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).     

应力对Ag颗粒增强SnCu基复合钎料蠕变性能的影响

使用搭接面积为1mm2的单搭接钎焊接头,研究了恒定温度下应力对Ag颗粒增强SnCu基复合钎料钎焊接头蠕变寿命的影响,结果表明:Ag颗粒增强SnCu基复合钎料的蠕变抗力优于99.3Sn0.7Cu基体钎料;随着应力的增大,复合钎料及其基体钎料钎焊接头的蠕变寿命均呈下降趋势,且应力对复合钎料钎焊接头蠕变寿命的影响比基体钎料明显.     

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.     

温度对Cu颗粒增强复合钎料蠕变性能的影响

蠕变性能是影响钎焊接头可靠性的重要指标之一.采用搭接面积为1 mm2的单搭接钎焊接头,在恒定载荷下,测定了Cu颗粒增强锡铅基复合钎料钎焊接头的蠕变寿命,分析并讨论了温度对该复合钎料蠕变寿命的影响.结果表明:Cu颗粒增强的锡铅基复合钎料的蠕变抗力优于传统63Sn37Pb共晶钎料;钎焊接头蠕变寿命随温度的升高而降低,并且温度对复合钎料钎焊接头蠕变寿命的影响较传统63Sn37Pb钎料明显.     

新型纳米结构颗粒增强无铅复合钎料性能

为了解决传统复合钎料制备中强化颗粒容易粗化的问题,提高无铅复合钎料的性能,选用共晶Sn-3.5Ag、Sn-3.0Ag-0.5Cu钎料作为基体,3种不同类型具有纳米结构的有机-无机笼型硅氧烷齐聚物(POSS) 颗粒作为增强相而制成复合钎料。研究了复合钎料的铺展性能、钎焊接头的力学性能和抗蠕变性能。结果表明,复合钎料的润湿性能均优于基体钎料的润湿性能,复合钎料钎焊接头的剪切强度和蠕变断裂寿命均明显提高。在相同条件下,Sn-Ag-Cu基复合钎料钎焊接头的性能优于Sn-Ag基复合钎料钎焊接头。      

Ag颗粒增强复合钎料钎焊接头蠕变断裂及强化机理研究

测定了不同应力和温度下Ag颗粒增强复合钎料及基体钎料63Sn37Pb钎焊接头蠕变寿命,分析了Ag颗粒增强复合钎料及基体钎料钎焊接头蠕变断裂机理.表明:Ag颗粒增强复合钎料钎焊接头蠕变寿命优于基体钎料;Ag颗粒表面Ag-Sn金属间化合物形成及Ag颗粒对富Pb层阻碍作用是复合钎料钎焊接头蠕变性能提高的主要因素;钎焊接头Cu基板上一薄层富Pb相区形成是蠕变裂纹主要原因.     

Comparison of drop performance between the Sn37Pb and the Sn3.8Ag0.7Cu solder joints subjected to drop test

This study was concerned with the drop performance between the Sn37Pb and the Sn3.8Ag0.7Cu (wt. %) solder joints when the specimens were subjected to drop test after soldering process. The U-notch butt-jointed specimen was adopted and a lab-designed drop tester was employed. Meanwhile, the electrical resistance values of two kinds of solder joints were measured and recorded after certain drop tests, and finally drop number versus resistance curves were plotted and compared. From the resistance variation with the drop number, it was observed that the Sn37Pb joints presented significantly higher drop performance than the Sn3.8Ag0.7Cu ones. For the Sn3.8Ag0.7Cu specimens, the average drop number before failure was approximately 15-18 and then the resistance values sharply increased. However, the average drop number of the Sn37Pb joints was over 110 and the increasing rate of the electrical resistance was smooth, which is consistent with the results of the board-level drop test. Moreover, one specimen of each kind was picked out and the microstructural observation was carried out to investigate the joint deformation behavior in the dynamic load. It was obvious that the plastic deformation capacity of the Sn37Pb joints was remarkably higher than the one of the Sn3.8Ag0.7Cu joints, proving that most of SnAgCu-based solders presented low deformation compatibility and low energy absorption.     

