Interfacial reactions between liquid Sn3.5Ag0.5Cu solders and Ag substrates

The morphology and growth kinetics of intermetallic compounds (IMCs) formed during the soldering reactions between Sn3.5Ag0.5Cu and Ag substrates at various temperatures ranging from 250 to 350 °C were investigated. The interfacial microstructure was quantified with scanning electron microscopy (SEM) for each processing condition. Experimental results show that the thickness of the scallop-shaped Ag₃Sn IMCs layer increased with increasing soldering time and temperature. Furthermore, Cu₆Sn₅ particle precipitates were observed in the Ag₃Sn IMCs layer around and thus suppressing the Ag₃Sn IMCs layer growth. Furthermore, the large Cu₆Sn₅ IMCs tend to appear in the vicinity of interfacial wicker-Ag₃Sn IMCs. Kinetics analyses showed that growth of the Ag₃Sn intermetallic compound was diffusion controlled. The activation energies for the growth of Ag₃Sn IMCs are calculated to be 66.7 kJ/mol.     

Electrochemical migration behaviour of Cu, Sn, Ag and Sn63/Pb37

The Electrochemical Migration (ECM) behaviour of leaded surface finishes was compared to other surface finishes that are applied in the electronics manufacturing. The studied surface finishes were as follows: bare copper (bCu), immersion tin (iSn), immersion silver (iAg) and Sn63Pb prepared by HASL (Hot Air Solder Leveling). The results were evaluated by Water drop test with the calculation of the Mean Time to Failure (MTTF) and by the investigation of the composition of the dendrites. The results have shown some contradictions relating bare copper and HASL compared to the ECM ranking published previously (Harsányi and Inzelt in Microelectron Reliab 41:229–237, 2001; Yu et al. in J Mater Sci: Mater Electron 17(3):229–241, 2006). The copper and the HASL can change their places in the ECM ranking depending on the technological circumstances of the investigations. This impact can be caused by the composition of lead alloys (eutectic or not), the solubility parameters of the metal hydroxides; the oxidation state of the copper surface, etc. Further and theoretical explanations and the necessary fine adjustment of the migration models are discussed in the paper.     

Effects of Ag particles content on properties of Sn0.7Cu solder

To improve properties of Sn0.7Cu solder, method of particles reinforced was employed. Effects of Ag particle contents (1, 3, 5, 7.5, and 10 vol.%) on spreadability, microstructure, shear strength and creep rupture life of Sn0.7Cu solders have been studied. The experimental results indicate that intermetallic compound (IMC) grows, Shear strength is increased and grains are fined with the increasing of Ag particles. When content of Ag particles is more than 5 vol.%, growth rate of IMC is increased significantly. When the content of Ag is 5 vol.%, the composite solder presents best spreadability and excellent creep rupture property which have maximum spreading area, minimum wetting angle and longest creep rupture life (about 22 times as long as that of Sn0.7Cu solder).     

Interfacial reaction and properties of Sn0.3Ag0.7Cu containing nano-TiN solder joints

Ultra-low silver Sn0.3Ag0.7Cu (SAC0307) solder is arousing widespread attention because of its low cost. In this paper, the morphology of interfacial intermetallic compounds, microstructure, melting point, wettability and mechanical property of SAC0307 containing nano-TiN solders were investigated using scanning electricity microscope, transmission electron microscopy, micro-joints strength tester and differential scanning calorimetry. Results show that the addition of trace nano-TiN into SAC0307 solder can restrict the growth behavior of interfacial IMC and refine the microstructure of the solder joints. When 0.2 wt% nano-TiN particles were added, the interfacial thickness of SAC0307 solder joint dropped from 2.1 to 1.92 μm. Moreover, the wettability and mechanical property of SAC0307 solder joints were also significantly enhanced, but it has little influence on the melting characteristics of the solder.

