Soldering Seam Research Articles

Interfacial reaction and strengthening mechanism of thermo-compression bonding foam Ni reinforced SAC105 and SAC105–0.3Ti solder joints

The foam Ni holds great potential as a reinforcement phase, attributed to its distinctive three-dimensional (3D) continuous structure. In this study, high-strength Cu connections were produced by vacuum thermo-compression bonding using Ni foam reinforced SAC105 and SAC105–0.3Ti solders. The microstructure, interfacial morphology and shear strength of the connections with different Ni foam composite solders were systematically examined. The results demonstrate that the incorporation of Ni foam as a reinforcing phase substantially enhances the strength of SAC105 solder. The introduction of foam Ni resulted in the formation of a prismatic (Cu, Ni)6Sn5 phase in the matrix and altered the composition of the IMC layer. As the bonding time increased, (Cu, Ni)6Sn5 further grew in the matrix and formed a double interpenetration structure with the foam Ni. The IMC layer, composed of (Cu, Ni)6Sn5 and Cu3Sn, exhibited a random orientation. The Cu/SAC105–0.3Ti-Foam Ni/Cu joints bonded for 10 min exhibited the highest shear strength of 70.23 MPa. Shearing failure predominantly occurs within the soldering seam. The double interpenetration structure and the random orientation of the interfacial IMC impeded crack propagation, thereby significantly enhancing the strength of the Cu joints.

Study on the properties of low silver Sn1.0Ag0.5Cu composite solder reinforced with nickel-plated zinc oxide and its soldering joint

Based on the preparation of nickel-plated zinc oxide (Ni-ZnO) by pyrolysis-reduction method, low silver Sn1.0Ag0.5Cu lead-free composite solders reinforced with Ni-ZnO were prepared by the powder metallurgy method, and the microstructure and properties of the soldering joints were investigated accordingly. The results showed that the particle size of ZnO was reduced after ball milling. The Ni-ZnO reinforcement phase was successfully prepared by pyrolysis-reduction method, in which Ni particles with an average particle size of 9.7 nm were uniformly and densely deposited on the surface of ZnO particles, and the interface between ZnO (002) and Ni (111) showed a semi-coherent relationship with a mismatch of 0.203. The moderate addition of Ni-ZnO had little effect on the electrical conductivity of the Sn1.0Ag0.5Cu composite solders reinforced with Ni-ZnO. But it refined the primary β-Sn grains in the composite solders and improved the wettability and tensile strength of the composite solders. At an addition of 1.0 wt% Ni-ZnO reinforcement phase, the tensile strength and shear strength of the composite solder and its soldering joint reached a maximum value of 41.8 MPa and 28.9 MPa, with an increase of 39.3 % and 41.7 % respectively compared to the base solder material. The fracture position of composite solder/Cu soldering joint occurred in the transition zone of the soldering seam and IMC (Intermetallic Compound) layers. With the increase of Ni-ZnO reinforcement phase addition, the shear fracture location of the soldering joint moved from the near copper substrate side to the near soldering seam side in the transition zone, and the fracture mode gradually changed from a mixed ductile-brittle fracture to a typical ductile fracture dominated by parabolic toughness dimples.

Evolution behavior of cavitation bubble in pure Sn liquid medium with narrow gap under low-amplitude ultrasound

In this study, a numerical model of cavitation bubble in the narrow-gap pure Sn liquid medium was established by two-dimensional compressible multiphase flow simulation. The effects of the pressure amplitude and the gap size on the shape, size and position of the cavitation bubble were investigated. The calculation results showed that the cavitation bubble in the narrow-gap soldering seam could exist stably after experiencing two stages of the nonlinear oscillation and the near-wall oscillation with the low-amplitude ultrasound and moved directionally on the metal substrate surface. When the pressure amplitude increased or the gap size decreased, the directional motion rate of the cavitation bubble increased and the shape of the bubble was elliptical due to the confinement effect of the substrate wall. The ultrasonic degassing mechanism of the narrow-gap soldering seam under the action of exponential decay ultrasonic vibration was analyzed by comparing the fluid pressure and velocity field variations. The flow field in the center of the soldering seam vibrated stronger than that of the peripheral regions, which could promote the outward motion of the cavitation bubble. Within the calculation time of 0.002 s, the maximum horizontal motion distance of bubble in the narrow-gap soldering seam was 1.13 mm.