Effect of addition of TiO2 nanoparticles on the microstructure,microhardness and interfacial reactions of Sn3.5AgXCu solder

In this work, TiO₂ nanoparticles were successfully incorporated into Sn3.5Ag and Sn3.5Ag0.7Cu solder, to synthesize novel lead-free composite solders. Effects of the TiO₂ nanoparticle addition on the microstructure, melting property, microhardness, and the interfacial reactions between Sn3.5AgXCu and Cu have been investigated. Experimental results revealed that the addition of 0.5 wt.% TiO₂ nanoparticles in Sn3.5AgXCu composite solders resulted in a finely dispersed submicro Ag₃Sn phase. This apparently provides classical dispersion strengthening and thereby enhances the shear strength of composite solder joints. After soldering, the interfacial overall intermetallic compounds (IMC) layer of the Sn3.5AgXCu lead-free solder joint was observed to have grown more significantly than that of the Sn3.5AgXCu composite solder joints, indicating that the Sn3.5AgXCu composite solder joints had a lower diffusion coefficient. This signified that the presence of TiO₂ nanoparticles was effective in retarding the growth of the overall IMC layer.     

Ag颗粒含量对SnCu基复合钎料性能的影响

利用颗粒增强原理研制了新型Ag颗粒增强SnCu基复合钎料,研究了Ag颗粒不同含量对复合钎料性能影响.结果表明:当Ag含量(体积分数)为5%时,复合钎料铺展面积最大,润湿角最小,钎焊接头蠕变寿命最长,比基体钎料提高23倍.     

Effects of rare earths on properties and microstructures of lead-free solder alloys

In order to further enhance the properties of lead-free solder alloys such as SnAgCu, SnAg, SnCu and SnZn, trace amount of rare earths were selected by lots of researchers as alloys addition into these alloys. The enhancement include better wettability, physical properties, creep strength and tensile strength. For Sn3.8Ag0.7Cu bearing rare earths, when the rare earths were La and Ce, the creep-rupture life of solder joints can be remarkably improved, nine times more than that of the original Sn3.8Ag0.7Cu solder joints at room temperature. In addition, creep-rupture lifetime of RE-doped solders increases by over four times for SnAg and seven times for SnCu. This paper summarizes the effects of rare earths on the wettability, mechanical properties, physical behavior and microstructure of a series of lead-free solders.     

Microstructures formed from mixed solders on copper substrate

Abstract

With the development and use of a variety of Pb free solders, it is probable that some solder joints in electronic assemblies may be made with solders of two different compositions. To investigate possible microstructures resulting from such procedure, samples were prepared using small balls of four different Sn–Ag–Cu (SAC) Pb free solders, as well as Sn–Zn–Al solder, melted together with eutectic Pb–Sn solder paste and also various SAC solder pastes, on a copper substrate. It was observed that using eutectic Pb–Sn solder paste with an SAC solder ball introduced some Pb–Sn eutectic microstructure and changed the ternary eutectic present from Ag₃Sn–Cu₆Sn₅–Sn to Ag₃Sn–Pb–Sn. Use of an SAC solder paste with Sn–Zn–Al solder introduced an apparent Ag–Cu–Zn ternary compound, replacing Zn lamellae of the Sn–Zn eutectic. With eutectic Pb–Sn solder paste, the Pb–Sn–Zn ternary eutectic was formed. It was noted that use of a high Sn solder results in rapid dissolution of the copper substrate.     

