400–2000 m) were used. The results show that as the amount of Cu and Al increased within Sn-9Zn alloy, the hardness of the alloy increased as well. Depending on the increase in hardness of the alloys produced by investment casting, it was observed that weight loss decreased during wear tests. Furthermore, the same proportion of added Al alloys’ hardness and weight loss were observed to be higher than the added Cu alloys. Furthermore, the Cu-added alloy exhibited higher hardness and lower weight loss than the Al-added alloy did.     

Synthesis and electrochemical evaluation of carbon coated Cu<Subscript>6</Subscript>Sn<Subscript>5</Subscript> alloy-graphite composite lithium battery anodes

With a view to minimize the unavoidable large volume changes of tin based Cu₆Sn₅ alloy anodes, a composite Cu₆Sn₅/graphite anode has been prepared via. a mechanical alloying process and subsequently coated with disordered carbon through pyrolysis of PVC. Phase pure products with better crystallinity and preferred surface morphology were obtained, as evident from PXRD and SEM respectively. Upon electrochemical charge-discharge, the intermetallic Cu₆Sn₅ alloy-graphite composite anode was found to exhibit an enhanced initial discharge capacity of 564 mAh g⁻¹ followed by significant capacity fade (>20%) especially after five cycles. On the other hand, carbon coated Cu₆Sn₅ alloy-graphite composite demonstrated promising electrochemical properties such as steady reversible capacity (∼200 mAh g⁻¹), excellent cycle performance (<5% capacity fade) and high coulombic efficiency (∼98%) via. significant reduction of volume changes. The carbon coating offers buffering and conductive actions on the anode active material and thereby enhances the electrochemical behavior of carbon coated Cu₆Sn₅ alloy/graphite composite anode material.     

Synthesis and electrochemical analysis of Sn2Fe-TiOx-C composite as a high-performance anode material for Li-ion batteries

Tin-based intermetallic compounds are regarded as a promising alternative for Li secondary battery anodes due to their high specific and volumetric capacity, as well as their low operating potential. However, the materials’ cycling performance still cannot meet the required standards for commercialization. In this study, we designed and synthesized a Sn₂Fe-TiO_x-C composite as a high-capacity anode material via high-energy mechanical milling and hydrogen treatment. The synthesized material was characterized by several analytical tools. The reaction mechanism of the composite electrode with Li was investigated with ex situ X-ray diffraction analysis, and the conversion of Sn₂Fe to Li–Sn alloy and Fe during Li insertion and its reversibility were confirmed. The results of an electrochemical test showed that a reversible capacity of 651 mAh g^?1 was retained after 100 cycles. This cycling stability could be attributed to the microstructure in which Sn₂Fe was uniformly distributed in the TiO_x and carbon matrix. Additionally, there was an improvement in rate performance after hydrogen treatment because titanium oxide produced during mechanical milling was partially reduced, which was helpful for enhancing the electrical conductivity of the composite electrode.     

Wetting and low temperature bonding of zirconia metallized with Sn0.3Ag0.7Cu-Ti alloys

The wettability of zirconia with Sn0.3Ag0.7Cu-Ti (SAC-Ti) alloys was investigated via the sessile drop method with the increase of temperature. Zirconia, pre-metallized with SAC-Ti metal powder at 900?°C, was brazed to copper using an SAC solder paste at the low temperature of 250?°C. The active element Ti reduced the contact angle as the temperature increased. The lowest contact angle of 8° was obtained with SAC-4?wt% Ti which possessed sufficient Ti and appropriate fluidity. When zirconia was pre-metallized with SAC-4?wt% Ti alloy, the typical microstructure of the copper/SAC/zirconia joint was copper/Cu₆Sn₅ layer/β-Sn layer containing Ti₃Sn and Ti₆Sn₅ phases/Ti₃Sn layer/TiO_x layer/zirconia. As the Ti content increased, more Ti-Sn intermetallic compounds remained in the seam, and the shear strength increased first and thereafter decreased. The highest shear strength of 19.1?MPa was achieved as zirconia was pre-metallized with SAC-4?wt% Ti. Fracture analyses indicated that brittle fracture was initiated at the reaction layers adjacent to zirconia and propagated in the seam during shear test.     

