Composite Solder Joints Research Articles

Shear deformation behavior and failure mechanisms of graphene reinforced Sn-based solder joints bonded by transient current

Graphene as a reinforcement is expected to improve the shear strength of solder joint. However, little is known about the deformation behavior and mechanisms of composite solder joints. In this study, sandwich joints are prepared using graphene nanosheets-reinforced Sn-Ag-Cu composite solder (GNSs/SAC) by transient current bonding technology in order to obtain dispersed graphene. Interrupted shear tests combined with orientation image microscopy are conducted at different strain to observe the morphology and crystal orientation evolution of solder joints in situ. Some twins rotate, and the orientation begins to spread during shear, while the orientation of large Sn grain shows a minimal change. Cracks tend to initiate and propagate along the boundary. The failure mechanisms of the solder joint is determined. Molecular dynamics results show that the strain concentration at the boundary. Continuous shear tests show that the shear strength was improved by approximately 50.7% with the addition of 0.1 wt% graphene. Based on microstructure analysis and calculation, load transfer is identified as the dominant strengthening mechanism for GNSs/SAC alloys, followed by Orowan system. Graphene does not refine the grain size of solder joints, and dislocation multiplication from thermal mismatch does not strengthen them.

Suppression of Sn whisker growth from SnAgCu solder alloy with TiO2 and ZnO reinforcement nano-particles by increasing the corrosion resistance of the composite alloy

The main joining process of the electronic industry is still soldering with different alloys of Sn. This work studied the relationship between Sn whisker growth and corrosion resistance of 99Sn0.3Ag0.7Cu–TiO2/ZnO (0.25wt%) composite solder alloys in a corrosive environment via scanning electron microscopy and focused ion beam techniques. The corrosive environment test showed that the application of TiO2 and ZnO nano-particles almost totally suppressed the Sn whisker growth and improved the corrosion resistance of the composite solder alloys compared to the reference 99Sn0.3Ag0.7Cu alloy. The microstructural analysis of the reference 99Sn0.3Ag0.7Cu solder alloy showed that the volumetric increase of the corroded β-Sn grains resulted in local mechanical stress in the solder joints, which was released by Sn whisker development. However, in the composite solder joints, the increased grain boundary fraction and segregation of the TiO2 and ZnO nano-particles to the grain boundaries resulted in a relatively uniform and compact protective oxide layer at the β-Sn grain boundaries. This suppressed the formation of SnOx, and via this, the corrosion-induced whisker growth.

Interface reaction and mechanical properties of Sn58Bi-XCr/Cu30Zn (Cu7Sn) solder joints under isothermal aging conditions

The interfacial reaction and mechanical properties of Sn58Bi-XCr/Cu30Zn and Sn58Bi-XCr/Cu7Sn (X = 0, 0.1, 0.2, 0.3 wt%) composite solder joints were investigated under 100 °C isothermal aging. The results show that the growth rate of intermetallic compound layer (IMCs) of Sn58Bi-XCr/Cu30Zn composite solder joint is faster than that of Sn58Bi-XCr/Cu7Sn composite solder joint, and the rapid growth of IMCs decreases the mechanical properties of the solder joint. As the aging time increases, the thickness of IMCs layer becomes thicker and the mechanical properties decrease. The addition of Cr inhibits the interdiffusion of atoms at the interface. The addition of Zn/Sn reduces the consumption of Sn and thus reduces the segregation of Bi phase. The Bi segregation at the interface of Sn58Bi-0.2Cr/Cu30Zn and Sn58Bi-0.2Cr/Cu7Sn composite solder joints is improved obviously. In addition, the comprehensive mechanical properties of Sn58Bi-XCr/Cu30Zn composite solder joint are higher than those of Sn58Bi-XCr/Cu7Sn composite solder joint. With the extension of aging time, mechanical strength increases first and then decreases. Among them, the mechanical strength of Sn58Bi-0.2Cr/Cu30Zn and Sn58Bi-0.2Cr/Cu7Sn composites is superior to other alloys. The fracture morphology of solder joints changes from brittle fracture mechanism to ductile-brittle fracture mechanism.

