Influence of Zn addition on the microstructure, melt properties and creep behavior of low Ag-content Sn–Ag–Cu lead-free solders (original) (raw)
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Effect of Ag addition on the creep characteristics of Sn-8.8 wt% Zn solder alloy
Journal of Alloys and Compounds, 2009
Full implementation of the new generation of lead-free solders requires detailed knowledge and understanding of their mechanical behavior. The materials used in the present study are Sn-8.8 wt%Zn (binary) and Sn-8.8 wt%Zn-1.5 wt%Ag (tertiary) alloys. Effect of Ag addition, deformation temperature T and the applied stress, , on the creep characteristics have been studied. Creep tests were performed under the effect of different stresses ranged from 17.8 to 26 MPa at the deformation temperatures 291, 303, 323 and 343 K. The transient creep parametersˇand n were found to be markedly affected by the creep test conditions, T and. The parameterˇwas found to be decreased by increasing T and/or while n was found to increase by increasing T irrespective of the applied stress. The steady-state creep rateέ st was found to increase with increasing both T and in both solder alloys. The steady-state creep rateέ st was related to the stress with the relationshipέ st = C m where m = (∂lnέ st /∂ln) is the stress exponent. This exponent is decreased with increasing T in both alloys. Addition of 1.5 wt%Ag to the binary alloy increased its creep resistance. This behavior was attributed to the formation of the intermetallic compounds (IMCs) AgZn and Ag 3 Sn during solidification. These IMCs played the role of pinning action for the moving dislocations and consequently leading to the increase of its creep resistance. Micro-structural changes were investigated by scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD) analysis.
For development of lead-free solder for advance electrical components, the correlation of microstructure with thermal and creep properties of novel Ni-doped Sn–0.5Ag–0.7Cu (SAC (0507)) lead free solders has been investigated. Results showed that addition of 0.05Ni into the lead-free SAC (0507) solder led to the microstructural refinement, more uniform distribution of the Ag 3 Sn, (Cu,Ni) 6 Sn 5 intermetallic compounds (IMCs) and small primary b-Sn grains. However, the SAC (0507)–0.1Ni alloy has relatively high fraction of the primary b-Sn phase and the IMCs appeared coarse within the matrix compared with the other examined alloys. DSC results showed that the addition of Ni did not produce any significant effect on the melting behavior. Interestingly, 0.05 wt.% Ni addition exhibited a drastically reduced und-ercooling to be 6.3 °C. In terms of creep behavior, the SAC (0507)–0.05Ni gave the highest creep resistance due to the fine dispersion of IMCs. Furthermore, 0.05 wt.% Ni addition can evidently increase the creep– rupture life, about 2.0 times greater than that of the baseline SAC (0507) and approximately 5.0 times better than that of SAC (0507)–0.1Ni solder. Meanwhile, the SAC (0507)–0.1Ni alloy shows lower creep resistance which is mainly attributable to smaller volume fraction of the precipitate phases. Based on the obtained stress exponents and activation energies, it is proposed that the dominant deformation mechanism in SAC (0507) solders is dislocation climb over the whole temperature range investigated.
Materials & Design, 2012
The eutectic Sn-0.7Cu solder alloy is widely used in electronic packaging in which the creep property of the solder joint is essential to meet the global demand for longer operating lifetime in their applications. In this study, the influence of Ag and In additions on tensile creep behavior and thermal properties of bulk eutectic Sn-Cu solder alloy is reported. Results show that addition of Ag and In resulted not only in the formation of new Ag 3 Sn and c-SnIn 4 intermetallic compounds (IMCs), but also in the refinement of grain size of Sn-0.7Cu solder from 0.50to0.50 to 0.50to0.15 lm. Accordingly, the creep properties of the Ag or In-containing solder alloys are notably improved. The creep strain rate increases and creep lifetime decreases as the applied stress level and temperature increase. Room and elevated-temperature creep rate of bulk Sn-Cu solder was reduced by 521.0% after Ag addition, but for In addition the reduction was about 200.7%. These differences are attributed to the presence of new Ag 3 Sn and c-SnIn 4 precipitates and their rules in classical dispersion strengthening as a separate phases. Moreover, the eutectic temperature of Sn-0.7Cu is decreased from 227.4 to 217.8 and 224.0°C with the addition of Ag and In, respectively.
Temperature Dependence of Creep and Hardness of Sn-Ag-Cu Lead-Free Solder
Journal of Electronic Materials, 2010
The creep behavior and hardness of Sn-3.5Ag-0.7Cu solder were studied using Berkovich depth-sensing indentation at temperatures of 25°C to 125°C. Assuming a power-law relationship between the creep strain rate and stress, an activation energy of 40 kJ/mol and stress exponents of 7.4, 5.5, and 3.7 at 25°C, 75°C, and 125°C, respectively, were obtained. The results revealed that, with increasing temperature, the creep penetration and steady-state creep strain rate increased whereas the stress exponent decreased. The stress exponent and activation energy results also suggested that the creep mechanism is dislocation climb, assisted by diffusion through dislocation cores in Sn. Furthermore, the hardness results exhibited a decreasing trend with increasing temperature, which is attributed to softening at high temperature.
Creep behavior of near-peritectic Sn–5Sb solders containing small amount of Ag and Cu
Materials Science and Engineering: A, 2011
Sn-5%Sb is one of the materials considered for replacing Pb-bearing alloys in electronic packaging. In the present study, the effects of minor additives of Ag and Cu on the as-cast microstructure and creep properties of the Sn-5Sb solder alloy are investigated by means of optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive X-ray spectroscope (EDS) and tensile tests. Results show that addition of Ag and Cu resulted not only in the formation of new Ag 3 Sn and Cu 6 Sn 5 intermetallic compounds (IMCs), but also in the refinement of the grain size of Sn-5Sb solder. Accordingly, the creep properties of the Ag or Cu-containing solder alloys are notably improved. Attention has been paid to the role of IMCs on creep behavior. The lead-free Sn-5Sb-0.7Cu solder shows superior creep performance over the other two solders in terms of much higher creep resistance and vastly elongated creep fracture lifetime. An analysis of the creep behavior at elevated temperatures suggested that the presence of hard Cu 6 Sn 5 and fine SbSn IMCs in the Sn-5Sb-0.7Cu alloy increases the resistance to dislocation movement, which improves the creep properties.
