Solder Alloy Systems Research Articles

Effect of Al addition on microstructure and wetting properties of quinary lead-free solder alloy systems

In this study, the wetting and microstructural properties of SACBi-xAl (x = 0.05, 0.1, 0.3, 0.5, and 0.6%) quinary lead-free solder alloys produced by adding various amounts of Al to the quaternary SAC-1Bi lead-free solder alloy (wt%) were investigated. The wetting and microstructural properties of Al-added quinary lead-free solder alloys on Cu substrate in an Ar gas atmosphere were investigated. It was reported that the best wetting angle (38.44° for the 325 °C temperature value) and melting temperature (212.5 °C) belonged to the SACBi-0.1Al solder alloy. When the microstructural properties are examined, it is seen with the help of SEM images that the CuAl IMC phase, which is rich in Al, has replaced Cu6Sn5 and Ag3Sn IMCs.

Effects of Bi content on thermal, microstructure and mechanical properties of Sn-Bi-In-Zn solder alloy systems

Effects of Bi content on thermal, microstructure and mechanical properties of Sn-Bi-In-Zn solder alloy systems

Numerical computation of wetting angles of Sn–(3−x)Ag–0.5Cu−x(Bi,In) quaternary Pb-free solder alloy systems on Cu substrate

This paper was aimed to study of the wetting angle ([Formula: see text]) of Sn–Ag–Cu, Sn–([Formula: see text])Ag–0.5Cu–([Formula: see text])Bi and Sn–([Formula: see text])Ag–0.5Cu–([Formula: see text])In ([Formula: see text], 1 and 2 in wt.%) Pb-free solder alloy systems at various temperatures (250, 280 and 310∘C) on Cu substrate in Ar atmosphere. The new Sn–([Formula: see text])Ag–0.5Cu–xBi and Sn–([Formula: see text])Ag–0.5Cu[Formula: see text]([Formula: see text]) In systems, low Ag content quaternary Pb-free solder alloys, were produced by adding 0.5%, 1% and 2% Bi and In separately to the near-eutectic Sn-3[Formula: see text]wt.%Ag–0.5[Formula: see text]wt.%Cu (SAC305) alloy. The wetting angles of new alloys, Sn[Formula: see text]2.5[Formula: see text]wt.%Ag[Formula: see text]0.5[Formula: see text]wt.%Cu[Formula: see text]0.5[Formula: see text]wt.%Bi (SAC-0.5Bi), Sn[Formula: see text]2[Formula: see text]wt.%Ag[Formula: see text]0.5[Formula: see text]wt.%Cu[Formula: see text]1[Formula: see text]wt.%Bi(SAC-1Bi), Sn[Formula: see text]1[Formula: see text]wt.%Ag[Formula: see text]0.5[Formula: see text]wt.%Cu[Formula: see text]2[Formula: see text]wt.%Bi(SAC-2Bi), Sn[Formula: see text]2.5[Formula: see text]wt.%Ag[Formula: see text]0.5[Formula: see text]wt.%Cu[Formula: see text]0.5[Formula: see text]wt.%In (SAC-0.5In), Sn[Formula: see text]2[Formula: see text]wt.%Ag[Formula: see text]0.5[Formula: see text]wt.%Cu[Formula: see text]1[Formula: see text]wt.%In (SAC-1In) and Sn[Formula: see text]1[Formula: see text]wt.%Ag[Formula: see text]0.5[Formula: see text]wt%.Cu[Formula: see text]2[Formula: see text]wt.%In (SAC-2In) were measured by sessile drop method. Experimental results showed that additions of Bi and In separately to SAC305 resulted in a continuous decrease in the [Formula: see text] up to 1[Formula: see text]wt.% above which the [Formula: see text] value was increased and it is appeared that a correlation among the [Formula: see text], alloys compositions and the test temperatures exists which recommended an empirical model to estimate the [Formula: see text] at a given Bi and In content and temperature for a given alloy systems. The numerical model estimates the [Formula: see text] understandably well with the present work.