Mechanical, photoelectric and thermal reliability of SAC307 solder joints with Ni-decorated MWCNTs for flip-chip LED package component during aging

PurposeThis study aims to study the mechanical, photoelectric, and thermal reliability of SAC307 solder joints with Ni-decorated MWCNTs for flip-chip light-emitting diode (LED) package component during aging. By adding nanoparticles (Ni-multi-walled carbon nanotubes [MWCNTs]) to the solder paste, the shear strength and fatigue resistance of the brazed joint can be improved. However, the aging properties of Ni-modified MWCNTs composite solder joints have not been deeply studied. In this research, the mechanical, photoelectric and thermal reliability of SAC307 packaged flip-chip LEDs with Ni-MWCNTs added during aging were studied.Design/methodology/approachCompared with SAC solder alloys, the effects of different contents (0, 0.05, 0.1 and 0.2 Wt.%) of Ni-MWCNTs on the photoelectric and thermal properties of composite solder joints were examined. To study the aging characteristics of composite solder joints, the solder joints were aged at 85°C/85% relative humidity.FindingsThe addition of an appropriate amount of reinforcing agent Ni-MWCNTs reduces the density of the composite solder to 96% of the theoretical value of the SAC solder alloy. In addition, the microhardness increases and the wetting angle decreases. Two different phase compositions were observed in the solder joints with Ni-MWCNTs reinforcement: Cu3Sn and (Cu, Ni)6Sn5. The solder joints of SAC307-0.1Ni-MWCNTs exhibit the highest luminous flux and luminous efficiency of flip-chip LED filaments, the lowest steady-state voltage and junction temperature. And with the extension of the aging time, its aging stability is the best. In short, when the addition amount of Ni-MWCNTs is 0.1 Wt.%, the solder joints exhibit the best wettability and the thinnest intermetallic compound layer. And the shear strength of the tested solder joints is the best, and the void ratio is the lowest. At this time, the enhancement effect of Ni-MWCNTs on the composite solder has been best demonstrated.Research limitations/implicationsThe content range of enhancer Ni-MWCNTs needs to be further reduced.Practical implicationsThe authors have improved the performance of Ni-modified MWCNTs composite solder joints.Originality/valueComposite solder with high performance has great practical application significance for improving the reliability and life of the whole device.

Microstructural Evolution of Cu/Sn-58Bi/Sn-3.0Ag-0.5Cu Composite Solder Joint during Isothermal Aging

A composite solder joints made of Cu/Sn-58Bi/Sn-3.0Ag-0.5Cu (in weight percent) was successfully fabricated. The composite solder was made from combining a Sn-3.0Ag-0.5Cu solder ball and Sn-58Bi solder paste. The composite solder was reflowed on Cu-OSP (copper-organic solderability preservatives) substrate to form a composite solder joint. The microstructure evolution of the composite solder joints under different reflow temperature and thermal aging conditions were investigated using an optical microscope. This study shows that a composite solder joint of SAC305/Sn-58Bi can be assembled at lower temperature (160 °C) and gradually mixed through isothermal aging.

Microstructural and compositional evolution of SAC305/TiN composite solder under thermal stressing

PurposeThe purpose of this paper is to investigate the effect of titanium nitride (TiN) on microstructure and composition of 96.5Sn3Ag0.5Cu (SAC305) lead-free solder joints under a large temperature gradient.Design/methodology/approachIn this paper, SAC305 lead-free composite solder containing 0.05 Wt.% TiN was prepared by powder metallurgy method. A temperature gradient generator was designed and the corresponding samples were also prepared. The microstructural evolution, internal structure and elemental content of SAC305 and SAC305/TiN solder joints before and after thermal loading were comparatively studied.FindingsThe experimental results show that the addition of the TiN reinforcing phase can effectively inhibit the diffusion and migration of copper atoms and, therefore, affect the distribution of newly formed Cu-Sn IMC in solder joints under the condition of thermal migration (TM). Compared with the SAC305 solder joint, the interconnection interface and internal structure of the composite solder joint after 600 h of TM are also relatively complete.Originality/valueThe TiN reinforcing phase is proven effective to mitigate the TM behavior in solder joints under thermal stressing. Specifically, based on the observation and analysis results of microstructure and internal structure of composite solder joint, the TiN particle can change the temperature gradient distribution of the solder joint, so as to suppress the diffusion and migration of Sn and Cu atoms. In addition, the results of Micro-CT and compositional analysis also indicate that the addition of TiN reinforcement is very helpful to maintain the structural integrity and the compositional stability of the solder joint. Different from other ceramic reinforcements, TiN has good thermo- and electro-conductivity and the thermal-electrical performance of composite solder will not be significantly affected by this reinforcement, which is also the main advantage of selecting TiN as the reinforcing phase to prepare composite solder. This study can not only provide preliminary experimental support for the preparation of high reliability lead-free composite solder but also provide a theoretical basis for the subsequent study (such as electro-thermo distribution in solder joints), which has important application significance.

