Ternary Solder Research Articles

Prediction of steady-state creep strain rate and rupture life for SnAg-based Lead-free solder joints by SP test

This is to predict the equation of steady-state creep strain rate and rupture life of Lead-free solder joints and to observed the fractographies of the surfaces of the fractured solder joints using the SP creep test method. In this research, Sn-4Ag, Sn-4Ag-0.5Cu, Sn-4Ag-1.0Cu and Sn-37Pb solders are used. So as to compare the Lead-free solder alloys with lead(Pb) containing solder alloys. In addition, SP creep tests are held at temperature of 30, 50 and 80¢™C. And the shear stresses used in the research are in the range of 3 to 22 MPa. The microstructure characterization and fractographic analysis of the fractured solder joints are conducted to fully describe the creep behavior of the solder joints. Increasing the testing temperature from 30 to 80°C has some effect on the fracture behavior of ternary SnAgCu solder joints during creep testing. The increased temperature made the joints more vulnerable to the brittle interfacial fracture. In addition, Sn-37Pb solder joint, dimples in the fractured surfaces are much smaller than that of the Lead-free solder joints. Also using the creep data, we obtained a prediction equation of steady-state creep strain rate and rupture life for Lead-free solder joint in this research.

Enhancing mechanical response of hypoeutectic Sn–6.5Zn solder alloy using Ni and Sb additions

In this paper, we report a convenient and informative procedure for improving the integrity and reliability of eutectic Sn–9Zn solder using minor alloying additions of Ni and Sb after reducing the amount of Zn phase. Results indicate that alloying of Ni or Sb into hypoeutectic Sn–6.5Zn resulted in slightly reduced the undercooling and pasty range with maintaining its melting temperature at the Sn–9Zn level. After 0.5% Sb addition, the enhanced solid solution effect and enlarged eutectic area with small needle-like α-Zn phase raised the creep resistance of hypoeutectic Sn–6.5Zn alloy, while the flower shaped (Ni,Zn)3Sn4 intermetallics (IMCs) and small spacing needle-like α-Zn phase produced by 0.5% Ni alloying results in small increase in its creep resistance. These results show that the creep strain rate of the entire alloys follows Garafalo hyperbolic sine equation, and the calculated creep stress exponent for three solders is reasonably close to other published data. Moreover, with the addition of Sb and Ni into Sn–6.5Zn solder, significant improvement in creep resistance of ∼270% and ∼182% is realized, respectively when compared with the hypoeutectic Sn–6.5Zn solder. This finding indicates the capability of newly developed ternary solder alloys to serve a much wider array of electronic applications.

The measurement of thermal conductivity variation with temperature for Sn-20 wt.% In based lead-free ternary solders

The variations of thermal conductivity with temperature for Sn–In based lead-free solders, Sn-20wt.% In-15wt.% [X] (X=Ag, Bi, Sb, Zn) were measured by using the linear heat flow apparatus. The thermal conductivities of lead free solders at their melting temperatures were obtained from graphs of thermal conductivity variations with temperature. The thermal temperature coefficients for Sn-20wt.% In based lead free ternary solders were obtained from the graphs of thermal conductivity variations with temperature.

Effect of Micron Size Ni Particle Addition on Microstructure, Thermal and Mechanical Properties of Sn-9Zn Lead-Free Solder Alloy

This study had been carried out to investigate the effect of micron size Ni particle addition on the microstructure, melting behavior and mechanical properties of the ternary Sn-9Zn solder alloys. Different weight percentage, viz. 0.25, 0.5 and 1 of micron size Ni particle was added in the liquid Sn-9Zn alloy and then cast into the metal mold. Melting behavior was studied by Differential Thermal Analyzer (DTA). Microstructural investigation was conducted using Optical and Scanning Electron Microscope (SEM). Tensile properties were determined at a strain rate 3.00 mm.min-1. The results indicated that Ni addition increased both the melting point and solidification range of the Sn-9Zn solder alloy. The microstructures of newly developed ternary Sn-9Zn-xNi solder alloys consisted of fine needle-like α-Zn phase dispersed in the β-Sn matrix. It was found that small amount of Ni (0.25 wt. %) addition refined and dispersed the Zn needles throughout the matrix. Besides, enhanced precipitation of Zn in the β-Sn matrix was also observed. All these structural changes increased the hardness and tensile strength of Sn-9Zn alloy with the addition of Ni particle to a certain amount.

