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Effects of trace amount addition of rare earth Nd on the properties of eutectic Sn-Zn solder were studied in this paper. Results indicate that adding trace rare earth element Nd could remarkably improve the solderability and mechanical properties of Sn-9Zn solder joints. Especially when the content of Nd was 0.06 wt%, the wettability of the solder was improved significantly, and the shear force of Sn-9Zn-0.06Nd solder joint was enhanced by 19.6% as well as pull force increased by 26.6% compared to that of Sn-9Zn solder joint,respectively. It is also found that addition of rare earth Nd could refine the microstructure of the solder and some NdSn phase appeared in the solder matrix. Moreover, the IMCs thickness at the solder/Cu interface was reduced. NdSn phase appeared at the interface with excessive addition of Nd, which is the key reason that deteriorates the mechanical properties of soldered joint. [ABSTRACT FROM AUTHOR]

Purpose - The purpose of this paper is to explore the formation and growth mechanism of bulk Cu6Sn5 intermetallic compounds, selecting Sn-Ag-Cu-Ce solders as specimens. Design/methodology/approach - In order to further enhance the properties of SnAgCu solder, trace amount of rare earth Ce was selected as alloying addition into the alloy; in previous investigations, the enhancements include better wettability, physical properties, creep strength and tensile strength. In this paper, the microstructure of Sn-Ag-Cu-Ce soldered joints and its interfacial intermetallic compounds were investigated. Moreover, different morphologies of Cu6Sn5 IMCs were enumerated and described, and Ostwald ripening theory was employed to interpret the formation mechanism of bulk Cu6Sn5 IMCs. Findings - In addition, based on finite element simulation, it is found that the von Mises stress concentrate around the bulk Cu6Sn5 IMCs inside the Sn-Ag-Cu-Ce soldered joints after three thermal cycling loading (-55-125°C). From the stress distribution, the failure site was predicted to fracture near the bulk Cu6Sn5 IMCs interface. This coincides with the experimental findings significantly. Originality/value - The results presented in this paper may provide a theory guide for developing novel lead-free solders as well as reliability investigation of lead-free soldered joints. [ABSTRACT FROM AUTHOR]

In this study, the interfacial reactions and joint reliabilities of Sn–9Zn/Cu and Sn–9Zn–0.3Ag/Cu were investigated during isothermal aging at 150 °C for aging times of up to 1,000 h. Cu5Zn8 IMCs layer is formed at the as-soldered Sn–9Zn/Cu interface. Adding 0.3wt.% Ag results in the adsorption of AgZn3 on the Cu5Zn8 IMCs layer. The as-soldered Sn–9Zn/Cu and Sn–9Zn–0.3Ag/Cu joints have sufficient pull strength. The thickness of the IMCs layer formed at the interface of Sn–9Zn/Cu and Sn–9Zn–0.3Ag/Cu both increase with increasing aging time. Correspondingly, both the pull forces of the Sn–9Zn and Sn–9Zn–0.3Ag soldered joints gradually decrease as the aging time prolonged. However, the thickness of the IMCs layer of Sn–9Zn–0.3Ag/Cu increases much slower than that of Sn–9Zn/Cu and the pull force of Sn–9Zn–0.3Ag soldered joint decreases much slower than that of Sn–9Zn soldered joint. After aging for 1,000 h, some Cu–Sn IMCs form between the Cu5Zn8 IMC and the Cu substrate, many voids form at the interface between the Cu5Zn8 layer and solder alloy, and some cracks form in the Cu5Zn8 IMCs layer of Sn–9Zn/Cu. The pull force Sn–9Zn soldered joint decreases by 53.1% compared to the pull force measured after as-soldered. Fracture of Sn–9Zn/Cu occurred on the IMCs layer on the whole and the fracture micrograph implies a brittle fracture. While the pull force of Sn–9Zn–0.3Ag soldered joint decreases by 51.7% after aging at 150 °C for 1,000 h. The fracture mode of Sn–9Zn–0.3Ag soldered joint is partially brittle at the IMCs layer, and partially ductile at the outer ring of the solder. [ABSTRACT FROM AUTHOR]

