Ag3Sn Intermetallic Compounds Research Articles

Growth kinetic of Ag3Sn intermetallic compound in micro-scale Pb-free solder alloys under a temperature gradient

The interfacial reaction of Ag3Sn intermetallic compounds (IMCs) in micro-scale Ag/SnAg/Ag sandwich structure was investigated under a temperature gradient of 168.9 °C/cm at 260 °C. In contrast to a symmetrical growth of Ag3Sn at both interfaces under isothermally annealed at 260 °C, the asymmetric growth of Ag3Sn IMCs at both interfaces was observed under a temperature gradient; the growth rate of Ag3Sn at colder interface was faster than that at hot side because of temperature gradient induced Ag atoms diffusion from the hot end toward the cold end. In addition, the findings indicate two-stage growth behavior of Ag3Sn IMC under a temperature gradient. The growth kinetic analysis suggests that the chemical potential gradient controls the thickness change of Ag3Sn at stage I (0–10 min) whereas force driving thermomigration becomes dominant at stage II (10–30 min). The molar heat of transport (Q*) of Ag in Sn in molten-state was calculated as 14.9 kJ/mol.

Asymmetrical Precipitation of Ag3Sn Intermetallic Compounds Induced by Thermomigration of Ag in Pb-Free Microbumps During Solid-State Aging

Three-dimensional integrated circuit technology has become a major trend in electronics packaging in the microelectronics industry. To effectively remove heat from stacked integrated circuitry, a temperature gradient must be established across the chips. Furthermore, because of the trend toward higher device current density, Joule heating is more serious and temperature gradients across soldered joints are expected to increase. In this study we used heat-sink and heat-source devices to establish a temperature gradient across SnAg microbumps to investigate the thermomigration behavior of Ag in SnAg solder. Compared with isothermal conditions, small Ag3Sn particles near the hot end were dissolved and redistributed toward the cold end under a temperature gradient. The results indicated that temperature gradient-induced movement of Ag atoms occurred from the hot side toward the cold side, and asymmetrical precipitation of Ag3Sn resulted. The mechanism of growth of the intermetallic compound (IMC) Ag3Sn, caused by thermomigration of Ag, is discussed. The rate of growth Ag3Sn IMC at the cold side was found to increase linearly with solid-aging time under a temperature gradient. To understand the force driving Ag diffusion under the temperature gradient, the molar heat of transport (Q*) of Ag in Sn was calculated as +13.34 kJ/mole.

Bonding copper ribbons on crystalline photovoltaic modules using various lead-free solders

The requirement for environmentally friendly technology has led to considerable efforts to develop photovoltaic (PV) modules. The copper (Cu) ribbon interconnects of PV modules require alternative bonding materials to replace the current solder that contains lead. Several candidate lead-free solder materials have been developed that are inexpensive and reliable. In this study, we evaluate Cu ribbon interconnection bonding with Sn–0.7Cu and Sn–48Bi–2Ag solder materials to address their feasibility for use in PV modules by investigating material degradation during thermal cycling. After thermal cycling, in the Sn–0.7Cu solder, considerable intermetallic compound (IMC) growth occurred at both interfaces, while Bi-rich grains coarsened with IMC growth in Sn–48Bi–2Ag solder. However, the degradation of the electrical performance of the PV modules was similar for those containing both solder materials. Cracks that appeared at the interface propagated from the fractures of the Ag3Sn IMC layers. This suggests that preventing IMC growth at the interface between the Cu ribbon and Ag sintered electrode is important to improve the reliability of interconnects in PV modules. The use of Pb-free solder in PV modules opens up a novel opportunity to realize high reliability at low cost.

Quantitative analyses of Ag3Sn intermetallic compound formation in SnAgCu solder alloys

In this paper, a new explicit state variable was introduced which describes the Ag3Sn intermetallic morphology inside of lead-free solder joints at different cooling rates. In the experiment, samples were prepared by melting standard Ag-content (4 % in wt%) and low Ag-content (0.3 % in wt%) solder alloys, and solidifying them at five different cooling rates between 0.8 and 3 K/s. Images were taken about the cross-section of solder joints by brightfield light-microscope to calculate the explicit state variables, which describe the morphology of precipitating Ag3Sn intermetallic compounds. The captured images were processed then with an in-house developed automatic image processing algorithm. It was found that the area of Ag3Sn intermetallic compounds followed exponential distribution, so a new state variable could be introduced, such as the amplitude of a certain exponential curve fitted to the area histogram of the Ag3Sn IMCs. It was proven that our new variable described the different Ag3Sn IMC morphologies obtained at different cooling rates better; it was more sensitive at both aforementioned solder alloys (4 and 0.3 % Ag content) than the widely applied parameters, like the mean-intercept length or the average area of particles.

