Ag3Sn Intermetallic Compound Particles Research Articles

Thermal aging effects on microstructure, elastic property and damping characteristic of a eutectic Sn–3.5Ag solder

The present work describes the microstructural changes and their impacts on the electrical resistivity, elastic modulus and damping property of a eutectic Sn–3.5wt% Ag solder material when exposed to high temperature. A detail microstructural study was conducted through the scanning electron microscopy with energy-dispersive spectroscopy analysis and electron backscattered diffraction technique. In as-cast eutectic Sn–Ag solder alloy, sub-micrometer size Ag3Sn intermetallic compound (IMC) particles and bamboo-like dendritic structure with a dimension of length 20–30 µm and width 3–5 µm formed during solidification. However, after thermal aging treatment at 150 °C for 60 days, the fine Ag3Sn IMC particles and β-Sn grain appeared with coarse microstructure with the formation of twinning having the twin axis and 60° rotation. As a result, microstructure and Sn-crystal orientation of Sn–Ag solder greatly impact on its overall properties and turned inferior. From material properties evaluation, it was confirmed that the electrical resistivity, elastic and shear moduli values were significantly reduced with aging time. Consequently, the values of damping capacity improved due to the reduction of moduli.

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.

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.

Effect of Ag Content and the Minor Alloying Element Fe on the Mechanical Properties and Microstructural Stability of Sn-Ag-Cu Solder Alloy Under High-Temperature Annealing

This study compares the high-Ag-content Sn-3Ag-0.5Cu with the low- Ag-content Sn-1Ag-0.5Cu solder alloy and the three quaternary solder alloys Sn-1Ag-0.5Cu-0.1Fe, Sn-1Ag-0.5Cu-0.3Fe, and Sn-1Ag-0.5Cu-0.5Fe to understand the beneficial effects of Fe on the microstructural stability, mechanical properties, and thermal behavior of the low-Ag-content Sn-1Ag-0.5Cu solder alloy. The results indicate that the Sn-3Ag-0.5Cu solder alloy possesses small primary β-Sn dendrites and wide interdendritic regions consisting of a large number of fine Ag3Sn intermetallic compound (IMC) particles. However, the Sn-1Ag-0.5Cu solder alloy possesses large primary β-Sn dendrites and narrow interdendritic regions of sparsely distributed Ag3Sn IMC particles. The Fe-bearing SAC105 solder alloys possess large primary β-Sn dendrites and narrow interdendritic regions of sparsely distributed Ag3Sn IMC particles containing a small amount of Fe. Moreover, the addition of Fe leads to the formation of large circular FeSn2 IMC particles located in the interdendritic regions. On the one hand, tensile tests indicate that the elastic modulus, yield strength, and ultimate tensile strength (UTS) increase with increasing Ag content. On the other hand, increasing the Ag content reduces the total elongation. The addition of Fe decreases the elastic modulus, yield strength, and UTS, while the total elongation is still maintained at the Sn-1Ag-0.5Cu level. The effect of aging on the mechanical behavior was studied. After 720 h and 24 h of aging at 100°C and 180°C, respectively, the Sn-1Ag-0.5Cu solder alloy experienced a large degradation in its mechanical properties after both of the aging conditions, whereas the mechanical properties of the Sn-3Ag-0.5Cu solder alloy degraded more dramatically after 24 h of aging at 180°C. However, the Fe-bearing SAC105 solder alloys exhibited only slight changes in their mechanical properties after both aging procedures. The inclusion of Fe in the Ag3Sn IMC particles suppresses their IMC coarsening, which stabilizes the mechanical properties of the Fe-bearing SAC105 solder alloys after aging. The results from differential scanning calorimetry (DSC) tests indicate that the addition of Fe has a negligible effect on the melting behavior. However, the addition of Fe significantly reduces the solidification onset temperature and consequently increases the degree of undercooling. In addition, fracture surface analysis indicates that the addition of Fe to the Sn-1Ag-0.5Cu alloy does not affect the mode of fracture, and all tested alloys exhibited large ductile dimples on the fracture surface.