Study on Microstructure and Mechanical Properties at Constant Electromigration Temperature of Sn2.5Ag0.7Cu0.1RE0.05Ni-GNSs/Cu Solder Joints

To solve the electromigration problem of micro-electronic connection solder joints, an ideal electromigration tester was designed, and the thickness of the intermetallic compounds (IMCs), average void diameter, grain orientation, failure, shear strength, and fracture path of Sn2.5Ag0.7Cu0.1RE0.05Ni-GNSs/Cu solder joints under constant-temperature electromigration were studied. The results indicate that the solder joints show evidence of typical electromigration polarity in the asymmetric growth of interfacial IMCs on the anode and cathode sides under the conditions of a current density ≥7 × 103 A/cm2 and an included angle between the c-axis of the β-Sn grains and the current direction θ ≤ 53.2°. The anode-side interfacial IMC is dominated by a Cu6Sn5 phase with a gradually increasing thickness, forming a Cu3Sn phase and showing evidence of microcracks. The Cu6Sn5 phase of the cathode-side interfacial IMC is gradually completely dissolved, and the growth of the Cu3Sn phase is accompanied by the formation of Kirkendall voids. The anisotropic diffusion of Cu atoms in the β-Sn of the micro-solder joints causes increased solder joint resistance and reduced shear strength. The shear fracture path of the solder joints moves from the cathode side near the IMC solder seam to the Cu3Sn interface. The shear fracture mechanism changes from ductile transgranular fracture dominated by β-Sn dimples to brittle fracture dominated by interfacial IMC cleavage and slip steps.

Properties of Cu/Zn+15%SAC0307+15%Cu/Al joints by different ultrasonic-assisted degrees

PurposeThis paper aims to investigate the effects of different ultrasonic-assisted loading degrees on the microstructure, mechanical properties and the fracture morphology of Cu/Zn+15%SAC0307+15%Cu/Al solder joints.Design/methodology/approachA new method in which 45 μm Zn particles were mixed with 15% 500 nm Cu particles and 15% 500 nm SAC0307 particles as solders (SACZ) and five different ultrasonic loading degrees were applied for realizing the soldering between Cu and Al at 240 °C and 8 MPa. Then, SEM was used to observe and analyze the soldering seam, interface microstructure and fracture morphology; the structural composition was determined by EDS; the phase of the soldering seam was characterized by XRD; and a PTR-1102 bonding tester was adopted to test the average shear strength.FindingsThe results manifest that Al–Zn solid solution is formed on the Al side of the Cu/SACZ/Al joints, while the interface IMC (Cu5Zn8) is formed on the Cu side of the Cu/SACZ/Al joints. When single ultrasonic was used in soldering, the interface IMC (Cu5Zn8) gradually thickens with the increase of ultrasonic degree. It is observed that the proportion of Zn or ZnO areas in solders decreases, and the proportion of Cu–Zn compound areas increases with the variation of ultrasonic degree. The maximum shear strength of joint reaches 46.01 MPa when the dual ultrasonic degree is 60°. The fracture position of the joint gradually shifts from the Al side interface to the solders and then to the Cu side interface.Originality/valueThe mechanism of ultrasonic action on micro-nanoparticles is further studied. By using different ultrasonic loading degrees to realize Cu/Al soldering, it is believed that the understandings gained in this study may offer some new insights for the development of low-temperature soldering methodology for heterogeneous materials.

Microstructure evolution and grain refinement of ultrasonic-assisted soldering joint by using Ni foam reinforced Sn composite solder.