Wetting characteristic of Sn-(3-x)Ag-0.5Cu-xBi quaternary solder alloy systems

PurposeThis paper aims to invastigate of the wetting and interfacial properties of Sn-(3-x)Ag-0.5Cu-(x)Bi (x = 0.5, 1 and 2 in Wt.%) Pb-free solder alloys at various temperatures ( 250, 280 and 310°C) on Cu substrate in Ar atmosphere.Design/methodology/approachIn this study, new Sn-(3-x)Ag-0.5Cu-xBi systems, low Ag content quaternary lead-free solder alloys, were produced by adding 0.5, 1 and 2% Bi to the near-eutectic SAC305 alloy. The wetting angles of three new alloys, Sn-2.5Ag-0.5Cu-0.5 Bi(SAC-0.5 Bi), Sn-2Ag-0.5Cu-1Bi(SAC-1Bi) and Sn-1Ag-0.5Cu-2Bi(SAC-2Bi) were measured by sessile drop technique on the Cu substrate in argon atmosphere.FindingsIn accordance with the interfacial analyses, intermetallic compounds of Cu3Sn, Cu6Sn5, and Ag3Sn were detected at the SAC-Bi/Cu interface. The results of wetting tests show that the addition of 1 Wt.% Bi improves the wetting properties of the Sn-3Ag-0.5Cu solder. The lowest wetting angle (θ) was obtained as 35,34° for Sn-2Ag-0.5Cu-1Bi alloy at a temperature of 310 °C.Originality/valueThis work was carried out with our handmade experiment set and the production of the quaternary lead-free solder alloy used in wetting tests belongs to us. Experiments were conducted using the sessile drop method in accordance with wetting tests.

The effect of micro via‐in pad design on surface‐mount assembly defects: part II – voiding and spattering

PurposeThe purpose of this paper is to propose a solution procedure to minimize/eliminate voiding and spattering defects in the assembly of 0201 chip components with micro via‐in pads and 95 wt.%Sn‐5 wt.%Sb solder alloy.Design/methodology/approachIn total, four different micro via‐in pad designs were compared (via‐hole opening size): ultra small via‐in pads (d: 10 μm), small via‐in pads (d: 20 μm), and large via‐in pads (d: 60 μm), as well as designs with no via‐in pads and capped via‐in pads. Two process variables were also evaluated for the goal of achieving a high‐yield assembly solution in micro via‐in pad and lead‐free solder systems. Potential factors, such as the preheat conditions of the reflow profile and stencil aperture size, which might affect voiding and spattering in solder joints with micro via‐in pad, were investigated. Solder voiding frequency and size were also determined from X‐ray inspection and sample cross‐section analysis.FindingsThe results indicated that larger via‐holes were seen to create bigger voiding than smaller via‐holes. For smaller via‐holes, spattering is a greater problem than voiding in solder joints. Ultra small via‐in pads generated higher spattering compared to no via‐in pads and capped via‐in pads. Capped via‐in pads exhibited the best results in preventing voiding and flux spattering, and provided a wide process window for the selection of process parameters. It is also indicated that spattering was found to rapidly reduced with both increasing stencil opening size and use of reflow profile with long‐preheat conditions.Originality/valueThe findings provide certain process guidelines for surface‐mount assembly with via‐in pad substrate design. The strategy is to prevent voiding and spattering by adopting capped via‐in pads, if possible, when applying micro via with the 95 wt.%Sn‐5 wt.%Sb solder alloy system.

Prognostication of Residual Life and Latent Damage Assessment in Lead-Free Electronics Under Thermomechanical Loads

Requirements for system availability for ultrahigh reliability electronic systems such as airborne and space electronic systems are driving the need for advanced health monitoring techniques for the early detection of the onset of damage. Aerospace electronic systems usually face a very harsh environment, requiring them to survive the high strain rates, e.g., during launch and reentry, and thermal environments, including extremely low and high temperatures. Traditional health monitoring methodologies have relied on reactive methods of failure detection often providing little or no insight into the remaining useful life of the system. In this paper, a mathematical approach for the interrogation of the system state under cyclic thermomechanical stresses has been developed for six different lead-free solder alloy systems. Data have been collected for leading indicators of failure for alloy systems, including Sn3Ag0.5Cu, Sn0.3Ag0.7Cu, Sn1Ag0.5Cu, Sn0.3Ag0.5Cu0.1Bi, Sn0.2Ag0.5Cu0.1Bi0.1Ni, and 96.5 Sn3.5Ag second-level interconnects under the application of cyclic thermomechanical loads. The methodology presented resides in the prefailure space of the system in which no macroindicators such as cracks or delamination exist. Systems subjected to thermomechanical damage have been interrogated for the system state and the computed damage state correlated with the known imposed damage. The approach involves the use of condition monitoring devices which can be interrogated for damage proxies at finite time intervals. The interrogation techniques are based on the derivation of damage proxies and system prior-damage-based nonlinear least square methods, including the Levenberg-Marquardt algorithm. The system's residual life is computed based on residual-life computation algorithms.

