Sn Intermetallic Compounds Research Articles

Efficient hydrothermal deoxygenation of methyl palmitate to diesel-like hydrocarbons on carbon encapsulated Ni−Sn intermetallic compounds with methanol as hydrogen donor

Efficient hydrothermal deoxygenation of methyl palmitate to diesel-like hydrocarbons on carbon encapsulated Ni−Sn intermetallic compounds with methanol as hydrogen donor

Study on the Microstructure Evolution and Mechanical Properties of Cu/Cu41Sn11/Cu Solder Joint During High-Temperature Aging

Abstract The paper focused on the changes in microstructure and mechanical properties of the full Cu41Sn11 solder joint (Cu/Cu41Sn11/Cu) during isothermal aging at 420 °C. It was motivated by potential applications of Cu–Sn intermetallic compounds (IMCs) solder joint in third-generation wide bandgap semiconductor devices. Experimental results revealed that the Cu41Sn11 phase was unstable under high-temperature conditions, the full Cu41Sn11 joint transformed into the full α(Cu) joint (Cu/α(Cu)/Cu) joint at 150 h during thermal aging. The formed α(Cu) phase was a Cu solid solution with inhomogeneous Sn atomic concentration, and its crystal structure and orientation were consistent with the original Cu plate. The conversion of the Cu41Sn11 to α(Cu) was accompanied by the formation of voids due to the volume shrinkage effect, predominantly near the middle of the solder joint interface. The α(Cu) solder joint presented a decrease in strength but an increase in strain rate sensitivity index compared to the Cu41Sn11 solder joint. Furthermore, the strain rate sensitivity index of α(Cu) and Cu41Sn11 is lower than that of ordinary Sn solders. After the shear test, the fractures that occurred in Cu41Sn11 grains were brittle, while the fractures in α(Cu) grains were ductile.

Effect of the reflow process on IMC growth for different devices and complex components

Intermetallic compound (IMC), as an inevitable part between pad and solder, has a severe effect on the strength and reliability of microelectronic interconnection. Here, an investigation was carried out on IMC growth for different devices and complex components. The device-level experiments were conducted with five factors: peak temperature, time duration above solder liquidus temperature, the thickness of solder paste, surface finish types, and package types including ball grid array (BGA) and quad flat package (QFP). Meanwhile, four complex components with the same reflow profile were conducted and compared for component-level experiments. A scanning electron microscopy (SEM) was used to measure the thickness and determine the spatial distribution of the elements through the IMC. The multivariate analysis of the formation and growth of IMC during reflow soldering was studied based on Nernst–Shchukarev’s equation and the results of the experiments. The difference in IMC thickness between BGA and QFP with different factors was discussed and compared separately. The results showed that the peak temperature and time above liquidus played a vital role in the IMC growth and the solder paste thickness and different pad metallization could not be ignored. SEM pictures of the solder and statistical results were revealed that the surface finish type has a marked impact on the formation of the IMC. For printed circuit board (PCB) with numbers of components, the IMC thickness and uniformity of solder joints at corner and center positions showed some regularity differences. Meanwhile, the bump shape (Cu1−x Ni x )6Sn5 IMC was observed for small size BGA with electroless nickel and immersion gold during the reflow process. The results have a significant meaning to optimize its reflow process parameters for complex components, to improve the interconnection reliability in engineering.

Forming mechanism and growth of Kirkendall voids of Sn/Cu joints for electronic packaging: A recent review

For the common Cu-Sn interconnection system in microelectronics packaging, a significant concern is the sporadic interfacial void formation within the Cu–Sn interface and intermetallic compound (IMC) layer during the service. The existence of these voids affects the electrical and mechanical properties of the joint and thus deteriorates reliability. Most scholars simply attribute the Kirkendall voids problem to the Kirkendall effect caused by the difference in Cu/Sn inter-diffusion coefficients. However, Kirkendall voids are formed for a combination of many reasons. The plating additives, current density, surface roughness, coating thickness, and substrate types affect the formation of Kirkendall voids. We believe that among the many factors affecting the formation of voids, the unbalanced diffusion of elements (Kirkendall effect) is the root cause, and impurities and Cu microstructure are the dominant factors. The addition of alloying elements to the solder affects the formation of voids by changing the unbalanced diffusion of elements. This paper releases the possible mechanism of Kirkendall voids and gives the perspective summary from three steps of void formation, and the available suppression method is given based on the final solution.

