Impression creep of the rare-earth doped Sn–2%Bi lead-free solder alloy

Creep behavior of the Sn–2Bi–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 Sn–2Bi alloy. The tests were carried out under constant punching stress in the range 70–190 MPa and at temperatures in the range 298–370 K. Results showed that for all loads and temperatures, Sn–2Bi–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–Bi, Sn–RE, and Sn–Bi–RE intermetallic particles which act as both strengthening agent and grain refiner in the RE-containing Sn–2Bi alloy. RE contents higher than 0.25 wt%, resulted in a lower creep resistance due to the formation of the same intermetallics but with much higher Bi content. This consumes the Bi content of the matrix and reduces the corresponding solid solution hardening, resulting in a lower creep resistance of the material. The stress exponents in the range 8–10.5, 8.4–11.5, 8.8–12.3, 8.4–11.6 and average activation energies of 64.5, 65.1, 67.4 and 68.0 kJ mol^?1 were obtained for Sn–2Bi, Sn–2Bi–0.1RE, Sn–2Bi–0.25RE, and Sn–2Bi–0.5RE, respectively. Although these activation energies are close to the activation energy of lattice self diffusion for β-Sn, the relatively high stress exponents of about 8–12 suggests that creep mechanisms associated with dislocation movement such as dislocation creep are prevailing.     

Creep of Pb–2·5Sb–0·2Sn alloy at low stresses

Abstract

The creep of a Pb–2·5Sb–0·2Sn alloy has been studied at stresses up to 6·5 MN m^?2 in the temperature range 318–348 K (0·53–0·58T_m) using helical specimens. At 333 K, a transition in the stress exponent from ~1 to 3 occurred at ~3 MN m^?2. The observed good agreements below the transition stress, both for experimental dE/do and predictions for Coble diffusional creep of lead, and for measured activation energy for creep and the activation energy for grain boundary self-diffusion in lead, suggest that grain boundary diffusional creep is the dominant mechanism. at low stresses. The presence of antimony does not seem to affect the magnitude of dE/do appreciably, and the results suggest that the grain boundary self-diffusivity of lead is not influenced by the presence of segregated antimony on the grain boundaries. The diffusional creep occurred above a threshold stress of magnitude ~0·5 MN m^?2, and its temperature dependence was characterised by an activation energy of ~20 kJ mol^?1, similar to the value of 23 ± 7 kJ mol^?1 typical of pure metals in the temperature range investigated. The stress exponent of ~3 observed for the power law regime suggests control by viscous glide of dislocations constrained by dragging of solute atmospheres. Preliminary tests on sagging beam specimens of as-worked material at an applied stress of 2·5 MN m^?2 and a test temperature of 333 K has provided the first direct evidence that anisotropic grain shape affects Coble creep. The specimen with the longest grain dimension along the stress axis underwent slower creep than the specimen with the longest grain dimension perpendicular to the stress axis. This observation is in qualitative agreement with theoretical predictions.

MST/1139     

Strengthening Sn60–Pb40 solder alloy by adding trace amount of La

The high temperature tensile strength of traditional Sn60–Pb40 solder alloy has been increased by 70% by adding trace amount of rare earth element La into it. Meanwhile, the thermal fatigue life of solder joints has been increased by two times. Such improvement is attributed to the modification effect of La on the microstructure of Sn60–Pb40 alloy.     