     

Development of Sn–Ag–Cu and Sn–Ag–Cu–X alloys for Pb-free electronic solder applications

The global electronic assembly community is striving to accommodate the replacement of Pb-containing solders, primarily Sn–Pb alloys, with Pb-free solders due to environmental regulations and market pressures. Of the Pb-free choices, a family of solder alloys based on the Sn–Ag–Cu (SAC) ternary eutectic (T _eut. = 217°C) composition have emerged with the most potential for broad use across the industry, but the preferred (typically near-eutectic) composition is still in debate. This review will attempt to clarify the characteristic microstructures and mechanical properties of the current candidates and recommend alloy choices, a maximum operating temperature limit, and directions for future work. Also included in this review will be an exploration of several SAC + X candidates, i.e., 4th element modifications of SAC solder alloys, that are intended to control solder alloy undercooling and solidification product phases and to improve the resistance of SAC solder joints to high temperature thermal aging effects. Again, preliminary alloy recommendations will be offered, along with suggestions for future work.     

Enhancing mechanical properties via adding Ni and Zn in Cu/Sn3.5Ag/Cu transient liquid phase bonding for advanced electronic packaging

Journal of Materials Science: Materials in Electronics - Recently, the transient liquid phase (TLP) bonding process has become a promising method in advanced electronic packaging. Full...     

Effect of praseodymium on the microstructure and properties of Sn3.8Ag0.7Cu solder

Effects of Pr addition on wettability, microstructure of Sn3.8Ag0.7Cu solder were studied, the mechanical properties of solder joints were investigated and the fracture morphologies were also analyzed in this paper. The results indicate that adding appropriate amount of Pr can evidently improve the wettability of solder, and it is also found that Pr can refine the β-Sn dendrites and reduce the intermetallic compounds growth inside the solder due to the fine PrSn₃ particles formed in the solder which can act as heterogeneous nucleation sites. Moreover, the joints soldered with the SnAgCuPr solders possess sound mechanical properties which may result from the finer microstructure improved by the Pr.     

Characteristics of Laser Reflow Bumping of Sn3.5Ag and Sn3.5Ag0.5Cu Lead-Free Solder Balls

ead-free Sn3.5Ag and Sn3.5Ag0.5Cu solder balls were reflowed by laser to form solder bumps. Shear test was performed on the solder bumps, and SEM/EDX （scanning electron microscopy/energy dispersive X-ray spectrometer） was used to analyze the formation of intermetallic compounds （IMCs） at interface region. A finite element modeling on the temperature gradient and distribution at the interface of solder bump during laser reflow process was conducted to elucidate the mechanism of the IMCs growth direction. The results show that the parameters window for laser reflow bumping of Sn3.5Ag0.5Cu was wider than that of Sn3.5Ag. The shear strength of Sn3.5Ag0.5Cu solder bump was comparable to that of Sn3.5Ag solder bump, and was not affected obviously by laser power and irradiation time when appropriate parameters were used. Both laser power and heating time had a significant effect on the formation of IMCs. A continuous AuSn4 intermetallic compound layer and some needle-like AuSn4 were observed at the interface of solder and Au/Ni/Cu metallization layer when the laser power is small. The formation of needle-like AuSn4 was due to temperature gradient at the interface, and the direction of temperature gradient was the preferred growth direction of AuSn4. With increasing the laser power and heating time, the needle-like AuSn4 IMCs dissolved into the bulk solder, and precipitated out once again during solidification along the grain boundary of the solder bump.     

Melting and solidification properties of the nanoparticles of Sn3.0Ag0.5Cu lead-free solder alloy

The Sn3.0Ag0.5Cu (wt.%) lead-free solder alloy is considered to be one of the most promising candidates to replace the traditionally used Sn–Pb solder. However, this alloy composition has some weaknesses, mainly as a result of its higher melting temperature compared to the eutectic Sn–Pb solder. In this paper, lead-free solder alloy nanoparticles of Sn3.0Ag0.5Cu were synthesized by chemical reduction with NaBH₄ as reducing agent. The experimental results indicated that the major particle size of Sn3.0Ag0.5Cu nanoparticles was smaller than 100 nm. The melting and solidification properties of the Sn3.0Ag0.5Cu nanoparticles were studied by differential scanning calorimetry at different scanning rates. It was evidenced by the differential scanning calorimetry curves that the melting temperature of Sn3.0Ag0.5Cu nanoparticles was lower than that of the bulk alloy. In addition, the undercooling of the Sn3.0Ag0.5Cu nanoparticles was in the range of 82.0–88.5 °C at different cooling rates, which was much larger than that of the Sn3.0Ag0.5Cu micro-sized particles, showing stronger cooling rate dependence.     