Structural and elastic properties of eutectic Sn–Cu lead-free solder alloy containing small amount of Ag and In

Sn–Cu alloys have been considered as a candidate for high temperature lead-free microelectronic solders. In the present study, the change in microstructure, attenuation and elastic behavior associated with alloying of Ag and/or In into the eutectic Sn–Cu solder alloy system have been evaluated. The study involved measurements of longitudinal and shear wave velocities, attenuation, hardness, bulk and shear moduli, Young's and Poisson's ratio. The results of attenuation show that a clear attenuating effect in the ternary Sn–Cu–Ag and Sn–Cu–In alloys is realized, whereas the quaternary Sn–Cu–Ag–In solder displays an obscure attenuating effect. The obscure effect is mainly attributed to the competition for In between Sn and Ag, which results in weak interface formed between intermetallic compounds (IMCs) and β-Sn matrix. Likewise, Poisson's ratio results indicate that its value decreases with increasing the elastic moduli and ultrasonic velocities of Ag and In-containing alloys. The analyzed enhanced ductility of Sn–0.7Cu and Sn–0.7Cu–2In alloys and brittleness of Sn–0.7Cu–2Ag and Sn–0.7Cu–2Ag–2In alloys were rationalized on the basis of Poisson's ratio and the quotient of shear modulus to bulk modulus (Pugh's ratio). Microstructural analysis revealed that the origin of change in the elastic properties of the ternary and quaternary alloys is ascribed to smaller β-Sn dendrite grain dimensions and formation of new IMCs in the ternary and quaternary alloys.

Effect of Adding Er on Interfacial Reactions between Sn-3.0Ag-0.5Cu Solder and Cu Substrate

The formation and the growth of Cu-Sn intermetallic compound (IMC) layer at the interface between Sn-3.0Ag-0.5Cu-xEr(x=0, 0.1) solder and Cu substrate during soldering and aging were studied. The results show that Cu6Sn5 IMC is observed at the interface between solder and Cu substrate in all conditions. After aging for 120 h, the Cu3Sn IMC is then obtained. With increasing aging time, the scalloped Cu6Sn5 structure changes to a plate structure. The Cu3Sn film always forms with a relatively planar interface. By adding a small amount of the rare earth element Er (only 0.1%, mass fraction) into the Sn-3.0Ag-0.5Cu solder alloy, the growth rate of the Cu-Sn IMC at the interface of solder alloy system is decreased. When the time exponent is approximately 0.5, the growth of the IMC layer is mainly controlled by a diffusion over the studied time range.

Design Envelopes and Optical Feature Extraction Techniques for Survivability of SnAg Lead-free Packaging Architectures Under Shock and Vibration

In this paper, a design-envelope approach based on optical feature extraction techniques has been investigated for drop and shock survivability of electronic packaging has been presented for 6-lead-free solder alloy systems. Solder alloy systems investigated include, Sn1Ag0.5Cu, Sn3Ag0.5Cu, Sn0.3Ag0.7Cu, Sn0.3Ag0.7Cu0.1Bi, Sn0.2Ag0.7Cu0.1Bi-0.1Ni, 96.5Sn 3.5Ag. Previously, digital image correlation (DIC) has been used for measurement of thermally induced deformation and material-characterization. In this paper, DIC has been used for transient dynamic measurements, and optical feature extraction. Board assemblies have been subjected to shock-impact in various orientations including the JEDEC zero-degree drop and the vertical free-drop. Transient deformation has been measured using both digital image correlation and the strain gages. Measurements have been taken on both the package and the board side of the assemblies. Accuracy of high-speed optical measurement has been compared with that from discrete strain gages. Package architectures examined include-flex ball-grid arrays, tape-array ball-grid arrays, and metal lead-frame packages. Explicit finite-element models have been developed and correlated with experimental data. Models developed include, smeared property models, and Timoshenko-beam models. The potential of damage identification and tracking for various solder alloys has been investigated. Data on identification of damage proxies for competing failure mechanisms at the copper-to-solder, solder-to-printed circuit board, and copper-to-package substrate has been presented. Design envelopes have been developed based on statistical pattern recognition. The design-envelope is intended for component integration to ensure survivability in shock and vibration environments at a user-specified confidence level.