Effects of Ag content on the reliability of LED package component with Sn–Bi–Ag solder

The effects of Ag content on the mechanical and electrical properties of the Sn–58Bi solder joints in light emitting diode (LED) package were studied. The Sn–58Bi, Sn–57.6Bi–0.4Ag and Sn–57Bi–1Ag solder were used as solder joints. The LED package was bonded on the printed circuit board (PCB) with the organic solderability preservative (OSP) surface finish, and then it was aged at 85 °C for 100, 300, 500 and 1000 h, respectively. In order to evaluate the mechanical and electrical properties, the shear test was conducted and the change of current versus voltage was measured. The shear strength and electrical conductivity of solder joints decreased with an increasing aging time. With an addition of 1.0 wt% Ag, the shear strength was improved and higher than those of other solder joints. The microstructure and composition of the solder joints were investigated with a scanning electron microscope, an energy dispersive spectrometer and an electron probe micro analyzer. The Cu6Sn5 intermetallic compounds (IMCs) formed between solder and OSP surface finished Cu pad of PCB. The thickness of the IMCs increased with an increasing aging time. By an addition of 0.4 wt% Ag, fine Ag3Sn particles were dispersed inside the solder matrix and large-sized primary Ag3Sn IMCs were formed with 1.0 wt% Ag addition.

Microstructure and properties of AgCu/2 wt% Ag-added Sn–Pb solder/CuBe joints fabricated by vapor phase soldering

The purpose of this paper is to investigate the effect of 2 wt% Ag addition in Sn–Pb eutectic solder on microstructure and mechanical properties of AgCu/solder/CuBe joint fabricated by vapor phase soldering. 63Sn37Pb and 62Sn36Pb2Ag solder pastes were used to join Cu(1.7 wt%–2.5 wt%)Be and Ag(2 wt%–5 wt%)Cu alloys. Two fracture modes are observed in 62Sn36Pb2Ag and 63Sn37Pb joints after lateral shear tests at room temperature or 120 °C, and shear forces of 62Sn36Pb2Ag joints are far higher than those of 63Sn37Pb joints. No obvious difference is observed in morphology and thickness of intermetallic compounds (IMCs) at interfaces of the 63Sn37Pb and 62Sn36Pb2Ag joints. Within the two kinds of joints, formation of big blocky or plate-like Ag3Sn is restrained. However, many Ag3Sn IMCs particles (1–3 μm in width) in isolated and dispersed distribution are observed within 62Sn36Pb2Ag joints. The Ag3Sn particles are responsible for the better mechanical properties of 62Sn36Pb2Ag joints than those of 63Sn37Pb joints. The results present in this paper may provide a guide for restraining formation of big blocky or plate-like Ag3Sn in joints with Ag pads or thick Ag surface finish on pads by utilizing vapor phase soldering process, and improving mechanical properties of Cu/SnPb/Ag joints by adding Ag in SnPb eutectic solder.

Influence of the aggregated Ag3Sn on the improvement of electromigration phenomenon in the doped Sn58Bi solder joints

Electromigration (EM) phenomenon has become more troublesome in the Sn–Bi solder joints as the increase of current density. Doping method is reported as one of the solution to improve solder joints. However, the doped particles are easily aggregated and formed large sized intermetallic compounds (IMCs) in the solder matrix during reflow soldering. In this research, EM phenomenon was studied in the Sn57.6Bi0.4Ag, Sn58Bi with 0.4 wt% Ag doping (Sn58Bi + 0.4Ag) and Sn58Bi solder joints to fully understand the influence of the aggregated Ag3Sn IMCs. The grain refinement effect of the Ag element was found to be the main reason of the improvement of EM phenomenon. Also, it was proved that Sn57.6Bi0.4Ag solder joints with uniformly distributed Ag3Sn IMCs performed well in preventing the segregation of Bi phase. However, Sn58Bi + 0.4Ag solder joints with the aggregated Ag3Sn IMCs did not perform well, forming thicker Bi rich layer at the anode. On the other hand, the addition of Ag element had minimal effect on the formation and consumption of Cu–Sn IMCs in the Sn–Bi solder joints. The thickness of Cu–Sn IMCs layer at the cathode in the Sn57.6Bi0.4Ag and Sn58Bi solder joints were found to be similar. However, the aggregated Ag3Sn IMCs in the Sn58Bi + 0.4Ag solder joints could promote the migration of Cu–Sn IMCs to the cathode.

