IMC Layer Research Articles

Microstructural Evolution of Intermetallic Compound Between SN100C Solder and ENIMAG Substrate During Isothermal Ageing

SN100C alloy emerges as a promising candidate when introducing lead-free solder alternativesdue to its mechanical properties and solderability. The study aims to explore interfacial reactions between SN100C solder and ENIMAG surface finish. Methods involve preparingENIMAG substrates, solder paste application, and reflow processes following JEDEC standards. Isothermal ageing treatments were conducted, and interfacial reactions were characterized using top surface and cross-section analyses via Optical Microscope (OM), Scanning Electron Microscope (SEM), and Energy Dispersive X-ray (EDX). Post-reflow, distinct IMC layers formed at the SN100C/ENIMAG solder joint's interface, evolving with ageing. Further analysis via cross-section confirms the initial formation of (Ni, Cu)3Sn4 layer followed by (Cu, Ni)6Sn5, each exhibiting varying appearance and thicknesses. Isothermal ageing increases IMC thickness, which is particularly influenced by Cu diffusion and exposure to high temperatures, and itfacilitates the growth rate of IMCs.

Investigation on electromigration failure behavior of SAC305/SnPb micro-hybrid solder joints for package-on-package techniques: Experiment and simulation

The failure mechanism of electromigration (EM) for electronic packaging technology has garnered interest. Electromigration-caused voids reduce electronic device dependability. Two-step reflow at 250℃ and 210℃ was employed to create SAC305/SnPb micro-hybrid solder connections. Finite element analysis confirmed electromigration failure. After 768 h at 10A, the anode interface IMC thickness increased by 149.8 %, while the cathode IMC increased less. Polarity accelerates anode IMC growth. Electromigration of Cu from cathode to anode causes structural flaws and 44.6 % shear strength loss to 35.1 MPa. Fractures shift from inside the solder joint to the IMC layer becoming brittle. COMSOL simulation demonstrates greatest current density, temperature, and stress at the current inlet and Cu pad-solder joint junction.

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.

New insights into the influencing mechanism of ultrasonic vibration on interface of Al/Mg bimetal composites by compound casting using simulation calculation and experimental verification

In this work, the numerical simulation of acoustic pressure distribution in ultrasonic vibration-assisted compound casting of Al/Mg bimetal composites was conducted. Relevant experimental verification was also performed to understand the influence of ultrasonic vibration treatment (UVT) on the interfacial microstructures and mechanical properties of the Al/Mg bimetal composites. Results revealed that the acoustic pressure distributions in the AZ91D melt were related to the vibration frequencies. The effective cavitation area at the Al/Mg interface reached the maximum percentage of 95.6 %, with the ultrasonic frequency of 20 kHz. The experimental results found that the Al/Mg interface without UVT was composed of Al–Mg intermetallic compounds (IMCs, i.e., Al3Mg2 and Al12Mg17) layer and eutectic layer. The oxide film and gas gap were existed between the two layers. The Mg2Si particles were gathered at the IMCs layer. The interfacial grains were coarse and their growth was directional. With UVT, the effective cavitation was occurred at the Al/Mg interface. The oxide film was broken, and the gas gap was eliminated. The interfacial microstructures were significantly refined. Due to the accelerated elemental diffusion and solute transfer by UVT, a more homogeneous Al/Mg interface was obtained. The Mg2Si particles were refined and formed at the eutectic layer. The microhardness mismatch of the IMCs layer and eutectic layer was decreased by UVT. The shear strength of the Al/Mg bimetal composites with UVT was enhanced to 62.2 MPa, which increased by 62.8 %, compared with that without UVT.

Microstructure, Corrosion and Mechanical Properties of Medium-Thick 6061-T6 Alloy/T2 Pure Cu Dissimilar Joints Produced by Double Side Friction Stir Z Shape Lap-Butt Welding