Prognostication of system-state in lead-free electronics equipment under cyclic and steady-state thermo-mechanical loads

In this paper, a mathematical approach for interrogation of system-state under cyclic thermo-mechanical stresses has been developed for three-different lead-free solder alloy systems. Data have been collected for leading indicators-of-failure for alloy systems including, Sn1Ag0.5Cu, Sn3Ag0.5Cu, Sn4Ag0.5Cu second-level interconnects under the application of cyclic thermo-mechanical loads. Methodology presented resides in the pre-failure space of the system in which no macro-indicators such as cracks or delamination exist. Systems subjected to thermo-mechanical damage have been interrogated for system state and the computed damage state correlated with known imposed damage. The approach involves the use of condition monitoring devices which can be interrogated for damage proxies at finite time-intervals. Interrogation techniques are based on non-linear least-squares methods. Various techniques including the Levenberg–Marquardt Algorithm have been investigated. The system’s residual life is computed based on residual-life computation algorithms. Detection of system-state significantly prior to catastrophic failure can significantly impact the reliability and availability of electronic systems. Requirements for system availability for ultra-high reliability electronic systems are driving the need for advanced heath monitoring techniques for early detection of onset of damage. Traditional health monitoring methodologies have relied on reactive methods of failure detection often providing little on no insight into the remaining useful life of the system.

Damage Progression Using Speckle‐Correlation and High‐Speed Imaging for Survivability of Leadfree Packaging Under Shock

Abstract: In this paper, a methodology to predict failure of electronics under shock and vibration loads has been investigated. Reliability prediction models have been developed using optical feature extraction techniques for 6‐leadfree solder alloy systems. Solder alloy systems investigated include, Sn1Ag0.5Cu, Sn3Ag0.5Cu, Sn0.3Ag0.7Cu, Sn0.3Ag0.7Cu0.1Bi, Sn0.2Ag0.7Cu0.1Bi‐0.1Ni, 96.5Sn3.5Ag. Previously, Digital Image Correlation (DIC) has been used for measurement of thermally‐induced deformation and material characterisation. In this paper, DIC has been used for transient dynamic measurements, and optical feature extraction. Board assemblies have been subjected to shock‐impact in various orientations including the zero‐degree JEDEC drop and the vertical free‐drop. Transient deformation has been measured using both DIC and the strain gages. Measurements have been taken on both the package and the board side of the assemblies. Accuracy of high‐speed optical measurement has been compared with that from discrete strain gages. Package architectures examined include‐flex ball‐grid arrays, tape‐array ball‐grid arrays, and metal lead‐frame packages. Explicit finite‐element models have been developed and correlated with experimental data. Three models were developed: smeared property models: Timoshenko‐beam models: and explicit sub‐models. The potential of damage identification and tracking for various solder alloys has been investigated. Data on the identification of damage proxies for competing failure mechanisms at the copper‐to‐solder, solder‐to‐printed circuit board, and copper‐to‐package substrate has been presented. Design envelopes have been developed based on Statistical Pattern Recognition (SPR). The design‐envelope is intended for component integration to ensure survivability in shock and vibration environments at a user‐specified confidence level.