Investigation on impact strength of the as-soldered Sn37Pb and Sn3.8Ag0.7Cu solder joints

Charpy impact specimens of eutectic Sn37Pb and Sn3.8Ag0.7Cu solder joints with U-type notch were prepared to investigate the joint impact strength. The gap sizes of the butt joint were selected at 0.3 and 0.8 mm. Compared with the values of 0.3 mm joint gap, the impact absorbed energies of two solder joints were increased at the joint gap of 0.8 mm. The impact strengths of Sn37Pb joints were higher than those of Sn3.8Ag0.7Cu joints in both cases. From the macrographic observation of the fracture path, when the gap was 0.3 mm, the crack initiation of two solder joints located at the root of U-type notch then propagated along one interface of the joint. For the Sn37Pb joints, the fracture path was not changed at 0.8 mm gap size. However, the fracture path of Sn3.8Ag0.7Cu joint was totally changed and the fracture occurred not at the root of pre-U notch but from one side of the solder/Cu interfaces. From the micrographic observation, the crack of the Sn37Pb joints was concentrated on the Pb-rich layer in the vicinity of interfacial intermetallic (IMC) layer and the fracture morphology mainly appeared to be a ductile-like structure. Meanwhile, the fracture of Sn3.8Ag0.7Cu joints propagated along either the interface of IMC/solder or within the IMC layer and showed a brittle failure mode.     

Microstructure and interfacial reaction of Sn–Zn–x(Al,Ag) near-eutectic solders on Al and Cu substrates

Sn–Zn–x(Al,Ag) near-eutectic solders, namely Sn–8.3Zn–0.73Ag, Sn–8.4Zn–0.44Al and Sn–7.4Zn–0.26Al–0.68Ag (in wt%) with melting points of 200.74, 198.00 and 197.32 °C, respectively, as well as the Sn–9Zn eutectic solder, were used to join Al and Cu substrates. The addition of Ag led to the formation of dendritic AgZn₃ phases, while the addition of Al obviously refined the microstructure of Sn–Zn eutectic, as well as the AgZn₃ phases. The Sn–Zn–Al solder possessed the best wettability on both Cu and Al substrates among the four solders. Al_4.2Cu_3.2Zn_0.7 intermetallic compound (IMC) layers formed at the Sn–Zn–x(Al,Ag)/Cu interfaces while Al-rich (Zn) solid solutions at the Sn–Zn–x(Al,Ag)/Al interfaces of all the as-soldered joints. The shear strength of the Al/Sn–Zn–Al/Cu solder joints was the highest among the four solder joints. The declining degree of the shear strength of the Sn–Zn–x(Al,Ag) solder joints in 3.5 % NaCl solution was in agreement with the corrosion-resistance order of the bulk solders. The Al/Sn–Zn–Ag/Cu joint thus owned the best corrosion resistance.     

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.     

Effect of ZnO nanoparticles addition on thermal, microstructure and tensile properties of Sn–3.5 Ag–0.5 Cu (SAC355) solder alloy

Regarding to the development of Sn–Ag–Cu (SAC) lead-free solders for advance electronic components, the effect of 0.5 wt% nano-sized ZnO particles on the thermal, microstructure and tensile properties of Sn–3.5 wt% Ag–0.5 wt% Cu (SAC355) lead-free solder alloy is investigated. The results showed that addition of 0.5 wt% nano-sized ZnO particles into the conventional lead-free SAC355 solder caused a slight increase of its liquidus temperature by about 1.1 K. Metallographic observations of SAC355–0.5 wt% ZnO (composite solder) revealed an obvious refinement in the microstructure compared with the SAC355 (non-composite) solder. Consequently, addition of nano sized-ZnO particles could improve the stress–strain characteristics proof stress (σ_y0.2) and ultimate strength (σ_UTS). This was rendered to suppressing effect of ZnO on the coarsening of the intemetallic compounds (IMCs) Ag₃Sn and Cu₆Sn₅ during the solidification process in the composite solder and subsequently dispersion strengthening is considered to be the dominating mechanism. This will allow the use of SAC355 composite lead-free solder alloy, to be consistent with the conditions of usage for conventional SAC solder alloys and to overcome the serious problem of the excessive growth of IMCs and the formation of microvoids in the SAC lead-free solder alloys.     