A novel double side friction stir Z shape lap-butt welding (DS-FSZW) process was proposed to achieve excellent mechanical properties of Al/Cu medium-thick dissimilar joints. The influence of welding parameters on weld microstructure and properties of DS-FSZW joint were systematically investigated. It indicated that defect-free medium-thick Al/Cu DS-FSZW joint could be achieved under an optimal welding parameter. DS-FSZW joint was prone to form void defects in the bottom of the second-pass weld. The recrystallization mechanisms at the top and middle of the weld nugget zone (WNZ) were continuous dynamic recrystallization (CDRX) and geometric dynamic recrystallization (GDRX). While the major recrystallization mechanism at the bottom of the WNZ was GDRX. DS-FSZW joint of the optimal welding condition with 850 r/min-400 mm/min was produced with a continuous thin and crack-free IMCs layer at the Al/Cu interface, and the maximum tensile strength of this joint is 160.57 MPa, which is equivalent to 65.54% of pure Cu base material. Moreover, the corrosion resistance of Al/Cu DS-FSZW joints also achieved its maximum value at the optimal welding parameter of 850 r/min-400 mm/min. It demonstrates that the DS-FSZW process can simultaneously produce medium-thick Al/Cu joints with excellent mechanical performance and corrosion resistance.

Thermal, microstructural, wettability and mechanical properties of Sn1.0Ag0.5Cu composite solder modified with Ti nanoparticles

In this study, highly active Ti nanoparticles (Ti NPs) were added to a low silver Sn-1.0Ag-0.5Cu (SAC105) solder. The thermal, microstructural, interfacial, wettability and mechanical properties of SAC105-xTi NPs (x = 0, 0.1, 0.2, 0.3, 0.4, 0.5 wt%) solders were investigated. The results showed that adding Ti NPs had little effect on the melting point and melting point range of SAC105 solder alloy. The solder alloy containing 0.2 wt% Ti NPs had the lowest coefficient of thermal expansion (CTE) of 21.1 × 10−6 m/°C. The SAC105–0.4 Ti NPs solder has a contact angle of 24.3°, 7.57° lower than the SAC105 solder. However, Ti NPs deteriorate the surface of the solder joint as they oxidize to produce TiO2 during the soldering process, resulting in a higher number of small solder balls precipitating from the surface of the joint. In addition, EPMA showed that Ti NPs adsorbed on the Cu6Sn5 grains, leading to changes in the morphology of the Cu6Sn5 grains and a decrease in the thickness of the IMC layer. The addition of Ti NPs had little effect on the mechanical properties of solder alloys. Excessive Ti NPs will agglomerate, leading to a sharp decrease in the shear strength of the solder joints.

Improving bonding strength of medium-thick Al-Cu dissimilar joint by a novel splat cooling assisted double side friction stir welding

To obtain a high-strength medium-thick Al-Cu dissimilar joint, a novel splat cooling assisted double side friction stir welding (SDS-FSW) is proposed. The microstructure and tensile properties of conventional double-side friction stir welding (DS-FSW) and the novel SDS-FSW joints under optimal welding parameters are systematically compared, it shows that the utilization of in-process splat cooling significantly reduces the welding peak temperature and the high-temperature dwell time. The in-process splat cooling causes significant grain refinement in the welding nugget zone (WNZ) of the Al-Cu dissimilar SDS-FSWed joint, it exists the lower recrystallization fraction and the higher KAM value. Although both DS-FSW and SDS-FSW joints fracture at the Al-Cu interface, the DS-FSW joint represents a brittle fracture characteristic, while the SDS-FSW joint represents a mixed ductile-brittle fracture mode. Under the drive of the mechanical stirring of the tool and the welding thermal cycle, the aluminium atoms and copper atoms diffuse to the copper base material and aluminium base material, respectively. Since copper diffuses in aluminium at a higher diffusion rate than aluminium diffuses in copper, and the solubility of copper in aluminium is much smaller than that of aluminium in copper, thus the Al2Cu becomes the first phase with the nucleation and growth. As the welding temperature and time continue to increase, Al2Cu reaches the supersaturation state, and the Al4Cu9 phase is produced between the Cu (Al) and the Al2Cu phase. In the end, the interface forms the stable double-layer IMCs structure (Al2Cu/Al4Cu9). The optimal tensile strength of the SDS-FSWed joint is 159 MPa, which is increased by 42% compared to the DS-FSWed joint at the same welding parameter. This was mainly because in-process splat cooling contributed to forming a thinner IMCs layer at the A-Al-Cu interface. It reveals that the application of in-process splat cooling is a versatile method to thin the IMCs layer at the Al-Cu medium-thick DS-FSW process.