Microstructure and shear property of Ni-coated carbon nanotubes reinforced InSn-50Ag composite solder joints prepared by transient liquid phase bonding

InSn-50Ag composite solder joints doping Ni-coated carbon nanotubes (Ni-CNTs) were fabricated by transient liquid phase (TLP) bonding, and then the effect of Ni-CNTs contents (x = 0, 0.01, 0.03, 0.05, 0.07, 0.1 wt%) on the microstructure and shear property of the composite solder joints was examined. The results showed that the microstructure of Cu/InSn-50Ag-x(Ni-CNTs)/Cu composite solder joints consisted of the interfacial region bamboo-type Cu3(In, Sn), solder center region Ag3In, Ni3Sn4, Ag particles and Ni-CNTs. The appropriate amounts of Ni-CNTs (about 0.07 wt%) are conducive to form a compact composite solder joint and restrain the growth of interfacial Cu3(In, Sn) IMC layer, and the morphologies of IMC layer are determined by Ni-CNTs suppressing atom diffusion and IMC grain orientation. The shear strength of composite solder joints relates to Ni-CNTs content, and the maximum shear strength reaches 42 MPa of Cu/InSn-50Ag-0.07(Ni-CNTs)/Cu. It is regulated by uniform distribution of Ni-CNTs, refined Ag3In grains and interface IMC layer with near-continuous voids. The fracture of the composite solder joints doped Ni-CNTs occurred near to the boundary between the interfacial IMC layer and solder center region, the fracture mechanism is ductile fracture.

Effects of rare earth Ce addition on the microstructure and shear property of Cu/In-50Ag/Cu composite solder joint

The microstructure and shear property of Cu/In-50Ag-xCe/Cu (x = 0, 0.3, 0.6, 1.2, 2 wt%) composite solder joints fabricated by transient liquid phase (TLP) bonding were investigated. The results showed that the appropriate amount of Ce particles refined the microstructure in the Cu/In-50Ag/Cu solder joint, and inhibited Cu2In phase formation at the Cu/solder interface. The refined Ag2In phases contribute to suppressing the formation of microstructural defects. The Ce particles can improve the microstructure uniformity of composite solder joint, the porosity of Cu/In-50Ag-0.6Ce/Cu solder joint is only 1.05%, and the excessive (1.2–2 wt%) Ce particles are harmful to the composite solder joints. Doping 0.3–0.6 wt% Ce particles can improve the shear strength of composite solder joints by reducing microstructural defects, refining Ag2In phases and improving the phase boundaries strength. The maximum shear strength value of the Cu/In-50Ag-0.6Ce/Cu composite solder joint reaches 17.58 MPa. The fracture mechanism is mainly brittle fracture, which occurs near the in-situ reaction zone. The Cu/In-50Ag-0.6Ce/Cu composite solder joint fabricated by TLP bonding with finer microstructure and higher mechanical properties is acceptable.

Impact of different aging conditions on the IMC layer growth and shear strength of Ni-modified MWCNTs reinforced Sn-Ag-Cu composite solder

