Behavior Of Solder Research Articles

Electrochemical migration behavior of Sn-based lead-free solder

In this paper, the water droplet experimental method was used to in situ study the electrochemical migration and related behaviors of Sn-based lead-free solder. Results showed that the electrochemical migration short-circuit time decreased with voltage increasing. Electrochemical migration was difficult to occur when the voltage was less than 1.5 V. However, when the voltage was above 5 V, metal deposits were generated in a short time and caused a bridge between two electrodes, which led to short circuit. As spacing increased, the short-circuit time prolonged. The three-dimensional pattern between voltage, spacing and short-circuit time had been constructed, which is beneficial to estimate the short-circuit time value under a combination of any voltage and spacing within a certain range. When changed the concentration of NaCl solution, it was founded that dendrites which surface covered much precipitates were formed at a low concentration. At medium concentration, there was no dendrites but only formed a large amount of precipitates. At a high concentration, the dendrites which surface with less precipitates were showed again. The formation mechanisms of dendrites under different NaCl solution concentrations were analyzed. In addition, the effects of different materials on electrochemical migration behavior were also studied, founding that electrochemical migration products of Sn, Sn0.7Cu and Sn3Ag were mainly Sn and Sn oxides. The electrochemical migration products of Sn9Zn contain much Zn element apart from Sn and Sn oxides. At a lower voltage, Sn9Zn solder had better electrochemical migration resistance than Sn, Sn0.7Cu and Sn3Ag, but this phenomenon was not obvious at a higher voltage.

Wetting behavior and interfacial characteristic of eutectic In-Ag solders on Au thin films

Soldering electrical contacts to gold thin films is a matter of consideration due to high soldering temperature, restricted wetting, excessive scavenging and low strength offered by most of the common soldering alloys. Indium alloys offer certain benefits for gold soldering justifying their increased cost. In the present study, hypo-, hyper- and eutectic In-Ag solder were prepared and investigated for compositional and structural homogeneity, soldering temperature, contact angle, spreading factor, scavenging zone and scavenging phase (i.e. AuIn2). It was found that addition of silver (~3.5%) ameliorated the above mentioned characteristics for better control of soldering practice with gold thin films besides lowering the soldering temperature.

Solder interconnects reliability subjected to thermal-vibration coupling loading

Experiments and finite element simulations are used to evaluate board-level reliability under vibration loading coupled with different temperatures (25 °C, 65 °C, 105 °C). The responses of the boards and solder interconnects are characterized, based on which the failure modes and failure life were studied and correlated with coupling conditions. Significant coupling influences are found on PCBs’ response, solder plastic behavior, the failure modes and life time of the solder interconnects. Studies indicated that the main root cause of these influences can be concluded as the temperature dependent materials behaviors of the assembly components. Elevated temperature within the range of 25–105 °C cause evident decrease of the PCB eigenfrequency, which will greatly affect the PCB amplitude of a fixed-frequency vibration test. The effect of temperature on solder interconnects can be deposed into two aspects, one is temperature induced change of applied loading (PCB responses), and the other is temperature induced change of solder behavior (alloy properties). Therefore, the stress and strain of solder interconnects in varied coupled tests performed as the combination outcomes from both varied PCB responses and varied materials behaviors of solder materials. The dominating factors are analyzed. Sever stress area are proposed to address the failure sites transform. Solder interconnects lifetime data condition are collected and fitted with each coupled condition.

Optimized high performance thermoelectric generator with combined segmented and asymmetrical legs under pulsed heat input power

In this study, a segmented asymmetrical thermoelectric generator (SASTEG) is numerically investigated to optimize its electrical performance and mechanical reliability under transient and steady state conditions. The thermal and electrical performance of the SASTEG and TEG under transient and steady state heating conditions are studied and compared. A three-dimensional numerical model is developed and solved using finite element method in COMSOL 5.3 Multiphysics software. Temperature dependent thermoelectric material properties are considered, and the elastoplastic behaviour of copper and solder is accounted for in the thermal stress analysis. The initial SASTEG geometry used in this study is subsequently optimized to reduce the maximum von Mises stress developed in its legs while maintaining its enhanced power output. Results obtained show that the optimized SASTEG provided a power output enhancement of 117.11% compared to that of the conventional TEG under rectangular pulsed heat condition. Also, the asymmetrical leg geometry used in the SASTEG n-type leg provided a reduced thermal stress of 39.21% in the lower segment (cold side) compared to the symmetrical leg geometry used in the p-type leg lower segment. This study will provide vital guidance in the design of high-performance TEG with improved mechanical reliability.