Double side friction stir Z shape butt lap welding of dissimilar titanium aluminum alloys

Achieving excellent mechanical performance of medium-thick Ti/Al dissimilar joints is important in many industrial applications. However, due to the inherent heat generation mode associated with conventional friction stir welding (FSW), it is impossible to achieve sound medium-thick Ti/Al dissimilar joints. Although double side friction stir welding (DS-FSW) has been reported to solve the problems of conventional FSW. The inherent problems of forming hook structure and interface cracking in the center of the DS-FSW joints significantly weaken the joint performance. Therefore, an innovative double-side friction stir Z shape butt-lap welding (DS-FSZW) process was proposed to eliminate the inherent problems of conventional DS-FSW. The research objective of this work was to reveal the physical mechanisms of the novel DS-FSZW by the combination of numerical simulation and experimental characterization for optimizing the welding parameters. The influence of tool shoulder diameter on the heat generation, heat transfer, plastic material flow, microstructure evolution and mechanical properties of medium-thick dissimilar Ti/Al DS-FSZW joint has been systematically studied. The results indicate that the innovative DS-FSZW process lowers the axial force compared to the conventional DS-FSW, and the centerlines of the first and the second sides welds are staggered. Those are beneficial to inhibiting the cracking of the first-side weld at the interface. In addition, the DS-FSZW method eliminates the hook structures and cracks at the center of the conventional DS-FSW joint and also adds a lap joining interface, which significantly enhances the tensile strength of the joint from 150.7 MPa to 262.5 MPa, which is increased by 74%. Optimization of the shoulder diameter of DS-FSZW from 18 mm to 12 mm reduces the welding heat input and significantly thins the thickness of the IMCs layers at the Ti/Al interface. This helps to suppress the cracking at the Ti/Al lap interface and refine the grains. As a result, thus the tensile strength of the DS-FSZW joint increases from 262.5 MPa to 312.5 MPa, which is increased by 19%. The medium-thick Ti/Al dissimilar DS-FSZW joint at the tool shoulder diameter of 12 mm fracture at the SZ. It proves that the novel DS-FSZW is a suitable welding method for joining medium-thick dissimilar Ti to Al alloys.

Joining thin galvanized low carbon steel sheet to AA6056-T4 by resistance spot welding and adhesive weld bounding

Multimaterial assemblies made by resistance spot welding (RSW) process offer a cost-efficient lightweight solution for automotive body-in-white production. However, joining different materials, such as steel (Fe) and aluminum (Al), brings issues due to their different physical properties and low weldability. The present work investigated the evolution of the weld between a thin galvanized low carbon steel sheet and an AA6056-T4 aluminum alloy from macroscopic observations to the evolution of the intermetallic compound layer (IMC) during RSW. Comparisons between homogeneous Al-Al RSW, Fe-Al RSW and Fe-Al adhesive weld bonding for different mechanical solicitations were also realized. Observations showed that the interface for short welding periods is composed of a thin and discontinuous IMC layer. The interface also presents defects that facilitate crack initiation and propagation, leading to an interfacial fracture mode. The different mechanical tests carried out demonstrated that the Al-Al and Fe-Al welds reached a similar maximum tensile load under the shear–tensile test. However, Fe-Al assemblies under cross-tensile test showed poor mechanical properties. The use of an adhesive layer with an Fe-Al spot weld seems to be a potential solution, as it is easily implementable on production lines and improves the mechanical properties of Fe-Al assemblies.

Effect of Sb and Ag Addition and Aging on the Microstructural Evolution, IMC Layer Growth, and Mechanical Properties of Near-Eutectic Sn-Bi Alloys

Effect of Sb and Ag Addition and Aging on the Microstructural Evolution, IMC Layer Growth, and Mechanical Properties of Near-Eutectic Sn-Bi Alloys

Effect of thermal exposure on microstructure, orientation relationship, residual stress and failure mechanism of ultrasonic-assisted Kovar/SnSb10/Kovar joints