In this investigation, ultrasonic-assisted soldering at 260°C in air produced high strength and high melting point Cu connections in 60s using Ni foam reinforced Sn composite solder. Systematically examined were the microstructure, grain morphology, and shear strength of connections made with various porosities of Ni foam composite solders. Results shown that Ni foams as strengthening phases could reinforce Sn solder effectively. The addition of Ni foam accelerated the metallurgical reaction due to great amount of liquid/solid interfaces, and refined the intermetallic compounds (IMCs) grains by ultrasonic cavitation. The joints had different IMCs by using Ni foam with different porosity. Layered (Cu,Ni)6Sn5 and (Ni,Cu)3Sn4 phases both existed in Cu/Ni60-Sn/Cu joint while only (Cu,Ni)6Sn5 IMCs grew in Cu/Ni98-Sn/Cu joint. As ultrasonic time increasing, Ni skeletons were dissolved and the IMCs were peeled off from substrates and broken into small particles. And then, the IMCs gradually dissociated into refined particles and distributed homogeneously in the whole soldering seam under cavitation effects. Herein, the Cu/Ni60-Sn/Cu joint ultrasonically soldered for 60s exhibited the highest shear strength of 86.9MPa, as well as a high melting point about 800℃ for the solder seam composed of Ni skeletons and Ni-Cu-Sn IMCs. The characterization indicated that the shearing failure mainly occurred in the interlayer of the soldering seam. The homogeneous distributed granular IMCs and Ni skeletons hindered the crack propagation and improved the strength of Cu alloy joints.

Thermal aging effects on the properties of the Cu/(SAC0307 powder + Zn-particles)/Cu joint ultrasonic-assisted soldered at low-temperature

PurposeThis study aims to evaluate the effect of thermal aging temperature on the properties of Cu/Cu joints.Design/methodology/approachA new method that 1 um Zn-particles and Sn-0.3Ag-0.7Cu (SAC0307) with a particle size of 25–38 µm were mixed to fill the joint and successfully achieved the micro-joining of Cu/Cu under ultrasonic-assisted at low-temperature, and then the effect of thermal aging temperature on the properties of Cu/Cu joints was researched.FindingsThe composition of the intermetallic compounds (IMCs) on the upper and lower interfaces of Cu/SACZ/Cu joints remained unchanged, which was Cu5Zn8 in aging process, and the thickness of the IMCs on the upper and lower interfaces of the Cu/SACZ/Cu joints increased accordingly. Compared with the as-received joints, the thickness of the upper and lower interfaces IMCs of the soldering aged time for 24 h increased by 404.7% and 505.5% at 150ºC, respectively. The IMCs formation tendency and the IMCs growth rate of the lower interface are larger than those of the upper interface because the soldering seam near the IMCs at the upper and lower interfaces of the as-received joints were mostly white SAC0307 balls black Zn-particles, respectively. The growth activation energy of IMCs in the upper and lower interfaces is about 89.21 and 55.11 kJ/mol, respectively. Under the same aging time, with the increase of the aging temperature, the shear strength of Cu/SACZ/Cu joints did not change significantly at first before 150ºC. When the aging temperature reached 150ºC, the shear strength of the joints decreased significantly; the shear strength of the joints was the smallest at 150ºC for 24 h, which was 39.4% lower than that of the as-received joints because the oxidation degree of Zn particles in the joint with the increase of aging temperature and time.Originality/valueCu/Cu joints were successfully achieved under ultrasonic-assisted at low-temperature.

Дослідження фазоутворення після дифузійного зварювання у вакуумі з’єднання нікель-ніобій

Diffusion welding is the ideal solution for joining dissimilar materials. This method is particularly effective if you should get a strong monolithic joint without the formation of a rough weld or solder seam. It is used if it is impossible to use standard fasteners. The main scope of this type of welding is the area of high technologies - aviation, space and other types of heavy engineering. All the advantages make the process indispensable under certain conditions and classify it as a high-tech type. This paper considers compounds of dissimilar metals nickel-niobium. In connection with the formation of many intermetallic compounds between these metals, the technology of diffusion welding in a vacuum was chosen. This method allows you to connect materials without melting due to the mutual diffusion of the components. The welding parameters affect the phase formation of the diffusion zone. To study the phase composition, a method of microstructural, X-ray microanalysis, as well as a state diagram of nickel-niobium, is proposed. When studying the weldability of the nickel-niobium system, samples were made in the form of a cube with a side of 10 mm, which was clamped in a mandrel and filled with Wood's alloy. The samples were not subjected to digestion, since during the polishing process, due to the different hardness of the phases, the structure turned out to be thermal polishing. The proposed scheme made it possible to study in detail the phase composition of individual layers of the diffusion zone, their dimensions and dependence on welding parameters. According to the results of quantitative X-ray microanalysis, we did not obtain accurate data on the phase composition and extent of diffuse layers. Qualitative X-ray spectral microanalysis, which was carried out by continuous scanning with an electron probe through the diffuse zone, made it possible to fix the phase reflections on the concentration curves and to determine the extent of the diffusion layers. For a more visual representation of the arrangement of the phases, a combined nickel-niobium diagram with a concentration curve is considered. The studies carried out made it possible to obtain a high-quality joint with mechanical properties that ensure reliability under operating conditions.

