Papers by Keyword: Pb-Free Solder

Abstract: Sn-Cu-Ni-Ge (SN100C®) is a high-performance Pb-free solder alloy widely used in the electronics manufacturing industry due to its excellent soldering performance and lower cost. SN100C has a huge potential to replace the commonly used Sn-Ag-Cu solders. This work investigates the effect of different strain rates (10^-3 to 8×10^-1s^-1) on tensile performance for bulk SN100C samples at room temperature. The tensile properties, e.g., elastic modulus (E), yield strength (σ_y) and tensile strength (σ_T) are determined from the stress-stress curves. The value of σ_y and σ_T increases with increasing strain rates and this increase becomes less prominent at higher strain rates. Necking and ductile fracture are observed for all samples with a significant number of dimples, voids and tongues formed. The level of ductility of the samples decreases with increasing strain rates, which is further confirmed by the stress-strain behaviour. The microstructural evolution of the samples is evaluated by optical microscope (OM), scanning electron microscope (SEM) and energy dispersive X-ray (EDX) to reveal the generation of recrystallisation and fracture of the intermetallic compounds (IMCs) at the fracture tips and identify the embedded of IMCs within the sample matrix.

Abstract: Conventionally, brass has toughness more than other metals, so there is a concern about its poor machinability. Therefore, improvement of machinability was attempted by adding lead to brass. This brass called free cutting brass, typified by JIS C3771. This free-cutting brass is used for piping components and machine parts. There is a concern about elution of the lead into drinking water. Hence, Drinking Water Quality Standards Law has been amended and it restricts lead content in the free cutting brass. Therefore, lead-free free-cutting brass with no lead or minimized content of lead is required.Consequently, a lead-free free-cutting brass had been developed to improve in machinability such as JIS C6931 and JIS C6803 that are added Si and Bi instead of lead respectively. Lead was also used for the solder for joining among pure copper pipes and brass valves. That causes elution of lead from the solder into drinking water. For this reason, Lead-free solder such as Sn-Sb and Sn-Ag-Cu have been used.A fire torch technology often was used for soldering of brass. The purpose of this study is investigating soldering-ability and wettability of lead-free solder on lead-free free-cutting brass. Hence, we investigated the soldering ability of lead-free solders, Sn-5%Sb and Sn-3%Ag-0.5%Cu, for pure Cu and brass joints with nonuniform heating by hot plate.

Abstract: This paper investigated the effect of trace addition of Al and Mg on the grain refinements of Cu₆Sn₅ in Sn-3wt%Ag-5wt%Cu high temperature solder alloys. Furthermore, the effect of Al and Mg addition on the Sn/Ag₃Sn eutectic were also investigated. It was found that the addition of both Al and Mg successfully refined the Cu₆Sn₅ in Sn-3wt%Ag-5wt%Cu solder alloy. In addition, Al suppresses the formation of Ag₃Sn in the Sn/Ag₃Sn eutectic; while Mg promotes the formation of fine Sn/Ag₃Sn eutectic microstructure. The refinement of Cu₆Sn₅ is believed to be due to heterogeneous nucleation by Al and Mg rich intermetallic particles respectively. Effect of Al and Mg addition on the undercooling of the Sn/Ag₃Sn eutectic was found to be similar, both reducing undercooling effectively at a low addition rate of 0.025wt%. The addition of Al and Mg have mixed effect on the nucleation temperature of Cu₆Sn₅. It is found that the nucleation temperature of Cu₆Sn₅ is increased with 0.025wt% Al and 0.1wt% Mg addition to the unmodified alloy, while the nucleation temperature slowly decreases again as the trace element addition rate increases.

Abstract: In present study, Sn–9Zn, Sn–9Zn–xCu and Sn–9Zn–xNi solders (x = 1.0, 2.0 and 3.0 wt%) were prepared via melting process. Effects of Cu and Ni addition on microstructure, thermal behavior, wettability and corrosion resistance of Sn–9Zn solders were investigated. The experimental result showed that microstructure of the Sn–9Zn was composed of β–Sn and Zn–rich phases. Addition of Cu to the Sn–9Zn solders, Cu₆Sn₅ and Cu₅Zn₈ IMCs were observed. While addition of Ni to the Sn–9Zn solders, Ni₃Sn₄ and Ni₅Zn₂₁ IMCs were observed. It was also found that, amount of those IMCs obviously increased with increasing of Cu and Ni contents. The results obtained from thermal analysis showed that melting temperature of the Sn–9Zn solder was 199.6°C. While melting temperatures of the Sn–9Zn–1.0Cu and Sn–9Zn–1.0Ni solders were 199.9°C and 204.2°C, respectively. The Cu and Ni contents had little effect on both spread rate and wetting angle of the Sn–9Zn–xCu and Sn–9Zn–xNi solders. However, increasing of Cu and Ni contents significantly increased the corrosion potentials of the Sn–9Zn–xCu and Sn–9Zn–xNi solders.