Retarding the Cu–Sn and Ag–Sn intermetallic compounds by applying Cu–xZn alloy on micro-bump in novel 3D-IC technologies

This study investigates the evolution of interfacial microstructures in Cu/Sn–3.5Ag/Cu and Cu/Sn–3.5Ag/Cu–15Zn (wt%) microbumps. Due to the small size of microbumps, Cu–Sn intermetallic compounds (IMCs) rapidly form from the Cu pads. These brittle IMCs occupy the entire joint and weaken joint reliability. Moreover, Ag3Sn tends to precipitate inside the solder in large plates, which results in the accumulation of thermal stress due to a CTE mismatch between Ag3Sn and β-Sn. It is demonstrated that doping Zn into one of the Cu substrates effectively suppresses the growth of Cu–Sn and Ag3Sn IMCs. The mechanisms involved are explained in detail using thermodynamic theories and undercooling effects. Owing to the effective suppression of Cu–Sn and Ag–Sn IMCs, Cu/Sn–3.5Ag/Cu–15Zn microbumps are potentially useful in strengthening the interconnections of novel 3D-IC technologies.

Effect of Y2O3 nanoparticles addition on the microstructure and tensile strength of Cu/Sn3.0Ag0.5Cu solder joint

A sort of composite solder was produced by adding Y2O3 nanoparticles in Sn3.0Ag0.5Cu solder. The microstructure and tensile strength of solder joint were investigated. It was found that the size of intermetallic compounds and tensile strength of solder joint were notably influenced by the nanoparticles. The growth behaviors of intermetallic compounds Ag3Sn and Cu6Sn5 were suppressed due to the addition of Y2O3 nanoparticles. The tensile test results revealed that the strength of composite solder joint was higher than that of solder joint without nanoparticles addition. It is indicated that Y2O3 nanoparticles should play important roles in strengthening of joint by hampering dislocation movement.

Study on coarsening of Ag3Sn intermetallic compound in the Fe-modified Sn–1Ag–0.5Cu solder alloys

The present study focuses on coarsening of Ag3Sn intermetallic compound in the Sn–1Ag–0.5Cu and Fe-modified Sn–1Ag–0.5Cu solder alloy. The investigations showed that the Ag3Sn intermetallics coarsened rapidly in the Sn–1Ag–0.5Cu solder alloy whereas the Ag3Sn intermetallics were found to be quite stable in the Fe-modified Sn–1Ag–0.5Cu solder alloy. The lattice strain in the Ag3Sn intermetallics and the blocking effect on Ag diffusivity in Sn matrix suggested the possible mechanisms for the coarsening suppression of the Ag3Sn intermetallics in the Fe-modified solder alloy.

Solid Liquid Interdiffusion Bonding of (Pb, Sn)Te Thermoelectric Modules with Cu Electrodes Using a Thin-Film Sn Interlayer

A (Pb, Sn)Te thermoelectric element plated with a Ni barrier layer and a Ag reaction layer has been joined with a Cu electrode coated with Ag and Sn thin films using a solid–liquid interdiffusion bonding method. This method allows the interfacial reaction between Ag and Sn such that Ag3Sn intermetallic compounds form at low temperature and are stable at high temperature. In this study, the bonding strength was about 6.6 MPa, and the specimens fractured along the interface between the (Pb, Sn)Te thermoelectric element and the Ni barrier layer. Pre-electroplating a film of Sn with a thickness of about 1 μm on the thermoelectric element and pre-heating at 250°C for 3 min ensures the adhesion between the thermoelectric material and the Ni barrier layer. The bonding strength is thus increased to a maximal value of 12.2 MPa, and most of the fractures occur inside the thermoelectric material. During the bonding process, not only the Ag3Sn intermetallics but also Cu6Sn5 forms at the Ag3Sn/Cu interface, which transforms into Cu3Sn with increases in the bonding temperature or bonding time.