Formation of intermediate intermetallic layers on interaction of electrodeposited Sn,Ni-Fe,Ni-B coatings with different metallic substrata

The structure of layers and formation of intermetallic phases after thermal treatment in the system of thin electrodeposited Sn, Ni-Fe and sputtered Cu, Fe-Ni layers (thickness 0.1-2.0 μm) and thick electrodeposited Sn (thickness 6-10 μm) and Fe-Ni and Ni-B layers (thickness 2 μm) have been investigated by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM), and by metallographic and X-ray diffraction (XRD) techniques. The formation of intermetallic phases NiSn₃, Ni₃Sn₂, FeSn₂ and considerable reduction in the formation of brittle layers Ni₃Sn₄, Cu₆Sn₅, Cu₃Sn are determined by the structure and purity of electrodeposited tin [C (0.5-5) x 10-²; N (1-5) x 10-²; Fe, Cu, Bi, Pb (0.15-5.0) x 10^-2 wt%] in the system Sn/Fe-Ni/Cu. Electrodeposited Fe-Ni (80% Ni) as barrier layer in the system Sn/Fe-Ni/sputtered Cu completely prevents formation of Cu₆Sn₅, Cu₃Sn as a result of thermal treatment at 170°C up to 75 h. An amorphous Ni-B layer [B 4-8; C (3-7) x 10^-2 wt%] prevents formation of Ni₃Sn₄ and Cu₆Sn₅ in the system Sn/Ni-B/Cu (or Cu-Zn alloy) as a result of thermal treatment at 130°C (200 h) and 170°C (150 h).     

Highly conductive polymer composites with excellent toughness,fluidity and temperature-independent conductivity

Conductive polymer composites of low melting point metal/ high melting point metal/polymer were prepared by melt mixing and investigated the effects of Sn-to-Cu content ratio on the microstructure and properties of Sn/Cu/PA6 ternary composites with a metal content of 53.3 vol %. The results show that Sn reacts with Cu to form intermetallic compounds during melting processing. When V_Sn/V_Cu is less than 1.5, the metal phase is a solid. However, if V_Sn/V_Cu is higher than 1.5, the metal phase is a suspension. As V_Sn/V_Cu increases, the morphology of metal phase changes from “islands” to physically continuous networks, and the Volume resistivity, impact strength and complex viscosity of the composites can reach 1.11 × 10⁻⁴ Ω cm, 3.8 kJ/m² and 2.4 × 10³ Pa s, respectively. Moreover, the resistivity of the composites with physically continuous networks is almost independent of temperature. The combination of low and high melt point metals can be considered as a useful strategy to prepare conductive polymer composites with high performance. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48820.     

无铅焊膏在电子封装组装中的应用

随着人们对环境的日益重视和电子封装组装焊接技术的发展，合金焊膏的无铅化和质量的要求越来越高，开发无铅、无毒焊膏成为焊膏开发的重要方向，本文论述了几种无铅焊膏Sn-Ag系，Sn-Bi和Sn-Zn系的特点，同时，也检测和评价了一种Sn-Ag免洗焊膏，其绝缘抗阻性，抗腐蚀性，产品清洁度和产品可靠性等均符合要求。     

弱酸性电镀Sn-Ag-Cu合金及镀层焊接性能的研究

对弱酸性甲磺酸盐-碘化物电镀Sn-Ag-Cu合金工艺进行了优化,镀层光亮、致密、平整,阴极电流效率提高到25%左右.Sn-Ag-Cu合金镀层耐蚀性好;部分Sn-Ag-Cu合金镀层在高温高湿条件下有锡须产生;回流焊后Sn-Ag-Cu合金镀层与Sn-3.0Ag-0.5Cu焊料间结合牢固.     

Electrochemical window of molten LiCl-KCl-CaCl2 and the Ag/Ag reference electrode

The electrochemical window of an LiCl-KCl-CaCl₂ eutectic melt (52.3:11.6:36.1 mol%) was determined by cyclic voltammetry and open-circuit potentiometry at 723-873 K. The reaction at the anodic limit was confirmed to be Cl₂ gas evolution. The reaction at the cathodic limit was found to be a liquid Ca-Li alloy formation on the basis of ICP analysis of the deposits. An Ag⁺/Ag reference electrode separated with a Pyrex membrane showed good stability for more than 1 week. The standard electrode potential of Ag⁺/Ag was determined in the temperature range of 723-823 K by measuring the potential of a silver electrode in different concentrations of Ag⁺ ions.     