Effects of Ni-decorated reduced graphene oxide nanosheets on the microstructural evolution and mechanical properties of Sn-3.0Ag-0.5Cu composite solders

Introducing foreign reinforcements into solder joints has been demonstrated to be beneficial to promoting the soldering reliability. In this work, Ni-decorated reduced graphene oxide (Ni-RGO) nanosheets as foreign reinforcements were prepared through the in-situ thermal decomposition of Ni-glycolate@RGO complexes. xNi-RGO/SAC305 composite solders (x = 0, 0.01, 0.03, 0.05, 0.07, 0.1 wt%) were fabricated by the powder metallurgy method. The results showed that Ni nanoparticles were finely and evenly anchored on both sides of RGO nanosheets. The grain size in xNi-RGO/SAC305 composite solders was significantly refined, while the thickness of the interfacial intermetallic compounds (IMCs) decreased with increasing of Ni-RGO content. The average tensile strength of Cu/(Ni-RGO/SAC305)/Cu solder joints reached 43.0 MPa (18.1% higher than that of the plain SAC305 solder joints) when the amount of Ni-RGO addition reached 0.03 wt%, in which the crack initiation formed occurred in the soldering seam zone. The crack initiated in the micropores between the copper parent metal and composite solder when the content of Ni-RGO nanosheets was above 0.05 wt%, which may due to the agglomerating of submicron-sized Ni-RGO at the interface. These results suggest that traces of Ni-RGO nanosheets (0.03 wt%) can efficiently improve the interfacial bonding strength and solderability of the Cu/(Ni-RGO/SAC305)/Cu solder joint.

Microstructure evolution and interfacial bonding mechanisms of ultrasonically soldered sapphire/Al dissimilar joints using Sn-based solders

Sapphire and 5A06 Al were ultrasonically soldered with Sn9Zn, SAC305 alloy solders and NiCu alloy foam added Sn-based composite solders, respectively. The microstructure and mechanical properties of joints were investigated and the interfacial bonding mechanism was analyzed. Cracks were observed at the sapphire/Sn matrix interface in joints soldered with alloy solders, which were disappeared in the joints soldered with composite solders. In the joint using NiCu–Sn9Zn composite solder, the solder seam was uneven and Al3Ni intermetallic compound (IMC) layer was formed on the surface of NiCu alloy skeletons. While in the joint using NiCu-SAC305 composite solder, fine particles of (Ni,Zn)3Sn4 were largely formed and homogeneously distributed in the solder seam. An amorphous Al2O3 transition layer was formed at the sapphire/Sn matrix interface, and Zn enrichment was found at the Sn matrix/amorphous Al2O3 interface. The action mechanism of Zn was analyzed by first-principles calculation. The joints soldered with NiCu-SAC305 composite solder exhibited the highest shear strength of 74.42 MPa, the shearing failure mainly happened in the soldering seam.

Effect of Cu content on properties of Cu/Zn+15%SAC0307+xCu/Al joint by ultrasonic excitation at low temperature

The ultrasonic-assisted soldering joint of Cu/Al with different contents of copper particles added to solder powder at low temperature was studied. In this study, 15%SAC0307 solder powder with a diameter of 500 nm, different amounts copper particles with a diameter of 500 nm were mixed with zinc particles of a diameter of 45 μm to fill the Cu/Al joint, and the soldered was heated to 240 °C for ultrasonic-assisted under the environmental atmosphere. Successfully achieved micro-joining of Cu/Al under ultrasonic-assisted at low-temperature. The results have shown that, when the copper content was 0%-15%, two layers of complete and continuous CuxZny compounds were formed at the copper side interface. When the copper content was more than 15%, the IMC layer of the copper side interface was not obvious, and a large amount of CuxZny compounds were formed near the copper side. The base metals on the aluminum side formed a solid solution combination with zinc. When the addition amount of copper powder was 15%, the soldering seam was smooth and flat, the defect between balls was not obvious, and the IMC was uniformly distributed, so the average shear strength reached the maximum value of 47.37 MPa.

