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This study synthesized Sn-0.7wt.%Cu/Xwt.%SiO2 nanocomposite solder by angular accumulative extrusion (AAE). AAE is a severe plastic deformation process used here to synthesize a metal matrix composite for the first time. The Sn-0.7wt.%Cu lead-free solder has proved to be an appropriate alternative for Sn–Pb solder due to its lower cost than other lead-free solders, good wetting and electrical conductivity, and high creep resistance. The characterization results showed that adding silica nanoparticles improved the solder properties compared to the monolithic sample. Compared to the monolithic sample, the tensile properties of as-extruded nanocomposite solder samples containing 0.5- and 1-wt% nanoparticles have increased by 22 and 12%, respectively. The joint shear strength of nanocomposite solders increased by 9% and 17%, tensile strength by 41% and 44% and microhardness by 14% and 32% after reflow for the samples containing 0.5 and 1% nanoparticles, compared to the monolithic sample, respectively. Moreover, adding nanosilica particles decreased the wetting angle with a copper substrate, refined the microstructure, and suppressed undesired intermetallic compound formation compared to the monolithic sample. Accordingly, the synthesis of nanocomposite solder by AAE has been successful. [ABSTRACT FROM AUTHOR]

A novel alloying elements of TeFeCoBi have been anticipated to modify Sn–3Ag–0.7Cu SAC(307) alloys in various attributes. This study inspects the influence of slight/trace addition of Te, Fe, and Co besides 2 wt% Bi on the enhancement of microstructural solidification, thermal behavior, and tensile properties of SAC(307) alloy. Using field emission-scanning electron microscopy (FE-SEM), microstructural analysis indicated that the addition of Te, Fe, Co, and Bi not only inhibited the growth of large platelet Ag3Sn IMC phase, but also the new TeSn, FeSn2, and (Cu, Co)6Sn5 phases together with Co3Sn and Bi particles were formed in the eutectic regions and verified from EDS analysis. The synergetic influence of these precipitates results in significant combination of high strength and large ductility of the new solder. The ultimate tensile strength of the SAC(307)-TeFeCoBi alloy is found to be 58.3 MPa, which is 1.7 times higher than the corresponding of SAC(307) alloy. Moreover, the ductility was improved by ~ 46% with high reliability, which enriched its dissipation ability of plastic energy at various processing situations. The addition of TeFeCoBi elements also markedly increased the undercooling while maintaining the eutectic temperature and pasty range to the same SAC(307) levels. [ABSTRACT FROM AUTHOR]

With excellent thermal cycling performance, active metal brazing (AMB) ceramic substrates have been highly competitive materials for high power packaging. In related researches, composite filler is an effective way to improve the comprehensive performance of ceramic substrates. The effects of particle hardness on microstructure and properties (i.e., coefficient of thermal expansion (CTE), elastic modulus and compression properties) of Ag–Cu–Ti–In composite fillers were studied in this paper. The results showed that the microstructures of composite fillers were refined with the increase of graphite and TiC content. Meanwhile, the reduction of CTE of composite fillers added with TiC particles is better than that of graphite particles. The CTE of G10 sample is 7.4% lower than that of the sample without particle, and T10 sample is 8.9% lower. Furthermore, TiC particles increased both elastic modulus and yield strength of the composite fillers while graphite particles mainly had an opposite effect. The bulk modulus of the composite fillers drops sharply from 95.96 to 12.64 GPa when the content of graphite particles was 10 wt% compared with that of the filler metal without particles. The yield strength of composite filler with graphite content of 1 wt% reaches 380 MPa, which is caused by the in situ reaction between graphite and Ti. However, the elastic modulus and the yield strength of the composite fillers increases with the increase of TiC content. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

During isothermal aging, the interfacial microstructure evolution of Au-12Ge/Ni joints as well as its influence on the shear strength and the fracture behavior have been investigated. Results showed that there was a duplex layer of NiGe and NiGe intermetallic compounds (IMCs) in the joints after soldering. The most obvious changes in morphology were the transformation from scallop type to planar type microstructure. EPMA data indicated that the growth of the total IMC layer was mainly attributed to the growth of NiGe phase. Furthermore, it was found that the grain boundary diffusion was the dominant growth-controlling mechanism of overall IMC layer and the activation energy was 82.23 kJ/mol. In addition, the shear strength decreased continuously with extended aging time. The fracture of as-produced joint was at solder/IMCs interface, showing both ductile and brittle morphology. After the subsequent aging process, a thicker IMC layer was formed at the interface, leading to the movement of the fracture to IMCs region, a transformation of fracture to brittle morphology and a deterioration in shear strength. [ABSTRACT FROM AUTHOR]

This study investigated the microstructure and grain orientation of Ni(V)/SAC396/OSP Cu and Ni(V)/SAC105/OSP Cu solder joints during thermal cycling test (TCT). In general, adjusting Ag content in solders influenced the performance of thermal cycling (TC). Nevertheless, it is still crucial to find the optimal condition of Ag and related mechanisms of crack formation during TCT. This study applied FE-SEM to observe the crack propagation and the precipitation of Sn-Ag IMCs in the solders. Moreover, FE-EPMA and EBSD were used to detect the elemental distribution and grain orientation near the cracks, respectively. The locations of crack initiation are strongly related to the CTE mismatch between Si chip and solder alloy. Besides, the large number of AgSn precipitations in the joint with high Ag content efficiently hinder the crack propagation due to the effects of precipitation hardening. It is revealed that the Ni(V)/SAC396/OSP Cu exhibits good thermal stability during thermal cycle test. [ABSTRACT FROM AUTHOR]

