Sn-Ag Solder Alloy Research Articles

Eutectic Solidification Morphologies in Rapidly Solidified Hypereutectic Sn–Ag Solder Alloy

The effect of rapid solidification upon hypereutectic Sn–Ag solder alloy has been investigated using a 6.5 m drop tube. Powder sizes ranging from > 850 to < 38 μm were produced, with equivalent cooling rates of 250 to 14,800 K s−1 for 850 and 38 μm droplets, respectively. At all cooling rates investigated, dendritic β-Sn was observed as the primary solidification phase, not proeutectic Ag3Sn as predicted by the phase diagram. The volume fraction of interdendritic eutectic was observed to decrease with increasing cooling rate, with the Ag concentration in the residual interdendritic liquid estimated at 12.5–15 wt pct Ag, far in excess of the eutectic concentration of 3.8 wt pct. Much of the Ag3Sn observed within the eutectic had a blocky, divorced eutectic appearance. A model is proposed which can explain these observations in terms of sluggish nucleation of the Ag3Sn intermetallic, coupled with a metastable phase diagram that permits significant supersaturation of Ag at modest undercooling.

Microstructural Evolution and Phase Transformation on Sn–Ag Solder Alloys under High‐Temperature Conditions Focusing on Ag3Sn Phase

This study investigates the microstructural and phase transformations in Sn–Ag solder alloys under high‐temperature conditions, utilizing X‐ray diffraction, scanning electron microscopy (SEM), and electron backscatter diffraction (EBSD) analyses. Analytical techniques are employed pre‐ and postcontrolled thermal cycling from 30 to 180 °C, aimed at emulating solder reflow processes. The analysis at room temperature demonstrates pronounced crystalline peaks, suggesting a preferred orientation within the crystal structure. Upon heating, peak broadening suggests grain growth and the onset of recrystallization. SEM and energy‐dispersive spectroscopy analyses corroborate these findings, displaying a fine‐grained, well‐distributed microstructure with a homogenous composition of Sn and Ag elements. EBSD provides insights into the orientation and texture of grains, revealing a weak‐to‐moderate texture across the phases. Postexperiment data indicate a dominant presence of larger grains and significant variation in grain size, with an area‐weighted mean grain size of 68.47 μm and a standard deviation of 8.68 μm; this suggests significant grain growth and coarsening of the Ag3Sn intermetallic compounds. These structural evolutions have crucial implications for the mechanical properties and reliability of the solder alloy in electronic assemblies, underscoring the need for further exploration of lead‐free solder materials in the electronics industry.

EBSD characterization of graphene nano sheet reinforced Sn–Ag solder alloy composites

This research explores the effects of incorporating Graphene Nano Sheets (GNS) on the microstructural characteristics and mechanical behavior of Sn–Ag solder alloys. The research was driven by the need for environmentally friendly, lead-free solder alloys with enhanced mechanical and thermal properties. The methodology involved incorporating graphene into the Sn–Ag alloy through stir casting, followed by a series of surface preparation techniques. The composite samples were then examined using EBSD to analyze crystallographic orientations and SEM/EDS for surface morphology and elemental composition. XRD provided insights into phase transformations and structural changes. Key findings reveal that the addition of GNS significantly refines the grain structure of the Sn–Ag alloy, leading to a bimodal grain size distribution. This refinement is attributed to the role of GNS as a nucleation site during solidification. Moreover, the study demonstrates a pronounced alteration in the texture of the material, with an increase in low-angle grain boundaries post-GNS addition. This texture change is indicative of enhanced mechanical properties. The results also show a shift in the orientation distribution function (ODF), suggesting a stronger crystallographic orientation due to GNS. These findings suggest that GNS incorporation could lead to improved mechanical and thermal properties in Sn–Ag solder, making them suitable for high-performance electronic applications. The study concludes that GNS not only serves as an effective reinforcement in Sn–Ag solder alloys but also significantly alters their microstructural and textural characteristics, contributing to the alloy's potential application in environmentally conscious electronic manufacturing.