Effect of Zn-powder content on the property of Cu/SAC0307 powder/Cu joint under ultrasonic assisted at low temperature

PurposeLow-Ag SAC solder will lead to a series of problems, such as increased the melting range and declined the solderability and so on. These research studies do not have too much impact on the improvement of solders’ performance but were difficult to achieve satisfactory results. It is urgent to develop new soldering technology to avoid the bottleneck of lead-free solder. low-temperature-stirring soldering and ultrasonic-assisted soldering was developed in the authors’ early work, but slag inclusion and pore would gather and grow up to lead decreasing of the shear strength. In this paper, Cu/SAC0307 +Zn power/Cu joints with ultrasonic-assisted at low-temperature was successfully achieved.Design/methodology/approach45um Zn-powder and SAC0307 No.4 solder powder were mixed to fill the Cu-Cu joint, and the content of Zn-powder were 0 and 5%, 7.5% and 10%, 12.5% and 15% respectively. During the soldering process under ambient atmosphere %252C the heating platform provided a constant 220%253 F and the ultrasonic vibrator applied a constant pressure of 4 MPa to the copper substrate. The soldering process was completed after holding 70 s at 300 W.FindingsThe Zn particles made the IMC at the joint interface and in the soldering seam from scallop-type Cu6Sn5 to flat-type Cu5Zn8. The shear strength of joints without Zn was only 12.43 MPa, the shear strength of joints with 10% Zn reached a peak of 34.25 MPa, and the shear strength of joints containing 10% Zn was 63.71% higher than that of joints without zinc particles, and then the shear strength decreased. In addition, with the increase of zinc content, the fracture mode of the joint changed from the brittle fracture of the original layered tears to the mixed tough and brittle fracture.Originality/valueA new method that Zn micron-size powders and SAC0307 micron-size powders was mixed to fill the joint, and successfully achieved micro-joining of Cu/Cu under ultrasonic-assisted without flux at low-temperature.

Microstructure and mechanical properties of Cu joints soldered with a Sn-based composite solder, reinforced by metal foam

In this study, Ni foam, Cu coated Ni foam and Cu-Ni alloy foams were used as strengthening phases for pure Sn solder. Cu-Cu joints were fabricated by soldering with these Sn-based composite solders at 260 °C for different times. The tensile strength of pure Sn solder was improved significantly by the addition of metal foams, and the Cu-Ni alloy/Sn composite solder exhibited the highest tensile strength of 50.32 MPa. The skeleton networks of the foams were gradually dissolved into the soldering seam with increasing soldering time, accompanied by the massive formation of (Cu,Ni)6Sn5 phase in the joint. The dissolution rates of Ni foam, Cu coated Ni foam and Cu-Ni alloy foams into the Sn matrix increased successively during soldering. An increased dissolution rate of the metal foam leads to an increase in the Ni content in the soldering seam, which was found to be beneficial in refining the (Cu,Ni)6Sn5 phase and inhibiting the formation of the Cu3Sn IMC layer on the Cu substrate surface. The average shear strength of the Cu joints was improved with increasing soldering time, and a shear strength of 61.2 MPa was obtained for Cu joints soldered with Cu-Ni alloy/Sn composite solder for 60 min.