The Nucleation of Sn in Undercooled Melts: The Effect of Metal Impurities

The dependence of the solidification temperature on the concentration x of impurity atoms, M, of Sn-M x alloys after cooling from the melt was measured separately for M = Co, Ni, Ag, and Cu. For a comparison, similar measurements were performed on SAC305-Ni x alloys. Large variations in undercooling were observed. It was found that the Ag atoms dissolved in the Sn-Ag melt significantly lowered undercooling, although the presence of Ag3Sn intermetallic compounds did not. While Cu6Sn5 intermetallic compounds in Sn-Cu melts did not significantly lower undercooling, the undercooling of a Sn-Cu melt in contact with a Cu interface was significantly reduced. The addition of Ni to Pb-free solder SAC305 caused a factor of two reduction in the undercooling, similar to that observed after the addition of Ni to high-purity Sn.

Structural Size Effect on Mechanical Behavior of Intermetallic Material in Solder Joints: Experimental Investigation

The elastic and plastic mechanical properties of intermetallic compound (IMC) phases of a lead-free Sn3.5Ag/Cu-substrate soldering system are investigated in different sized joints using nano-indentation. The specimens were prepared using solid–liquid interdiffusion soldering process with joint sizes ranging from 15 to 450 μm. Solder joints were subjected to 360 °C soldering temperature for 20 min and then air cooled to room temperature to create testable IMCs thicknesses. Nano-indentation was used to extract the elastic and plastic properties of Cu6Sn5, Cu3Sn, and Ag3Sn IMCs and β-tin and copper materials. Cu–Sn IMCs formed in specimens with smaller joint size show higher elastic modulus, hardness, and yield strength and lower work hardening exponent. This was attributed to the dimensional constraints associated with decreasing joint size and the local stresses developed during fabrication in joints with different sizes. Local elastic modulus and hardness of single grains of Cu6Sn5 were obtained using a combination of nano-indentation and electron backscatter diffraction (EBSD) techniques. Grains with c-axis at a 45 deg angle with respect to the nano-indentation loading direction show higher elastic modulus (∼8.70% higher) and hardness (8.85% higher) compared to the grains that have a c-axis that is almost perpendicular to the nano-indentation loading direction.

Nanoscale characterization of 1D Sn-3.5Ag nanosolders and their application into nanowelding at the nanoscale

One-dimensional Sn-3.5Ag alloy nanosolders have been successfully fabricated by a dc electrodeposition technique into nanoporous templates, and their soldering quality has been demonstrated in nanoscale electrical welding for the first time, which indicates that they can easily form remarkably reliable conductive joints. The electrical measurement shows that individual 1D Sn-3.5Ag nanosolders have a resistivity of 28.9 μΩ·cm. The morphology, crystal structure and chemistry of these nanosolders have been characterized at the nanoscale. It is found that individual 1D Sn-3.5Ag alloy nanosolders have a continuous morphology and smooth surface. XPS confirms the presence of tin and silver with a mass ratio of 96.54:3.46, and EDX elemental mappings clearly reveal that the Sn and Ag elements have a uniform distribution. Coveragent beam electron diffractions verify that the crystal phases of individual 1D Sn-3.5Ag alloy nanosolders consist of matrix β-Sn and the intermetallic compound Ag3Sn. The reflow experiments reveal that the eutectic composition of the 1D Sn-Ag alloy nanowire is shifted to the Sn rich corner. This work may contribute one of the most important tin-based alloy nanosolders for future nanoscale welding techniques, which are believed to have broad applications in nanotechnology and the future nano-industry.

Influence of cerium oxide (CeO2) nanoparticles on the microstructure and hardness of tin–silver–copper (Sn–Ag–Cu) solders on silver (Ag) surface-finished copper (Cu) substrates