PurposeThe purpose of this paper is to develop a new composite solder to improve the reliability of composite solder joints. Nano-particles modified multi-walled carbon nanotubes (Ni-MWCNTs) can indeed improve the microstructure of composite solder joints and improve the reliability of solder joints. Although many people have conducted in-depth research on the composite solder of Ni-MWCNTs. However, no one has studied the performance of Ni-MWCNTs composite solder under different aging conditions. In this article, Ni-MWCNTs was added to Sn-Ag-Cu (SAC) solder, and the physical properties of composite solder, the microstructure and mechanical properties were evaluated.Design/methodology/approachIn this study, the effect of different aging conditions on the intermetallic compound (IMC) layer growth and shear strength of Ni-modified MWCNTs reinforced SAC composite solder was studied. Compared with SAC307 solder alloy, the influence of Ni-MWCNTs with different contents (0, 0.1 and 0.2 Wt.%) on composite solder was examined. To study the aging characteristics of composite solder joints, the solder joints were aged at 80°C, 120°C and 150°C.FindingsThe experimental results show that the content of Ni-MWCNTs affects the morphology and growth of the IMC layer at the interface. The microhardness of the solder increases and the wetting angle decreases. After aging at moderate (120°C) and high temperature (150°C), the morphology of the Cu6Sn5 IMC layer changed from scallop to lamellar and the grain size became coarser. The following two different phase compositions were observed in the solder joints with Ni-MWCNTs reinforcement: Cu3Sn and (Cu, Ni)6Sn5. The fracture surface of the solder joints all appeared ductile dents, and the size of the pits increased significantly with the increase of the aging temperature. Through growth kinetic analysis, Ni-modified MWCNTs in composite solder joints can effectively inhibit the diffusion of atoms in solder joints. In short, when the addition amount of Ni-MWCNTs is 0.1 Wt.%, the solder joints exhibit the best wettability and the highest shear strength.Originality/valueIn this study, the effects of aging conditions on the growth and shear strength of the IMC layer of Ni modified MWCNTs reinforced SAC307 composite solder were studied. The effects of Ni MWCNTs with different contents (0, 0.1 and 0.2 Wt.%) on the composite solder were examined.

Interfacial reaction and mechanical properties of Sn58Bi-XCr solder joints under isothermal aging conditions

Sn–Bi solder is considered a promising lead-free solder which meets the performance requirements with the advantages of low melting point, good wettability and mechanical properties. The interfacial reaction and mechanical properties of Sn58Bi-XCr (X = 0, 0.1, 0.2, 0.3) composite solder joints have been studied. After isothermal aging treatment at 100 °C, the microstructure and reaction mechanism of the interface were analyzed. The results show that the microstructure of Sn58Bi composite solder joint with 0.2wt.% Cr element is obviously refined. At the same time, the average thickness of the interface intermetallic compounds (IMCs) becomes thinner with the addition of Cr content. In addition, the tensile strength of Sn58Bi composite solder joint decreases gradually with the extension of aging time, but the tensile property of Sn58Bi-0.2Cr is better than that of other alloy components. However, with the extension of aging time, the shear strength of Sn58Bi composite solder joints generally decreases at first and then increases, and the fracture morphology of solder joints changes from brittle fracture mechanism to ductile fracture mechanism.

Effect of transient current bonding on interfacial reaction in Ag-coated graphene Sn–Ag–Cu composite solder joints

To address the problem of floating and aggregation of Ag–GNSs in the molten pool during the traditional reflow soldering process, Cu/SAC/Ag–GNSs/Cu sandwich joints were prepared under an applied current density (1.0×104 A/cm2) for a few hundred milliseconds to produce Ag-coated graphene-reinforced Sn–Ag–Cu (SAC/Ag– GNSs) solder joints. The experimental results showed that Ag–GNSs were homogenously dispersed in the solder joints, providing more Cu6Sn5 grain nucleation sites, which refined these grains and reduced the thickness difference at the anode and cathode. In addition, the Cu6Sn5 morphology changed from rod-like to plate-shaped because of the uniform distribution of Ag–GNSs and constitutional supercooling. The significantly increased shear strength of the transient current bonding and the change in the fracture mechanism were due to the uniformly distributed Ag–GNSs and the microstructural changes.

