Oxidation of Ag–Sn–La Alloy Powders

The gas atomized Ag-9.26wt%Sn-0.44wt%La alloy powders were oxidized in air between 400 and 900 °C. The oxidation thermodynamics, kinetics and microstructure of the alloy were investigated. We suggested that the addition of La may accelerate oxidation of Sn and prevent the formation of the dense SnO₂ film. The suitable oxidation temperature of the alloy powders is 800 °C in air. After internal oxidation, many cracks were observed on the surface of the alloy powders. In addition, the whole oxidation process of the alloy powders is controlled by the oxygen diffusion. The diffusion coefficient of oxygen in the alloy powders at 800 °C is about 1.5 times larger than that at 700 °C on the initial stage of internal oxidation, while that is 4.5 times on the subsequent stage.     

Phase equilibria of the Sn–Ag–Ni ternary system and interfacial reactions at the Sn–Ag/Ni joints

There are no previous phase equilibria studies of the Sn–Ag–Ni ternary system, even though the phase equilibria information is important for the electronic industry. The isothermal section of the Sn–Ag–Ni ternary system at 240 °C has been determined in this study both by experimental examination and thermodynamic calculation. Experimental results show no existence of ternary compounds in the Sn–Ag–Ni system, and all the constituent binary compounds have very limited solubilities of the ternary elements. The binary Ni₃Sn₂ phase is very stable and is in equilibrium with most of the phases, Ag₃Sn, ζ-Ag₄Sn, Ag, Ni₃Sn₄ and Ni₃Sn phases. A preliminary thermodynamic model of the ternary system is developed based on the models of the three binary constituent systems without introducing any ternary interaction parameters. This ternary thermodynamic model is used with a commercial software Pandat to calculate the Sn–Ag–Ni 240 °C isothermal section. The phase relationships determined by calculation are consistent with those determined experimentally. Besides phase equilibria determination, the interfacial reactions between the Sn–Ag alloys with Ni substrate are investigated at 240, 300 and 400 °C, respectively. It is found that the phase formations in the Sn–3.5wt%Ag/Ni couples are very similar to those in the Sn/Ni couples.     

Interrelation of wettability–microstructure–tensile strength of lead-free Sn–Ag and Sn–Bi solder alloys

A comparative investigation on the wettability and tensile strength of a Sn–2Ag, a Sn–40Bi and the traditional eutectic Sn–Pb solder alloys was carried out. The wettability is represented by thickness of covered layer (TCL) and spread area (SA) while the mechanical behaviour by the ultimate tensile strength (UTS). It is shown that the TCL of studied alloys decreased with the increase in the dipping temperature. It is also shown that TCL and SA have opposite behaviour with respect to the cooling rate. The Sn–Bi solder alloy has lower SA when compared with those of the Sn–Ag solder when similar cooling rates are considered. The Sn–Bi solder exhibits the best UTS/SA combination for dendritic spacings between 25 and 27?µm, associated with cooling rates ～2°C?s^?1, 2× lower than those of the Sn–Ag alloy. Besides, the Sn–Bi alloy has shown SA >70～80% associated with higher UTS (～80?MPa) as compared with the other alloys examined.     

Microstructure and mechanical property of Sn–Ag–Cu solder material

Among the lead-free solder materials,Sn-AgCu alloys have many advantages,such as good wetting property,superior interfacial properties and high creep resistance.In this article,the organization and welding performance of Sn-Ag-Cu material were investigated.The surface morphology of the two alloys was observed by stereoscopic microscope and scanning electron microscope(SEM).Chemical constitution was examined by X-ray energy-dispersive spectroscopy(EDS).The mechanical properties of Sn-Ag-Cu solder were evaluated systematically compared with those of Sn-Cu solder.The results show that Sn-Ag-Cu solder based on different solder pads has different welding properties.The thickness of intermetallic compound(IMC) at the interface increases with aging time.For the gold-plated pads,there are a large number of IMC graphic,and in the welding interface,it can reduce the reliability of electrical connection.The Sn-AgCu solder joints show a superior mechanical property over the traditional Sn-Cu solder.The number of dimples decreases and that of cavities increases for Sn-Cu0.7 alloy and the fracture surfaces of Sn-Ag3.0-Cu0.5 alloy have many small size dimples which are homogeneously distributed.     

