Mechanical properties and intermetallic compound formation at the Sn/Ni and Sn-0.7wt.%Cu/Ni joints

The Ni/Sn/Ni and Ni/Sn-0.7wt.%Cu/Ni couples are reacted at 200°C for various lengths of time. The tensile strengths of these annealed specimens are determined at room temperature. In addition, the interfacial reactions and fracture surfaces of the specimens are examined as well. These properties are important for the evaluation of the usage of Sn-0.7wt.%Cu lead-free solders, which has been not available in the literature. Only the Ni₃Sn₄ phase is formed at the Sn/Ni interface, but both the Cu₆Sn₅ and Ni₃Sn₄ phases are formed at the Sn-0.7wt.%Cu/Ni interface. The thickness of the intermetallic compound layers grows, while the joint strength decreases with longer reaction time. With a 1-h reaction at 200°C, the fracture surface is in the solder matrix for both of the two kinds of couples. Shifting toward the compound layer with longer reaction time, the fracture surface is in the Ni₃Sn₄ layer in the Sn/Ni couple and is at the interface between the Cu₆Sn₅ and Ni₃Sn₄ in the Sn-0.7wt.%Cu/Ni after reacting at 200°C for 240 h.     

Interfacial Reactions of Sn-8wt.%Zn-3wt.%Bi Solder with Cu,Ag, and Ni Substrates

Sn-Zn-Bi alloys are promising Pb-free solders. Interfacial reactions between the Sn-8wt.%Zn-3wt.%Bi (Sn-13.80at.%Zn-1.62at.%Bi) alloy and the Cu, Ag, and Ni substrates are examined. Two different kinds of substrates, the bulk plate and the electroplating layer, are used, and the reactions are carried out at 250°C and 220°C. Although the Zn content is only 13.8 at.%, two Zn-Cu compounds, γ-Cu₅Zn₈ and ε-CuZn₅ phases, are formed in the Sn-13.80at.%Zn-1.62at.%Bi/Cu couples. The ε-CuZn₅ phase is scallop shaped, and the γ-Cu₅Zn₈ phase is planar. In the Sn-13.80at.%Zn-1.62at.%Bi/Ag couples, three Zn-Ag compounds are observed, and they are ε-AgZn₃, γ-Ag₅Zn₈, and ζ-AgZn phases. In the Sn-13.80at.%Zn-1.62at.%Bi/Ni couples, a Zn-Ni compound, γ-Ni₅Zn₂₁ phase, is formed. Similar results are found in the couples prepared with an electroplating layer: the reaction phases are the same, but the growth rates are different.     

Effect of Microstructural Development on Mechanical and Electrical Properties of Inkjet-Printed Ag Films

The microstructural characterization of inkjet-printed Ag films sintered at various conditions was carried out to analyze the effect of microstructure on mechanical and electrical properties. As expected, the films became denser with grain growth with increasing sintering time and temperature, which resulted in improvement in mechanical properties. However, the resistivity of the films reached a minimum value of 3.0 μΩ cm before full densification. In order to improve the mechanical properties, pressure-assisted sintering was introduced. As a result, inkjet-printed Ag films sintered at 250°C under 5 MPa showed a tensile strength of 550 MPa, elongation of 2.4%, Young’s modulus of 55 GPa, and resistivity of ~3.0 μΩ cm.     

Microstructural and Electronic Properties of Rapid Thermally Grown MoS2|Silicon Hetero-Junctions with Various Process Parameters

Semiconductors - Molybdenum disulphide (MoS2) has gained tremendous attention due to its tunable semiconducting properties and versatile applications in future electronic and optoelectronic...     

Interfacial reactions and mechanical strength of Sn-3.0Ag-0.5Cu/Ni/Cu and Au-20Sn/Ni/Cu solder joints for power electronics applications

The mechanical strength of Sn-3.0Ag-0.5Cu (SAC305) and Au-20Sn solder joints and their interfacial reaction with a Ni-plated ceramic substrate were evaluated to assess their suitability for use as die attach materials in power module applications. The compatibility between the two solder alloys and the Ni substrate was assessed during isothermal long-term aging, while the mechanical strength of the two solder joints was measured by die shear testing. A higher intermetallic compound (IMC) growth rate and Ni consumption rate was observed in the SAC305 solder joint, with the formation of a thick IMC layer and weak interface resulting in brittle fracture. The Au-20Sn solder joint, on the other hand was found to exhibit superior high temperature interfacial stability and joint strength.     