Tensile creep behavior of Sn–Ag–Cu–Ni multicomponent lead-free solder alloy

In the process of electronic packaging, the dissolution of under bump metallizations, such as Cu and Ni, into liquid solder occurs during soldering, which can change the original solder to a multicomponent one. Under the trend of miniaturization, it is quite necessary to evaluate the properties of multicomponent solder with excessive Cu and Ni compositions. In this study, the tensile creep behavior of Sn–3.5Ag–2.0Cu–0.5Ni multicomponent lead-free solder alloy is investigated at three temperatures, i.e., 303, 348 and 393 K. The steady-rate creep rates are obtained in the range of 10^?4–10^?8 s^?1, when the normalized stress, σ/E, is in the range of 10^?4–10^?3. Based on the Dorn equation, the apparent stress exponent (n _a), threshold stress (σ _th), and activation energy of creep (Q _C) are calculated at the three temperatures. It is found that the Sn–3.5Ag–2.0Cu–0.5Ni solder alloy shows a better creep performance than pure tin and eutectic Sn–3.5Ag solder due to the strengthening effect of Ag₃Sn and (Cu,Ni)₆Sn₅ IMC precipitations. The true stress exponent for creep is identified to be 7, indicating that the creep behave is controlled by the dislocation-pipe diffusion in the tin matrix.     

Study on creep characterization of nano-sized Ag particle-reinforced Sn–Pb composte solder joints

In the present work, the creep strain of solder joints is measured using a stepped load creep test on a single specimen. Based on the experimental results, the constitutive model on the steady-state creep strain is established by applying a linear curve fitting for the nano-sized Ag particle-reinforced Sn37Pb based composite solder joint and the Sn37Pb solder joint, respectively. It is indicated that the activation energy of the Ag particle-reinforced Sn37Pb based composite solder joints is higher than that of Sn37Pb solder joints. It is expected that the creep resistance of the Ag particle-reinforced Sn37Pb based composite solder joints is superior to that of Sn37Pb 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.     

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.     

Structural characterization and creep resistance of nano-silicon carbide reinforced Sn–1.0Ag–0.5Cu lead-free solder alloy

Nano-sized, non-reacting, non-coarsening SiC particles were successfully fabricated by high energy ball milling. Mechanically mixing was adopted to prepare SiC-particulate reinforced Sn–1.0Ag–0.5Cu (SAC105) composite solders. The effects of SiC addition on the melting behavior, microstructure and the corresponding creep properties were explored. It is found that the addition of 0.35–0.75 wt.% SiC nano-sized particles can effectively decrease the undercooling, while the melting temperature is sustained at the SAC(105) level, indicating that the novel composite solder is fit for existing soldering process. After the addition of 0.35% SiC nano-particles, a fine microstructure of Ag₃Sn and Cu₆Sn₅ IMCs with small spacing appeared in the β-Sn matrix. Moreover, the creep rate of the composite solder exhibited a consistently lower value than that of plain SAC(105) solder due to a second phase dispersion strengthening mechanism as well as a refinement of IMCs. Hence, the composite SAC(105)/0.35% SiC solder displayed a higher creep resistance (3.1 times) and fracture lifetime (3 times) than that of plain solder. However, this effectiveness is reduced when 0.75% SiC addition starts constricting the growth Ag₃Sn and Cu₆Sn₅ IMC and forming a weak interface with the enlarged β-Sn matrix.     

Impression creep behavior of Al–1.9%Ni–1.6%Mn–1%Mg alloy

In the present study, microstructure and creep behavior of an Al–1.9%Ni–1.6%Mn–1%Mg alloy were studied at temperature ranging from 493 to 513 K and under stresses between 420 and 530 MPa. The creep test was carried out by impression creep technique in which a flat ended cylindrical indenter was impressed on the specimens. The results showed that microstructure of the alloy is composed of primary α(Al) phase covered by a mantle of α(Al)+Ni₃Al intermetallic compound. Mn segregated into Al_xMn_yNi_z or Al₆Mn phases distributed inside the matrix phase. It was found that the stress exponent, n, decreases from 5.2 to 3.6 with increasing temperature. Creep activation energies between 115 kJ/mol and 151 kJ/mol were estimated for the alloy and it decreases with rising stress. According to the stress exponent and creep activation energies, the lattice and pipe diffusion- climb controlled dislocation creep were the dominant creep mechanism.     

