Intermetallic Compound Layer Research Articles

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 Characterization and Mechanical Properties of AA5083 Aluminum to AISI 1018 Steel Welds by Electro Spark Microwelding

ABSTRACT Welding of aluminium alloys to steels has been always challengeable. There are a certain number of methods to join these dissimilar metals all have their advantages and disadvantages. Advancement of any aluminium to steel welding strategies is an approach to control the size and nature of the intermetallic compound layer. A new method of electro spark microwelding has been developed for dissimilar welding of an aluminium alloy to steel to improve the joint mechanical properties. The microstructure of the welds are investigated by scanning transmission electron microscopy. The maximum tensile strength reached 206 MPa representing 65% of the tensile strength of the parent aluminium alloy with a ductile fracture locating at the fusion zone. The excellent bonding of the aluminium alloy and steel was based on the combined effects of the formation of about 4 μm thick nanoscale Fe rich intermetallic compound layer and complex mechanical inter-locking. The current research confirmed that aluminium could be successfully welded to steel via electro spark microwelding process.

Interfacial engineering of heterojunction copper-cobalt-nickel nitride as binder-free electrode for efficient water splitting

Good interfacial compatibility is essential to grow intermetallic compound layer on the surface of substrates for the potential application of electrocatalytic reactions. Here, an interface strategy is proposed to prepare a free-standing copper-cobalt-nickel nitride electrode，in which copper-cobalt-nickel nitride is anchored on hydrophilic treated nickel foam. Compared to bi-metal hierarchical catalysts, the as-fabricated epitaxial heterostructure shows excellent oxygen evolution reaction (OER) activity with an ultralow overpotential of 190 mV, as well as an overpotential of 63 mV for hydrogen evolution reaction (HER) at the current density of 10 mA cm–2. Most importantly, the modified tri-metal nitrides exhibit improved interfacial compatibility due to the interfacial defects, which can increase electron transport across the junction during the catalytic reactions. Density functional theory calculations reveal that the synergistic effect between copper, cobalt, and nickel nitride creates a proper electronic structure that lowers the reaction barriers of HER/OER.

Characteristics of Cracking Failure in Microbump Joints for 3D Chip-on-Chip Interconnections under Drop Impact.

With the rapid development of microelectronics packaging and integration, the failure risk of micro-solder joints in packaging structure caused by impact load has been increasingly concerning. However, the failure mechanism and reliability performance of a Cu-pillar-based microbump joint can use little of the existing research on board-level solder joints as reference, due to the downscaling and joint structure evolution. In this study, to investigate the cracking behavior of microbump joints targeted at chip-on-chip (CoC) stacked interconnections, the CoC test samples were subjected to repeated drop tests to reveal the crack morphology. It was found that the crack causing the microbump failure first initiated at the interface between the intermetallic compound (IMC) layer and the solder, propagated along the interface for a certain length, and then deflected into the solder matrix. To further explore the crack propagation mechanism, stress intensity factor (SIF) of the crack tip at the interface between IMC and solder was calculated by contour integral method, and the effects of solder thickness and crack length were also quantitatively analyzed and combined with the crack deflection criterion. By combining the SIF with the fracture toughness of the solder–Ni interface and the solder matrix, a criterion for crack deflecting from the original propagating path was established, which can be used for prediction of critical crack length and deflection angle for the initiation of crack deflection. Finally, the relationship between solder thickness and critical deflection length and deflection angle of main crack was verified by a board level drop test, and the influence of grain structure in solder matrix on actual failure lifetime was briefly discussed.