Thermodynamics of Oxidation on Pb-Free Solders at Elevated Temperature

Based on the available thermodynamic and phase equilibria data, the thermodynamic criteria for oxidation in tin-based lead-free solders under soldering condition was deduced. The dependence of Gibbs free energy on temperature in Pb-free solder oxidation reaction was calculated by applying MATLAB program. The characteristics of oxidation reaction of a varity of solder alloy systems such as Sn-Ag, Sn-Cu, Sn-Sb, Sn-Zn, Sn-Ag-Cu and Sn-Pb eutectic alloys at elevated temperature were analyzed. The results suggested that zinc preferentially oxidized in Sn-Zn solder alloys in the elevated temperature state, while tin preferentially oxidized in the other alloys. The oxidation potential of the Sn-Zn eutectic alloys was higher than that of the pure tin at elevated temperature, whereas the oxidation potentials of Sn-Ag, Sn-Cu, Sn-Sb and Sn-Ag-Cu eutectic alloys were approxiately equal to that of the pure tin. All tin-based Pb-free solder alloys more easily oxidized than the Sn-Pb solder alloys. Oxidizability of these alloys followed in a decreasing order: Sn-Zn＞Sn-Sb＞Sn-Cu＞Sn-Ag＞Sn-Ag-Cu＞Sn-Pb.

Effect of adding Ce on interfacial reactions between Sn-3.0Ag-0.5Cu solder and Cu substrate

The formation and the growth of Cu-Sn intermetallic compound (IMC) layer at the interface between Sn-3.0Ag-0.5Cu-xCe solder and Cu substrate during soldering and aging were studied. The results show that Cu6Sn5 IMC is observed at the interface between solder and Cu substrate in all conditions. After aging for 120 h, the Cu3Sn IMC is then obtained. With increasing aging time, the scalloped Cu6Sn5 structure changes to a plate structure. The Cu3Sn film always forms with a relatively planar interface. By adding a small amount of the rare earth element Ce (only 0.1%, mass fraction) into the Sn-3.0Ag-0.5Cu solder alloy, the growth rate of the Cu-Sn IMC at the interface of solder alloy system is decreased. When the time exponent is approximately 0.5, the growth of the IMC layer is mainly controlled by a diffusion over the studied time range.

Effect of Interfacial Compound Formation on Contact Resistivity of Soldered Junctions Between Bismuth Telluride-Based Thermoelements and Copper

Two different solder alloys, Sn-37Pb and Sn-4Ag-0.5Cu, were used to joint p- and n-type bismuth telluride-based thermoelements with copper. SnTe and Pb 1-x Sn x Te were identified to be the major interfacial compounds for the Sn-Ag-Cu and Sn-Pb soldered junctions, respectively. The contact resistivity measured is around 10 -4 to 10 -5 Ω cm 2 , which depends on both the thickness and composition of interfacial compounds. The study shall lead to the effective strategy for choosing appropriate solder alloy systems to improve the contact property of bismuth telluride-based thermoelectric coolers.

Effects of bismuth on growth of intermetallic compounds in Sn-Ag-Cu Pb-free solder joints

The effects of Bi addition on the growth of intermetallic compound (IMC) formation in Sn-3.8Ag-0.7Cu solder joints were investigated. The test samples were prepared by conventional surface mounting technology. To investigate the element diffusion and the growth kinetics of intermetallics formation in solder joint, isothermal aging test was performed at temperatures of 100, 150, and 190 °C, respectively. The optical microscope (OM) and scanning electron microscope (SEM) were used to observe microstructure evolution of solder joint and to estimate the thickness and the grain size of the intermetallic layers. The IMC phases were identified by energy dispersive X-ray (EDX) and X-ray diffractometer (XRD). The results clearly show that adding about 1.0% Bi in Sn-Ag-Cu solder alloy system can refine the grain size of the IMC and inhibit the excessive IMC growth in solder joints, and therefore improve the reliability of the Pb-free solder joints. Through observation of the microstructural evolution of the solder joints, the mechanism of inhibition of IMC growth due to Bi addition was proposed.