Investigation of phase equilibria of the Au–Ni–Sn ternary system and interfacial reactions in the Au/Sn/Ni/Cu multilayer couple

Au and Ni are widely used in the under-bump metallization, whereas Sn and Cu serve as common bonding materials and substrates, respectively. Solder joints consisting of an Au/Sn/Ni/Cu multilayer structure are widely found in the electronic packaging. Both phase equilibria of the Au–Ni–Sn ternary alloys and interfacial reactions of the Au/Sn/Ni/Cu multilayer structure were applied to the solid/solid-state reaction couple technique. The results showed that the Ni3Sn2 and AuSn4 phases respectively had a great solubility of the third element and the ternary AuNi2Sn4 phase existing in the Au–Ni–Sn ternary alloys was formed at 180 and 240 °C. The Sn/Ni/Cu multilayer structure was prepared by electroplating Sn/Ni layers on the Cu substrate. Afterward, the Sn/Ni/Cu multilayer and Au foil were screwed together to obtain the Au/Sn/Ni/Cu multilayer structure, followed by reactions at 150, 180 and 200 °C for different durations. The thickness of the intermetallic compounds (IMCs) increased with the increase in the reaction time and temperature. The IMC evolution in the couple remained unchanged at different temperatures. An increase in the reaction time converted the AuSn4 and AuSn2 phases to the AuSn phase. The voids formed in the couple were attributed to the volume shrinkage effect, which decreased with an increase in the reaction temperature. The (Ni, Au)3Sn2 phase was formed at the Ni side; the Ni layer functioned as an effective diffusion barrier to prevent the formation of the Cu–Sn IMCs.

Effects of Initial Morphology on Growth Kinetics of Cu6Sn5 at SAC305/Cu Interface during Isothermal Aging.

Solder/Cu joints are important components responsible for interconnection in microelectronics. Construction of the solder/Cu joints through liquid/solid (L/S) reactions accompanies the formation of the Cu–Sn intermetallic compounds (IMCs) at the joint interface. The Cu6Sn5 IMC exhibits remarkable distinctions in thickness and morphology upon increasing the L/S reaction time. Effects of the initial characteristics of thickness and morphology on the growth kinetics of Cu6Sn5 during subsequent isothermal aging were investigated. SAC305 solder was reflowed on a Cu electroplated layer at 265 °C for 1 to 60 min to produce the Cu6Sn5 IMC with different thickness and morphology at the SAC305/Cu interface. The as-fabricated SAC305/Cu joint samples were aged at 200 °C for 72 to 360 h to investigate the growth kinetics of Cu6Sn5. The results show that the initial characteristics of thickness and morphology significantly influenced the growth kinetics of Cu6Sn5 during the subsequent solid/solid (S/S) reaction. A prolonged L/S reaction time of 60 min (L/S-60) produced a scallop-type Cu6Sn5 IMC with a larger grain size and a thicker thickness, which reduced the quantity of fast diffusion path (grain boundary) and the magnitude of concentration gradient, thus slowing down the growth rate of Cu6Sn5. According to the growth kinetics analysis, the growth rate constant of Cu6Sn5 could be remarkably reduced to 0.151 µm/h0.5 for the L/S-60 sample, representing a significant reduction of 70 % compared to that of the L/S-1 sample (0.508 µm/h0.5 for L/S reaction time of 1 min).