Sn-Ag-Cu based alloys are a series of important candidates of lead-free solders. However the melting temperatures are still higher than the traditional Sn-Pb solder. Gallium (Ga) is one of the candidate elements to be alloyed with the Sn-Ag-Cu solder. The present work aims at investigating the influence of Ga addition (<1.5 wt%) on properties of the Sn-Ag-Cu alloys, e.g. melting performance, wetting behaviour, formation of intermetallic compounds on the interface, and shear strength of the solder joints. When adding more Ga into the Sn-Ag-Cu alloy, the solder firstly shows poorer wettability (<2 wt%) while the wettability becomes better (>2 wt%). This phenomenon has been explained by change of interfacial energy qualitatively. It has also been found that addition of Ga can decrease the melting point of the Sn-Ag-Cu alloy after differential scanning calorimetry tests. As-cast microstructure of the Sn-Ag-Cu-Ga alloys has been analysed using optical microscopy. Thinner intermetallic compounds have formed when more Ga is added. The shear strength decreases slightly when Ga is added, but remains unchanged with more Ga addition. [ABSTRACT FROM AUTHOR]

In order to investigate the effects of alloying Cu substrate on microstructure and coarsening behavior of CuSn grains of soldered joints, in the paper, four types of wetting layers (Cu, Cu-8 wt% Zn, Cu-15 wt% Zn and Cu-30 wt% Zn) reaction with Sn-3.0Ag-0.5Cu (SAC305) solder were fabricated. The effects of reflowing and isothermal aging on the interface of soldered joints and the morphology of CuSn grains were studied. Experimental results show that the scallop-shaped CuSn formed at the interface of SAC/Cu after reflowing. After isothermal aging for 120 h, a bi-layer structure of CuSn and CuSn formed at the interface of SAC/Cu and some AgSn grains decorated in CuSn, and Kirkendall voids were observed inside the CuSn layer after aging for 240 h. However, CuSn was the predominant reaction product and CuSn and Kirkendall voids were not observed at the interface of SAC/Cu-Zn irrespective of aging time. The thickness of IMC layer increases with increasing aging time. Compared to SAC/Cu, the additions of Zn can effectively suppress the growth of IMC. During the aging process, the growth rate constants of IMC layers of SAC/Cu, SAC/Cu-8Zn, SAC/Cu-15Zn and SAC/Cu-30Zn were obtained by using fitting method from the experimental data, which were 7.78 × 10, 5.42 × 10, 2.51 × 10 and 1.46 × 10 m s, respectively. The mean diameter of IMC grains increases with the increasing aging time. The relationships of the mean diameter of CuSn grains of SAC/Cu, SAC/Cu-8Zn, SAC/Cu-15Zn, SAC/Cu-30Zn interface joints and aging time were given, i.e., d = 1.49 t, d = 1.46 t, d = 1.43 t and d = 1.71 t, respectively. [ABSTRACT FROM AUTHOR]

In this study, copper particles with different sizes 20-30 nm, 3 and 10 μm were incorporated into Sn-3.5Ag solder paste to form Sn-Ag-Cu composite solder. The Cu particles were added at 0.7 and 3% by paste mixing for 30 min. The composite solder samples were prepared on copper substrate at 240°C for 60 s. Differential scanning calorimetry was conducted to measure the melting point of the composite solder. The wetting angle and microstructure of the composite solder were studied using optical microscope and scanning electron microscope. Micro hardness was measured using a 10 gf load. It was reported that the lowest melting point was obtained at 216.3°C when Cu nanoparticles was added at 3% to Sn-3.5Ag. The microstructure of Sn-3.5Ag solder structure was dendritic in nature. With the addition of Cu nanoparticles, the microstructures were modified with more refined Sn structures. The existence of sunflower morphology of un-melted copper was observed when Cu microparticles were added. [ABSTRACT FROM AUTHOR]

In this research, the typical nano-structured Polyhedral Oligomeric Silsesquioxane (POSS) particles were incorporated into the Sn–3.5Ag eutectic solder paste by mechanically mixing to form lead-free composite solder. The effects of nano-structured POSS additions on the microstructure and mechanical properties of as-fabricated composite solder alloys were systematically investigated. Experimental results indicated that the average size and spacing distance of Ag3Sn intermetallic compounds (IMCs) in composite solder matrix decreased as compared to the Sn–3.5Ag eutectic solder. The 3 wt% addition of nano-structured POSS particles could enhance the microhardness of composite solder by 18.4% compared with the Sn–3.5Ag eutectic solder matrix. The average grain size and spacing distance of Ag3Sn IMCs in Sn–Ag + 3 wt% POSS composite solder matrix reduced from 0.35 to 0.23 μm and from 0.54 to 0.32 μm, respectively. The refined Ag3Sn IMCs, acting as a strengthening phase in the solder matrix, could enhance the microhardness of the composite solders. [ABSTRACT FROM AUTHOR]

Due to the ongoing miniaturization in modern microelectronics reliability and quality control of microelectronics devices will also depend on a detailed understanding of the complex mechanical and thermal of solder joints. Therefore the question of the occurrence of size effects or dimensionally induced constraints, which could change the mechanical properties of solder joints in small dimensions dramatically, came into focus of investigation. Tensile tests were performed to investigate the influence of joint size on the tensile strength and fracture strain. Strains across the solder joint were measured using a non-contacting laser speckle sensor. Scanning electron microscopy (SEM) was used to analyze the complex modes of fracture and crack propagation in the solder interconnect. The variation of the gap size influenced also the crack growth behavior. The observed behavior can be interpreted in terms of an existing theory for brazed joints to complement Finite Element Analysis that is usually used for a description of these phenomena. [ABSTRACT FROM AUTHOR]