Thermal exposure is often accompanied by the accumulation of inhomogeneous element diffusion, continued solid-state phase transformation, and occurrence of residual stress, causing the failure of the joint directly. In this work, we focused on the orientation relationship (OR) alternation, residual stress distribution, and failure mechanism of the reflow/ultrasonic-assisted Kovar/SnSb10/Kovar joint after thermal exposure. Especially, the role of Ni element during thermal exposure was analyzed in detail. It was noticed that the thickness of interfacial intermetallic was merely lower than 4 μm, even after thermal exposure for 45 d. The interfacial ORs of IMC/Kovar, whether ultrasound was applied or not, changed to an incoherent state. However, it did not deteriorate the ultimate shear strength, which reached over 50 MPa even after thermal exposure at 160 °C for 45 d. Compared to the reflow process after thermal exposure, the joints with ultrasonic improves the strength by about 10%. However, it dramatically decreased to only 20 MPa after thermal exposure at 200 °C for 45 d. The rationale was that ultrasonic-induced supersaturated Ni elements in solder and the Ni elements from the Kovar alloy diffused into the IMC region simultaneously, forming the (Fe, Ni)Sn2 IMC layer with relatively high residual stress and acting as the fracture origin region. The current findings demonstrated that the Kovar/SnSb10 interface proposed outstanding microstructure stability and mechanical reliability and was a promising alternative for a more extensive range of high-temperature applications.

Resistance rivet welding of aluminum/titanium dissimilar materials

Typical dissimilar combination of Al and Ti alloy was joined by resistance rivet welding (RRW) for the first time based on the semi-tubular TC4 rivet. The formation mechanism, microstructure characteristics and mechanical performance of Al/Ti RRW joints were elucidated in detail. The unique forming process of Al/Ti RRW joint includes the melting of intercepted Al alloy, the generation of AlTi IMCs layer and then disappearance, and the subsequent co-melting of Al, TC4 rivet and sheet. The concentration of Al in the Al/Ti mixed nugget is 15.56 at.%, 14.82 at.% and 12.64 at.% for the welding parameters 7 kA-200 ms, 8 kA-200 ms and 9 kA-200 ms, respectively. The microstructure of Al/Ti mixed nugget is composed of basket-weaved α' martensite, α' martensite colony and α2-AlTi3 ordered phases. The hardness of the Al/Ti mixed nugget is 493.4 HV which is higher than that of both TIG welded and Ti/Ti RSWed nugget. The solid solution hardening of Al element and the formation of α2-AlTi3 are mainly responsible for the hardness increment, which contributes about 9.3 % and more than 25.0 %, respectively. The Al/Ti RRW joint can exhibit a sound lap-shear strength up to 605.7 MPa. This study proved that RRW was a reliable joining process of Al/Ti dissimilar materials.

Properties study on Ti/Al butt joining by GMAW/GTAW hybrid welding-brazing

For adjusting the distribution of welding heat to obtain sound Ti/Al butt joints, Gas Metal Arc Welding (GMAW)/Gas Tungsten Arc Welding (GTAW) hybrid welding-brazing was introduced to join 5A06 to TC4. Then two kinds of tensile strength was tested. And the weld microstructure was observed by Scanning Electron Microscope (SEM), X-ray diffraction (XRD) and Energy Dispersive Spectrometer (EDS). Effects of welding parameters on weld reinforcement and interface characteristics were investigated. Results revealed TiAl3 IMCs layer was formed in the weld area of the titanium alloy side. The other area of weld was composed of α-Al matrix and Mg2Si+Al+Si eutectic. The back welding reinforcement was improved with the welding heat of the joint back increasing. But this may lead to a large number of molten metal flowing to the back of weld, the face reinforcement of the weld became poor. However, effects of welding parameters on the interface bonding strength was different. It was depended on the thickness and morphology of IMCs. When serrated IMCs of 2–6μm thickness were formed, the highest tensile strength without reinforcement was 240.3 MPa. Through comprehensive analyzing, when the welding parameters were welding speed of 15 mm s−1, GTAW current of 80–90 A and GMAW/GTAW position of −1 mm, the weld reinforcement and interface bonding strength were also high. So the excellent butt joints of TC4/5A06 were achieved. The maximum average value of TC4/5A06 joints tensile strength with reinforcement was 265 MPa with fracture inside the weld far from IMCs layer.

Microstructure evolution and tensile strength of Al/Cu inertia friction welded joint

To save production costs and reduce the weight of structures, it is one of the common ways to replace copper (Cu) with aluminum (Al) in some industries such as the refrigeration industry. The high-quality welding of Al to Cu determines the application of the Al/Cu hybrid structure. The inertia friction welding process was used to weld Al pipe to Cu pipe and the Taguchi experiment method was used to study the effects of inertia friction welding parameters on the mechanical properties of the welded joints, and the results show that the initial speed has the greatest influence on the tensile strength of welded joints. Meanwhile, the analyses of the microstructures of the joint show that Al–Cu IMCs formed at the friction interface to realize the metallurgical bonding of the welded joints. The formation sequence of Al–Cu IMCs in the friction welding process is Al2Cu, Al4Cu9, and AlCu. Whereas the type and thickness of IMCs are closely related to the tensile strength of the joints. When the welded joint forms Al2Cu and Al4Cu9, the interfacial misfit between the IMCs layer and base materials is minimized and the tensile strength of the joint is optimized.