Effects of Solder Powder Particle Size and Substrate Surface Finish on Degradation Properties of Solder Joints

In this study, the degradation characteristics of solder joints composed of powder-size Sn-3.0Ag-0.5Cu and the substrate surface finish are compared. Reflow is performed at a N2 ambient to apply an organic solderability preservative (OSP), electroless nickel/immersion gold (ENIG) substrates, and solder pastes of Type 6 (5-15 ㎛) and Type 7 (2-11 ㎛). Subsequently, a thermal shock test (TST) is performed for 1,500 cycles at a temperature of -40 ℃ to 125 ℃ (dwell time of 10 min) to analyze the deterioration characteristics. After N2 reflow is performed, the void content of the OSP substrate/solder joints is higher than that of the ENIG substrate/solder joints, and the shear strength of the ENIG substrate/solder joints is higher than that of the OSP substrate/solder joints. After 500 TST cycles, the shear strength at the OSP substrate/Type 7 solder joints does not decrease, whereas the shear strength at the ENIG substrate/Type 7 solder joints decreases by approximately 25%. Cross-sectional analysis shows that Cu6Sn5 and (Ni,Cu)3Sn4 intermetallic compounds (IMCs) emerged in the OSP and ENIG interfaces, respectively. The increasing rate of IMC thickness at the Type 7 solder joints is higher than that at the Type 6 solder joints. Fracture analysis shows that the OSP and ENIG joints fractured in the solder and solder/IMC interfaces, respectively. The IMC of the OSP and ENIG joints exhibit scallop and needle shapes, respectively. The ENIG joints fractured at the solder/IMC interface because of a stress concentration in the needle-type IMC. After 1500 TST cycles, the shear strength of all samples decreases by more than 50%. Cross-sectional analysis shows a crack at the solder joints of all samples after 1,000 cycles. The decrease in shear strength is caused by these cracks.

Highly Robust Ti Adhesion Layer during Terminal Reaction in Micro-Bumps.

The use of scaled-down micro-bumps in miniaturized consumer electronic products has led to the easy realization of full intermetallic solder bumps owing to the completion of the wetting layer. However, the direct contact of the intermetallic compounds (IMCs) with the adhesion layer may pose serious reliability concerns. In this study, the terminal reaction of the Ti adhesion layer with Cu–Sn IMCs was investigated by aging the micro-bumps at 200 °C. Although all of the micro-bumps transformed into intermetallic structures after aging, they exhibited a strong attachment to the Ti adhesion layer, which differs significantly from the Cr system where spalling of IMCs occurred during the solid-state reaction. Moreover, the difference in the diffusion rates between Cu and Sn might have induced void formation during aging. These voids progressed to the center of the bump through the depleting Cu layer. However, they neither affected the attachment between the IMCs and the adhesion layer nor reduced the strength of the bumps. In conclusion, the IMCs demonstrated better adhesive behavior with the Ti adhesion layer when compared to Cr, which has been used in previous studies.

Microstructural evolution of intermetallic compounds between crystalline/amorphous Cobalt-Phosphorous coatings and lead-free solders

In the advanced microelectronic packaging, Cu/Sn joints require high-quality diffusion barriers to inhibit Cu–Sn intermetallic compounds (IMCs) growth and improve the interface brittleness. Cobalt-Phosphorous (Co–P) alloy coatings are ideal candidates due to their good wettability, promising diffusion resistance and low interfacial brittleness. In this work, the microstructural evolution of IMCs between crystalline/amorphous Co–P coatings and lead-free solders during the solid-state diffusion were systemically investigated. The microstructure, phase distribution, and grain characteristics of coatings and IMCs were carefully characterized by SEM, EPMA, EBSD, and TEM. It was found that the consumption rate of crystalline Co–P, 21.2 nm/h, was significantly slower than that of amorphous Co–P, 96.4 nm/h, and exhibited an excellent diffusion resistance, which was attributed to the nanocrystalline structure and the P-rich layer which performed the diffusion barriers for Sn and Cu atoms. Compared with Ni, amorphous Co–P coatings could better improve the interfacial brittleness with soft and ductile Co–Sn compounds (hardness of 3.0 GPa) growing with the rapid diffusion of Co, and the toughened Co–Sn–P attributing to the diffusion of Sn. Kinetic analysis showed that the growth rate-controlling process of Co–Sn IMCs was jointly controlled by interfacial reaction and volume diffusion, and the effect of the interfacial reaction is more pronounced in the amorphous system, which leads to coarse Co–Sn grains that are beneficial to the softness and ductility of IMCs. Crystalline and amorphous Co–P coatings can be applied to the surface treatment for die pads and print-circuit-board pads according to their own characteristics, respectively.