Abstract: The changes of microstructure in pure-Sn after deformation were investigated by electron microscopy. Two types of specimens were prepared: Sample-1; pure-Sn/Fe-42Ni, Sample-2; single crystalline pure-Sn. The growth of curling whiskers on Sample-1 was observed in-situ in a scanning electron microscope (SEM). A thin foil specimen of the curling whisker was made with a focused ion beam (FIB) mill. Transmission electron microscope (TEM) analysis confirmed that the curling whisker was of a single crystal regardless of its external shape. New models for growth process of a bent single-crystalline whisker were proposed. The models are composed of epitaxial growth and recrystallization. Electron back scatter diffraction (EBSD) analysis was performed for Sample-2. The results of EBSD strongly suggested that recrystallization proceeds even at room temperature. These experimental results are very important to understand the behavior of dynamical deformation and recrystallization of Sn metal, and useful in consideration the mitigation of whiskers.

Abstract: Aiming at Pbfree solder Sn4.0Ag0.5Cu (in short, SAC405), the uniaxial tensile tests are accomplished with constant strain-rate under different temperature and strain-rate load conditions. The elastic-viscoplastic behaviors of SAC405 solders are studied. The rate-dependent material main properties are analyzed, such ad yield limit, tensile strength, saturation stress, etc. Partitioned constitutive model is accepted to describe the constitutive behavior of SAC405 solder. The seven parameters in partitioned model are determined by experiment data. The results of numerical simulation are fitted with the experimental values.

Abstract: The use of Pb-free solder alloys are just newly developed materials and their properties are not well established and documented yet. So, the research to substitute the critical problem of the Pb solder alloy are increasing widely. To evaluate the shear property of solder joints according to temperature condition was predicted through the Shear-Punch test and FEM. By using the database according to this, the reliability evaluation technology of the solder joints tries to be formulated. In this paper, the solder used the Sn37Pb, Sn-4Ag and the Sn4Ag0.5Cu. When solder melted in the copper interface, the solder joints according to reflow times, each modeling required for the Shear- Punch was made in consideration of the IMC layer thickness. And the micro shear punch test was performed to obtain material properties of solder according to temperature condition. The shear properties of specimen which was modeled was predicted through FEM. It compared with the test value in which it obtains from Shear-Punch. Also, a method which can obtain shear properties of Pb-free solder joints easily and quickly using FEM was proposed.

Abstract: Currently, Pb-free is the primary trend of development for solder alloys, and the existing Pb-free solder alloys are still difficult to replace the traditional tin-lead solder alloys. How to further improve the welding properties of Pb-free solder alloys is the issue we currently faced. In this paper, through melt overheating treatment, the influence of liquid-liquid structure change (LLSC) on the structure and properties of SnZn8Bi3 Pb-free solder alloy has been studied. Experimental results show that the LLSC has obvious effects on the solidification process and solidified microstructure of SnZn8Bi3 alloy: bigger solidification undercooling degree in the solidification process, finer and more dispersed solidification structure, and more importantly, the mechanical and welding properties of the solder alloy have also been obviously improved.

Abstract: The lap-shear test is frequently used in the microelectronics industry to obtain mechanical properties of solder joints. In these tests, solder joints formed between slender metallic substrates are pulled apart in a simple shear configuration. Although it is known that calculation of stress-strain curves from lap shear tests is not straightforward due to rotation of the joints and strain inhomogeneity within the joint, these tests still find widespread use due to their simplicity and apparent ease of use. Chawla and co-workers [1, 2] show that the state of strain near the solder-substrate interfaces is significantly different from that in the interior of the joint and that this effect is only minimized for large joints. In the present work, we offer experimental evidence for these conclusions by presenting full-field strain measurements on solder joints in double-lap shear configuration, obtained using Digital Image Correlation (DIC). While confirming that significant strain gradients exist within the joint, the present work also indicates that a simple calculation of shear strain as axial displacement of the joint divided by joint thickness is misleading due to the presence of a significant gradient of the transverse displacement along the loading direction. This gradient persists through the course of the deformation and results in the actual average shear strain in the joint being smaller than that computed from the axial displacement alone.

Abstract: Reaction diffusion in liquid Pb free solder- and solid Pb free solder- pure Cu systems has been investigated in the temperature range between 397 K and 563 K. The Pb free solder of which composition is 95.7 mass% Sn, 2.8 mass% Ag, 1.0 mass% Bi and 0.5 mass% Cu and 99.99 mass% oxygen free Cu has been used. In the liquid Pb free solder-pure Cu system, as soon as the solder melted down, an intermetallic compound phase formed preferentially, and grew with increasing diffusion time. Only the phase exists in the experimental time up to 120 seconds. The layer thickness of the phase obeyed the parabolic law. On the other hand, in the solid Pb free solder-pure Cu system two intermetallic compounds  phase and ’ phase form and grew with increasing diffusion time, although the  phase forms after an incubation time at low temperature. The layer thickness of these intermetallic compounds obeyed the parabolic law. The growth rate of ’ phase is greater than that of the  phase. The growth kinetics of the intermetallic compounds and the diffusion behavior in the ’ phase have been investigated.