MEMS镍平面弹簧非线性力学性能仿真及研究

工程应用中,平面微弹簧存在弹性系数的非线性现象且难以被忽略,弹簧结构的几何非线性是引起这种现象的主要原因。针对特定形状的弹簧运用Ansys软件进行了非线性有限元静力学仿真,计算出弹簧弹性力F与弹性形变x之间的对应关系,并与采用MEMS微细加工技术制得弹簧样品实测实验结果比较,相对误差低于3.2%,验证了分析模型的可靠性。而后设计了5种不同平面形状的微弹簧,仿真计算它们的力学性能曲线,以及改变弹簧臂宽度厚度后的力学性能曲线,分别进行比较以讨论影响非线性的主要因素,为弹簧的设计工作提供参考依据。     

Evolution of Optical and Mechanical Properties of Semiconductors over 40 Years

We discuss the evolution, over a 40-year period, of the optical and mechanical properties of selected monoatomic, binary, and ternary semiconductors. From this systematic monitoring it can be shown that diffusion and stress relaxation processes over time lead to the host atoms migrating to their proper equilibrium positions, and a more uniform redistribution of impurities or structural defects is formed. We demonstrate that the highly ordered nature that develops over time, 40 years in this case, facilitates enhanced stimulated emission and increases the radiative recombination efficiency and spectral range of luminescence. This suggests new ways to realize semiconductor devices with greater temporal stability.     

Isothermal Ageing of SnAgCu Solder Alloys: Three-Dimensional Morphometry Analysis of Microstructural Evolution and Its Effects on Mechanical Response

Due to the high homologous temperature and fast cooling rates, the microstructures of SnAgCu (SAC) solders are in a meta-stable state in most applications, which is the cause of significant microstructural evolution and continuous variation in the mechanical behavior of the joints during service. The link between microstructures evolution and deformation behavior of Sn-4.0Ag-0.5Cu solder during isothermal ageing is investigated. The evolution of the microstructures in SAC solders are visualized at different scales in 3D by using a combination of synchrotron x-ray and focused ion beam/scanning electron microscopy tomography techniques at different states of ageing. The results show that, although the grain structure, morphology of dendrites, and overall volume fraction of intermetallics remain almost constant during ageing, considerable coarsening occurs in the Ag₃Sn and Cu₆Sn₅ phases to lower the interfacial energy. The change in the morphometrics of sub-micron intermetallics is quantified by 3D statistical analyses and the kinetic of coarsening is discussed. The mechanical behavior of SAC solders is experimentally measured and shows a continuous reduction in the yield resistance of solder during ageing. For comparison, the mechanical properties and grain structure of β-tin are evaluated at different annealing conditions. Finally, the strengthening effect due to the intermetallics at different ageing states is evaluated by comparing the deformation behaviors of SAC solder and β-tin with similar grain size and composition. The relationship between the morphology and the strengthening effect due to intermetallics particles is discussed and the causes for the strength degradation in SAC solder during ageing are identified.     

Mechanical and corrosion resistances of a Sn–0.7 wt.%Cu lead-free solder alloy

Sn–Cu alloys are interesting lead-free solder alternatives, with particular interest in the eutectic/near-eutectic compositions. However, little is known about the corrosion responses of these solders while subjected to corrosive environments. The present study examines the Sn–0.7 wt.%Cu solder alloy and the experimental results include a range of cooling rates and growth rates during solidification, metallography with comprehensive characterization of the distinct dendritic and cellular regions and the resulting corrosion and tensile mechanical parameters (potential, corrosion rate, polarization resistance, tensile strength). A β-Sn phase having a dendritic morphology is shown to characterize regions that are associated with higher cooling rates during solidification, while for lower cooling rates (<0.9 K/s) the prevalence of eutectic cells is observed. It was found that lower corrosion resistance and higher mechanical strength are associated with a microstructure formed by an arrangement of very fine dendritic branches and Cu₆Sn₅ fibrous intermetallic compound (IMC).     

Ni对Sn-0.7Cu焊料微观组织和力学性能的影响

研究了添加微量Ni元素对Sn-0.7Cu焊料的力学性能、微观组织和断裂特性的影响.结果表明,微量的Ni可已细化焊料合金的微观组织,显著提高焊料的塑性,从而提高焊料的综合力学性能;但Ni含量太高,焊料的塑性反而受到弱化,合适的Ni添加量为0.133%,此时焊料的拉伸强度为35.7 MPa,延伸率为50%.     