Interfacial IMC evolution and shear strength of MWCNTs-reinforced Sn–5Sb composite solder joints: Experimental characterization and artificial neural network modelling

Abstract The continuous miniaturization of electronic products and the constantly rising functionality demand by final users necessitate major challenges for the academia and the industry to produce reliable lead-free solders for long-term service. In the present study, an analysis on the influence of MWCNTs (multi-walled carbon nanotubes) on the interfacial IMC (intermetallic compound) evolution and shear strength of Sn–5Sb solder joint was performed. The composite solder joint samples were developed through the reflow soldering process and thereafter subjected to isothermal aging at different temperatures (120 °C, 150 °C and 170 °C). Given the promising properties of MWCNTs, empirical findings showed that inhibited interfacial IMC evolution and enhanced shear strength were markedly achieved due to the presence of MWNCTs in the Sn–5Sb solder alloy. Artificial neural network (ANN) model was developed by making use of the experimental data to characterize the composite solder joints. Various influential parameters that affect the thickness of the IMC layer and the shear strength performance of the composite solder joints including the MWCNTs content, aging temperature and aging time were considered as the input parameters for the ANN model. Having used the statistical parameters such as the coefficient of determination (R2) and root mean square error (RMSE) to evaluate the model, the ANN model developed in this study adequately predicted the IMC layer thickness (R2 = 0.9913; RMSE = 0.0234) and shear strength (R2 = 0.9798; RMSE = 0.0314) of the composite solder joints.

Effect of isothermal ageing on the microstructure, shear behaviour and hardness of the Sn58Bi/SnAgCuBiNi/Cu solder joints

ABSTRACT The microstructure, shear behaviour and hardness of the SnBi/SACBN/Cu solder joint before and after isothermal ageing were investigated in comparison with the SnBi/Cu and SACBN/Cu solder joints. The experimental results indicated that the pre-soldered SACBN joint had a significant effect on the formation and growth of the β-Sn grains in the SnBi bulk solder. The brittleness of the SnBi/SACBN/Cu composite solder joint was also suppressed and its failure mode transformed from brittle failure to brittle-ductile failure after reflow. However, the shear strength and failure mode of the SnBi/SACBN/Cu composite solder joint became similar to those of the SnBi/Cu joints after 600 h isothermal ageing. The shear strength of the three kinds of solder joints decreased after isothermal ageing, but the SnBi/SACBN/Cu composite solder joint showed higher shear strength than SnBi/Cu did during ageing. The shear strength of the composite solder joint was 67.1MPa after ageing. Due to the diffusion of elements in the isothermal ageing process, the microstructure of the composite solder joint was significantly coarsened after ageing for 600 hours. This phenomenon further led to the decrease of the hardness and shear strength of the three kinds of solder joints.

Study on the microstructure and mechanical property of Cu-foam modified Sn3.0Ag0.5Cu solder joints by ultrasonic-assisted soldering

Cu-foam sheets with the thicknesses of 0.15 mm and 0.5 mm were utilized as strengthening structure to improve the performances of the Sn3.0Ag0.5Cu (SAC305)/Cu solder joints. The ultrasonic-assisted soldering was applied to manufacture the solder joints. The effects of Cu-foam and ultrasound-assisted soldering time on microstructure and mechanical property of solder joints were researched. Experimental results showed that excellent metallurgical bonding was generated between the copper substrate and the Cu-foam/SAC305 composite solder layer. The average thickness of interfacial intermetallic compound (IMC) layer decreased with the increase of ultrasonically soldering time, and a thinner interfacial IMC layer was found in the joints with ultrasonic treatment in narrow channels. With the ultrasonic soldering time prolonged, the Cu 6 Sn 5 grains became more refined. Some round-shape Cu 6 Sn 5 grains were transformed into hexagonal prismatic with the increase of the ultrasonic soldering time. The shear test was conducted for the solder joints under different soldering conditions. It was found that the shear strength of the Cu-foam/SAC305 composite solder joints were higher than that of SAC305 solder joints. The grain refinement caused by ultrasonic cavitation significantly improved the shear strength of the solder joints. Besides, the fracture behavior of solder joints without ultrasonic vibration was classified to be ductile-brittle mixed type while that with ultrasonic vibration was changed to be ductile type.