Effect of aging treatment on microstructure and creep behaviour of Sn–Ag and Sn–Ag–Bi solder alloys

Abstract

The present study was undertaken to investigate the influence of aging temperature on the creep behaviour of Sn–Ag and Sn–Ag–Bi solder alloys at testing temperatures ranging from 333 to 363 K under constant stress of 7·80 MPa. The steady state creep rate was found to increase continuously with increasing aging temperature at all testing temperatures. Results show that addition of Bi to the binary Sn–Ag solder alloy led to a significant increase in the strength and improvement in the creep resistance. The activation energy for the creep process of Sn–Ag and Sn–Ag–Bi solder alloys was found to have an average value of 36 and 45 kJ mol^?1 respectively. This might be characterised by diffusion of Ag in Sn. The microstructure of the aged samples for both alloys examined by X-ray diffraction measurements supported the improvement in the creep resistance for Sn–Ag alloy by adding a small trace of Bi.     

Effects of nano-structured particles on microstructure and microhardness of Sn–Ag solder alloy

In this research, the typical nano-structured Polyhedral Oligomeric Silsesquioxane (POSS) particles were incorporated into the Sn–3.5Ag eutectic solder paste by mechanically mixing to form lead-free composite solder. The effects of nano-structured POSS additions on the microstructure and mechanical properties of as-fabricated composite solder alloys were systematically investigated. Experimental results indicated that the average size and spacing distance of Ag₃Sn intermetallic compounds (IMCs) in composite solder matrix decreased as compared to the Sn–3.5Ag eutectic solder. The 3 wt% addition of nano-structured POSS particles could enhance the microhardness of composite solder by 18.4% compared with the Sn–3.5Ag eutectic solder matrix. The average grain size and spacing distance of Ag₃Sn IMCs in Sn–Ag + 3 wt% POSS composite solder matrix reduced from 0.35 to 0.23 μm and from 0.54 to 0.32 μm, respectively. The refined Ag₃Sn IMCs, acting as a strengthening phase in the solder matrix, could enhance the microhardness of the composite solders.     

Effect of Al on the microstructure and properties of Sn–0.7Cu solder alloy

Effect of Al on the microstructure and mechanical properties were investigated. The results showed that Al could depress the formation of eutectic phase in Sn–Cu–Al solder alloy. The intermetallic compounds of Sn–0.7Cu–0.03Al were refined compared with that of Sn–0.7Cu–0.015Al. Segregated CuAl intermetallic compound was observed in Sn–0.7Cu–0.15Al and Sn–0.7Cu–0.5Al solder alloy. Sn-whisker was observed on the polished surface of Sn–0.7Cu–0.15Al and Sn–0.7Cu–0.5Al. The ultimate tensile strength of Sn–0.7Cu–0.03Al and Sn–0.7Cu–0.5Al was found to be higher than that of Sn–0.7Cu–xAl (x = 0, 0.015 and 0.15). The elongation of Sn–0.7Cu–0.015Al was the highest. The creep performance of Sn–0.7Cu–0.03Al and Sn–0.7Cu–0.5Al was similar and higher than that of Sn–0.7Cu and Sn–0.7Cu–0.15Al.     

Effects of triethanolamine and polyethylene glycol additives on electrodeposition of Sn–Ag solder alloy

Abstract

The effects of triethanolamine (TEA) and polyethylene glycol 600 (PEG600) on the polarisation behaviour and composition of electrodeposited eutectic Sn–3·5Ag film were systematically investigated in order to widen the deposition current density range for the simplicity and potential for cost effective production. The addition of TEA to the bath with PEG600 increased the tin deposition, which was inhibited by PEG600 addition. The addition of both TEA and PEG600 helped to obtain dense and fine grained Sn–Ag alloy films and also widened the operating window.     

Effect of adding nanometric ZnO particles on thermal,microstructure and tensile creep properties of Sn–6.5 wt%Zn–3 wt%In solder alloy

Mechanical properties of solders benefit from uniform dispersion of fine precipitates and small effective grain sizes. Metallurgical methods of attaining such a beneficial microstructure have been investigated in the plain Sn–6.5 wt%Zn–3 wt%In (plain) solder and Sn–6.5 wt%Zn–3 wt%In–0.3 wt%ZnO (composite) solder. It has been found that a small alloying addition of ZnO nano particles has a beneficial effect on the microstructure. It improves the tensile creep properties of the composite solder alloy. The improvement is attributed to uniform distribution and refining of the β-Sn dendrites and the effective refined grain size in the solidified microstructure. Thereby the composite solder has better mechanical properties than the plain solder alloy.     