Thermal Management and Interfacial Properties in High-Power GaN-Based Light-Emitting Diodes Employing Diamond-Added Sn-3 wt.%Ag-0.5 wt.%Cu Solder as a Die-Attach Material

The thermal management of high-power GaN-based light-emitting diodes (LEDs) soldered with Sn-3 wt.%Ag-0.5 wt.%Cu (SAC305) solder and diamond-added SAC305 solder was evaluated. Diamond addition was found to significantly reduce the surface temperature and total thermal resistance of the LEDs, revealing that diamond-added SAC305 solder is a promising die-attach material for high-power LED packaging. Interfacial reactions in the LED solder joints were also investigated. The thin Au wetting layer in the chip’s backside metallization was rapidly consumed in the initial stage of reflow, forming an AuSn₄ phase at the interface. Subsequently, the AuSn₄ phase detached from the interface, leading to dewetting of the SAC305 solder from the LED chip. To avoid dewetting, a new backside metallization of LED chips should be developed for SAC305 solder.     

Measurements of Microhardness and Thermal and Electrical Properties of the Binary Zn-0.7wt.%Cu Hypoperitectic Alloy

Zn-0.7wt.%Cu hypoperitectic alloys were directionally solidified upwards with different temperature gradients (3.85 K/mm to 9.95 K/mm) at a constant growth rate (0.042 mm/s), and with different growth rates (0.0083 mm/s to 0.436 mm/s) at a constant temperature gradient (3.85 K/mm), using a Bridgman-type growth apparatus. Measurements of microhardness of the directionally solidified samples were carried out. The dependence of micro- hardness (HV) on growth rate (V) and temperature gradient (G) was analyzed. According to these results, it has been found that, for increasing values of G and V, the value of HV increases. Variations of electrical resistivity (ρ) and electrical conductivity (σ) for cast samples with temperature from 300 K to 670 K were also measured by using a standard direct-current (DC) four-point probe technique. The variation of the Lorenz coefficient with temperature for the Zn-0.7wt.%Cu hypoperitectic alloy was determined using the measured values of electrical conductivity and thermal conductivity. The enthalpy of fusion for the same alloy was determined by means of differential scanning calorimetry (DSC) from the heating trace during the transformation from liquid to solid.     

Impact of Thermal Aging on the Microstructure Evolution and Mechanical Properties of Lanthanum-Doped Tin-Silver-Copper Lead-Free Solders

An extensive study is made to analyze the impact of pure lanthanum on the microstructure and mechanical properties of Sn-Ag-Cu (SAC) alloys at high temperatures. Different compositions are tested; the temperature applied for the isothermal aging is 150°C, and aging times of 10 h, 25 h, 50 h, 100 h, and 200 h are studied. Optical microscopy with cross-polarized light is used to follow the grain size, which is refined from 8 mm to 1 mm for as-cast samples and is maintained during thermal aging. Intermetallic compounds (IMCs) present inside the bulk Sn matrix affect the mechanical properties of the SAC alloys. Due to high-temperature exposure, these IMCs grow and hence their impact on mechanical properties becomes more significant. This growth is followed by scanning electron microscopy, and energy-dispersive spectroscopy is used for elemental mapping of each phase. A significant refinement in the average size of IMCs of up to 40% is identified for the as-cast samples, and the coarsening rate of these IMCs is slowed by up to 70% with no change in the interparticle spacing. Yield stress and tensile strength are determined through tensile testing at 20°C for as-cast samples and after thermal aging at 150°C for 100 h and 200 h. Both yield stress and tensile strength are increased by up to 20% by minute lanthanum doping.     

Effects of Microstructural Evolution on the Thermoelectric Properties of Spark-Plasma-Sintered Ti0.3Zr0.35Hf0.35NiSn Half-Heusler Compound

The MNiSn (M = Ti, Zr, Hf) half-Heusler semiconducting compounds are widely investigated due to their good potential for thermoelectric (TE) power generation applications. In the current work, the evolution of the transport and structural properties of the Ti_0.3Zr_0.35Hf_0.35NiSn compound upon various thermal treatments was studied. The nominal composition was arc melted, ball milled, and spark plasma sintered (SPS). Following SPS, large Hf-rich domains were found by scanning electron microscopy (SEM) and energy-dispersive x-ray spectroscopy (EDS). Subsequently, the samples were subjected to homogenization treatments at 1163 K for 480 h and 610 h under argon atmosphere. Following these thermal treatments, the relative amount of the Hf-rich domains was reduced and they became smaller in size, with increasing thermal treatment duration. Nevertheless, no uniphased structure was reached. The dissolution of the Hf-rich domains in the half-Heusler matrix resulted in increase of both the Seebeck coefficient and electrical resistivity values and a decrease of the carrier concentration, attributed to elimination of these metallic domains. Resulting from the high atomic disorder caused by substitution at the M site, low thermal conductivity values of ~3.8 W m^?1 K^?1 were obtained leading to high ZT values of up to 0.82 following SPS.