Annealing effect to constitutive behavior of Sn–3.0Ag–0.5Cu solder

Sn–Ag–Cu based solder alloys are replacing Sn–Pb solders in electronic packaging structures of commercial electric devices. In order to evaluate the structural reliability, the mechanical property of solder material is critical to the numerical simulations. Annealing process has been found to stabilize material properties of Sn–37Pb solder material. In the current study, the annealing effect on tensile behaviour of Sn–3.0Ag–0.5Cu (SAC305) solder material is investigated and compared with Sn–37Pb solder. It is found that the tensile strength for both materials are more stabilized and consistent after the annealing process, nevertheless, the annealing process will improve the plasticity of SAC305 solder dominated by dislocation motion, and impede the occurrence of hardening deformation in Sn–37Pb solder dominated by grain-boundary sliding mechanism. Furthermore, the annealing effect is quantified in the proposed constitutive model based on unified creep–plasticity theory. The parameters are calibrated against the measured stress–strain relationships at the tensile strain rates ranging from 1?×?10^?4 to 1?×?10^?3 s^?1. The numerical regressions for dominant parameters in the proposed model reveal the intrinsic differences between SAC305 and Sn–37Pb solders under annealing treatment.     

Characters of multicomponent lead-free solders

In the process of electronic packaging, such as flip chip technology, under bump metallization (UBM) can be consumed gradually by solder during soldering. Then dissolution of Ni, Au and Cu from UBM into the solder may change the original solder to a multicomponent one especially under the trend of miniaturization. It is quite necessary to evaluate the properties of the multicomponent solders that have new composition after soldering. In this study, the microstructure, thermal and mechanical properties of five types of multicomponent lead-free solders, i.e. Sn–2Cu–0.5Ni, Sn–2Cu–0.5Ni–0.5Au, Sn–3.5Ag–0.5Ni, Sn–3.5Ag–1Cu–0.5Ni and Sn–3.5Ag–2Cu–0.5Ni (all in wt% unless specified otherwise) were investigated. Comparison with eutectic Sn–0.7Cu, Sn–3.5Ag and Sn–3.5Ag–0.7Cu solders was made. There was no obvious difference of the melting point between the multicomponent lead-free solders and the eutectic ones. For Sn–2Cu–0.5Ni solder, Cu₆Sn₅ and (Cu,Ni)₆Sn₅ intermetallic compounds (IMCs) formed. In the case of Sn–2Cu–0.5Ni–0.5Au, besides (Cu,Ni)₆Sn₅, (Cu,Au)₆Sn₅ and (Cu,Ni,Au)₆Sn₅ were also observed. The IMCs formed in Sn–3.5Ag–0.5Ni solder were Ag₃Sn and Ni₃Sn₄. In both Sn–3.5Ag–1Cu–0.5Ni and Sn–3.5Ag–2Cu–0.5Ni solders, Ag₃Sn and (Cu,Ni)₆Sn₅ were detected. The mechanism for the formation of the IMCs was discussed. Tensile test was also conducted. The fractography indicated that all of the multicomponent lead-free solders exhibited a ductile rupture.     

Influence of cerium oxide (CeO2) nanoparticles on the microstructure and hardness of tin–silver–copper (Sn–Ag–Cu) solders on silver (Ag) surface-finished copper (Cu) substrates