Preparation of Sn–Ag–In Solder Bumps by Electroplating of Sn–Ag and Indium in Sequence and the Effect of Indium Addition on Microstructure and Shear Strength

This paper focused on the feasibility of preparing Sn-Ag-In ternary solder bumps with small size by two-step electroplating. The interfacial reaction and shear strength between three different solders (Sn2.2Ag, Sn1.8Ag9.4In, and Sn1.6Ag21.7In) and Cu under bump metallization (UBM) were investigated. After the reflow for 10 min, η Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> (Sn,In) <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> and ε Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> (Sn,In) intermetallic compounds (IMC) were formed at the interface near the solder matrix and Cu UBM, respectively. Indium addition lowered the reflow temperature and improved the interface between solder and IMCs. The mean shear strength of Sn1.8Ag9.4In solder bump was higher than that of Sn2.2Ag and Sn1.6Ag21.7In solder bumps. After long time reflow, the mean shear strength increased.

Preparation of Sn—Ag—In ternary solder bumps by electroplating in sequence and reliability

This paper describes a technique that can obtain ternary Sn—Ag—In solder bumps with fine pitch and homogenous composition distribution. The mainfeature of this process is that tin-silver and indium are electroplated on copper under bump metallization (UBM) in sequence. After an accurate reflow process, Sn1.8Ag9.4In solder bumps are obtained. It is found that the intermetallic compounds (IMCs) between Sn—Ag—In solder and Cu grow with the reflow time, which results in an increase in Ag concentration in the solder area. So during solidification, more Ag2In nucleates and strengthens the solder.

Shear test parameters for brittle fracture of flip chip solder joint

Compared to conventional Sn-Pb solder, ternary Pb free solder alloys are particular susceptible to brittle fracture through the formation of intermetallic compound layers. However, the conventional shear test of the solder ball joint has been reported to be inappropriate for confirming the susceptibility to brittle fracture of ball grid array solder joints. In this study, we investigated the effects of two shear test parameters, the shear height and shear speed to determine the optimum shear conditions for the brittle fracture of flip chip solder joints. The solder composition and process used in this study were Sn-3·0Ag-0·5Cu and low cost bumping with electroless nickel immersion gold followed by solder paste screen printing. Increasing shear height, at a fixed shear speed, decreased the shear force, whereas increasing the shear speed, at a fixed shear height, increased the shear force. The experimental and computational simulation results indicated that a low shear height and high shear speed improve the bonding force and are generally more appropriate for the brittle fracture of flip chip solder joints. The failure mechanisms were discussed in terms of the von Mises stresses and equivalent plastic strain distributions.

Thermal fatigue endurance of Sn3Ag0.5Cu0.5In0.05Ni and Sn2.5Ag0.8Cu0.5Sb solders in composite solder joints of LTCC/PWB assemblies

PurposeThe purpose of this paper is to investigate the thermal fatigue endurance of two lead‐free solders used in composite solder joints consisting of plastic core solder balls (PCSB) and different solder materials, in order to assess their feasibility in low‐temperature cofired ceramic (LTCC)/printed wiring board (PWB) assemblies.Design/methodology/approachThe characteristic lifetime of these joints was determined in a thermal cycling test (TCT) over a temperature range of −40‐125°C. Their failure mechanisms were analyzed after the TCT using scanning acoustic and optical microscopy, scanning electronic microscope, and field emission scanning electronic microscope investigation.FindingsThe results showed that four different failure mechanisms existed in the test assemblies cracking in the mixed ceramic/metallization zone; or a mixed transgranular/intergranular failure occurred at the low temperature extreme; whereas an intergranular failure within the solder matrix; or separation of the intermetallic layer and the solder matrix occurred at the high temperature extreme. Sn3Ag0.5Cu0.5In0.05Ni was more resistant to mixed transgranular/intergranular failure, but had poor adhesion with the Ag3Sn layer. On the other hand, cracking in the mixed ceramic/metallization zone typically existed in the joints with Sn2.5Ag0.8Cu0.5Sb solder, whereas the joints with Sn3Ag0.5Cu0.5In0.05Ni were practically free of these cracks. The characteristic lifetimes of both test joint configurations were at the same level (800‐1,000) compared with joints consisted of Sn4Ag0.5Cu solder and PCSB studied earlier.Originality/valueThe study investigated in detail the failure mechanisms of the Sn3Ag0.5Cu0.5In0.05Ni and Sn2.5Ag0.8Cu0.5Sb solders under harsh accelerated test conditions. It was proved that these solders behaved similarly to the ternary SnAgCu solders in these conditions and no improvement can be achieved by utilizing these solders in the non‐collpasible solder joints of LTCC/PWB assemblies.