ZnTe:Cu多晶薄膜结构和电性质

用共蒸发法在室温下制备了ZnTe：Cu多晶薄膜,利用XRD、AFM和XPS等测试技术对样品进行了表征,研究了掺Cu浓度和退火温度对薄膜物相和晶粒度的影响,分析了薄膜表面的元素状态。根据铜离子的变价行为对异常的电阻率温度关系作了解释。并确定了最佳掺铜浓度和退火温度。     

Suppression effect of Cu and Ag on Cu3Sn layer in solder joints

Cu₃Sn intermetallic compound (IMC) layer is usually formed in solder joints. Since the formation of Cu₃Sn could induce large volume shrinkage, and further cause a lot of reliability issues, many works focused on suppressing the formation or growth of the Cu₃Sn layer. This work explored that Cu and Ag alloying elements also have benefit in suppressing the Cu₃Sn growth during isothermal aging stage. The Cu₆Sn₅ IMC layer seems to be much stable in the Sn/Cu solder joint during aged at 150 and 180 °C, its thickness changed little, while the Cu₃Sn IMC layer grew much quickly. After about 300 h, the thickness of Cu₃Sn layer exceeds that of Cu₆Sn₅ layer. For the Sn-3.5Ag/Cu and Sn-0.7Cu/Cu solder joints, the thickness of Cu₃Sn layer is near half of that of Cu₆Sn₅ layer. According to the relation between interface location and aging time, the reaction generated at the Cu₆Sn₅/Cu₃Sn interface, which is governed by atom fluxes, controls the growth of Cu₃Sn IMC layer. Since Ag and Cu alloying elements suppress the coarsening of Cu₆Sn₅ IMC grains, the diffusion paths for Cu atoms toward the solder are more for Ag or Cu containing solder joints. Therefore, the growth of the Cu₃Sn layer by consuming Cu₆Sn₅ layer is slower in the SnAg/Cu and SnCu/Cu solder joints than that in the Sn/Cu joints.     

Effect of deep cryogenic treatment on mechanical properties and microstructure of Sn3.0Ag0.5Cu solder

The effect of deep cryogenic treatment on the performance of steels and alloys has attracted wide attention in the past decades. Deep cryogenic treatment can improve the strength and hardness of steel at room temperature, provide microstructure stability and improve wear or fatigue resistance of material. In the current study, the effect of deep cryogenic treatment on the microstructure and mechanical properties of Sn3.0Ag0.5Cu solders are investigated. The influence to microstructure, tensile strength and ductility improvement are discussed. Experimental analysis shows that the tensile strength of Sn3.0Ag0.5Cu solder increases from 36.76 to 46.27 MPa after 600 h of deep cryogenic treatment at 77 K (??196 °C), the observed strength-time relation is similar to the Taylor theory for the yield strength and dislocation density. Large particles presented in the fracture of Sn3.0Ag0.5Cu samples are caused by the high cooling rate as well as the concentration difference between the β-Sn and the eutectic system. The precipitated Ag₃Sn particles exhibit relatively uniform distribution in deep cryogenic treated Sn-rich matrix, and the size of Ag₃Sn particles becomes smaller with longer deep cryogenic treatment time. It is noted that deep cryogenic treatment can increase the internal stress and the dislocation density, higher dislocation density and good ductility lead to movement of the pre-existing dislocations and specific dislocation configurations. Microscopic experiments on solder joints were performed to investigate the microstructure change. The Intermetallic layers were measured which showed negligible change in thickness. A unified creep and plasticity constitutive model is proposed to simulate the stress–strain relationship under deep cryogenic treatment, the predictions show good agreement compared with experimental results.     

