Study on properties of Sn–9Zn–Ga solder bearing Nd

The effects of Nd on wettability, microstructure and mechanical properties of Sn–9Zn–Ga–xNd lead-free solder were investigated. The results indicate that adding moderate amount of rare earth Nd, the wettability as well as mechanical properties of Sn–9Zn–0.5Ga solder were evidently improved, and when the content of Nd is at 0.08 wt%, the best wettability and comprehensive properties of soldered joint were obtained. It was also found that the addition of rare earth Nd could refine the microstructure of the solder, but some dark NdSn₃ phase appeared when the addition of Nd exceeded 0.15 wt%. Moreover, the IMCs thickness at the solder/Cu interface was reduced with the addition of Nd which gave a favorable influence on the mechanical property of the soldered joints.     

Effects of rare earth Ce on properties of Sn–9Zn lead-free solder

The influences of different Ce content on the properties of Sn–9Zn lead-free solder were investigated. The results indicate that Ce plays an important role not only in the structure and the solderability, but also in the interfacial structure of Sn–9Zn–xCe/Cu and mechanical property of soldered joint. Sn–9Zn–0.08Ce shows finer and more uniform microstructure than Sn–9Zn, and when the quantity of Ce is 0.5–1 wt%, some dark Sn–Ce compounds appear in the solder. With the addition of 0.08 wt% Ce, the solderability of solder is significantly improved because the surface tension of molten solder is decreased. Adding Ce makes the Cu5Zn8 IMCs formed at the interface of solder/Cu become much thicker than that of Sn–9Zn/Cu because much more content of Zn diffuse to the interface of solder/Cu to react with Cu. Results also indicate that adding 0.08 wt% Ce to the solder enhances mechanical property of soldered joint. When the Ce content is 0.1–0.5 wt%, some hard and brittle Cu–Zn IMCs appear in the bottom of dimples and the pull force of soldered joint decreases.     

Effects of Ga,Al, Ag,and Ce multi-additions on the properties of Sn–9Zn lead-free solder

Wetting balance method is used to evaluate the effects of Ga, Al, Ag, and Ce multi-additions on the solderability of Sn–9Zn lead-free solders, results show that the optimal addition amounts of Ga, Al, Ag, and Ce is 0.2, 0.002, 0.25, and 0.15 wt% respectively. The surface property of Sn–9Zn–0.2Ga–0.002Al–0.25Ag–0.15Ce solder is studied by X-ray photoelectron spectroscopy and auger electron spectroscopy analysis; results indicate that Al aggregates on the surface as a compact aluminum oxide film which prevents the further oxidation. The aggregation of Ce on the subsurface can reduce the surface tension of solder, and improve the solderability accordingly. Meanwhile, SEM and XRD analysis indicate that Cu₅Zn₈ and AgZn₃ intermetallic compounds form at the interface between Sn–9Zn–0.2Ga–0.002Al–0.25Ag–0.15Ce solder and Cu substrate, while AuZn₃ and AuAgZn₂ form at the interface between solder and Cu/Ni/Au substrate. Moreover, results also indicate that the mechanical property of soldered joints is improved duo to the dispersion strengthening effects of AgZn₃ in Sn–9Zn–0.2Ga–0.002Al–0.25Ag–0.15Ce solder.     

Mechanical properties of Sn–Zn lead-free solder alloys based on the microstructure array

The aim of this study is to develop a comparative experimental study interrelating mechanical properties, solidification thermal parameters and microstructure characteristics of a hypoeutectic Sn–4 wt.% Zn, a hypereutectic Sn–12 wt.% Zn and a eutectic Sn–9 wt.% Zn solder alloys. A water-cooled vertical upward unidirectional solidification system was used to obtain the samples. It was found that a more homogeneous distribution of the eutectic mixture, which occurs for smaller dendritic spacings in hypoeutectic and hypereutectic alloys, increases the ultimate tensile strength. The resulting microstructure of the eutectic Sn-9 wt.% Zn alloy has induced higher mechanical strength than those of the Sn–4 wt.% Zn and Sn–12 wt.% Zn alloys. It was found that the eutectic alloy experiences a microstructural transition from globular-to-needle-like Zn-rich morphologies which depend on the solidification growth rate. It is also shown that a globular-like Zn-rich morphology provides higher ultimate tensile strength than a needle-like Zn-rich eutectic morphology.     