Investigations on deformation and fracture behaviors of the multi-alloyed SnAgCu solder and solder joint by in-situ observation

Recently multi-alloying has been used for optimization of the SnAgCu (SAC) solder. To comprehensively reveal the effects of multi-alloying on mechanical property of the SAC solder, in this study the Sb, Bi, Ni, In and Ce elements were added into the Sn-3.8Ag-0.7Cu (wt%) solder, then the deformation and fracture behaviors of the multi-alloyed SAC solder (MAS) and MAS/Cu solder joint were in-situ observed and compared with the SAC. The results reveal that more intermetallic compounds (IMCs) and some Bi particles are formed in the MAS, while the (Cu,Ni)6Sn5 IMC in the MAS is refined. Due to the solid solution strengthening and precipitation strengthening, yield strength of the MAS increases by about 25 % compared with the SAC. Under tensile stress, severe slip and grain rotation occurs in the SAC solder, while plastic deformation of the MAS is restrained to a high extent by the dispersed particles within it. The MAS fractures in a tearing mechanism without obvious necking, but still shows a relative high elongation (~35 %), and the MAS has superior creep resistance since the dislocation motion and grain rotation are restrained. The deformation mismatch between the MAS and the Cu substrate is less serious, and the IMC at the MAS/Cu interface are less likely to fracture, resulting in a higher tensile strength (~160 MPa). Multi-alloying is recommended to improve the strength and creep resistance of the SAC.

Study on the evolution of interfacial (Cu,Ni)6Sn5 and shear property of (111)Cu/Sn/Ni micro joints under isothermal and TG-bonding

Single-crystal Cu can be potentially applied as pad or micro bump in bonding technology for advanced packaging. A novel bonding method with an extra temperature gradient (TG, TG-bonding) was carried out to bonding single-crystal (111)Cu and poly-crystal Ni substrates with Sn as interlayer. The morphology and orientation evolution, elemental distribution and growth kinetics of interfacial (Cu,Ni)6Sn5 intermetallic compound (IMC) in (111)Cu/Sn/Ni micro joints during isothermal and TG-bonding were investigated. Regular roof-type (Cu,Ni)6Sn5 grains along three intersectant directions with an angle of 60° formed at the initial Sn/(111)Cu interface and maintained the roof-type morphology with (112‾0) preferred orientation throughout the isothermal bonding. For TG-bonding, TG-induced atomic thermomigration (TM) and Cu–Ni cross-interaction co-played a critical role in the morphology, grain feature and growth kinetics of the interfacial IMCs. Moreover, rapid growth of (Cu,Ni)6Sn5 phase was achieved by TG-bonding with (111)Cu as hot end to fabricate full IMC joints which had higher shear strength than the cases of isothermal and TG-bonding with (111)Cu as cold end. The proposed method would provide a further insight for developing bonding technology for advanced packaging.

Evaluation of the thermal effusivity of intermetallic compounds using a modulated thermoreflectance method

In this study, we evaluated thermal properties of the matrix phase and intermetallic compounds in solder joints by a frequency-domain thermoreflectance method with high spatial resolution realized by two two laser beams and considering thermal diffusion length. The values of the thermal effusivities of a tin matrix phase (Sn matrix) and the intermetallic compounds (IMCs) in solder joints were determined for each heating frequency using calibration curves given by standard samples with known thermal properties. These measured heat effusivities of these Sn matrix and IMCs were estimated various values affected thermal conductivity of addition elements. Moreover, to convert from thermal effusivity to thermal conductivity, numerical calculations were conducted with assumed various thermal conductivity of molybdenum-reflector film on the sample surface and the volumetric heat capacity of IMCs. Finally, it is found that the apparent thermal conductivity of the Mo film was 0.5 W m−1 K−1 and the thermal conductivity of IMCs were shown 25–37 W m−1 K−1 with composition dependence clearly.