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.     

Diffusion controlled reactions in Au/Pb–Sn solder system

Abstract

The microstructures resulting from the reaction between gold and Pb–Sn solder at temperatures of 80, 125, 140, and 160°C have been studied in the scanning electron microscope and measurements have been made of the reaction kinetics. In the initial stages, the growth rate of the layers of Au–Sn intermetal1ic product was found to be proportional to t^1/2 with an activation energy of (0·84±0·02) eV. At longer times, the growth rate fell below the t^1/2 dependence. This was thought to be owing to a restriction in the supply of gold to the reaction.

MST/1599a     

Effect of addition of Al and Cu on the properties of Sn–20Bi solder alloy

This study investigates the effect of the composite addition of Al and Cu on the microstructure, physical properties, wettability, and corrosion properties of Sn–20Bi solder alloy. Scanning electron microscopy and X-ray diffraction were used to identify the microstructure morphology and composition. The spreading area and contact angle of the Sn–20Bi–x (x?=?0, 0.1 wt% Al, 0.5 wt% Cu, and 0.1 wt% Al–0.5 wt% Cu) alloys on Cu substrates were used to measure the wettability of solder alloys. The results indicate that the alloy with 0.1 wt% Al produces the largest dendrite and the composite addition of 0.1 wt% Al and 0.5 wt% Cu formed Cu₆Sn₅ and CuAl₂ intermetallic compounds in the alloy structure. And the electrical conductivity of Sn–20Bi–0.1Al is the best, which reaches 5.32 MS/m. The spread area of the solder alloy is reduced by the addition of 0.1 wt% Al and 0.5 wt% Cu, which is 80.7 mm². The corrosion products of Sn–20Bi–x solder alloys are mainly lamellar Sn₃O(OH)₂Cl₂ and the corrosion resistance of 0.1 wt% Al solder alloy alone is the best. The overall corrosion resistance of Sn–20Bi–0.1Al–0.5Cu is weakened and the corrosion of solder alloy is not uniform.

     

Influence of small Sb nanoparticles additions on the microstructure, hardness and tensile properties of Sn–9Zn binary eutectic solder alloy

In the present study, different weight percentages of Sb nanoparticles (100–120 nm) ranging from 0 to 1.5 wt% were added to Sn–9Zn eutectic solder alloy to investigate the effect of third element addition on the microstructure, mechanical properties as well as thermal behavior of the newly developed composite solder alloys. The results indicate that the Sb nano-particle based intermetallic compounds (IMC) were found uniformly distributed, refined the microstructure and formed IMC particles in the eutectic solder alloy. After the addition of nano Sb particles in Sn–9Zn solder, fine α-Zn phase and ε-Sb₃Zn₄ IMC particles were clearly observed in the β-Sn matrix. The ε-Sb₃Zn₄ IMC particles were uniformly distributed in the β-Sn phase, which resulted in an increase in the tensile strength due to the second phase dispersion strengthening mechanism. However, in the doped Sn–9Zn/1.5Sb alloys, α-Zn phases were broken enormously, depleted and round shaped compared to the normal rod shaped α-Zn phase microstructure in plain Sn–9Zn solder. In comparison, the ε-Sb₃Zn₄ IMC particle in the doped Sn–9Zn/1.0Sb alloy were star shaped. The average tensile strength and micro-hardness of the Sb doped Sn–9Zn solder alloys were consistently higher than the plain un-doped Sn–9Zn solder. The tensile strength and the microhardness increased with increasing Sb nano-particle content, up to 1.0 wt% of Sb content, and then decreased beyond that threshold value. Consequently the percentage (%) elongation of the Sb nanoparticle doped Sn–9Zn solder decreased with increasing Sb nano-particle content, up to 1.0 wt% of Sb content, and then increased beyond that threshold value.