Die attach properties of Zn–Al–Mg–Ga based high-temperature lead-free solder on Cu lead-frame

Several candidate alloys have been suggested as high-temperature lead-free solder for Si die attachment by different researchers. Among them, Zn–Al based alloys have proper melting range and excellent thermal/electrical properties. In this study, Zn–Al–Mg–Ga solder wire was used to attach Ti/Ni/Ag metallized Si die on Cu lead-frame in an automatic die attach machine. Die attachment was performed in a forming gas environment at temperature ranging from 370 to 400 °C. At the interface with Cu lead-frame, CuZn₄, Cu₅Zn₈ and CuZn intermetallic compound (IMC) layers were formed. At the interface with Si, Al₃Ni₂ IMC formed when 200 nm Ag layer was used at the die back and AgZn and AgZn₃ IMC layers when the Ag layer was 2,000 nm thick. Microstructure of the bulk solder consists of mainly two phases: one with a brighter contrast (about 80.9 wt% Zn) and the other one is a mixture of light (about 73.7 wt% Zn) and dark phases (about 45 wt% Al). Zn–Al–Mg–Ga solder wetted well on Cu lead-frame, covered entire die area and flowed in all directions under the Si die. Less than 10% voids were found in the die attach samples at die attach temperatures of 380 and 390 °C. Die shear strength was found within the acceptable limit (21.8–29.4 MPa) for all the die attach temperatures. Die shear strength of standard Pb–Sn solder was also measured for comparison and was found to be 29.3 MPa. In electrical test, maximum deviation of output voltage after 1,000 thermal cycles was found 12.1%.     

Interfacial microstructure and mechanical properties of In–Bi–Sn lead-free solder

The interfacial microstructure and mechanical properties of a low melting temperature lead-free solder of In-18.75Bi-22.15Sn (in at.%) (In–Bi–Sn) were investigated. The microstructure analysis of bulk In–Bi–Sn revealed that irregular lamellar γ-Sn phases distributed in the In₂Bi matrix. There was only a single endothermic peak with an onset temperature of 62 °C on the DSC curve, indicating that In–Bi–Sn is close to a ternary eutectic solder. The ultimate tensile strength of the bulk In–Bi–Sn was 21.76 MP at a strain rate of 10^?2s^?1 at 25 °C. The elongation of the bulk In–Bi–Sn solder reached 87 %, indicating an excellent ductility of the In–Bi–Sn solder. Two intermetallic compounds (IMCs), needle-like Cu(In,Sn)₂ and laminar Cu₆(In,Sn)₅, formed at the In–Bi–Sn/Cu interface. An IMC layer of polyhedral crystallites of InNi formed at the In–Bi–Sn/Ni interface. The shear strength of Cu/In–Bi–Sn/Cu solder joints was 21.15 MP, and the shear fractograph showed that the ductile fracture with dimples appearance occurred in the solder.     

Effect of zinc additions on structure and properties of Sn–Ag eutectic lead-free solder alloy

The effects of a third element, i.e., Zn in the range of 0.5–2.5 wt.%, on structure and properties of the binary Sn–Ag eutectic lead-free solder alloy were investigated. To identify the structure of the resulting alloys, X-ray diffraction analysis has been carried out. Resistivity, contact angles, Vickers microhardness and Young’s modulus have been measured. The results showed that all Zn contents were restricted in formation of Ag-Zn compound indicated by X-ray diffraction peaks, which increased continuously in the number and intensity as Zn content increased. Adding Zn up to 1.5 wt.% improved the wetting and mechanical properties. Above that, wetting angle increased due to the increase in AgZn compound, which may accumulated at the interface between solders and copper- substrate resulting a decrease in the adhesive strength. The alloy of composition Sn-3.5Ag-1.5Zn has the most improved properties between the others.     

Effects of Ga addition on microstructure and properties of Sn–0.5Ag–0.7Cu solder

The effects of rare element Ga on solderability, microstructure, and mechanical properties of Sn–0.5Ag–0.7Cu lead-free solder were investigated. The experimental results show that Ga plays a positive role in improving the wettability and the microstructure of the solder. When the content of Ga is at 0.5 wt%, the grain size of the solder is smaller and the shear force is enhanced greatly. It is also found that the thickness of the IMCs at the solder/Cu interface is reduced with proper addition of Ga. The increase of mechanical properties may be related to the refining of IMCs of the solder due to Ga addition.     