Effect of rotating magnetic field on the microstructure and properties of Sn-Ag-Sb lead-free solder alloys

PurposeThe purpose of this paper is to study the microstructure and properties of Sn-3.5Ag and Sn-3.5Ag-0.5Sb lead-free solder alloys with and without a rotating magnetic field (RMF).Design/methodology/approachOptical microscopy, scanning electron microscopy and X-ray diffraction were used to analyze the effect of an RMF on the microstructure of the solders. Differential scanning calorimetry was used to study the influence of the RMF on the thermal characteristics of the solders. The mechanical properties of the alloys were determined by tensile measurements at different strain rates.FindingsThe ß-Sn grains and intermetallic compounds for the Sn-3.5Ag and Sn-3.5Ag-0.5Sb lead-free solder alloys were refined under an RMF, and the morphology of the ß-Sn grains changed from dendritic to equiaxed. The pasty range was significantly reduced under an RMF. The ultimate tensile strength (UTS) of Sn-3.5Ag improved under the RMF, whereas the UTS of Sn-3.5Ag-0.5Sb decreased slightly. The addition of Sb to the Sn-3.5Ag alloy significantly enhanced the UTS and elongation (El.%) of the samples. The UTS of the solder increased with increasing strain rate.Originality/valueThe results revealed that the application of RMF in the molten alloy had a significant effect on its microstructure and mechanical properties. The thermal characteristics of the Sn-3.5Ag and Sn-3.5Ag-0.5Sb solder alloys were improved under the RMF. This research is expected to fill a knowledge gap regarding the behaviour of Sn-Ag solder alloys under RMF.

Characterization of femtosecond laser ablation processes on as-deposited SnAg solder alloy using laser ablation ionization mass spectrometry

Laser ablation ionization mass spectrometry studies on polished surface structures of hard, high melting point multicomponent interconnect structures using our femtosecond-laser time-of-flight mass spectrometer have previously been proven capable of providing spatially resolved chemical depth profile data at the micro- and nanometer level. Transfer of experimental protocols tailored to suit such type of samples to low melting point materials with high surface roughness, however, is highly challenging, as thermal effects caused by interactions of the laser light with the targeted surface play a severe role in the latter case and may significantly deteriorate the analysis outcome. In this contribution we present a dedicated and detailed comparison of the distinct effects of near infrared and ultraviolet irradiation on the ablation process in femtosecond laser ablation ionization mass spectrometry studies on low melting point materials. As model substrate we use high surface roughness, as-deposited SnAg solder alloy, a material of major industrial relevance in microchip fabrication. We will demonstrate herein that polydimethylsiloxane replica casting is possible also from granularly structured, high surface roughness samples. Characterization of the laser ablation craters as well as of their polydimethylsiloxane replicas is carried out by mass spectrometric analysis, Scanning Electron Microscopy imaging, and furthermore, as a novel approach for this purpose, by white light interferometry. Integration of all obtained results significantly adds to the detailed understanding of laser ablation processes on low melting point, high surface roughness materials and allows identifying optimal depth profiling conditions for these demanding samples.

Development and characterization of eutectic Sn-Zn, Sn-Ag, Sn-Bi and Sn-Cu solder alloys

AbstractThis paper reports the comparative study of the microstructure, melting point, hardness and electrical resistivity of as-cast eutectic Sn-8.8 wt.% Zn, Sn-3.5 wt.% Ag, Sn-43 wt.% Bi and Sn-0.7 wt.% Cu lead-free solder alloys. Sn-3.5 wt.% Ag eutectic solder alloy was found to have the lowest electrical resistivity of 1.91 μΩ · cm whereas the highest electrical resistivity of 14.17 μΩ · cm was observed in the case of Sn-43 wt.% Bi eutectic solder alloy. The lowest melting point of 141.60°C was observed in the case of Sn-43 wt.% Bi eutectic alloy whereas the highest melting point of 243.28°C was observed in the case of Sn-3.5 wt.% Ag solder alloy. The results of the various solder alloys were compared with the properties of commercially available Sn-38.1 wt.% Pb eutectic solder alloy.

Nickel effects on the structural and some physical properties of the eutectic Sn-Ag lead-free solder alloy