Influence of porous Cu interlayer on the intermetallic compound layer and shear strength of MWCNT-reinforced SAC 305 composite solder joints

In this study, the synergetic effect of multi-walled carbon nanotubes (MWCNTs) and porous Cu interlayer (PCI) on the intermetallic compound (IMC) formation and shear strength of Sn–3.0Ag–0.5Cu (SAC 305) solder system was investigated. The solder joints were prepared by subjecting two different series of MWCNTs-reinforced SAC 305 solder systems (i.e., SAC–0.01CNT and SAC–0.04CNT) sandwiched with porous Cu interlayer having pores per inch (PPI) of 15, 25 and 50 to reflow soldering on Cu substrate. Electron microscopy and spectroscopy techniques were used to view and detect the intermetallic compound phases, respectively. The scallop-shaped Cu6Sn5 IMC phase was observed at the solder/PCI interface, while on the other hand, an additional layer-type Cu3Sn IMC phase formed alongside the Cu6Sn5 IMC at the solder/Cu interface. Given the promising properties of PCI material, empirical findings showed that the presence of PCI in the solder joint inhibited the formation of interfacial IMC layer at the solder/Cu substrate with the SAC–0.01CNT–25PCI exhibiting the least IMC thickness. More so, the PCI material effectively enhanced the shear strength of the MWCNTs-reinforced composite solder joints. Generally, the strengthening capacity of the PCI material was greatly underscored in the SAC–0.01CNT–xPCI series with the sample prepared with PCI of 15 PPI demonstrating the superior shear strength of 21.1 MPa.

Stabilized Interfacial Intermetallic Compound Evolution in Ni-Coated Carbon Fiber Reinforced Sn-3.5Ag Composite Solder Joint

Stabilized Interfacial Intermetallic Compound Evolution in Ni-Coated Carbon Fiber Reinforced Sn-3.5Ag Composite Solder Joint

Performance of 96.5Sn–3Ag–0.5Cu/fullerene composite solder under isothermal ageing and high-current stressing

Purpose The purpose of this paper is to investigate the effect of fullerene (FNS) reinforcements on the microstructure and mechanical properties of 96.5Sn3Ag0.5Cu (SAC305) lead-free solder joints under isothermal ageing and electrical-migration (EM) stressing. Design/methodology/approach In this paper, SAC305 solder alloy doped with 0.1 Wt.% FNS was prepared via the powder metallurgy method. A sandwich-like sample and a U-shaped sample were designed and prepared to conduct an isothermal ageing test and an EM test. The isothermal ageing test was implemented under vacuum atmosphere at 150°C, whereas the EM experiment was carried out with a current density of 1.5 × 104 A/cm2. The microstructural and mechanical evolutions of both plain and composite solder joints after thermal ageing and EM stressing were comparatively studied. Findings A growth of Ag3Sn intermetallic compounds (IMCs) in solder matrix and Cu-Sn interfacial IMCs in composite solder joints was notably suppressed under isothermal ageing condition, whereas the hardness and shear strength of composite solder joints significantly outperformed those of non-reinforced solder joints throughout the ageing period. The EM experimental results showed that for the SAC305 solder, the interfacial IMCs formulated a protrusion at the anode after 360 h of EM stressing, whereas the surface of the composite solder joint was relatively smooth. During the stressing period, the interfacial IMC on the anode side of the plain SAC305 solder showed a continuous increasing trend, whereas the IMC at the cathode presented a decreasing trend for its thickness as the stressing time increased; after 360 h of stressing, some cracks and voids had formed on the cathode side. For the SAC305/FNS composite solder, a continuous increase in the thickness of the interfacial IMC was found on both the anode and cathode sides; the growth rate of the interfacial IMC at the anode was higher than that at the cathode. The nanoindentation results showed that the hardness of the SAC305 solder joint presented a gradient distribution after EM stressing, whereas the hardness data showed a relatively homogeneous distribution in the SAC305/FNS solder joint. Originality/value The experimental results showed that the FNS reinforcement could effectively mitigate the failure risk in solder joints under isothermal ageing and high-current stressing. Specifically, the FNS particles in solder joints can work as a barrier to suppress the diffusion and migration of Sn and Cu atoms. In addition, the nanoidentation results also indicated that the addition of the FNS reinforcement was very helpful in maintaining the mechanical stability of the solder joint. These findings have provided a theoretical and experimental basis for the practical application of this novel composite solder with high-current densities.