Effect of nanosized graphite on properties of Sn–Bi solder

A novel Sn–Bi composite solder reinforced by nanosized graphite was studied. Effect of nanosized graphite content on spreadability was studied by spreading test. Microstructure of Sn–Bi solder and Sn–Bi composite solder was observed by scanning electron microscope. The tensile test and creep test for Sn–Bi solder and Sn–Bi composite solder joints were conducted in a micro-mechanical test system. The results show that the addition of nanosized graphite is harmful to the spreadability of Sn–Bi solder. The microstructure of Sn–Bi composite solder is refined gradually with the content of graphite increased. The ultimate tensile strength of Sn–Bi composite solders joints is reduced with the addition of nanosized graphite and the ultimate tensile strength of Sn–Bi + 0.07 wt% solder joint is almost unchanged compared with Sn–Bi solder joint. There is a great improvement in elongation of Sn–Bi + 0.07 wt% graphite solder joint. Furthermore, Sn–Bi + 0.07 wt% composite solder has a better creep performance compared with Sn–Bi solder.     

Effects of Ga–Ag, Ga–Al and Al–Ag additions on the wetting characteristics of Sn–9Zn–X–Y lead-free solders

The effects of Ga–Al, Ga–Ag and Al–Ag binary additions on the wetting characteristics of Sn–9Zn–X–Y lead-free solders are studied by the wetting balance method. Experimental results show that Sn–9Zn–1.0Ga–0.3Ag, Sn–9Zn–0.005Al–0.3Ag, and Sn–9Zn–0.3Ga–0.002Al possess better wettability than the other alloys tested. The mechanism by which Ga, Al, and Ag additions improve the wettability is also proposed. It appears that dense aluminum oxide film formation and the enrichment of Ga on the surface may protect the bulk liquid solder from further oxidation. Moreover, results also indicate that, AgZn₃ IMCs layer formed at the interface, which may release reaction energy during the wetting, results in improving the wettability of the solder.     

Room-temperature indentation creep of lead-free Sn–Bi solder alloys

Creep behavior of the lead-free Sn–Bi alloys with bismuth contents in the range of 1–5 wt.% was studied by long time Vickers indentation testing at room temperature. The materials were examined in the homogenized cast and wrought conditions. The stress exponents, determined through different indentation methods, were in good agreement. The exponents of 13.4–15.3 and 9.2–10.0, found respectively for the cast and wrought conditions, are close to those determined by room-temperature conventional creep testing of the same material reported in the literature. Due to the solid solution hardening effects of Bi in Sn, creep rate decreased and creep resistance increased with increasing Bi content of the materials. Cast alloys, with a rather coarser grain structure and some Bi particles at the grain boundaries, showed typically higher resistance to indentation creep compared to the wrought materials. These two factors have apparently resulted in a less tendency of the material for grain boundary accommodated deformation, which is considered as a process to decrease the creep resistance of soft materials.     

Enhanced mechanical properties and corrosion behavior of Zn–30Sn–2Cu high-temperature lead-free solder alloy by adding Sm

Journal of Materials Science: Materials in Electronics - Zn–30Sn–2Cu–xSm (x?=?0, 0.1, 0.3, 0.5, and 1.0 wt%) solders were prepared to investigate its...     

Interfacial microstructures and mechanical properties of Sn–9Zn–0.5Ga–xNd on Cu substrate with aging treatment

The interfacial microstructures and mechanical properties of Sn–9Zn–0.5Ga–xNd on Cu substrate with aging treatment were investigated. Unlike the previous results, no Sn–RE phase was formed near the interface of Sn–9Zn–0.5Ga–xNd soldered joint after aging treatment at 150 °C for 1200 h. The combined action of Ga and Nd inhibited the formation of Sn–RE phase and resulted in an enhanced reliability of the soldered joint. The shear force of Sn–Zn–0.5Ga–0.08Nd soldered joint after aging treatment for 1200 h was twice the amount of Sn–9Zn joint and approaching the origin as-soldered joint of Sn–9Zn. Further, the fracture type of soldered joint still performed ductile after aging treatment for 1200 h. Synthesized the results of interfacial microstructures, mechanical test and fracture morphologies, Sn–9Zn–0.5Ga–0.08Nd solder has shown great potential to satisfy the increasing reliability requirements in electronics industry.     

Effect of the soldering time on the formation of interfacial structure between Sn–Ag–Zn lead-free solder and Cu substrate

The evolution of interfacial structure between the Sn–3.7%Ag–0.9%Zn lead-free solder and Cu substrate were systematically explored for different soldering times (1, 5, and 10 min). According to microstructural observations, it is found that the longer the soldering time is, the thicker the soldered interface becomes. The interface soldered for 1 min is composed of the Cu₅Zn₈ intermetallic compounds (IMCs) layer locating above the Cu₆Sn₅ IMCs layer. The interfaces soldered for 5 and 10 min are mainly made up of the Cu₆Sn₅ IMCs with some bulk Ag₃Sn IMCs randomly distributing within it. The evolution of the IMCs layer in the soldered interface can be divided into three stages: the Cu₅Zn₈ IMCs firstly forms, then Cu₆Sn₅ IMCs separated out from the bottom (controlled by diffusion of Sn in the Cu₅Zn₈), finally, subsequent growth of the Cu₆Sn₅ IMCs layer is controlled by diffusion of Sn in Cu₆Sn₅ IMCs.     