PurposeThis study aims to investigate the structural, mechanical, thermal and electrical properties of tin–silver–nickel (Sn-Ag-Ni) melt-spun solder alloys. So, it aims to improve the mechanical properties of the eutectic tin–silver (Sn-Ag) such as tensile strength, plasticity and creep resistance by adding different concentrations of Ni content.Design/methodology/approachTernary melt-spun Sn-Ag-Ni alloys were investigated using x-ray diffractions, scanning electron microscope, dynamic resonance technique (DRT), Instron machine, Vickers hardness tester and differential scanning calorimetry.FindingsThe results revealed that the Ni additions 0.1, 0.3, 0.5, 0.7, 1, 3 and 5 Wt.% to the eutectic Sn-Ag melt-spun solder were added. The “0.3wt.%” of Ni was significantly improved its mechanical properties to efficiently serve under high strain rate applications. Moreover, the uniform distribution of Ag3Sn intermetallic compound with “0.3wt.%” of Ni offered the potential benefits, such as high strength, good plasticity consequently and good mechanical performance through a lack of dislocations and microvoids. The tensile results showed improvement in 17.63 per cent tensile strength (26 MPa), 21 per cent toughness (1001 J/m3), 22.83 per cent critical shear stress (25.074 MPa) and 11 per cent thermal diffusivity (2.065 × 10−7 m2/s) when compared with the tensile strength (21.416 MPa), toughness (790 J/m3), critical shear stress (19.348 MPa) and thermal diffusivity (1.487 × 10−7 m2/s) of the eutectic Sn-Ag. Slight increments have been shown for the melting temperature of Sn96.2-Ag3.5-Ni0.3 (222.62°C) and electrical resistivity to (1.612 × 10−7 Ω.m). It can be said that the eutectic Sn-Ag solder alloy has been mechanically improved with “0.3wt.%” of Ni to become a suitable alloy for high strain rate applications. The dislocation movement deformation mechanism (n = 4.5) without Ni additions changed to grain boundary sliding deformation mechanism (n = 3.5) with Ni additions. On the other hand, the elastic modulus, creep rate and strain rate sensitivity with “0.3wt.%” of Ni have been decreased. The optimum Ni-doped concentration is “0.7wt.%” of Ni in terms of refined microstructure, electrical resistivity, Young’s Modulus, bulk modulus, shear modulus, thermal diffusivity, maximum shear stress, tensile strength and average creep rate.Originality/valueThis study provides nickel effects on the structural of the eutectic Sn-Ag rapidly solidified by melt-spinning technique. In this paper, the authors have compared the elastic modulus of the melt-spun compositions which has been resulted from the tensile strength tester with these results from the DRT for the first time to best of the authors’ knowledge. This paper presents new improvements in mechanical and electrical performance.

Thermal aging effects on microstructure, elastic property and damping characteristic of a eutectic Sn–3.5Ag solder

The present work describes the microstructural changes and their impacts on the electrical resistivity, elastic modulus and damping property of a eutectic Sn–3.5wt% Ag solder material when exposed to high temperature. A detail microstructural study was conducted through the scanning electron microscopy with energy-dispersive spectroscopy analysis and electron backscattered diffraction technique. In as-cast eutectic Sn–Ag solder alloy, sub-micrometer size Ag3Sn intermetallic compound (IMC) particles and bamboo-like dendritic structure with a dimension of length 20–30 µm and width 3–5 µm formed during solidification. However, after thermal aging treatment at 150 °C for 60 days, the fine Ag3Sn IMC particles and β-Sn grain appeared with coarse microstructure with the formation of twinning having the twin axis and 60° rotation. As a result, microstructure and Sn-crystal orientation of Sn–Ag solder greatly impact on its overall properties and turned inferior. From material properties evaluation, it was confirmed that the electrical resistivity, elastic and shear moduli values were significantly reduced with aging time. Consequently, the values of damping capacity improved due to the reduction of moduli.

Back Cover: Advanced Engineering Materials 8∕2015

Advanced Engineering MaterialsVolume 17, Issue 8 p. 1244-1244 Back CoverFree Access Back Cover: Advanced Engineering Materials 8∕2015 First published: 06 August 2015 https://doi.org/10.1002/adem.201570031AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Graphical Abstract Micromechanical testing enables us to determine the mechanical properties of small volumes, microstructural phases, and constituents. Although traditionally limited to time independent deformation, we have now used the micropillar compression technique to characterize the stress and temperature dependent creep properties of microscopic phases (shown in the graph). Many materials, such as Sn-Ag solder alloys, have complex inhomogeneous microstructures (as shown in the background). For the first time ever, this new technique allowed us to probe and understand the creep properties of individual constituents, in this case pure tin and eutectic regions (shown in the inset SEM images). For details see the article by N. Chawla and co-workers on page 1168. Volume17, Issue8August 2015Pages 1244-1244 RelatedInformation

Interfacial reaction and intermetallic compound formation of Sn–1Ag/ENIG and Sn–1Ag/ENEPIG solder joints