Preparation and Characterization of Silver‐Doped Cu(In,Ga)Se2 Films via Nonvacuum Solution Process

Cu(In,Ga)Se₂ films doped with different contents of silver ions (Ag⁺) were successfully prepared using nonvacuum spin coating followed by selenization at elevated temperatures. Increasing the Ag⁺ ion content increased the lattice parameters of the chalcopyrite structure, and shifted the A1 mode in the Raman signals to low frequencies. The band gaps of the prepared (Ag,Cu)(In,Ga)Se₂ (ACIGS) films were considerably increased, thereby increasing the open‐circuit voltage (V_oc) of the solar cells. As Ag⁺ ion content increased, the microstructures of ACIGS films became densified because the formed (Cu,Ag)₂In alloy phase with a low melting point facilitated liquid‐phase sintering. The evaporation of selenium species was correspondingly suppressed in the films during selenization, thereby reducing the selenium vacancies. The improvement in the microstructures and the defects of ACIGS films increased short‐circuit current (J_sc) and fill factor of the solar cells. The spectral response of the solar cells was also enhanced remarkably. This study demonstrated that incorporation of Ag⁺ ions into Cu(In,Ga)Se₂ films substantially improved the efficiency of the solar cells.     

Highly efficient double perovskite (Bi,Gd)-codoped Cs2Ag0.4Na0.6InCl6 phosphors for warm white LEDs

Bi-doped lead-free double perovskite Cs₂Ag_0.6Na_0.4InCl₆ phosphors have been proved to be effective for use in white LEDs. To further improve the luminescence effect of this promising material, Bi³⁺/Gd³⁺ co-doped lead-free perovskite Cs₂Ag_0.6Na_0.4InCl₆ phosphors were successfully synthesized using the oil bath method. The quantum efficiency of orange-emitting Cs₂Ag_0.6Na_0.4InCl₆:1% Bi³⁺ was effectively improved from 79.72% to 87.57% by co-doping Gd³⁺ ions. White LEDs were prepared by mixing the synthesized phosphor Cs₂Ag_0.40Na_0.60InCl₆: 1%Bi³⁺,10%Gd³⁺ and commercial blue phosphor BaMgAl₁₀O₁₇:Eu²⁺. Excellent warm white LEDs with colour coordinates (0.3464, 0.3224), colour rendering index of 93.9, and colour temperature of 4818 K were produced. The results of this study provide a meaningful reference for new lead-free halide perovskite luminescent material systems.     

Mineralizer effect on the synthesis of two types of one-dimensional chains silver-selenogermanate and selenostannate

Two type of one-dimensional compounds, K₂Ag₂GeSe₄(2) and K₃AgSn₃Se₈(4), were synthesized with thiophenol as a mineralizer, whilst two oligomers, Cs₄Ge₂Se₆ (1) and K₄Sn₃Se₈(3), were obtained in absence of thiophenol. Compounds 1 and 3 contain dimeric [Ge₂Se₆]^4? and trimeric [Sn₃Se₈]^4? anions, respectively. Compound 2 contains isolated GeSe₄ tetrahedra connected by linear-coordinated Ag⁺ ions to form an infinite anionic chains [Ag₂GeSe₄]^2?. The building blocks [Sn₃Se₈]^4? are linked by tetrahedral coordinated Ag⁺ ions to generate infinite chain [AgSn₃Se₈]^3? of 4.     

Microstructure and performance of brazed diamonds with multilayer graphene-modified Cu–Sn–Ti solder alloys

This study aims to improve the hardness of solidified Cu–Sn–Ti solder alloys and reduce the erosion of diamonds caused by these solder alloys during brazing. To achieve this aim, a new type of multilayer graphene-modified Cu–Sn–Ti composite solder alloy was proposed for brazing diamonds. The brazed diamond specimens were subjected to morphological observation, characterization of the interfacial microstructures. The static compressive strength and impact toughness of brazed diamond grits were measured. The Vickers microhardness of the solidified solder alloy was quantified, and the microstructure of the solidified solder alloy was also analysed. The results show that brazed diamond specimens fabricated with the No. 2 composite alloy containing 1 wt% multilayer graphene exhibited the best morphology. Addition of excess multilayer graphene reduced the flow properties of the molten Cu–Sn–Ti composite solder alloy. The dominant phases in the solidified Cu–Sn–Ti solder alloys were α-(Cu), Sn₃Ti₅, and CuSn₃Ti₅. Cu, Sn, and Ti were adsorbed by the multilayer graphene, forming C-rich and TiC-dominant phases. Consequently, erosion of the diamonds was reduced during brazing, and TiC was formed in the solidified solder alloy. Thus, increasing the content of multilayer graphene enhanced the static compressive strength and impact toughness of the brazed diamond grits, and increased the hardness of the solidified Cu–Sn–Ti solder alloy.