Microstructural evolution and tensile properties of Sn–5Sb solder alloy containing small amount of Ag and Cu

The near peritectic Sn–5Sb Pb-free solder alloy has received considerable attention for high temperature electronic applications, especially on step soldering technology, flip-chip connection. In the present study, a separate addition of the same amount of Ag and Cu are added with the near-peritectic Sn–5Sb solder alloy to investigate the effect of a third element addition on the microstructural, thermal and mechanical properties of the newly developed ternary solder alloys. The results indicate that the melting point of Sn–5Sb solder is enhanced by Ag and Cu additions. Besides, the Ag and Cu content refine the microstructure and form new intermetallic compounds (IMCs) with the near-peritectic Sn–5Sb solder alloy. The tensile tests revealed that all alloys exhibit higher mechanical strength with increasing strain rate and/or decreasing testing temperature, suggesting that the tensile behavior of the three alloys is strain rate and temperature dependence. The yield and ultimate tensile strength are higher for Sn–5Sb–0.7Cu alloy compared with Sn–5Sb and Sn–5Sb–0.7Ag alloys. Good mechanical performance of Sn–5Sb–0.7Cu solder is often correlated to a fine β-Sn grain size and more dispersed Cu-Sn IMC particles, which makes the solder exhibit high strength and yield stress.

Stress-strain characteristics, dynamic recrystallization, grain growth, and melting point of the binary and ternary solder alloys

An advanced solder alloy, Pb-10wt%Sn-3wt%Zn, has been developed to improve the mechanical properties of the Pb-10wt%Sn based solders. Deformation behavior of Pb-10wt%Sn and Pb-10wt%Sn-3wt%Zn alloys was investigated in tension at strain rates from 0.005% to 0.25% s^{-1} in the temperature range 383--433 K. The stress-strain characteristics curves showed two deformation modes: (i) continuous work softening and fracture following a sharp stress in Pb-10wt%Sn, (ii) work hardening with steady-state flow and fracture just after yielding in Pb-10wt%Sn-3wt%Zn. In the work softening type, relatively coarse grains ranging from 30 to 60 \mu m are produced by dynamic recrystallization (DRX). In the work hardening with steady-state flow type, fine grains less than 10\mu m are developed by alloying with zinc. Adding Zn into the solder makes the microstructure finer and more uniform. Microstructural characterization using optical microscope analysis (OMA) were conducted to investigate the deformation behavior and cleared that the grain boundary sliding is the dominant mechanism observed in the Pb-10wt%Sn-3wt%Zn. The melting points have been determined using differential thermal analysis (DTA) and differential scanning calorimetry (DSC). These temperatures are 587 and 555 K for Pb-10wt%Sn and Pb-10wt%Sn-3wt%Zn, respectively. The addition of a small amount of Zn leads to reduce high temperature performance and melting point.

Influence of Lanthanum Additions on the Microstructure and Microhardness of Sn-3.5Ag Solder

This study evaluates the effects of different amounts of lanthanum (La) additions on the microstructure and microhardness of Sn-3.5Ag solders. Sn-3.5Ag-xLa ternary solders were prepared by adding 0 wt.% to 1.0 wt.% La to Sn-3.5Ag alloy. Copper substrates were then dipped in the molten solders and these samples aged at 150°C for up to 625 h. The microstructure and microhardness of the as-solidified solder and the aged solder/copper samples were investigated. The Sn-3.5Ag-xLa solders comprised β-Sn, Ag3Sn, and LaSn3 phases, and their microstructure was refined by La additions. As-cast, the addition of La increased the microhardness of the Sn-Ag solder due to the refining effect of Ag3Sn particles and increased formation of LaSn3 compounds. As the aging time was increased, the microhardness of the solders decreased and the Ag3Sn compounds coarsened. However, the coarsening of Ag3Sn compounds was retarded by La, and the size and amount of LaSn3 compounds did not change perceptibly with aging time. Therefore, La additions can improve the microhardness and thermal resistance of solder joints.

Influence of small amount of Al and Cu on the microstructure, microhardness and tensile properties of Sn–9Zn binary eutectic solder alloy

In the present study, a separate addition of the same amount of Al and Cu are added with the Sn–9Zn eutectic solder alloy to investigate the effect of a third element addition on the microstructural and mechanical properties as well as thermal behavior of the newly developed ternary solder alloys. The results indicate that both Al and Cu refine the microstructure and form intermetallic compounds with the eutectic solder alloy. The microstructures of the newly developed ternary Sn–9Zn–X solder alloys were composed of fine needle-like α-Zn phase with some IMC dispersed in the β-Sn matrix. The relatively small and compact shaped Al 6Zn 3Sn IMC was found to be uniformly distributed in the β-Sn phase which results in an increase in the tensile strength, due to the second phase dispersed strengthening mechanism. On the contrary, the large flower shaped Cu 6Sn 5 and rod shaped Cu 5Zn 8 IMC develops some sort of weak interface with the parent β-Sn matrix results in a decrease in the tensile strength. The microhardness of the Sn–9Zn–0.5Al ternary solder alloys was also higher than that of the Sn–9Zn–0.5Cu alloy.