Influence of TiO2 and Al2O3 Nanoparticles Addition on Thermal, Wettability and IMC Growth of Sn-3.0Ag-0.5Cu Lead-Free Solder at Different Reflow Temperature

This study investigated the influence of adding 0.50 wt% and 1.0 wt% titanium dioxide (TiO2) and aluminium oxide (Al2O3) nanoparticles on the properties of Sn3.0Ag0.5Cu (SAC305) lead-free solder alloy. In terms of thermal properties, SAC305 lead-free solder with or without addition of TiO2 and Al2O3 nanoparticles, the melting temperature is very similar and comparable. The wetting performance of the SAC305 nanocomposite solder was determined by the contact angle. The best contact angle recorded is 31.65° at reflow temperature of 250°C for 0.50 wt% addition of TiO2 and Al2O3 nanoparticles. The thickness of the IMC layer was observed using an Optical Microscope and measured. Results show that the thickness of the IMC layer decreased when TiO2 and Al2O3 nanoparticles were reinforced into the SAC305 solder system, which shows significant decrease when 0.50wt% of TiO2 and Al2O3 nanoparticles were added. However, beyond 0.50 wt% the thickness of IMC layer increases along with increasing reflow temperature. The results reveal that the adsorption effect of TiO2 and Al2O3 nanoparticles will restrict the growth of the IMC layer under controlled concentration of the nanoparticles and reflow temperature. The optimal parameters to enhance the performance of SAC305 solder by reinforcing TiO2 and Al2O3 nanoparticles are reflowed at 250°C at 0.50 wt% concentration of TiO2 and Al2O3 nanoparticles.

Microstructure and mechanical properties of Ti/Al laminates fabricated by ultrasonic additive manufacturing assisted by Joule heat and post-welding heat treatment

In this study, a novel electrical-current assisted ultrasonic additive manufacturing (UAM) method was proposed and CP-Ti/Al3003 laminates were prepared by this process. The concept is that the Joule heat generated by the electrical current flowing through the CP-Ti foil is used to improve the material's plasticity, promote the interfacial bonding strength and continuous ultrasonic consolidation ability. Ti/Al laminates with excellent interfacial bonding strength and mechanical properties can be obtained by alternating the use of Ti foil and Al foil and subsequently applying post-welding heat treatment for interfacial strengthening. The current density distribution at the CP-Ti foil and Ti/Al interface was studied by finite element model. The interfacial microstructure of the laminates was characterized and analyzed by optical microscopy, scanning electron microscopy-energy dispersive spectroscopy, and X-ray diffraction, and the inhibition effect of current on the resonance cracking of Ti foil during the UAM process was verified. The effect of current on the interfacial bonding strength of the Ti/Al interface and the tensile strength of the laminates was investigated by peel test and tensile test. The growth kinetics of TiAl3 under the assisted current was also studied and CP-Ti/Al laminates with the tensile strength of 242.4 MPa in the rolling direction. The combined effect of Joule heating of current and subsequent post-weld heat treatment strengthened the reaction between Ti/Al and formed TiAl3 IMC layer and obtained CP-Ti/Al laminates without interface defects.

Influence of process parameters on bead geometry and its effect on mechanical properties of CMT welding of automotive grade steel and aluminium alloy using aluminium based filler wire

This investigation aims to examine the effectiveness of torch position, welding-brazing parameters on the embedded bead profile and load carrying potential of the brazed joint of zinc coated DP600 steel and Al 5052 joined by cold metal transfer (CMT) technique. The base metals were joined at different torch position (−0.6, 0 and 0.6 mm) in lap joint position using Al-based filler wire. At different wire feed rate (WFR) 3, 4 and 5 m/min changes in bead shape and its geometry were observed. The various modes of failure were classified based on effective bonding length (LH–LV) and LH/θ ratio. The best combination of welding-brazing parameters at which the maximum load bearing capacity of 4.1 kN and enhanced bead properties was achieved at 0.6 mm torch position and WFR 5 m/min. The intermetallic compound layers formed during the process affect the tensile properties of weld-brazed joint. The possible intermetallics and the presence of major elements in intermetallic layer were analyzed by energy-dispersive X-ray spectroscopic analysis. Furthermore, in this investigation, it was also observed that the thickness of IMC layer increases with the increasing WFR and heat input up to a critical value of 10 µm.