Electroplating of 3D Sn-rich solder for MEMS packaging applications

Electroplating is a popular method to produce solders in microelectromechanical systems (MEMS) encapsulation and interconnection applications. In this work, a fabrication process is introduced for the generation of three-dimensional (3D) Sn solder microstructures. An aluminum membrane was employed as the conducting layer while electroplating. Based on the proposed method, Sn solders with different heights can be easily obtained after reflow. Taking advantage of these 3D structures, MEMS packaging, electrical interconnections, hermetic seals and metal-armoring can be formed simultaneously in one step. Metal-armoring provided by the solder–solder contact can be used at the extremes of the suspension travel, greatly increasing the capability of shock resistance. The helium leak rates of the packaged samples are lower than the reject limit (5 × 10−8 atm cc s−1 based on MIL-STD-883E standard). The bonding strength of samples is measured by a die shear strength tests with an average value of 7.4 MPa. In addition, the ohmic behavior of the Sn solder bonding is verified as well. These excellent results show an outstanding packaging quality in MEMS encapsulation applications.

Lifetime Prediction of IGBT Modules in Suspension Choppers of Medium/Low-Speed Maglev Train Using an Energy-Based Approach

Maglev trains attracted to suspend above tracks without mechanical contact is a promising type of track transportation. Suspension choppers with levitation magnets resembling wheels of traditional trains or tires of automobiles are responsible for levitation and support of maglev trains. With successful launch of the first Chinese medium/low-speed maglev line, lifetime prediction of power devices in suspension choppers becomes a crucial topic. This paper analyzes the lifetimes under two typical daily mission profiles of suspension choppers. Using look-up tables of IGBT/diode losses, a widely used RC thermal network is established. A test rig is built to measure the IGBT/diode transient case temperature and extract the thermal impedance of a heat sink. Therefore, the junction temperatures under these typical mission profiles are estimated. Using comprehensive equations to describe solder behavior, the stress–strain curves under different temperature profiles can be plotted by means of Clech's algorithm. Finally, an energy-based approach is utilized for lifetime evaluation. The daily mission profile where maglev trains operate without landing during operation hours is expected to survive much longer.

Temperature Effect on Tensile Behaviour of Sn-Pb Eutectic Solder

The mechanical behaviour of tin-lead eutectic solder is experimentally investigated by performing tensile tests subjected to the temperatures ranging from -50°C to 150°C. It covers the widely-accepted extreme working environment of high-power electronic devices in the aerospace industry. The regime of strain rates between 1×10-4 s-1 and 1×10-3 s-1 are applied. Despite scatter of the ultimate failures, experimental results demonstrate that tensile strength of Sn-Pb eutectic solder is mainly associated with strain rate and working temperature. With increasing the applied temperature above the room temperature, both Young’s modulus and tensile strength of Sn-Pb specimens exponentially decays.

Effect of TiO2 Nanoparticles Addition on the Thermal, Microstructural and Room-Temperature Creep Behavior of Sn-Zn Based Solder

The effect of adding TiO2 nanoparticles as well as aging time on the thermal, microstructural and creep properties of Sn-6.5Zn solder was studied. The Sn-6.5Zn composite solders were prepared by mechanically dispersing different weight percentages (0.0 wt.%, 0.25 wt.%, 0.50 wt.%, 0.75 wt.% and 1.0 wt.%) of TiO2 nanoparticles into Sn-6.5Zn solder. After being solution heat treated at 453 K for 4 h, specimens were cooled by water quenching at 273 K. Specimens were artificially aged at 393 K for durations ranging from 15 to 120 min, followed by water quenching at 273 K to cease further aging. The thermal behavior of the composite solders was investigated using differential scanning calorimetry (DSC). X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to observe the microstructure of the solders. The mechanical properties were characterized using tensile creep tests and correlated with microstructural features. The investigation revealed that the minimum creep rate of solders decreased with the increase in the content of TiO2, while it increased with increasing aging time. The data from microstructure-properties analysis showed that the nano-TiO2 particles had significantly refined the microstructure and improved the creep resistance in comparison with the Sn-Zn solder. The calculated stress exponent values were close to 7.