Electromigration Reliability and Morphologies of 62Sn–36Pb–2Ni and 62Sn–36Pb–2Cu Flip-Chip Solder Joints

The near-eutectic Sn-Pb-Cu and Sn-Pb-Ni ternary solder alloys were developed based on the consideration of strength and fatigue reliability enhancement of solder joints in part via the altering of formation of interfacial intermetallic compounds. In this work, we examine electromigration reliability and morphologies of 62Sn-36Pb-2Ni and 62Sn-36Pb-2Cu flip-chip solder joints subjected to two test conditions that combine different average current densities and ambient temperatures: 5 kA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> at 150 degC and 20 kA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> at 3 degC. Under the test condition of 5 kA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> at 150 degC, 62Sn-36Pb-2Cu is overwhelmingly better than 62Sn-36Pb-2Ni in terms of electromigration reliability. However, under the test condition of 20 kA/cm2 at 30 degC, the electromigration fatigue life of 62Sn-36Pb-2Ni shows a profuse enhancement and exceeds that of 62Sn-36Pb-2Cu. Electromigration-induced morphologies are also examined on the cross sections of solder joints using scanning electron microscopy.

Properties of solders with low melting point

The aim of the work is to analyse thermal properties and microstructure of solders, which should be suitable for application in electronics. The solders must have low enough working temperature to avoid thermal damage of the assembly and uniform microstructure in whole bulk. For solders presented in this work the required temperatures are less than 150 °C. They represent alternative, for example, to the conductive adhesives, which are in use. Five types of solders have been studied. They were created from the metals: Sn, In, Bi, Cd. The solder on the basis of Bi/Sn, has the composition of 58 wt.% Bi and 42 wt.% Sn of eutectic point of the alloy and the melting point of 141 °C. The second solder of the composition of 53 wt.% Bi, 26 wt.% Sn and 21 wt.% Cd proved the melting temperature of 103 °C. The next both solders are on Sn/In basis. The solder with composition of 70 wt.% In and 30 wt.% Sn has the melting point temperature of 126 °C. The second solder of nearly eutectic composition, 50 wt.% Sn and 50 wt.% In has lower melting temperatures about 117 °C. The last one is ternary solder with composition of 53 wt.% Sn, 37 wt.% Bi and 10 wt.% In with the melting point between 100 and 123 °C. Differential scanning calorimetry (DSC) was used to determine the thermal properties of these solders. For the study of microstructure light microscopy and X-ray diffraction analysis were used. The analysis of solders microstructure show that almost all solders have homogenous distribution of two or three phases in the microstructure.

Environmentally friendly solders 3–4 beyond Pb-based systems

Based on environmental considerations, global economic pressures, enacted by legislations in several countries, have warranted the elimination of lead from solders used in electronic applications. Sn3.5Ag, SnAgCu, and Sn0.7Cu have emerged among various lead-free candidates as the most promising solder alloys to be utilized in microelectronic industries. However, with the vast development and miniaturization of modern electronic packaging, new requirements such as superior service capabilities have been posed on lead-free solders. In order to improve the comprehensive property of the solder alloys, two possible approaches were adopted in the current research and new materials developed were patented. One approach was involved with the addition of alloying elements to make new ternary or quaternary solder alloys. Proper addition of rare earth element such as La and Ce have rendered solder alloys with improved mechanical properties, especially creep rupture lives of their joints. Another approach, the composite approach, was developed mainly to improve the service temperature capability of the solder alloys. Composite solders fabricated by mechanically incorporating various reinforcement particles to the solder paste have again exhibited enhanced properties without altering the existing processing characteristics. The recent progress and research efforts carried out on lead-free solder materials in Beijing University of Technology were reported. The effects of rare earth addition on the microstructure, processing properties, and mechanical properties were presented. The behaviors of various Sn-3.5Ag based composite solders were also explicated in terms of the roles of reinforcement particles on intermetallic growth, steady-state creep rate, the onset of tertiary creep, as well as the overall creep deformation in the solder joints. Thermomechanical fatigue (TMF) behavior of the solder alloys and composite solders were investigated with different parameters such as ramp rate, dwell time, etc. The damage accumulation features and residual mechanical properties of the thermomechanically-fatigued composite solder joints were compared with non-composite solder joints. To match the lead-free alloys, various types of water soluble no-clean soldering flux have also been developed and their properties were presented.