Effect of rare earth element additions on the impression creep of Sn–9Zn solder alloy

Creep behavior of the Sn–9Zn–RE alloys containing 0.1, 0.25 and 0.5 wt.% rare earth (RE) elements was studied by impression testing and compared to that of the eutectic Sn–9Zn alloy. The tests were carried out under constant punching stress in the range 40–135 MPa and at temperatures in the range 298–420 K. Results showed that for all loads and temperatures, Sn–9Zn–0.25RE had the lowest creep rate, and thus the highest creep resistance among all materials tested. This was attributed to the formation of Sn–RE second phase precipitates which act as the main strengthening agent in the RE-containing Sn–Zn alloys. RE contents higher than 0.25 wt.%, resulted in a lower creep resistance due to a reduction in the volume fraction of Zn-rich phase caused by the formation of Sn–Zn–RE intermetallics. The average stress exponents of 6.8, 6.9, 7.1, 6.8 and activation energies of 42.6, 40.6, 43.0 and 44.9 kJ mol⁻¹ were obtained for Sn–9Zn, Sn–9Zn–0.1RE, Sn–9Zn–0.25RE, and Sn–9Zn–0.5RE, respectively. These activation energies were close to 46 kJ mol⁻¹ for dislocation climb, assisted by vacancy diffusion through dislocation cores in the Sn. This, together with the stress exponents of about seven suggests that the operative creep mechanism is dislocation climb controlled by dislocation pipe diffusion.     

Creep deformation behavior of Sn–Zn solder alloys

Creep properties of three Sn–Zn solder alloys (Sn–9Zn, Sn–20Zn, and Sn–25Zn, wt%) were studied using the impression creep technique. Microstructural characteristics were examined using a scanning electron microscope. The alloys exhibited stress exponents of about 5.0. The activation energy for creep was calculated to be ~50–75 kJ/mol with a mean value of 66.3 kJ/mol. The likely creep mechanism was identified to be the low temperature viscous glide of dislocations.     

Research on Bi contents addition into Sn–Cu-based lead-free solder alloy

Journal of Materials Science: Materials in Electronics - This work aimed to investigate the effects of some Bi additions (x?=?0, 1, 3, and 5 wt%) added to Sn–2Cu solder alloy on...     

Effects of 0.1 wt% Ni addition and rapid solidification process on Sn–9Zn solder

Effects of 0.1 wt% Ni addition and rapid solidification process on Sn–9Zn solder alloy were investigated. Characteristics of Sn–9Zn–0.1Ni alloy were analyzed compared with those of as-solidified Sn–9Zn alloy. Mechanical properties and interfacial microstructure of solder/Cu joints obtained using these solders were comparatively studied. By comparison with as-solidified Sn–9Zn alloy, the wettability of solder was obviously improved with 0.1 wt% Ni addition, and the melting behavior of the solder was promoted due to the rapid solidification process. The corrosion resistance of as-solidified and rapidly solidified Sn–9Zn–0.1Ni alloys was improved due to the formation of Ni–Zn intermetallic compound (IMC) and the refining of Zn-rich phases. Formation and growth of IMCs at the interface of Sn–9Zn–0.1Ni/Cu joints was significantly depressed. Rapid solidification process promoted the interfacial reaction during soldering and improved the bonding strength of joints.     

Effect of doping Al on the liquid oxidation of Sn–Bi–Zn solder

The liquid oxidation behaviors of Sn–40Bi–2Zn and Sn–40Bi–2Zn–0.005Al solders were investigated from thermal dynamics and kinetics analysis. The characteristics of surface oxidation film at 170 °C were studied by thermo gravimetric analysis and X-ray photoelectron spectroscopy (XPS). Sn–40Bi–2Zn solder performed inferiorly in oxidation prevention performance, due to the formation of ZnO, which exhibits lower Gibbs free energy of formation and higher growth rate. Trace amount of Al addition, however, alleviated the oxidation behavior of Zn. XPS depth profile results indicated that the surface layer of Sn–40Bi–2Zn–0.005Al consisted of oxides of Al and Zn formed on the outer surface of the solder film and in the subsequent layer, mainly formed by the oxides of Sn, Bi. Al, basically formed as Al₂O₃, segregated towards the outer surface, seemed to deter the Zn oxidation on the solder surface.