Influence of Grain Refinement via ECAP to the Corrosion Behaviour of SAC 305 Solder

Equal Channel Angular Pressing or ECAP has been generating interest due to the ability to form bulk ultra-fine grains (UFG) or nanostructured materials. This formation of ultra-fine grains leads to a favorable combination of strength and ductility. Solder materials, which function as the mechanical bridge joining chip to substrate, or package to mother board, could very well benefit from this combination. High strength would offer better joint, and enhanced ductility would enable solder to have better fracture toughness and drop-impact resistance as solder joint regularly being subjected to vibration and impact. This paper reports about corrosion behaviour of ECAPed SAC 305 alloy formed via route Bc up to four passes. The focus is on the effect of grain refinement on corrosion behaviour of bulk solder in 3.5 wt.% NaCl solution. The resulting microstructure was observed by Scanning Electron Microscope (SEM). The grains formed after different passes of ECAP were observed, along with the distribution of intermetallic compound or IMC within the bulk solder. Finer grains were formed with increasing number of ECAP passes leading to reduction of corrosion rate and increased strength of SAC305. The high fraction of grain boundaries in the microstructure with increased of ECAP passes reduced the corrosion rates by accelerating the passivation process.

Wetting behavior and interfacial characteristic of eutectic In-Ag solders on Au thin films

Soldering electrical contacts to gold thin films is a matter of consideration due to high soldering temperature, restricted wetting, excessive scavenging and low strength offered by most of the common soldering alloys. Indium alloys offer certain benefits for gold soldering justifying their increased cost. In the present study, hypo-, hyper- and eutectic In-Ag solder were prepared and investigated for compositional and structural homogeneity, soldering temperature, contact angle, spreading factor, scavenging zone and scavenging phase (i.e. AuIn2). It was found that addition of silver (~3.5%) ameliorated the above mentioned characteristics for better control of soldering practice with gold thin films besides lowering the soldering temperature.

Effect of Long-Term Room Temperature Aging on the Fatigue Properties of SnAgCu Solder Joint

Solder joints in electronic assemblies are subjected to mechanical and thermal cycling. These cyclic loadings lead to the fatigue failure of solder joints involving damage accumulation, crack initiation, crack propagation, and failure. Aging leads to significant changes on the microstructure and mechanical behavior of solder joints. While the effect of thermal aging on solder behavior has been examined, no prior studies have focused on the effect of long-term room temperature aging (25 °C) on the solder failure and fatigue behavior. In this paper, the effects of long-term room temperature aging on the fatigue behavior of five common lead-free solder alloys, i.e., SAC305, SAC105, SAC-Ni, SAC-X-Plus, and Innolot, have been investigated. Several individual lead-free solder joints on printed circuited boards with two aging conditions (no aging and 4 years of aging) have been prepared and subjected to shear cyclic stress–strain loadings until the complete failure. Fatigue life was recorded for each solder alloy. From the stress–strain hysteresis loop, inelastic work and plastic strain ranges were measured and empirically modeled with the fatigue life. The results indicated that 4 years of room temperature aging significantly decreases the fatigue life of the solder joints. Also, inelastic work per cycle and plastic strain range are increased after 4 years of room temperature aging. The fatigue life degradation for the solder alloys with doped elements (Ni, Bi, Sb) was relatively less compared to the traditional SAC105 and SAC305.

Effects of Al2O3 nanoparticles on the microstructure and properties of Sn58Bi solder alloys

In this work, Al2O3 nanoparticles with various contents (0, 0.5, 1.0, 1.5 wt%) were incorporated into Sn58Bi solder alloy. The microstructure, tensile properties, thermal properties, corrosion resistance, creep behavior and hardness of the synthetic solders were investigated. The results show that moderate additions of Al2O3 nanoparticles can make the Sn-rich and Bi-rich phases more evenly distribute. The ultimate tensile stress and hardness of Sn58Bi–0.5Al2O3 solder individually display about 22 and 19% enhancement compared with the pure solder. The thermal properties, corrosion resistance and creep performance are strengthened to varying degrees. Furthermore, there is a fracture mode transition in tensile process and a creep mode conversion in creep process.