Primary solidification phases of the Sn-rich Sn-Ag-Cu-Ni quaternary system

The eutectic and near-eutectic Sn-Ag-Cu solders are the most promising lead-free solders, and nickel is frequently used as the barrier layer material. Nickel dissolves into the molten Sn-Ag-Ni alloy during the soldering process, and the ternary solder becomes a Sn-Ag-Cu-Ni quaternary melt near the nickel substrate. Liquidus projection is the projection of the liquidus trough and it delineates the boundaries of various primary solidification phases. Information of liquidus projection is helpful for understanding the alloys’ solidification behavior. This study prepared the Sn-Ag-Cu-Ni alloys of various compositions at the Sn-rich corner. The alloys were melted at higher temperatures and solidified in air. The solidified alloys were metallographically examined to determine the phases formed, especially the primary solidification phases. No ternary or quaternary compounds were found. The knowledge of the primary solidification phases, phase formation sequences, and reaction temperatures determined in this study were put together with all of the available liquidus projections of the constituent ternary systems to determine the primary solidification phases of the quaternary Sn-Ag-Cu-Ni system at the Sn-rich corner.

Structural, mechanical, hardness indentation measurements of Sn65-xAg25Sb10Cuxsolder alloys rapidly solidified from melt at cooling rate 1.1×105K s-1

Structural, mechanical properties, and hardness indentation measurements of Sn65−x Ag25Sb10Cu x (x=0, 0.5, 1.0, 1.5, 2.0, and 2.5 wt %) solder alloys have been studied and analyzed. The alloy exhibits mechanical properties superior to those in both the Sn–Ag25 binary and Sn–Ag25Sb10 ternary solder alloys. The addition of small amounts of Cu is found to refine the effective grain size, while retaining the uniform distribution of Ag3Sn, SnSb, and Cu10Sn3 precipitates in the solidification microstructure, thus significantly improving the ductility and strength.

The compression stress-strain behavior of Sn-Ag-Cu solder

The yield-stress behavior was investigated for the 95.5Sn-4.3Ag-0.2Cu (wt.%), 95.5Sn-3.9Ag-0.6Cu, and 95.5Sn-3.8Ag-0.7Cu ternary lead-free solders using the compression stress-strain test technique. Cylindrical specimens were evaluated in the as-cast or aged (125°C, 24 h) condition. The tests were performed at −25°C, 25°C, 75°C, 125°C, and 160°C using strain rates of 4.2×10−5s−1 or 8.3×10−4s−1. Specially designed Sn-Ag-0.6Cu samples were fabricated to compare the yield stress of the dendritic microstructure versus that of the equiaxed microstructure that occurs in this alloy.

Electrochemically Deposited Tin-Silver-Copper Ternary Solder Alloys

A study on film properties of electrochemically deposited tin-silver-copper (SnAgCu) alloys was performed with an alkaline bath. This research focused on the bath and process development for dendrite-free, near-eutectic SnAgCu alloy deposition through the investigation of cathodic polarization, morphological transition, and film composition. Effects of process parameters on surface morphology, film composition, and diffusion-limited current density (LCD) were also examined. Ternary alloys were obtained only when the current density was driven beyond the mass-transfer limitation of noble metals (silver and copper), which seemed to cause the transition of surface morphology and film composition with increasing current density. The morphological transition occurred through four stages (dendrites, suppression of dendrites, nodules, and columns/dendrites), and the content of noble metals in the film tended to drop with increasing current density. With increasing the concentration of noble metals, bath temperature, and agitation, the morphology at low current densities became increasingly dendrite-dominated and the content of noble metals in the film was enhanced at a fixed current density. The morphology of stage four was influenced by the ratio of the applied current density to the LCD, where the LCD was significantly influenced by the metal concentration, bath temperature, and agitation. © 2002 The Electrochemical Society. All rights reserved.

Interaction relation in 60Sn–Pb–0.05La ternary solder alloy

Interaction relations of the adding element with the constituent elements is important to deeply understand the modification effect of small amount of La in the traditional 60Sn–40Pb solder alloy. Miedema formation energy model for binary system with Tanaka modification by excess entropy have been illustrated to be suitable to nonferrous and rare earth element systems. By further introducing Chou geometric model, thermodynamic analysis had been done for the 60Sn–Pb–0.05La ternary system. The calculating results indicate that the rare earth element La with small addition has higher affinity to the constituent element Sn rather than Pb. This conclusion is an important foundation to further investigate the improved properties of 60Sn–Pb–0.05La solder alloy.