In-situ fusion process and Cu–Sn compounds evolution mechanism of nano-intermetallic compound mixed solder joints

This study investigated the fusion and phase-transformation processes of nano-intermetallic compound (nano-IMC) mixed solder pastes. In particular, the interfacial reaction with the Cu substrate, the kinetics and mechanism of Cu6Sn5 growth inside the solder joint, and the shear strength of the solder joint were investigated. In-situ SEM and XRD results showed that the SAC305 and Sn–10Cu powders fused and the liquid solder ball completely melted at 227 °C. A higher initial Cu concentration in the mixed solder joints resulted in a lower Cu concentration gradient that inhibited the diffusion of Cu atoms. The growth activation energy of the IMC layer of a SAC305 + 20 wt% Sn–10Cu solder joint was 104.81 kJ/mol, which was higher than that of the SAC305 IMC layer (75.75 kJ/mol). During aging, Cu6Sn5 rods within the mixed solder joint formed gullies on the outer facets, and the Cu6Sn5 rods continued to grow along the [0001] crystal direction. The number of Sn grains and the proportion of high-angle grain boundaries in the mixed solder joints were higher after reflow. After aging at 150 °C for 1000 h, the shear strength of the SAC305 + 20 wt% Sn–10Cu solder joints was 34.25 MPa, slightly higher than that of SAC305 (33.12 MPa).

The effectiveness of Ni microalloying on the microstructure and mechanical properties of low temperature In-35 wt%Sn/Cu solder joint

The effects of 0.05 wt%Ni additions on In-35 wt%Sn (In–35Sn) alloy on the ex-situ interfacial reactions, in-situ microstructures formation during solidification, and mechanical properties during reflow soldering on Cu substrate were systematically studied. Reaction of In–35Sn with Cu resulted in the formation of two intermetallic Cu3(Sn,In) layers were found at the interface. When Ni is added, Ni is participated in the interfacial (Cu,Ni)3(Sn,In) layer formed at the In–35Sn-0.05Ni/Cu interface, causing the morphology of the IMC layer at the solder side to become more refined. Adding Ni resulted in the degree of undercooling In–35Sn decreasing close to zero. The in-situ real-time synchrotron x-ray imaging confirmed that the presence of Ni is responsible for the spontaneous β-In3Sn grain nucleation and formation of equiaxed grain in the solder joint. The grain refinement on the (Cu,Ni)3(Sn,In) IMC layer in In–35Sn-0.05Ni/Cu solder joint leads to minor increment in the shear strength. This study demonstrated the effectiveness of Ni microalloying in low temperature In–35Sn/Cu solder joint in modifying the β-In3Sn dendrite growth at the bulk solder and the microstructure refinement at the interface of the solder joints, which could potentially enhance the overall joint strength.

The microstructure evolution and failure mechanism of Sn37Pb solder joints under the coupling effects of extreme temperature variation and electromigration

The effect of electromigration and thermal shock on the microstructure evolution and failure mechanism in the Sn37Pb/Cu solder joints were investigated in this study. With increasing thermal shock cycles, Pb atoms acted as the dominant effective charge carrier, which migrated with the electron flow and accumulated at the anode side. As the number of thermal shocks extended to 20 cycles, the dissolution of Cu trace was found at the corner positions where the current was crowded in the solder joints. High and low temperature thermal shock demonstrated the acceleration of solder failure that accompanies an increase in peak temperature and shock frequency during electromigration process. Combining the extreme temperature thermal shock (–196 to 120 °C) with the current density of 2.0 × 104 A/cm2, the cracks were prone to initiate at the corner and then propagate along the IMC layers with thermal shock cycles. The high thermal stress caused by the thermal expansion mismatch between Sn37Pb solder and Cu pad with the large temperature variation (ΔT = 316 °C) significantly aggravated the crack propagation, which induced the failure of Sn37Pb solder joints after 22 cycles.