Effect of TiO2 nanoparticles on the microstructure, mechanical and thermal properties of rapid quenching SAC355 lead-free solder alloy

PurposeThis study aims to investigate the effect of a small amount of TiO2 NPs addition on the microstructure, thermal, mechanical and electrical properties of environmentally friendly eutectic (SAC355)100-x(TiO2)x (x = 0.1, 0.3, 0.5, 0.7 and 1 wt.%) solder alloys.Design/methodology/approachMechanical, thermal and electrical properties and microstructure conditions are taken into major consideration in any study of materials containing nanoparticles. Dynamic resonance technique, X-ray diffraction and scanning electron microscopy were carried out to study stiffness, identification of the phases and the morphology features of the solder. Structure and microstructure analysis indicated that the presence of rhombohedral β–Sn phase in addition to orthorhombic intermetallic compound (IMC) Ag3Sn and Cu3Sn phase dispersed in Sn matrix. In addition, the results showed that TiO2 NPs addition at a small trace amount into SAC355 system reduces and improves the particle size of both rhombohedral β–Sn and orthorhombic IMC Ag3Sn and Cu3Sn. The interstitial dispersion of TiO2 NPs at grain boundaries resulted in Ag3Sn being more uniform needle-like, which is distributed in the β–Sn matrix. The fine and uniform microstructure leads to improvement of mechanical strength.FindingsSome important conclusions are summarized as follows: microstructure investigations revealed that the addition of TiO2 NPs particles to eutectic SAC355 inhibited in reducing and refines the crystallite size as well as the Ag3Sn IMC, which reinforced the strength of plain solder alloy. The mechanical properties values such as Young’s modulus and Vickers microhardness of SAC355 solder alloy can be significantly improved by adding a trace amount of TiO2 NPs compared with plain solder because of the existence of appropriate volume fraction of Ag3Sn IMC. The results show that the best creep resistance is obtained when the addition of 0.3 wt.% of TiO2 NPs is compared to plain solder. TiO2 NPs addition could increase the melting temperature, compared with plain solder. All results showed that TiO2 NPs addition is an effective method to enhance new solder joints.Practical implicationsNew solder alloys.Originality/valueDevelopment of TiO2 NPs-doped eutectic SAC355 lead-free solder for electronic packaging.

Effects of temperature and strain rate on tensile properties of (Ag,Cu)-Sn intermetallic compounds: A molecular dynamics study

With the advent of environment friendly microelectronic packaging technologies, the demand of lead-free solders alloy has escalated. Leadfree solder material is an alloy of Tin (Sn), Silver (Ag) and Copper (Cu) and is widely known as SAC solder. Intermetallic compounds (IMC) like Ag3Sn, Cu3Sn and Cu6Sn5 are proven to adversely affect the mechanical properties of lead-free solder joints. This study presents the effects of temperature and strain rate on mechanical performances of these IMCs found in SAC solders. In addition, weakest and most sensitive IMC among these is detected. Modified embedded atom method potential parameters are used in LAMMPS to simulate the stress-strain behavior with deformation evolution of intermetallic compounds in different temperature and strain rates. The simulation was performed at 298 K–498 K with 50 K regular increment and at the strain rates of 108 s−1, 109 s−1, and 1010 s−1. Insight from this study suggest that the tensile properties of these IMCs increased with the increased in strain rates and decrease in temperature. Furthermore, the effect of temperature on tensile strength is observed to be higher at low strain rate whereas strain rate influence is lower at low temperatures. Among all the intermetallic, Ag3Sn exhibits lowest tensile properties with lowest stability, conversely Cu3Sn exhibits highest tensile properties with highest stability.