The influence of a small amount of Al and Ni nano-particles on the microstructure, kinetics and hardness of Sn–Ag–Cu solder on OSP-Cu pads

In order to identify the effect of the addition of Al and Ni nano-particles to Sn–Ag–Cu solder, the interfacial microstructure between the composite solders and Organic Solderability Preservative (OSP)-Cu pads has been investigated as a function of reaction time at various temperatures as well as aging time. Also the hardness of the solder joints was evaluated with the reaction time. In Sn-Ag-Cu-0.5Ni composite solder joints, a scallop-shaped Sn–Ni–Cu intermetallic compound (IMC) layer was clearly observed at the interfaces. However, after long time aging, a very thin Cu3Sn IMC was formed between the Sn–Ni–Cu IMC layer and the OSP-Cu substrate. On the other hand, a layer type Cu6Sn5 and Cu3Sn IMC layers were found at the interfaces in the solder joints containing Al nano-particles. In addition, the Cu3Sn IMC layer thickness was substantially increased with an increase in the aging time. In solder ball regions, very fine Sn–Ni–Cu IMC particles in the Sn-Ag-Cu-0.5Ni composite solder and very fine Sn–Ag–Al IMC particles in the Sn-Ag-Cu-0.5Al composite solder joints were uniformly distributed in the β-Sn matrix as well as the Ag3Sn IMC particles. From kinetic analysis, the calculated activation energies for the Sn–Ni–Cu for the Sn-Ag-Cu-0.5Ni IMC and total (Cu6Sn5+Cu3Sn) IMC layers for Sn-Ag-Cu-0.5Al composite solder joints on OSP-Cu pads were 49.3 and 55.1 kJ/mol, respectively. In addition, solder joints containing Ni nano-particles displayed a higher hardness due to the uniform distribution of fine Sn–Ni–Cu IMC particles. The hardness values of Sn-Ag-Cu-0.5Ni and Sn-Ag-Cu-0.5Al composite solder joints after 5 min reaction at 250 °C were about 16.7 Hv and 16.1 Hv, respectively while, their hardness values after 30 min reaction were about 15.0 Hv and 14.7 Hv, respectively.

Microstructure and Tensile Properties of Sn-1Ag-0.5Cu Solder Alloy Bearing Al for Electronics Applications

This work investigates the effects of 0.1 wt.% and 0.5 wt.% Al additions on bulk alloy microstructure and tensile properties as well as on the thermal behavior of Sn-1Ag-0.5Cu (SAC105) lead-free solder alloy. The addition of 0.1 wt.% Al reduces the amount of Ag3Sn intermetallic compound (IMC) particles and leads to the formation of larger ternary Sn-Ag-Al IMC particles. However, the addition of 0.5 wt.% Al suppresses the formation of Ag3Sn IMC particles and leads to a large amount of fine Al-Ag IMC particles. Moreover, both 0.1 wt.% and 0.5 wt.% Al additions suppress the formation of Cu6Sn5 IMC particles and lead to the formation of larger Al-Cu IMC particles. The 0.1 wt.% Al-added solder shows a microstructure with coarse β-Sn dendrites. However, the addition of 0.5 wt.% Al has a great effect on suppressing the undercooling and refinement of the β-Sn dendrites. In addition to coarse β-Sn dendrites, the formation of large Sn-Ag-Al and Al-Cu IMC particles significantly reduces the elastic modulus and yield strength for the SAC105 alloy containing 0.1 wt.% Al. On the other hand, the fine β-Sn dendrite and the second-phase dispersion strengthening mechanism through the formation of fine Al-Ag IMC particles significantly increases the elastic modulus and yield strength of the SAC105 alloy containing 0.5 wt.% Al. Moreover, both 0.1 wt.% and 0.5 wt.% Al additions worsen the elongation. However, the reduction in elongation is much stronger, and brittle fracture occurs instead of ductile fracture, with 0.5 wt.% Al addition. The two additions of Al increase both solidus and liquidus temperatures. With 0.5 wt.% Al addition the pasty range is significantly reduced and the differential scanning calorimetry (DSC) endotherm curve gradually shifts from a dual to a single endothermic peak.