Materials Science and Engineering: A, 2003
Understanding and quantification of creep behavior of lead-free solder joints are essential for lifetime prediction of electronic systems. This is especially true for circuits with surface mount and chip components that are subjected to severe environments and higher temperatures. Creep deformation behavior of Sn Á/4Ag Á/0.5Cu, Sn Á/3.5Ag Á/0.5Ni and Sn Á/2Ag Á/1Cu Á/1Ni solder alloys was determined at room temperature (25 8C) and at elevated temperature (85 8C) using miniature single shear lap joint specimens that are comparable in size to actual solder joints used in electronic packaging. Various creep parameters such as global creep strain, secondary creep rates as well as the strain for the onset of tertiary creep in the solder joint were determined. The effects of Cu and Ni alloy additions on the creep properties of eutectic Sn Á/3.5Ag solder joints were studied by comparing with the creep deformation behavior of eutectic Sn Á/3.5Ag solder joints that were used as the baseline. General findings in this study revealed that the creep resistance of Sn Á/4Ag Á/0.5Cu solder joints is comparable to but slightly higher than that of eutectic Sn Á/3.5Ag solder joints at both room and elevated testing temperatures, particularly at lower stresses. The Sn Á/3.5Ag Á/0.5Ni solder joints have comparable creep resistance to Sn Á/4Ag Á/0.5Cu and eutectic Sn Á/3.5Ag solder joints at 85 8C, but much better creep resistance at room temperature. The Sn Á/2Ag Á/1Cu Á/1Ni solder joints were two orders of magnitude less creep resistant than solder joints made with other solder materials at 85 8C. However, the shear strains for the onset of tertiary creep in Sn Á/2Ag Á/1Cu Á/1Ni solder joints were found to be the highest at 85 8C. Microstructural analysis showed significant creep deformation along Sn grain boundaries. #
Properties enhancement of low Ag-content Sn–Ag–Cu lead-free solders containing small amount of Zn
This study examines the effect of Zn addition on the microstructure, melt properties and tensile behavior of low Ag-content Sn–1.0Ag–0.3Cu (SAC103) lead-free solder. The results show that addition of 2.0 wt.% Zn to SAC(103) solder resulted in an excessive tensile strength and low ductility, which may be attributed to the dual effect of grain refinement and formation of course (Cu, Ag) 5 Zn 8 intermetallic compound (IMC) particles. Meanwhile, the alloy with 3.0 wt.% Zn exhibited both the highest strength and large ductility, which may be due to the high volume percentage of fine (Cu, Ag) 5 Zn 8 particles and fiber-like Ag 3 Sn precipitates. These eutectic micro-constituents contributed more significantly to the obstacles for disloca-tion pileup along the slip systems in Zn-containing SAC(103) solders, as it shows better deformation resistance than the plain SAC(103) solder. Besides, the addition of Zn not only reduced the liquidus and melting temperatures, but also decreased the undercooling and pasty range of SAC(103) solder.
Creep properties of Sn–Sb based lead-free solder alloys
Journal of Alloys and Compounds, 2009
Full implementation of the new generation of lead-free solders requires detailed knowledge and understanding of their mechanical behavior. This paper reports on structure, thermal and tensile creep properties of Sn-5 wt.%Sb, Sn-5 wt.%Sb-3.5 wt.%Ag, and Sn-5 wt.%Sb-1.5 wt.%Au lead-free solder alloys. The results show that the microstructure of Sn-5Sb alloy is characterized by the presence of cubed intermetallic compound (IMC) of SbSn particles (<5 m) within -Sn matrix. The two ternary alloys exhibit additional constituent phases of IMCs Ag 3 Sn for Sn-5Sb-3.5Ag and AuSn 4 for Sn-5Sb-1.5Au alloys. Attention has been paid to the role of IMCs on creep behavior. The tensile creep tests were performed within the temperature range 25-130 • C at constant applied stresses. Activation energy (Q) and stress exponent (n) were determined to clarify the deformation mechanism. This study revealed that the solder alloy Sn-5Sb-1.5Au have potential to gave a good combination of higher creep resistance and rupture time, lower melting temperature and higher fusion heat compared with the other two alloys.
Metallurgical and Materials Transactions A, 2007
Metallurgical, mechanical, and environmental factors all affect service reliability of lead-free solder joints and are under extensive study for preparation of the transition from Sn-Pb eutectic soldering to lead-free soldering in the electronic industry. However, there is a general lack of understanding about the effects of solidification conditions on the microstructures and mechanical behavior of lead-free solder alloys, particularly on the long-term reliability. This study attempts to examine the creep resistance of the SnAg -Cu eutectic alloy (Sn-3.8Ag-0.7Cu, SAC387) with a variety of solidification conditions with cooling rates ranging from 0.3°C/s to 17°C/s. Results indicate that solidification conditions have a major influence on the creep resistance of SAC387 alloy; up to two orders of magnitude change in the steady-state creep rates were observed at low stress levels. An understanding of the mechanical property change with microstructures, which are determined by the solidification conditions, should shed some light on the fundamental deformation and fracture mechanisms of lead-free solder alloys and can provide valuable information for long-term reliability assessment of lead-free solder interconnections.