The effect of microstructural and geometrical features on the reliability of ultrafine flip chip microsolder joints

A thermodynamic approach was used to investigate solder alloy systems containing Sn, Ag, Sb, and Pb, during both equilibrium and Scheil cooling conditions. The modeled microstructure was used to explore recent experimental results and to establish the microstructure-property relationships in microsolder joints. This approach is shown to be very useful in the transition from Pb-Sn to lead-free solders by enabling the consideration of contamination by a small amount of Pb. Molten solder interacts with the under bump metallization or print circuit board (PCB) metallization to form intermetallic compounds (IMCs). A truncated sphere structure was used to predict the solder joint geometry, and a two-dimensional finite-element (FE) method was adopted to investigate the kinetics of the dissolution of Au during the reflow process. The dissolution of Au into different volumes of solder material for three sizes of joints has been studied. In the modeling of the dissolution kinetics, the Nernst-Brunner equation is found to have poor validity for these calculations because of the dramatic change in the microscopic geometry and boundary conditions for joints at 100 µm in size or smaller. A combined thermodynamic and kinetic modeling approach, with a novel interface for implementation, is also briefly discussed.

Coefficient of thermal expansion for solder alloys based on cluster expansion method

Theoretical calculations of the thermal expansion coefficients of the solder alloy systems Sn–Pb and Sn–Ag were attempted by using a cluster expansion method. Five ordered fcc phases for each system were employed to perform the matrix inversion and to determine the correlation coefficients in cluster expansion formalism. The coefficients of thermal expansion of the ordered alloys were obtained through first-principles electronic structure calculations coupled with a Debye treatment of the vibrating lattice. The correlation functions for disordered alloys were derived through Monte-Carlo simulations. The calculated results are in very good agreement with experiments, indicating the feasibility of using cluster expansion theory for thermal expansion coefficient calculations. This study may provide a simple approach to estimating thermal expansion coefficients of disordered structures.

Kinetics of interface reaction in 40Sn-Bi/Cu and 40Sn-Bi-2Ag/Cu systems during aging in solid state

The characteristics of thickening kinetics of the intermetallic compounds (IMC) (Cu/sub 6/Sn/sub 5/+Cu/sub 3/Sn) during aging at 120/spl deg/C and 90/spl deg/C in solid state were studied by quantitative metallographic analysis for three solder alloy systems: 40Sn-Bi/Cu, 40Sn-Bi-2Ag/Cu and Sn-37Pb/Cu. The diffusion couples were prepared by hot immersion in the molten solder bath. The results showed that the rate of the IMC thickening increases in the order Sn-37Pb/Cu<40Sn-Bi/2-Ag/Cu<40Sn-Bi/Cu. The IMC thickening rate in the Sn-Bi eutectic system is one order of magnitude faster than that in Sn-Pb eutectic system. The time exponents are different from each other. The relationship between the increase of IMC and aging time follows a parabolic function in the Sn-Pb system, and a linear relation in the Sn-Bi system. Addition of Ag in Sn-Bi inhibits the IMC thickening process.

Investigation of microstructural coarsening in Sn-Pb alloys

The central theme of this work is to investigate the kinetics of microstructural evolution at high volume fractions of the dispersed phase in a solid-liquid mixture. Until recently, the kinetics of coarsening in the high volume fraction range was not clearly established. A recent study focused on high volume fractions (V v >0.90) revealed that the temporal scaling laws that describe phase coarsening change from the conventional cube root of time behavior to a fourth-power relationship. This work probes the variation of the temporal exponent with volume fraction of the dispersed phase (V v >-0.60). An overview of the fundamentals of the physics involved in diffusion-limited coarsening is presented. Also explained is the relevance of phase coarsening in various applications. A succinct review of the attempts to understand the various parameters involved in coarsening is provided, with the Sn-Pb system chosen for this study for reasons apart from its importance as a commercial solder alloy system. Details of the experimental procedures are described, and, following this, the results are outlined and the underlying mechanisms discussed. The findings reveal that the temporal exponent changes as the volume fraction of the dispersed phase changes.

A thermodynamic study on the AgSbSn system

A thermodynamic assessment for the AgSbSn solder alloy system has been attempted through the least squares optimization procedure taking available thermodynamic and phase equilibria information into account. The low-order AgSb and AgSn binary systems have been re-evaluated and thermodynamic properties of the ternary alloys have been extrapolated from these of the three binary systems using the Muggianu model. The calculated phase diagrams and thermodynamic quantities of the AgSb and AgSn binary systems show very good agreement with the experimental data, and liquidus projection and isoenthalpy curves in the ternary liquid alloys are well reproduced with the assessed thermodynamic model parameters.