Interfacial reactions and intermetallic compound (IMC) formation of Sn–1wt.%Ag solder with two different surface finishes, electroless nickel–immersion gold (ENIG) and electroless nickel–electroless palladium–immersion gold (ENEPIG), were evaluated during a reflow process. We first compared the interfacial reactions of the two solder joints and identified a relationship between the interfacial reaction behavior and solder/substrate compatibility. The Sn–1Ag/ENIG joint exhibited stable IMC growth and superior interfacial stability compared with the Sn–1Ag/ENEPIG joint. The growth rate of the interfacial IMC layer and consumption rate of the Ni(P) layer were closely related to the interfacial microstructure and morphology of the IMCs. The layer-type well-attached interfacial IMCs had advantages with respect to IMC growth rate and Ni(P) consumption rate. Compared to the previous Sn–3.0Ag–0.5Cu study, ENEPIG performed very well with Sn–Ag–Cu solder alloy. On the other hand, ENEPIG proved not to be a suitable surface finish for Sn–Ag solder alloy in this study.

Effect of aging treatment on microstructure and creep behaviour of Sn–Ag and Sn–Ag–Bi solder alloys

The present study was undertaken to investigate the influence of aging temperature on the creep behaviour of Sn–Ag and Sn–Ag–Bi solder alloys at testing temperatures ranging from 333 to 363 K under constant stress of 7·80 MPa. The steady state creep rate was found to increase continuously with increasing aging temperature at all testing temperatures. Results show that addition of Bi to the binary Sn–Ag solder alloy led to a significant increase in the strength and improvement in the creep resistance. The activation energy for the creep process of Sn–Ag and Sn–Ag–Bi solder alloys was found to have an average value of 36 and 45 kJ mol−1 respectively. This might be characterised by diffusion of Ag in Sn. The microstructure of the aged samples for both alloys examined by X-ray diffraction measurements supported the improvement in the creep resistance for Sn–Ag alloy by adding a small trace of Bi.

The Effects of Microstructure and Ag3Sn and Cu6Sn5 Intermetallics on the Electrochemical Behavior of Sn-Ag and Sn-Cu Solder Alloys

The Effects of Microstructure and Ag3Sn and Cu6Sn5 Intermetallics on the Electrochemical Behavior of Sn-Ag and Sn-Cu Solder Alloys

Material Analysis of Lead Free Solder Deposited by Electrochemical Deposition

Lead-free solders have essentially replaced lead-tin solders for new microelectronic applications. At the same time, many products are continuing to go through miniaturization, so the behavior of the solder material is changing as a function of the connection size. As lead-tin solder has been replaced by lead-free alloys, electrodeposited SnAg has become the standard solder alloy used on wafers. Tin-based solders exhibit a complex material structure in the deposit, as recrystallization occurs in the deposit, and as intermetallic compounds form. Understanding the complex nature of these materials is becoming increasingly important to the performance of our electronic products. We have characterized ECD SnAg solder alloy deposits in terms of composition, grain size, phase, microstructure, and texture using EBSD analysis. We will discuss the effects of modifying the process parameters on the microstructure which could implications on the performance of the solder bump as a chip-level interconnect. We have seen that the metals deposit as β-tin with finely dispersed intermetallic grains. We have also seen evidence of recrystallization of the deposit subsequent to deposition, although the recrystallization behaviour is significantly different than the well-characterized copper recrystallization. Finally, the metal at the interface below the solder reacts with Sn to form intermetallic compounds, the compositions of which are dependent on the materials present. The effects of the process parameters on the deposit properties are becoming increasingly important to understand in order to control the properties of the interconnection, and how it changes over its lifetime. We have characterized the incorporation of trace organic materials in the deposit as a function of plating parameters. The deposition of SnAg from an MSA-based plating bath is very different from the deposition of copper from a copper sulfate plating bath. We have noticed that the incorporation of organic additive materials, as well as the grain size, increases as the deposition rate is increased in the deposition of SnAg.