Electrochemical Behaviors and Thermodynamic Properties of Ce on Liquid Bi, Sn, and Zn Electrodes in Molten LiCl-KCl Salt

This study presents the electrochemical behaviors and thermodynamic properties of Ce on liquid Bi, Sn, and Zn electrodes in molten LiCl-KCl eutectic salt. First, the Ce-metal binary systems on the solid tungsten electrode were investigated to determine the formation of Ce-metal intermetallic compounds during the electrowinning process. In these experiments, the formation of five Ce–Bi intermetallic compounds, eight Ce–Sn intermetallic compounds, and nine Ce–Zn intermetallic compounds was confirmed from the oxidation peaks of cyclic voltammetry. The standard Gibbs free energy of formation of each intermetallic compound was calculated from plateaus of the open-circuit chronopotentiometry. Subsequently, the electrochemical behaviors of Ce were investigated on liquid Bi, Sn, and Zn electrodes using cyclic voltammetry. In particular, while the reduction potentials of Li and Ce were too close to differentiate on the liquid Bi and Sn electrodes, they were not on the liquid Zn electrode. Peak potentials from cyclic voltammetry were utilized to calculate the activity coefficients of Ce in the liquid Bi, Sn, and Zn electrodes, which were 3.16 × 10−14, 1.82 × 10−12, and 9.05 × 10−10, respectively.

Effect of Cu, Ni, Ag addition on creeping properties of Sn5Sb-0.5Cu-0.1Ni-0.5Ag for high temperature packaging

PurposeThis paper aims to investigate the effect of the Cu, Ni and Ag addition in Sn5Sb-based alloy on the mechanical properties and its mechanism.Design/methodology/approachThe micro-indentation, creeping test of the Cu/Sn5Sb–0.5Cu–0.1Ni–0.5Ag/Cu and Cu/Sn–5Sb/Cu were conducted, and its microstructure was analysed. The scanning electron microscope and the metallographic microscope characterized the microstructure of the Sn5Sb–0.5Cu–0.1Ni–0.5Ag/Cu and Sn–5Sb/Cu joints.FindingsThe microstructure of Cu/Sn5Sb–0.5Cu–0.1Ni–0.5Ag/Cu is distributed with the fine (Cu,Ni)6Sn5 and Ag3Sn intermetallic compounds (IMCs), whereas the Cu6Sn5 and Sn3Sb2 in Cu/Sn–5Sb/Cu is larger and far more less. This investigation reveals that the addition of the Cu, Ni and Ag elements reinforced mechanical properties and provided a technical basis for the development of Sn–Sb alloy with good mechanical properties.Originality/valueThis paper reveals that the hardness and the modulus of the bulk solder Cu/Sn–5Sb/Cu solder joints were improved with the addition of Cu, Ni and Ag trace elements. Meanwhile, the creep resistance and plasticity were also improved. This study has a great value for exploring high-performance Sn–Sb based solder alloy and has proved an example.

Controlling the distribution of porosity during transient liquid phase bonding of Sn-based solder joint

The rapid growth of (Cu,Ni)6Sn5 intermetallic compounds (IMCs) when Sn reacts with Cu containing 6 wt%Ni (Cu-6Ni) offers huge potential for resolving the lengthy transient liquid phase (TLP) processing time. However, the uncontrolled formation of voids at the centre of the joint remains a serious issue. Therefore, we have studied the influence of different Ni concentrations (0, 2 and 6 wt%) in the Cu substrate and the relative location of the porosity when reacting with Sn-0.7Cu solder in the sandwich structure of the joint. Through in-situ X-ray microradiography, the changes in the void positions and the reaction time required to form the IMC joints was interpreted with reference to growth kinetics equations. The results indicate that the different growth rates of (Cu,Ni)6Sn5 and Cu6Sn5 IMCs due to the different Ni concentrations of the Cu-Ni substrates can control the location of the porosity and influence the shear strength of the TLP lap joint. This discovery is a potential gateway to developing reliable electronic interconnects for the power device industry.