The system Ce–Ag–Sn: phase equilibria and magnetic properties

Phase relations in the ternary system Ce–Ag–Sn have been established for an isothermal section at 750°C. Experimental techniques used were optical microscopy, EPMA and X-ray powder analysis of arc-melted samples which had been annealed at 750°C for 10 days and quenched to room temperature. Phases equilibria are characterized by the formation of three ternary compounds: CeAgSn (CaIn₂-type), Ce₅AgSn₃ (Hf₅CuSn₃-type), and Ce₃Ag₄Sn₄ (Gd₃Cu₄Ge₄-type). CeAg₂Sn₂, earlier reported to form and crystallize in the CaBe₂Ge₂-type, was not observed in the present study. All these ternary phases order magnetically at low temperature; our measurements reveal that Ce₅AgSn₃ is ferromagnetic below T_C=5 K, and Ce₃Ag₄Sn₄ is antiferromagnetic below T_N=9 K.     

Modification of Sn–1.0Ag–0.5Cu solder using nickel and boron

Effects of Ni and B additions on the microstructure and growth behavior of the intermetallic compound(IMC) of Sn–1.0Ag–0.5Cu alloys(SAC105) were investigated in this study. Results show that microadditions of Ni and B result in volume fraction of primary Sn increasing and the grain size decreasing observably. It is found that a large number of fine reinforcement particles with network-like shape are found in the solder, and the thickness of interfacial IMC layer in the solder joint is grew less than that of SAC105 with longer aging time. Shear test results reveal that as-soldered solder joints of microalloyed SAC105 have better shear strength than that of SAC105 solder alloy.     

Improving the shear strength of Sn–Ag–Cu–Ni/Cu–Zn solder joints via modifying the microstructure and phase stability of Cu–Sn intermetallic compounds

This study focuses on the correlation between high-speed impact tests and the interfacial reaction in Sn-3.0Ag-0.5Cu-0.1Ni/Cu (wt%) and Sn-3.0Ag-0.5Cu-0.1Ni/Cu-15Zn solder joints. Adding Ni into the Sn–Ag–Cu solder alters the interfacial morphology from scallop type to layer type and exhibits high shear strength after reflow in both solder joints. However, the shear strength of Sn-3.0Ag-0.5Cu-0.1Ni/Cu solder joints degrades significantly after thermal aging at 150 °C for 500 h. It is notable that Sn-3.0Ag-0.5Cu-0.1Ni/Cu-15Zn solder joints still present higher shear strength after aging at 150 °C. The weakened shear strength in Sn-3.0Ag-0.5Cu-0.1Ni/Cu solder joints is due to stress accumulation in the interfacial (Cu,Ni)₆Sn₅ compound induced by the phase transformation from a high-temperature hexagonal structure (η-Cu₆Sn₅) to a low-temperature monoclinic structure (η'-Cu₆Sn₅). However, doping small amounts of Zn into (Cu,Ni)₆(Sn,Zn)₅ can inhibit the phase transformation during thermal aging and maintain strong shear strength. These experiments demonstrate that Sn-3.0Ag-0.5Cu-0.1Ni/Cu-15Zn solder joints can act as a stable connection in the micro-electronic packaging of most electronic products at their average working temperatures.     

金属间化合物Ag3Sn对Sn3.8Ag0.7Cu焊料合金拉伸性能的影响

利用不同凝固速率和等通道挤压法制备不同组织结构的Sn3.8Ag0.7Cu合金,使其包含不同形貌、大小及分布的Ag3Sn金属间化合物;拉伸曲线的比较分析和变形后组织的电镜观察表明,大的针状化合物对合金起着纤维增强的作用,但自身脆性断裂造成空洞,降低了材料的塑性;微细颗粒状化合物起着弥散强化作用,分布在小的等轴晶粒晶界上的化合物颗粒能够阻碍晶界的滑动,起到增强的作用.     

The isothermal section at 400 °C of the Pr–Ag–Sn ternary system

The phases and equilibria involved in the isothermal section at 400 °C of the Pr–Ag–Sn ternary system have been here investigated after different annealing times by X-ray diffraction, optical and scanning electron microscopy and electron probe microanalysis. Three ternary compounds have been confirmed: PrAgSn hP6 LiGaGe type, Pr₃Ag₄Sn₄ oI22 Gd₃Cu₄Ge₄ type and Pr₅AgSn₃ hP18 Hf₅CuSn₃ type. The solid solubility ranges of the binary compounds have been considered and trends of their lattice parameters studied. The tie-triangles of the ternary system have been defined. The general features of the section are discussed and compared to those of the other R–Ag–Sn ternary systems.     