Influence of dual ceramic nanomaterials on the solderability and interfacial reactions between lead-free Sn-Ag-Cu and a Cu conductor

This study examined the addition of dual ceramic nanomaterials, TiO2 and graphene (0, 0.03, 0.12, 0.21, and 0.60 wt %), to a lead-free Sn-3.0 wt %Ag-0.5 wt %Cu (SAC305) solder alloy. TiO2 and graphene nanomaterials were mixed simultaneously at equal weight fractions into the SAC305 molten solder by mechanical mixing and melting to produce a bulk nanocomposite solder. The effects of the dual nanomaterials on the melting point, microstructure, solderability, and intermetallic compound (IMC) growth were conducted. The structural and morphological features of the samples were characterized by field emission scanning electron microscopy, energy dispersive spectroscopy, and transmission electron microscopy. In addition, the melting behavior of the nanocomposite solder was characterized by differential scanning calorimetry. The nanocomposite solder with 0.21 wt % nanomaterials showed 33.67% enhancement in wettability and an 8.66% increase in spreadability due to the increased fluidity and decreased surface tension of molten solder in the presence of dual nanomaterials. In addition, the thickness of the IMCs was reduced after adding the dual nanomaterials to the monolithic SAC alloy. The optimal concentration of the dual nanomaterials in the monolithic SAC alloy was found to be 0.21 wt %.

Microstructural Evolution and Mechanical Behavior of High Temperature Solders: Effects of High Temperature Aging

This paper explores the effects of aging on the mechanical behavior, microstructure evolution and IMC formation on different surface finishes of two high temperature solders, Sn-5 wt.% Ag and Sn-5 wt.% Sb. High temperature aging showed significant degradation of Sn-5 wt.% Ag solder hardness (34%) while aging has little effect on Sn-5 wt.% Sb solder. Sn-5 wt.% Ag experienced rapid grain growth as well as the coarsening of particles during aging. Sn-5 wt.% Sb showed a stable microstructure due to solid solution strengthening and the stable nature of SnSb precipitates. The increase of intermetallic compound (IMC) thickness during aging follows a parabolic relationship with time. Regression analysis (time exponent, n) indicated that IMC growth kinetics is controlled by a diffusion mechanism. The results have important implications in the selection of high temperature solders used in high temperature applications.

Study on the Tensile Creep Behavior of Carbon Nanotubes-Reinforced Sn-58Bi Solder Joints

The microstructure and tensile creep behavior of plain Sn-58Bi solder and carbon nanotubes (CNTs)-reinforced composite solder joints were investigated. The stress exponent n under different stresses and the creep activation energy Q c under different temperatures of solder joints were obtained by an empirical equation. The results reveal that the microstructure of the composite solder joint is refined and the tensile creep resistance is improved by CNTs. The improvement of creep behavior is due to the microstructural change of the composite solder joints, since the CNTs could provide more obstacles for dislocation pile-up, which enhances the values of the stress exponent and the creep activation energy. The steady-state tensile creep rates of plain solder and composite solder joints are increased with increasing temperature and applied stress. The tensile creep constitutive equations of plain solder and composite solder joints are written as $$ \dot{\varepsilon }_{s1} = 14.94\left( {\sigma /G} \right)^{3.7} \exp \left( { - \frac{81444}{RT}} \right) $$ and $$ \dot{\varepsilon }_{s2} = 2.5\left( {\sigma /G} \right)^{4.38} \exp \left( { - \frac{101582}{RT}} \right) $$ , respectively. The tensile creep mechanism of the solder joints is the effects of lattice diffusion determined by dislocation climbing.

Effect of the Angle Between Sn Grain c-Axis and Electron Flow Direction on Cu-Reinforced Composite Solder Joints Under Current Stressing

With a body-centered tetragonal crystal structure, Sn grains were demonstrated to have highly anisotropic behaviors in various properties. The electromigration behavior of lead-free solder was impacted by the grain orientations. In this paper, the angle between the c-axis and the electron flow direction in composite solder joints (angle θ) was proven to be an important factor during electromigration. The effects of angle θ on the electromigration of composite solder joints were investigated in this paper. Cu particle-reinforced Sn3.5Ag solder joints were stressed under a current density of 104 A/cm2 at room temperature. After 336 h current stressing time, different electromigration phenomena occurred at the two sides of the grain boundary in the composite solder joint which contained two Sn grains with different angle θ. The Sn grains with the larger angle θ had a smaller growth rate of Cu6Sn5. In addition, a composite solder joint with a single Sn grain was set as the contrast and its angle θ was smaller than that of the composite solder joint with two Sn grains. The growth rate of Cu6Sn5 in the composite solder joint with a single grain was faster than that of the composite solder joint with two Sn grains.