Systematic investigation of the effect of Ni concentration in Cu-xNi/Sn couples for high temperature soldering

High temperature solders have experienced a marked increase in demand due to the boom of high power interconnects in electric vehicles and the miniaturisation of electronic devices. Transient liquid phase (TLP) bonding is a promising technology for these applications. Alloys from the Cu-Sn system widely used in conventional soldering processes have potential for high temperature applications if the relatively low melting point Sn phase can be consumed in a TLP process. This process results in a joint composed of Cu6Sn5 or Cu3Sn intermetallic compounds (IMCs) which have higher melting points than Sn. Alloying Ni to the Cu substrate promotes the growth rate of the (Cu,Ni)6Sn5 IMCs, significantly reduces the TLP processing time and costs, while suppressing the formation of (Cu,Ni)3Sn. However, the properties of the (Cu,Ni)6Sn5 formed also change significantly depending on the Ni concentration in the system. In this work, the composition, morphology, grain sizes and crystal structure of the (Cu,Ni)6Sn5 formed via the reaction of Sn and Cu-xNi substrates of different Ni concentrations are studied in detail via electron microscopy and synchrotron powder X-ray diffraction to provide a basis for further understanding of the physical, electrical and mechanical properties. The findings are further verified by density functional theory calculations. Additionally, the complex interplay of grain boundary diffusion rates and the IMC nucleation rate which accelerate with increasing Ni concentration, along with the Cu-xNi dissolution rate and the crystal growth rate which decrease with increasing Ni concentration are identified to be the main factors affecting the IMC growth rates.

Investigation of microstructure, thermal properties, and mechanical performances of Ni-added Sn-5.0Sb-0.5Cu/Cu solder joints

Small amounts of Ni were added to Sn-5.0Sb-0.5Cu (SSC505) solder alloy. The added Ni slightly increased the melting temperature and slightly reduced the melting range of the alloy. The microstructure of the SSC505 solder included a β-Sn phase, and SbSn and Cu6Sn5 intermetallic compound (IMC) phases distributed in the solder matrix. The addition of Ni produced a new (Cu0.7,Ni0.3)6Sn5 IMC phase with a mixed morphology comprising hexagonal and flake-shaped phases. The addition of 0.1wt.%Ni increased the ultimate tensile strength (UTS) and hardness of the SSC505 solder to 43.31 MPa and 17.52 HV, respectively, but the addition of 0.2wt.%Ni increased the size and number of the IMC phases, which weakened both properties. The interfacial layers of SSC505/Cu solder joints were composed of Cu6Sn5 and Cu3Sn IMC layers. The addition of Ni inhibited the growth of the Cu3Sn IMC layers, but produced a new, thicker, dendritic IMC layer identified by energy dispersive X-ray spectroscopy (EDS) as (Cu0.96,Ni0.04)6Sn5. As a result, the shear strength of the SSC505-0.2Ni/Cu solder joint was low. This work showed that the microstructure and mechanical performances of both a SSC505 solder alloy and SSC505/Cu solder joint were improved by the addition of 0.1wt.%Ni.

Growth kinetics of (CuxNi1-x)6Sn5 intermetallic compound at the interface of mixed Sn63Pb37/SAC305 BGA solder joints during thermal aging test

Sn63Pb37/SAC305 mixed solder joint is inevitably in the electronic device requiring high reliability, such as health care, aerospace etc. However, the usage history of mixed solder joint is relatively short and as such their interfacial behaviour and reliability in service has not been completely figure out. Herein, the evolution of microstructures in fully mixed Sn63Pb37/SAC305 BGA solder joints during high-temperature storage were systematically studied. After reflow soldering process, the Pb-rich phases uniformly distributed in the fully mixed joint. During the thermal aging test, the size of Pb-rich phases gradually coarsened. The intermetallic compound (IMC) layers thickness at the two-side interface (upper interface: between the pad on substrate and solder; lower interface: between the pad on PCB and solder) were also increased. Moreover, the growth kinetics models of two-side IMC layer were successfully established according to the Arrhenius equation. IMC layer grows faster at higher temperature, because of higher diffusion coefficient. With the increasing of aging time, the fracture position partially moved from the interface between Ni layer and IMC layer into IMC internal. These results may provide support for the reliable applications of mixed Sn63Pb37/SAC305 solder joints.