Interfacial reactions of Sn–Zn–Ag–Cu alloy on soldered Al/Cu and Al/Al joints

This work shows the effect on the soldering process of the addition of Ag and Cu to Sn–Zn alloys. Soldering of Al/Cu and Al/Al joints was performed for a time of 3?min, at a temperature of 250°C, with the use of flux. Aging was carried out at 170°C for Al/Cu and Al/Al joints for 1 and 10 days. During the aging process, intermetallic layers grew at the interface of the Al/Cu joint at the Cu substrate. Intermetallic layers were not observed during wetting of Al/Al joints. On the contrary, dissolution of the Al substrate and migration of Al-rich particles into the bulk of the solder were observed. The experiment was designed to demonstrate the effect of Ag and Cu addition on the dissolution of Al substrate during the soldering and aging processes. In the solder alloys, small precipitates of AgZn₃ and Cu₅Zn₈ were observed.     

The ternary Er–Co–Sn system

The isothermal section of the phase diagram of the Er–Co–Sn ternary system has been constructed at 670 K. The existence of seven ternary intermetallic compounds which crystallize with known structure types has been confirmed. The temperature dependence of the magnetic susceptibility (χ) for ErCo₃Sn and Er₃Co₆Sn₅ has been measured. The ErCo₃Sn stannide orders ferrimagnetically at 24 K, and the Er₃Co₆Sn₅ stannide is a Curie–Weiss paramagnet. For Er₃Co₆Sn₅, electrical resistivity (ρ) and differential thermopower (α) have been measured in the range 80–400 K.     

电沉积Ag／Sn偶界面反应及其动力学

采用扫描电子显微镜(SEM)、电子能谱仪(EDS)、X射线衍射仪(XRD)对室温时效及125～225 ℃热处理的电沉积Ag/Sn偶反应区结构及相组成进行分析,研究Ag/Sn界面固相反应的动力学过程.研究表明:在刚电沉积的Ag/Sn偶中发生Ag/Sn界面固相反应,形成Ag3Sn;在室温时效过程中Ag3Sn层生长缓慢,但随着热处理温度的提高(125～200 ℃),Ag3Sn层生长速率显著提高;Ag/Sn界面固相反应为一扩散控制的反应过程,反应的激活能为70.0 kJ/mol.     

Magnetic and crystal structure of Th–Fe–Sn intermetallics: ThFe0.22Sn2 and Th4Fe13Sn5

The crystal and magnetic structures of two new ternary phases in the Th–Fe–Sn system: ThFe_0.22Sn₂ and Th₄Fe₁₃Sn₅ have been investigated by high-resolution neutron powder diffraction. The ThFe_0.22Sn₂ phase crystallizes in an orthorhombic crystal structure, space group Cmcm, whilst Th₄Fe₁₃Sn₅ crystallizes in the tetragonal space group P4/mbm. In agreement with bulk magnetization measurements, the compound ThFe_0.22Sn₂ does not order magnetically in the temperature range investigated, while Th₄Fe₁₃Sn₅ orders below 375 K, with the easy magnetization direction of the Fe moments aligned along the tetragonal c-axis.     

WLCSP器件Sn3.9Ag0.6Cu焊点疲劳寿命预测

基于蠕变模型采用有限元法对WLCSP30器件Sn3.9Ag0.6Cu焊点可靠性及疲劳寿命进行预测.研究发现WLCSP器件整体的最大应力集中在阵列最拐角焊点的上表面处,该部位可能成为焊点裂纹的发源地,试验结果也验证了模拟结果的正确性.对焊点应力—应变分析,发现焊点部位出现明显的蠕变应变和蠕变应变能累积现象,结合焊点疲劳寿命方程,预测焊点疲劳寿命,发现基于蠕变应变能密度的计算结果和试验结果较吻合,但是基于蠕变应变的预测结果和试验结果相差较大,因此基于蠕变应变的疲劳寿命预测方程需要进一步的研究.