Nano-sized, non-reacting, non-coarsening CeO2 particles with a density close to that of solder alloy were incorporated into Sn–3.0 wt%Ag–0.5 wt%Cu solder paste. The interfacial microstructure and hardness of Ag surface-finished Cu substrates were investigated, as a function of reaction time, at various temperatures. After the initial reaction, an island-shaped Cu6Sn5 intermetallic compound (IMC) layer was clearly observed at the interfaces of the Sn–Ag–Cu based solders/immersion Ag plated Cu substrates. However, after a prolonged reaction, a very thin, firmly adhering Cu3Sn IMC layer was observed between the Cu6Sn5 IMC layer and the substrates. Rod-like Ag3Sn IMC particles were also clearly observed at the interfaces. At the interfaces of the Sn–Ag–Cu based solder-Ag/Ni metallized Cu substrates, a (Cu, Ni)–Sn IMC layer was found. Rod-like Ag3Sn and needle-shaped Cu6Sn5 IMC particles were also observed on the top surface of the (Cu, Ni)–Sn IMC layer. As the temperature and reaction time increased, so did the thickness of the IMC layers. In the solder ball region of both systems, a fine microstructure of Ag3Sn, Cu6Sn5 IMC particles appeared in the β-Sn matrix. However, the growth behavior of the IMC layers of composite solder doped with CeO2 nanoparticles was inhibited, due to an accumulation of surface-active CeO2 nanoparticles at the grain boundary or in the IMC layers. In addition, the composite solder joint doped with CeO2 nanoparticles had a higher hardness value than the plain Sn–Ag–Cu solder joints, due to a well-controlled fine microstructure and uniformly distributed CeO2 nanoparticles. After 5 min of reaction on immersion Ag-plated Cu substrates at 250 °C, the micro-hardness values of the plain Sn–Ag–Cu solder joint and the composite solder joints containing 1 wt% of CeO2 nanoparticles were approximately 16.6 and 18.6 Hv, respectively. However after 30 min of reaction, the hardness values were approximately 14.4 and 16.6 Hv, while the micro-hardness values of the plain Sn–Ag–Cu solder joints and the composite solder joints on Ag/Ni metallized Cu substrates after 5 min of reaction at 250 °C were approximately 15.9 and 17.4 Hv, respectively. After 30 min of reaction, values of approximately 14.4 and 15.5 Hv were recorded.

Electromigration Behaviors and Effects of Addition Elements on the Formation of a Bi-rich Layer in Sn58Bi-Based Solders

This study investigates the electromigration (EM) behaviors and effects of the addition elements on the formation of a Bi-rich layer in Sn58Bi-based solders including Sn58Bi (SB), Sn58Bi0.5Ag (SBA) and Sn58Bi0.5Ag0.1Cu0.07Ni0.01Ge (SBACNG) solders. The EM tests were conducted at a relatively high temperature of 373 K and at a current density of 30 kA/cm2. Although the dominant diffusing atom was Bi, hillocks were formed from Sn more easily than from Bi. The electrical resistance increased in the solder during the current stressing, and the dominant factor was attributed to the formation of a Bi-rich layer. SBACNG solder showed the highest resistance to the formation of a Bi-rich layer, followed by SBA, and then SB solder. The possible addition elements enhancing the resistance of SBACNG solder are Ag, Ni and Ge. The effects of the addition elements are summarized as follows: (1) Ag distributes in the Sn phase as Ag3Sn intermetallic compounds (IMCs) that enhance the mechanical strength of Sn; (2) Ni distribution in Bi as Ni-Bi IMCs stabilizes Bi and suppresses its migration; and (3) Ge may distribute in Bi, stabilizing Bi, or Ge exists at the phase boundaries as a precipitate that inhibits Bi migration.

Effect of microstructure and Ag3Sn intermetallic compounds on corrosion behavior of Sn–3.0Ag–0.5Cu lead-free solder

In this paper, the effects of microstructure on the corrosion behavior of Sn–3.0Ag–0.5Cu (SAC305) lead-free solder were investigated by potentiodynamic polarization and atmospheric corrosion test. Scanning electron microscopy and X-ray diffraction were used to characterize the samples after the electrochemical and atmospheric corrosion tests. Results showed that commercial SAC305 solder exhibits better corrosion resistance than air-cooled and furnace-cooled SAC305 solders both in 3.5 wt% NaCl solution and at 60 °C/100 % relative humidity condition.

Early stage growth characteristics of Ag3Sn intermetallic compounds during solid–solid and solid–liquid reactions in the Ag–Sn interlayer system: Experiments and simulations