Structure, mechanical metallurgy and electrical transport properties of rapidly solidified Pb50Sn50-xBix alloys

Electrical transport properties, structure and mechanical properties of Pb₅₀Sn_50-xBi_x(0≤x≤50) alloys have been studied and analyzed. The addition of bismuth in the amounts of 30 wt % and 50 wt % results in the appearance of the crystalline metastable χ(Pb-Bi) phase. Y phase is also identified and it is found at 50 wt % bismuth. Electrical transport is sensitive to the alloys composition, decreasing as the bismuth content increases. The Vickers hardness number is sensitive to the structure of the quenched ribbons. The lowest value of H_v is 55 MPa for the Pb₅₀Sn₂₀Bi₃₀ alloy, which is attributed to the formation of the metastable χ(Pb-Bi) after a rapid quench from the melt. Values of the equivalent Fermi temperature, T_F Fermi velocity, V_F and the Fermi wave vector, K_F , are also computed. © 2000 Kluwer Academic Publishers     

Evolution of Ag3Sn compounds and microhardness of Sn3.5Ag0.5Cu nano-composite solders during different cooling rate and aging

This paper presents the microstructure and Vickers microhardness of Sn3.5Ag0.5Cu solder doped with trace amounts of TiO₂ nanopowders, obtained with different cooling rate and aging conditions. The experiment results that the coupling effect by cooling rate and TiO₂ nanopowders additions significantly affected primary β-Sn phase, Ag₃Sn grain size and spacing of the Ag₃Sn phase, as well as the morphology of Ag₃Sn. Ag₃Sn was relatively spherical at the water-cooling rate and had a needle-like morphology at the air-cooling rate. However, the Ag₃Sn IMC not obviously roughed after aging time at 125 °C for 7 days. Due to both nano-Ag₃Sn IMC and uniform microstructure of the nano-composite solders, the Vickers microhardness improved, in good agreement with the prediction of the classic theory of dispersion strengthening. It appears that adding trace TiO₂ nanopowders are an efficient way to develop novel high-performance solders.     

Viscosity and electrical conductivity of liquid Sn–Ti and Sn–Zr alloys

Viscosity and electrical conductivity of liquid Sn–Ti and Sn–Zr alloys on the Sn-rich side were investigated in a wide temperature range above the melting temperature. It was shown that admixtures of Ti and Zr considerably increased the viscosity of liquid Sn. The electrical conductivity of the melts decreased with an increase of the Ti and Zr content. The conductivity results are interpreted in the context of the s–d hybridization model.     

Structure and electrical properties of crystalline and glassy Ag2PbP2O7

Single crystals of Ag₂PbP₂O₇ have been prepared by melting of the crystalline phase under phosphate flux. Ag₂PbP₂O₇, isotype of Na₂PbP₂O₇, is of triclinic symmetry with the space group P(−1) (Z=2). The unit cell parameters are: a=5.502(6) Å, b=7.008(8) Å, c=10.018(9) Å, α=106.63(6)°, β=93.89(7)°, γ=110,68(6)°. The lattice of Ag₂PbP₂O₇ consists of corner-shared structural units {Pb₂P₄O₁₄}⁴⁻, which form ribbons parallel to the [010] direction. The {Pb₂P₄O₁₄}⁴⁻ units result from the association of corner-shared PbO₅ polyhedra and P₂O₇ pyrophosphate groups. The ribbons are interconnected by Pb–O–P bridges in the [100] direction and form lamina parallel to (001) plan. Silver atoms are located between two alternating lamina. Glasses with the same composition as the crystalline phase have been synthesized. A study of transport properties of Ag₂PbP₂O₇ in the crystalline and glassy forms is reported.     

Stress relaxation behavior of Cu/Sn/Cu micro-connect after electrical current

The effect of electromigration on stress relaxation behavior of pure tin solder joints was investigated. It was found that the stress relaxation rate was accelerated significantly after the sample was subjected to current stressing. The accelerating effect increased with the current stressing time. Measurements of the activation energy and stress exponent suggested that the dominant mechanism of the stress relaxation of pure tin solder joint went from dislocation climb to grain boundary diffusion after electromigration. As a result of grain boundary diffusion and sliding, grain boundary grooves were observed on the surface of the tin solder joints after electromigration. The groove was associated with the divergence of vacancy concentration at the grain boundaries. The vacancy concentration at the grain boundaries, which increased with the current stressing time, promoted the atomic diffusion along the grain boundaries, resulting in a higher stress relaxation rate.