Nano-sized, non-reacting, non-coarsening CeO₂ particles with a density close to that of solder alloy were incorporated into Sn–3.0 wt%Ag–0.5 wt%Cu solder paste. The interfacial microstructure and hardness of Ag surface-finished Cu substrates were investigated, as a function of reaction time, at various temperatures. After the initial reaction, an island-shaped Cu₆Sn₅ intermetallic compound (IMC) layer was clearly observed at the interfaces of the Sn–Ag–Cu based solders/immersion Ag plated Cu substrates. However, after a prolonged reaction, a very thin, firmly adhering Cu₃Sn IMC layer was observed between the Cu₆Sn₅ IMC layer and the substrates. Rod-like Ag₃Sn IMC particles were also clearly observed at the interfaces. At the interfaces of the Sn–Ag–Cu based solder-Ag/Ni metallized Cu substrates, a (Cu, Ni)–Sn IMC layer was found. Rod-like Ag₃Sn and needle-shaped Cu₆Sn₅ IMC particles were also observed on the top surface of the (Cu, Ni)–Sn IMC layer. As the temperature and reaction time increased, so did the thickness of the IMC layers. In the solder ball region of both systems, a fine microstructure of Ag₃Sn, Cu₆Sn₅ IMC particles appeared in the β-Sn matrix. However, the growth behavior of the IMC layers of composite solder doped with CeO₂ nanoparticles was inhibited, due to an accumulation of surface-active CeO₂ nanoparticles at the grain boundary or in the IMC layers. In addition, the composite solder joint doped with CeO₂ nanoparticles had a higher hardness value than the plain Sn–Ag–Cu solder joints, due to a well-controlled fine microstructure and uniformly distributed CeO₂ nanoparticles. After 5 min of reaction on immersion Ag-plated Cu substrates at 250 °C, the micro-hardness values of the plain Sn–Ag–Cu solder joint and the composite solder joints containing 1 wt% of CeO₂ nanoparticles were approximately 16.6 and 18.6 Hv, respectively. However after 30 min of reaction, the hardness values were approximately 14.4 and 16.6 Hv, while the micro-hardness values of the plain Sn–Ag–Cu solder joints and the composite solder joints on Ag/Ni metallized Cu substrates after 5 min of reaction at 250 °C were approximately 15.9 and 17.4 Hv, respectively. After 30 min of reaction, values of approximately 14.4 and 15.5 Hv were recorded.     

Creep behavior in Cu and Ag particle-reinforced composite and eutectic Sn-3.5Ag and Sn-4.0Ag-0.5Cu non-composite solder joints

Creep properties were determined for small, geometrically realistic Pb-free solder joints. Solder joints were prepared with eutectic Sn-3.5Ag and Sn-4.0Ag-0.5Cu solder alloys. Composite solder joints were made using the eutectic Sn-3.5Ag alloy as the matrix with 15 vol % of mechanically added 6 m size Cu and 4 m size Ag reinforcing particles. Creep tests were conducted on these joints at 25 °C, 65 °C and 105 °C representing homologous temperatures ranging from 0.61 to 0.78. Qualitative and quantitative evaluations of creep behavior were obtained from the distortion of excimer laser-induced surface ablation markings on the solder joint. Various creep parameters, such as global and localized creep strain, variation of creep strain and strain-rate, activation energy for creep, and the onset of tertiary creep were determined. General findings in this study revealed that the creep resistance in composite solder joints is significantly improved with Cu particle reinforcements. In contrast, the improvement in the creep properties of Ag particle-reinforced composite solder joints was far less even though highly uniform deformation in the joint was observed. The strain noted at the onset of tertiary creep for Cu and Ag reinforced composite solder joints was typically lower compared to non-composite solder joints. The activation energies for creep were similar for all the solder materials investigated in this study. © 2001 Kluwer Academic Publishers     

Microstructural evolutions of the Ag nano-particle reinforced SnBiCu-xAg/Cu solder joints during liquid aging

Ag nano-particle reinforced Sn30Bi0.5Cu-xAg (x = 1 wt%, 2 wt% and 5 wt%) solder pastes were prepared and reflowed on Cu substrates at 523 K. Then, the solder joints were liquid aged at 473 K for 6 and 12 h. Microstructural evolutions of these solder joints were observed by scanning electron microscopy (SEM). The results show that Bi-rich phase was refined in the as-reflowed Sn30Bi0.5Cu-xAg composite solder matrices. With the increase of the liquid aging time, Bi-rich phase was refined both in the Sn30Bi0.5Cu solder and in the Sn30Bi0.5Cu-xAg composite solders. The addition of Ag nano-particles changed the growth rate of the IMC layers during liquid aging due to the absorption effect of the Ag₃Sn micro-particles.