For quad flat packages (QFP256), lead-free soldered joints reliability in service is a critical issue. In this paper, soldering experiments of quad flat package (QFP256) devices were carried out by means of infrared reflow soldering system with Sn–3.8Ag–0.7Cu and Sn–3.8Ag–0.7Cu–0.03Ce lead-free solders, respectively, and the mechanical properties of micro-joints of the QFP devices were tested and studied by STR micro-joints tester. The results indicate that the tensile strength of Sn–Ag–Cu–Ce soldered joints is better than that of Sn–Ag–Cu soldered joints. In particular, the addition of trace Ce to the Sn–Ag–Cu solder can refine the microstructures and decrease the thickness of the intermetallic compound layer of Sn–Ag–Cu solder alloys. In addition, the stress–strain response of Sn–Ag–Cu/Sn–Ag–Cu–Ce soldered joints in quad flat packaging was investigated using finite element method based on Garofalo–Arrhenius model. The simulated results indicate creep distribution of soldered joints is not uniform, the heel and toe of soldered joints, the area between soldered joints and leads are the creep concentrated sites. The creep strain of Sn–Ag–Cu–Ce soldered joints is lower than that of Sn–Ag–Cu soldered joints. [ABSTRACT FROM AUTHOR]

The microstructures, wettabilities and mechanical properties of Sn–9Zn–xAg ( x = 0, 0.1, 0.3, 0.5, 1 wt%) lead-free solders were investigated, respectively in this paper. Results show that, when the quantity of Ag added to the solder is 0.3 wt%, the microstructure of the solder becomes finer and more uniform than Sn–9Zn, and when the quantity of Ag is exceeded 0.3 wt% (upto 0.5–1 wt%), the AgZn3 intermetallic compounds appear in the solder. In particular, adding 0.3 wt% Ag improves the wettability due to the better oxidation resistance of the Sn–9Zn–0.3Ag solder. Results also indicate that adding 0.3 wt% Ag to the solder enhances mechanical property of soldered joint, at which the fracture micrographs show that plenty of small and uniform dimples could be observed on the Sn–9Zn–0.3Ag soldered joints fractures. When the content of Ag is upto 1 wt%, some Cu–Zn and Ag–Zn intermetallic compounds appear on the bottom of dimples, and the mechanical property of the soldered joint decreases. [ABSTRACT FROM AUTHOR]

The article presents a study which investigates the impacts of minor addition of the rare earth (RE) element cerium (Ce) on the microstructures and creep properties of tin (Sn)-Silver (Ag)-Copper (Cu) solder alloys. The study used glass rod in performing mechanical stirring every 10 minutes to homogenize the solder alloy. The study also employed optical microscopy, scanning electron microscopy (SEM), and energy dispersive X-ray (EDX) to examine the microstructures and identify the elemental compositions. The results revealed that the creep rupture life could be increased by up to 7.5 times over than that of the original Sn-Ag-Cu alloy if the Ce accounts for 0.30 percent.

Sn–Zn solder alloys have been considered as one of the more attractive lead-free solders since it can easily replace Sn–Pb eutectic alloy without increasing the soldering temperature. However, there are still some problems to be resolved, such as the argument about the poor oxidation resistance and embrittlement behavior. In order to overcome these drawbacks, and further enhance the properties of Sn–Zn lead-free solder alloys, a small amount of alloying elements (rare earths, Bi, Ag, Al, Ga, In, Cr, Cu, Sb, Ni, Ge) added into Sn–Zn alloys were selected by many researchers. For example, a small amount of Al, P, Bi, Ga can improve the high-temperature oxidation resistance of Sn–Zn solders remarkably as well as Cr. This paper summarizes the effects of alloying elements on the wettability, oxidation resistance, melting behavior, mechanical properties, creep properties, microstructures and intermetallic compounds layer of Sn–Zn lead-free solders. [ABSTRACT FROM AUTHOR]

Ternary lead free solder alloys Sn–Ag–Cu were considered as the promising alternatives to conventional SnPb alloys comparing with other solders. In the present work, effects of trace amounts of rare earth Ce on the wettability, mechanical properties and microstructure of Sn–Ag–Cu solder have been investigated by means of scanning electron microscopy and energy dispersive X-ray analysis systematically. The results indicate that adding trace amount of rare earth Ce can remarkably improve the wettability, mechanical strength of Sn–Ag–Cu solder joint at different temperature, especially when the content of rare earth Ce is at about 0.03%, the tensile strength will be 110% times or more than that of the lead free solder joint without rare earth Ce addition. Moreover, it was observed that the trace amount of rare earth Ce in Sn–Ag–Cu solder may refine the joint matrix microstructure, modify the Cu6Sn5 intermetallic phase at the copper substrate/solder interface, and the intermetallic compound layer thickness was reduced significantly. In addition, since rare earth Ce possesses a higher affinity to Sn in the alloy, adding of rare earth Ce can also lead to the delayed formation and growth of the intermetallic compounds of Ag3Sn and Cu6Sn5 in the alloy. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]