Microstructure, mechanical, and thermal properties of the Sn–1Ag–0.5Cu solder alloy bearing Fe for electronics applications

This work investigates the effect of Fe addition on the microstructural, mechanical, and thermal properties of the Sn–1Ag–0.5Cu (SAC105) solder alloy. The addition of Fe leads to the formation of large circular FeSn2 intermetallic compound (IMC) particles, which produce a weak interface with the β-Sn matrix. The addition of Fe also leads to the inclusion of Fe in the Ag3Sn and Cu6Sn5 IMC particles. Moreover, Fe-bearing solders have been shown to form large primary β-Sn grains. The weak interface between the large FeSn2 IMC particles and the β-Sn matrix together with the presence of the large primary β-Sn grains results in a significant reduction on the elastic modulus and yield strength of the Fe-bearing solders. Moreover, the improved plasticity of the large primary β-Sn grains causes the Fe-bearing solders to exhibit large total elongation. The addition of Fe also significantly reduces the effect of aging. After aging at 100°C and 180°C, it has been observed that the Fe-bearing solders significantly suppress the coarsening of the Ag3Sn IMC particles; consequently, they exhibit stable mechanical properties. This effect can be attributed to the inclusion of Fe in the Ag3Sn IMC particles. In addition, fracture surface analysis indicates that the addition of Fe to the SAC105 solder alloy does not affect the mode of fracture, and all tested solders exhibited large ductile-dimples on the fracture surface. Moreover, the addition of Fe did not produce any significant effect on the melting behavior. As a result, the use conditions of the Fe-bearing solders are consistent with the conditions for conventional Sn–Ag–Cu solder alloys.

Novel Fe-containing Sn–1Ag–0.5Cu lead-free solder alloy with further enhanced elastic compliance and plastic energy dissipation ability for mobile products

This work investigates the effects of small additions (0.1 and 0.3wt.%) of Fe on the microstructure, mechanical, and thermal properties of the Sn–1Ag–0.5Cu (SAC105) solder alloy. The addition of Fe leads to the formation of large FeSn2 intermetallic compound (IMC) particles located in the eutectic regions besides the small Ag3Sn and Cu6Sn5 IMC particles. Fe-bearing solders have also been shown to form large primary β-Sn grains. The formation of large FeSn2 IMC particles, together with the presence of large primary β-Sn grains have resulted in a significant reduction on the elastic modulus and yield strength. Moreover, the presence of large primary β-Sn grains causes the Fe-bearing solders to maintain the total elongation at the SAC105 level. This effect can increase the elastic compliance and plastic energy dissipation ability of the bulk solder, which play an important role in drop impact performance enhancement. The addition of Fe did not produce any significant effect on the melting behavior. As a result, the use conditions of the Fe-bearing solders are consistent with the conditions for conventional Sn–Ag–Cu solder alloys.

Correlation between displacement rate and shear force in shear test of Sn–Pb and lead free solder joints

An experimental investigation was combined with a non-linear finite element analysis using an elastic–viscoplastic constitutive model to study the effect of ball shear speed on the shear forces of ball grid array (BGA) solder joints. Two solder compositions were examined in the present work: Sn–37Pb and Sn–3·5Ag. Within the Sn–3·5Ag solder, Ag3Sn intermetallic compound particles were found. For both types of solder used, a Ni3Sn4 intermetallic compound layer was observed at the interface between the nickel plated layer and solder, while a gold layer appeared to have dissolved into the liquid solder leaving no observable gold at the interface. The shear force was observed to increase linearly with increasing shear speed and reached a maximum value at the highest shear speed in both the experimental and the computational results. All test specimens fractured in a ductile mode. The failure mechanisms are discussed in terms of von Mises stresses and plastic strain energy density distributions.