Transient Liquid Phase Bonding (TLPB) makes use of the isothermal solidification of a liquid interlayer through the formation of intermetallic compounds (IMC). This work investigates the Ag3Sn IMC formation in a thin, electroplated Ag–Sn interlayer system appropriate for TLPB – while covering as-coated conditions, growth initiation up to a few minutes of holding time – with experimental and numerical methods. Both solid-state and solid–liquid reactions at 200, 250 and 300°C, respectively, were covered under identical and near-isothermal conditions with a novel experimental setup. Morphological aspects like the lateral IMC grain size or the scallop roughness were proven to strongly depend on temperature. Growth kinetics were captured by power laws, growth exponents n were determined as 0.24, 0.36 and 0.29, parabolic growth constants k as 1.32⋅10−11, 4.04⋅10−10 and 7.24⋅10−10cm2/s at 200, 250 and 300°C, respectively, and the activation energy Q as 30.6kJ/mol. Predominant diffusion mechanisms, i.e. volume or GB diffusion, as well as coarsening effects were identified as temperature and time dependent at early stages. A mathematical model was developed based on the Arrhenius relationship including a growth correction function zIMC,corr to calculate and predict IMC growth as a function of temperature and time. The study was completed by multiphase-field simulations which targeted to mimic kinetic and morphological features of Ag3Sn IMC under various conditions. Good agreement between experiments and simulations was found for a limited set of parameters which allowed drawing conclusions about the dominant transport mechanisms for the reacting elements.

The roles of dendritic spacings and Ag3Sn intermetallics on hardness of the SAC307 solder alloy

Sn–Ag–Cu alloys have emerged as the most promising lead-free solder series among a number of alternatives. These alloys generally present a dendritic Sn-rich matrix surrounded by a eutectic mixture (β+α), where β is the Sn-rich phase and α is the Ag3Sn intermetallic compound. The present study aims to investigate the effects of dendritic (λ2, λ3) and eutectic (λ) spacings and the morphology of Ag3Sn particles on hardness of the Sn–3.0wt%Ag–0.7wt%Cu alloy (SAC307). In order to establish correlations between λ2,3 and hardness, transient directional solidification (DS) experiments were performed permitting a wide range of different microstructures to be examined. The techniques used for microstructure characterization included dissolution of the Sn-rich matrix, optical/scanning electron microscopy. A dendritic microstructure prevailed in the entire DS casting. It is shown that the hardness tends to decrease with the increase in λ2, λ3 and λF (eutectic spacing for Ag3Sn having a fiber morphology). Experimental equations relating microstructural spacings to hardness are proposed.

Interfacial microstructure and hardness of nickel (Ni) nanoparticle-doped tin–silver–copper (Sn–Ag–Cu) solders on immersion silver (Ag)-plated copper (Cu) substrates

Sn–Ag–Cu composite solder has been prepared by adding Ni nanoparticles. Interfacial reactions, the morphology of the intermetallic compounds (IMC) that were formed, the hardness between the solder joints and the plain Cu/immersion Ag-plated Cu pads depending on the number of the reflow cycles and the aging time have all been investigated. A scallop-shaped Cu6Sn5 IMC layer that adhered to the substrate surface was formed at the interfaces of the plain Sn–Ag–Cu solder joints during the early reflow cycles. A very thin Cu3Sn IMC layer was found between the Cu6Sn5 IMC layer and the substrates after a lengthy reflow cycle and solid-state aging process. However, after adding Ni nanoparticles, a scallop-shaped (Cu, Ni)–Sn IMC layer was clearly observed at both of the substrate surfaces, without any Cu3Sn IMC layer formation. Needle-shaped Ag3Sn and sphere-shaped Cu6Sn5 IMC particles were clearly observed in the β-Sn matrix in the solder-ball region of the plain Sn–Ag–Cu solder joints. Additional fine (Cu, Ni)-Sn IMC particles were found to be homogeneously distributed in the β-Sn matrix of the solder joints containing the Ni nanoparticles. The Sn–Ag–Cu–0.5Ni composite solder joints consistently displayed higher hardness values than the plain Sn–Ag–Cu solder joints for any specific number of reflow cycles–on both substrates–due to their well-controlled, fine network-type microstructures and the homogeneous distribution of fine (Cu, Ni)–Sn IMC particles, which acted as second-phase strengthening mechanisms. The hardness values of Sn–Ag–Cu and Sn–Ag–Cu–0.5Ni on the Cu substrates after one reflow cycle were about 15.1 and 16.6 Hv, respectively–and about 12.2 and 14.4 Hv after sixteen reflow cycles, respectively. However, the hardness values of the plain Sn–Ag–Cu solder joint and solder joint containing 0.5 wt% Ni nanoparticles after one reflow cycle on the immersion Ag plated Cu substrates were about 17.7 and 18.7 Hv, respectively, and about 13.2 and 15.3 Hv after sixteen reflow cycles, respectively.