Electrochemical behavior of a lead-free SnAg solder alloy affected by the microstructure array

The aim of this study is to evaluate the electrochemical corrosion behavior of a Sn–Ag solder alloy in a 0.5 M NaCl solution at 25 °C as a function of microstructural characteristics. Different microstructure morphologies, which can be found in Sn–Ag solder joints and that are imposed by the local solidification cooling rate, are evaluated and correlated to the resulting scale of the dendritic matrix and the morphology of the Ag 3Sn intermetallic compound. Cylindrical metallic molds at two different initial temperatures were employed permitting the effect of 0.15 °C/s and 0.02 °C/s cooling rates on the microstructure pattern to be experimentally examined. Electrochemical impedance spectroscopy (EIS) diagrams, potentiodynamic polarization curves and an equivalent circuit analysis were used to evaluate the electrochemical parameters. It was found that higher cooling rates during solidification are associated with fine dendritic arrays and a mixture of spheroids and fiber-like Ag 3Sn particles which result in better corrosion resistance than coarse dendrite arrays associated with a mixture of fibers and plate-like Ag 3Sn morphologies which result from very slow cooling rates.

Effects of triethanolamine and polyethylene glycol additives on electrodeposition of Sn–Ag solder alloy

The effects of triethanolamine (TEA) and polyethylene glycol 600 (PEG600) on the polarisation behaviour and composition of electrodeposited eutectic Sn–3·5Ag film were systematically investigated in order to widen the deposition current density range for the simplicity and potential for cost effective production. The addition of TEA to the bath with PEG600 increased the tin deposition, which was inhibited by PEG600 addition. The addition of both TEA and PEG600 helped to obtain dense and fine grained Sn–Ag alloy films and also widened the operating window.

Measurement and prediction of contact angles of Pb-free Sn-Ag solder alloys on Cu substrate

The contact angle (Θ) of molten Sn and Sn-Ag alloys (0.5, 1.5, 3.5, 6 wt.% Ag) on Cu substrates have been studied by using sessile drop method at various temperatures (230, 250, 275 and 300 °C). Experimental results showed that additions of Ag to Sn resulted in a continuous decrease in the Θ up to 3.5 wt.% above which the Θ value was increased. Increasing alloy temperature also decreased the Θ proportionally. Experimental results revealed that a correlation between the Θ, alloy composition and the alloy temperature exists which yielded an empirical model to predict the Θ at a given Ag content and temperature for a given Sn-Ag alloy. The empirical model predicts the Θ reasonably well with the present work and the other published works.

Thermomigration of Cu–Sn and Ni–Sn intermetallic compounds during electromigration in Pb-free SnAg solder joints

Abstract

The effect of cooling rate on the dendritic spacing and morphology of Ag 3Sn intermetallic particles of a SnAg solder alloy

The size and morphology of intermetallic compounds of Sn–Ag solder alloys can have a significant influence on the mechanical strength of solder joints. The aim of the present study is to characterize the as-cast microstructure of a Sn–2 wt.% Ag solder alloy, and to correlate the resulting scale of the dendritic matrix and the morphology of the Ag 3Sn intermetallic compound (IMC) with the corresponding solidification cooling rate. Pre-heated low-carbon steel molds and a water-cooled solidification apparatus were used permitting a significant range of solidification cooling rates to be experimentally examined. It is shown that under very slow cooling conditions (0.02 °C/s) the microstructure of the sample is formed by a coarse dendritic matrix and a mixture of fiber and plate-like Ag 3Sn IMC in the interdendritic region with the fibers located along the board line separating the matrix. For cooling rates from 0.15 to 1.15 °C/s a mixture of spheroid and fiber-like IMC and secondary dendrite arm spacings between 15 and 40 μm, with the spheroids located in the center of the interdendritic region. At higher cooling rates, of about 8 °C/s only Ag 3Sn spheroids (of about 0.5 μm in diameter) prevail in the eutectic mixture.

A novel method of reducing melting temperatures in SnAg and SnCu solder alloys

With the increasing use of lead-free solder alloys in modern electronics, low melting materials are often required to protect the heat-sensitive parts during soldering operation. Alloy systems based on Sn/Cu/Ag offer more reliable solutions and address the current problems involved with soldering process. Nanoparticles melt relatively at low temperatures compared to their bulk counter parts and we introduce a robust method of synthesizing nanoscale solder pastes for wave soldering applications. Nanoparticles of Sn-3.5Ag and Sn-0.7Cu alloys were prepared with stir casting followed by mechanical attrition. The size dependent melting properties of the eutectic alloys were studied by differential scanning calorimetry technique and the results showed a reduction of 4.7 and 5.0 °C melting temperatures in the alloys when reduced from bulk to 92 nm and 96 nm sizes respectively. The nanosize effects were also theoretically calculated and compared with experimental data.

Effects of nano-structured particles on microstructure and microhardness of Sn–Ag solder alloy

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.