Bonding and strengthening mechanism of ultrasonically soldered 7075 Al joint using Ni-foam/Sn composite solder foil

Ni-foam reinforced Sn-based composite solder was employed to join ultrafine grain 7075 Al alloy with the assistance of ultrasound. The solder seam was mainly composed of Ni skeletons, Sn-based solder, α-Al phase and very fine (hundreds of nanometers to several microns diameter) Ni3Sn4 particles. Discontinuous networks surrounded by the fine Ni3Sn4 and α-Al particles were in-situ formed in the solder seam, the diameter of which was decreased with increasing soldering time. Smooth transition of the lattice from Al substrate to Sn-based solder was achieved by the formation of an amorphous Al2O3 interlayer at the interface. The microstructure evolution mechanism and the amorphous Al2O3 interlayer formation mechanism are discussed in detail. The shear strength of Al/Ni-Sn/Al joints increased with prolonging soldering time. The Al/Ni-Sn/Al joint ultrasonically soldered for 60 s exhibits a shear strength of 71.4 MPa, which was approximately 37% higher than that soldered with pure Sn solder.

Microstructure and Interfacial Evolution of Sintered NdFeB Permanent Magnet/Steel Joint Soldered with Zn-Sn Alloy

Sintered NdFeB permanent magnets and steel were soldered successfully using Zn-Sn alloy. The effects of Sn content on the microstructure and mechanical properties of soldered joints were investigated. The results showed that the typical interfacial microstructure represented NdFeB/NdFe5.5Zn(B) + ξ-FeZn13/Zn + β-Sn/ξ-FeZn13 + δ-FeZn10 + Γ-Fe3Zn10/steel. With the addition of Sn, the thickness of the NdFe5.5Zn(B) phase increased, while more β-Sn was observed in the soldering seam. The maximum shear strength reached 45.3 MPa with a Sn proportion of 6 wt.%, and excessive growth of the NdFe5.5Zn(B) phase in the joints deteriorated the mechanical properties. The fracture morphology exhibited a ductile-to-brittle transition with the occurrence of interfacial fractures due to thick intermetallic compounds.

Dynamic Observation of Interfacial IMC Evolution and Fracture Mechanism of Sn2.5Ag0.7Cu0.1RE/Cu Lead-Free Solder Joints during Isothermal Aging.

Dynamic observation of the microstructure evolution of Sn2.5Ag0.7Cu0.1RE/Cu solder joints and the relationship between the interfacial intermetallic compound (IMC) and the mechanical properties of the solder joints were investigated during isothermal aging. The results showed that the original single scallop-type Cu6Sn5 IMC gradually evolved into a planar double-layer IMC consisting of Cu6Sn5 and Cu3Sn IMCs with isothermal aging. In particular, the Cu3Sn IMC grew towards the Cu substrate and the solder seam sides; growth toward the Cu substrate side was dominant during the isothermal aging process. The growth of Cu3Sn IMC depended on the accumulated time at a certain temperature, where the growth rate of Cu3Sn was higher than that of Cu6Sn5. Additionally, the growth of the interfacial IMC was mainly controlled by bulk diffusion mechanism, where the activation energies of Cu6Sn5 and Cu3Sn were 74.7 and 86.6 kJ/mol, respectively. The growth rate of Cu3Sn was slightly faster than that of Cu6Sn5 during isothermal aging. With increasing isothermal aging time, the shear strength of the solder joints decreased and showed a linear relationship with the thickness of Cu3Sn. The fracture mechanism of the solder joints changed from ductile fracture to brittle fracture, and the fracture pathway transferred from the solder seam to the interfacial IMC layer.

Ultrasonic bonding of 2024 Al alloy using Ni-foam/Sn composite solder at ambient temperature

Ultrasonic bonding of 2024 Al alloy was successfully performed at ambient temperature by using Ni-foam reinforced Sn-based composite solder foils. Ni-foam sheets with porosities of 60% and 80% were used to strengthen pure Sn solder. The Ni skeletons in the solder seam changed from three-dimensional continuous network structure into strip type with increasing ultrasonic bonding time, accompanied with the formation of Ni3Sn4 phase on Ni skeleton surface and Al3Ni intermetallic compound (IMC) layer on Al substrate surface. While, further prolonging the ultrasonic bonding time could largely consume Sn solder and break the Ni skeletons. The Sn-based solder added with 80% porosity Ni-foam exhibited better soldering performance than that added with 60% porosity Ni-foam. The Al/Ni80–Sn/Al joint ultrasonically bonded for 4 s exhibited the highest shear strength of 52.34 MPa, the shearing failure mainly happened in the composite solder layers.