Microstructure evolution and hardness of MWCNT-reinforced Sn-5Sb/Cu composite solder joints under different thermal aging conditions

In this work, multi-walled carbon nanotubes (MWCNTs) reinforced Sn-5Sb/Cu composite solder joints were synthesized and the effects of MWCNTs addition on the microstructure evolution and hardness of the Sn-5Sb solder alloy during various thermal aging conditions were investigated. After conducting a thorough microstructural analysis, the SbSn and Cu6Sn5 intermetallic compounds (IMCs) were observed in the β-Sn matrix of the composite solder joints subjected to reflow soldering while the latter was also present at the solder/Cu interface. However, after subjecting the composite solder joints to isothermal aging, the Cu3Sn IMC emerged between the Cu6Sn5 IMC at the solder/Cu interface and the Cu substrate. With the promising properties exhibited by MWCNTs as a reinforcement material, experimental results showed that MWCNTs refined the bulk solder microstructure and inhibited growth of the interfacial IMC layer in the Sn-5Sb-xCNT/Cu samples. In general, the composite sample reinforced with 0.05 wt% MWCNTs showed the least IMC layer thickness and diffusion coefficient in the ranges of 2.6–11.99 μm and 1.07 × 10−14-14.9 × 10−14 cm2/s respectively. Meanwhile, the strengthening mechanism triggered by MWCNTs addition was clearly evident in the MWCNT-reinforced Sn-5Sb/Cu as superior hardness values within a range of 20.6–15.3 HV were registered for the as-soldered and aged composite solder joints with 0.05 wt% MWCNTs reinforcement.

Microstructural, compositional and hardness evolutions of 96.5Sn–3Ag–0.5Cu/TiC composite solder under thermo-migration stressing

A 96.5Sn3Ag0.5Cu (SAC305) lead-free composite solder containing 0.1 wt% titanium carbide (TiC) was prepared using the powder metallurgy method and a thermal migration (TM) experiment was then carried out. A temperature gradient generating device was designed and a TM sample with an asymmetric sandwich structure was prepared in order to achieve this. The microstructure, the composition and the mechanical properties of both the SAC305 and SAC305/TiC solder joints were investigated under a temperature gradient of 1070 K/cm that was generated by the TM device that had been designed. The results showed that the addition of a TiC reinforcing phase was able to effectively inhibit both the diffusion and migration of the Cu atoms, and that this affected the distribution of the Cu6Sn5 intermetallic compounds (IMC) under the thermal migration conditions in the solder joint. It has also been shown that, compared with the plain SAC305 solder joint, the interconnect interface of the composite solder joint was relatively intact after 600 h of thermal loading. The results of the nanoindentation test also showed that the addition of the TiC reinforcing phase was able to significantly weaken the distribution gradient of the hardness of the solder joint caused by element migration.

Microstructural and shear strength properties of RHA-reinforced Sn–0.7Cu composite solder joints on bare Cu and ENIAg surface finish

In this study, the joint effect of rice husk ash (RHA) reinforcement as an alternative silica source and electroless nickel immersion silver (ENIAg) surface finish on the intermetallic compound (IMC) formation and shear strength of the Sn–0.7Cu solder system was investigated. A series of plain and composite lead-free solder systems (Sn–0.7Cu−xRHA; x = 0, 0.01, 0.05 and 0.1 wt%) was successfully developed and subjected to reflow soldering on bare Cu and ENIAg surface finish. After conducting a comprehensive microstructural study using the scanning electron microscopy and energy dispersive spectroscopy techniques, the Cu6Sn5 and Cu3Sn intermetallic compound (IMC) phases were observed at the interface of the Sn–0.7Cu−xRHA/Cu composite solder joints. On the other hand, the (Cu,Ni)6Sn5 and Ni3Sn4 IMC phases dominated the interface of the Sn–0.7Cu−xRHA/ENIAg counterparts. Given the promising potential of the ENIAg surface finish, the Sn–0.7Cu−xRHA/ENIAg exhibited IMC thickness values within a range of 3.81–4.74 µm as compared to the 6.13–9.3 µm range exhibited by the Sn–0.7Cu−xRHA/Cu counterpart. More so, the ENIAg surface finish was effective in improving the shear strength of the plain solder joint, with the Sn–0.7Cu/ENIAg exhibiting 13.44 MPa relative to the 11.5 MPa exhibited by the Sn–0.7Cu/Cu counterpart. Overall, the strengthening effect of the RHA reinforcement was well marked in the Sn–0.7Cu−xRHA/Cu composite solder joints with the composite having 0.1 wt% RHA exhibiting the highest shear strength (14.6 MPa) across the board.