Crack Initiation and Propagation Evaluation for Sn–5Sb Solder Under Low-Cycle Fatigue

In this study, a crack initiation and propagation behavior of Sn–5Sb lead-free solder under low-cycle fatigue is discussed. Cyclic push–pull loading tests with a single-hole specimen have been conducted at 313 K to investigate the crack initiation and propagation behavior of Sn-5Sb solder which has a higher melting point temperature than that of Sn–Ag–Cu solders. A fatigue life ratio correlates with the crack length within a small scatter. Crack initiates at the early stage, and almost all the life period is crack propagation process independent of strain range and strain rate. The crack propagation rate depends on the strain range and the strain rate. The adaptation of J-integral value for Sn–5Sb solder is also discussed. J-integral value is a suitable parameter for crack propagation rate evaluation.

Isothermal bending fatigue response of solder joints in high power semiconductor test structures

Fatigue and cyclic delamination behavior of PbSnAg solders which are typically used as die attach material in power semiconductors was investigated. Isothermal bending fatigue tests were performed by using multilayered model test structures consisting of Si chips soldered on ceramic substrates and failure probability curves were obtained up to 1e8 loading cycles. The fatigue experiments were conducted by using an ultrasonic fatigue testing machine equipped with a three point bending set-up at a constant testing temperature of 80°C. Detailed failure analysis of the fatigued samples revealed a dependency of the failure mode on the chemical composition of the high-Pb soft solders. The main failure modes included interfacial delamination of the Si-chip from the die attach, degradation due to crack propagation in the solder layer and in some cases partial fracture of the chip. Finally the feasibility of high frequency mechanical fatigue testing for screening and evaluation of solder joints in multilayered electronic systems is discussed.

Effect of Ag nanoparticles on microstructure, damping property and hardness of low melting point eutectic tin–bismuth solder

This paper investigates the effects of nanosized Ag particles on microstructure, physical and mechanical properties of environmental-friendly low melting point eutectic Sn–Bi solder on Au/Ni-plated Cu substrate. During the soldering process a very thin Ni3Sn4 intermetallic compound (IMC) layer was found to be adhered at their interfaces in both types of solder system. This IMC layer thickness was increased with increasing the reaction time and temperature. However, from microstructural evaluation it was confirmed that the addition of Ag nanoparticles significantly affects the soldering behavior retarding the growth of IMC layer at the solder/substrate surface. The calculated activation energy for the Ni3Sn4 IMC layer for the reference solder system was about 56.45 kJ/mol, while the activation energy for Ag nanoparticles doped solder system was about 60.73 kJ/mol. Addition of Ag nanoparticles maximize the activation energy which reduce the reaction rate. Furthermore, the adding Ag nanoparticles react with matrix phase and form very fine Ag3Sn IMC particles that obstacle the formation of coarse matrix grain. This fine matrix grain and fine Ag3Sn IMC particles act as a second phase strengthening mechanism that positively impact on the storage modulus and hardness values in composite solder systems.

A Review of Recent Research on the Mechanical Behavior of Lead-Free Solders

Due to the restriction of lead-rich solder and the miniaturization of electronic packaging devices, lead-free solders have replaced lead-rich solders in the past decades; however, it also brings new technical problems. Reliability, fatigue, and drop resistance are of concern in the electronic industry. The paper provides a comprehensive survey of recent research on the methodologies to describe the mechanical behavior of lead-free solders. In order to understand the fundamental mechanical behavior of lead-free solders, the visco-plastic characteristics should be considered in the constitutive modeling. Under mechanical and thermal cycling, fatigue is related to the time to failure and can be predicted based on the analysis to strain, hysteresis energy, and damage accumulation. For electronic devices with potential drop impacts, drop resistance plays an essential role to assess the mechanical reliability of solder joints through experimental studies, establishing the rate-dependent material properties and proposing advanced numerical techniques to model the interconnect failure. The failure mechanisms of solder joints are complicated under coupled electrical-thermal-mechanical loadings, the increased current density can lead to electromigration around the current crowding zone. The induced void initiation and propagation have been investigated based on theoretical approaches to reveal the effects on the mechanical properties of solder joints. To elucidate the dominant mechanisms, the effects of current stressing and elevated temperature on mechanical behavior of lead-free solder have been reviewed. Potential directions for future research have been discussed.