The Interface Microstructure and Shear Strength of Sn2.5Ag0.7Cu0.1RExNi/Cu Solder Joints under Thermal-Cycle Loading

The interface microstructure and shear strength of Sn2.5Ag0.7Cu0.1RExNi/Cu solder joints under thermal-cycle loading were investigated with scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and physical and chemical tests. The results show that an intermetallic compound (IMC) layer of Sn2.5Ag0.7Cu0.1RExNi/Cu solder joints evolved gradually from the scalloped into larger wavy forms with increasing number of thermal cycles. The roughness and average thickness of IMC increased with thermal-cycle loading. However, at longer thermal-cycle loading, the shear strength of the joints was reduced by about 40%. The fracture pathway of solder joints was initiated in the solder seam with ductile fracture mechanism and propagated to the solder seam/IMC layer with ductile-brittle mixed-type fracture mechanism, when the number of thermal cycles increased from 100 to 500 cycles. By adding 0.05 wt.% Ni, the growth of the joint interface IMC could be controlled, and the roughness and average thickness of the interfacial IMC layer reduced. As a result, the shear strength of joints is higher than those without Ni. When compared to joint without Ni, the roughness and average thickness of 0.05 wt.% Ni solder joint interface IMC layer reached the minimum after 500 thermal cycles. The shear strength of that joint was reduced to a minimum of 36.4% of the initial state, to a value of 18.2 MPa.

Effect of bonding temperature on microstructure and shear strength of the dissimilar Al/Al-27Si joints bonded by partial transient liquid phase bonding

The microstructure and shear strength of the Al alloy/Al-27Si alloy (Al/Al-27Si) joints with Cu interlayer bonded at different temperatures were investigated in the present study. Results show that a soldering seam with many eutectic phases is obtained in the Al/Al-27Si joints. These eutectic phases are mainly composed of θ-CuAl2 phase, α-Al phase and Si phase. With the increase of bonding temperature, the width of soldering seam and the average size of Si particles gradually increase, while the density of eutectic θ-CuAl2 phase deceases. The morphologies of Si phases transform from the granular particles into the needle-like shape when the temperature increases to 560 °C. The penetration of eutectic phases into the Al matrix along the grain boundaries is generated and the non-planar Al/soldering-seam interfaces are developed. With the increase of bonding temperature, the shear strengths of Al/Al-27Si joints firstly increase because of the better joining effect and less micro-cracks, and then decrease resulting from the morphology transformation of Si phases. The maximum shear strength of 70.4 MPa is achieved at 550 °C.

Effect of ultrasonic vibration on the interfacial IMC three-dimensional morphology and mechanical properties of Sn2.5Ag0.7Cu0.1RE0.05Ni/Cu halogen free solder joints

Sn2.5Ag0.7Cu0.1RE0.05Ni/Cu halogen free solder joints were fabricated by an ultrasonic vibration (USV)-assisted soldering process. The effects of the USV power on the three-dimensional (3-D) morphology of the intermetallic compounds (IMC) and mechanical properties of the halogen free solder joints were characterized systematically. Results showed that the root-mean-square roughness (Rrms) and the mean spacing of adjacent peaks of the profile (λave) of the interfacial IMC were linearly correlated with shear strength of the halogen free solder joints. It was more comprehensive to adopt the λave and Rrms evaluation parameters to characterize the relationship between the interfacial IMC 3-D morphology and shear strength of the halogen free solder joints. With increasing USV power, the eutectic microstructure of the solder seam was refined, and the proportion of eutectic microstructure in the solder seam and microhardness increased. When the USV power increased to 130 W, the Rrms and average thickness of the interfacial IMC decreased (decreases of 37.6% and 56.4%, respectively) and the corresponding λave and shear strength of the solder joint increased (increases of 68.7% and 45.8%, respectively). With increasing USV power, the fracture mechanism of the halogen free solder joint changed from brittle fracture to the ductile–brittle mixed fracture, and the fracture pathway transferred from the interfacial transition zone consisting of the solder seam and the interfacial IMC layer to the solder seam.