Investigation of interfacial reactions between Sn–Ag–Bi–In solder and (Cu, electroless Ni–P/Cu) substrate

Abstract The growth kinetics of intermetallic compound layers formed between Sn–3Ag–8Bi – 5In solder and (Cu, electroless Ni – P/Cu) substrate were investigated at temperatures between 70 and 170 °C for 1 to 60 days. The layer growth of the intermetallic compounds in the Sn–Ag– Bi – In/Cu and Sn–Ag –Bi – In/electroless Ni –P systems satisfied the parabolic time law. As a whole, because the values of time exponent have approximately 0.5, the layer growth is mainly controlled by diffusion. The apparent activation energies for the growth of the Cu6Sn5 and Ni3Sn4 intermetallic compounds are 81.4 and 67.1 kJ/mol, respectively.

Microstructure evolution and mechanical properties changes during the formation of full Cu41Sn11 joint in high-temperature electronic packaging

In this study, Cu/Sn/Cu structure under a pressure of 1.5 N was soldered at 390–450 °C. Then, microstructure evolution and changes in mechanical properties of solder joint during the formation of full Cu41Sn11 joint were systematically analyzed. Experimental results showed that Cu6Sn5 and Cu3Sn were observed in the interfacial region at 420 °C in the early stage of soldering. The Cu/Sn/Cu structure completely transformed into Cu/Cu3Sn/Cu at 1 h. With the further progress of the interfacial reaction, Cu41Sn11 appeared and grew at the expense of Cu3Sn. Eventually, the full Cu41Sn11 joint was formed at 10 h. The growth of Cu41Sn11 was controlled by volume-diffusion. Moreover, diffusion activation energy of Cu41Sn11 was about 108.19 kJ/mol. The shear strength of full Cu3Sn joints was 45 MPa, while that of the solder joints with 25, 50, 75 and 100% Cu41Sn11 was 50, 52.2, 59 and 64.5 MPa, respectively. For full Cu3Sn and full Cu41Sn11 joints, respectively, the fracture occurred partly within intermetallic compounds (IMCs) layers and partly along the Cu/IMC interface. However, for the joints composed of Cu3Sn and Cu41Sn11, all fractures occurred in the IMCs layer. Besides, all IMCs joints were brittle fracture, and the fracture of Cu3Sn was mainly intergranular, while the fracture that occurred in Cu41Sn11 was mainly transgranular.

Interface stability and fracture mechanism of Al/Steel friction stir lap joints by novel designed tool

A novel welding tool, characterized by the enlarged pin design was developed to solve the hook feature or insufficient interface deformation for Al/steel friction stir lap welded joints. The welding tool enhanced the interface deformation effect and eliminated hook feature. The thickness of the intermetallic compound (IMC) layer at the interface decreased from 3.3 μm to 0.46 μm, when the welding speed increased from 30 mm/min to 300 mm/min. The laminated structure composed of IMCs and fine steel grains gradually disappeared, with the interface gradually changing from serrated to straight as welding speed increased. The nanohardness value of the microstructure reached 9.4 ± 0.3 GPa at a distance of 10 μm from the interface layer. Due to the larger metallurgical bonding area, the best line load 499.4 N/mm reached 52 % of the 3 mm 6082-T6 alloy, which was obtained at the rotational speed of 1200 r/min and the welding speed of 50 mm/min. Four different interface failure modes were found and established during the shearing process. The strain concentration phenomenon of the successive occurrence, development and transfer of interface failure presented obvious interval characteristics in time and space.

Microstructural evolution and mechanical properties of the Al–Cu dissimilar joint enhanced by stationary-dynamic shoulder friction stir welding

Material mixing and intermetallic compounds (IMCs) are the key factors that affect the mechanical properties of dissimilar metal joints. In this paper, a feasible method of stationary-dynamic shoulder friction stir welding has been developed, which reduces the mixing of materials and inhibit the growth of IMCs during the Al-Cu welding process. The stationary-dynamic shoulder was composed of a stationary shoulder with a larger diameter and a rotational shoulder with a smaller diameter. While the stationary shoulder provided the upsetting force to guarantee the weld formation, the rotational shoulder served for material stirring and heat input. Compared with conventional friction stir welding, the mechanical properties of joints obtained by the new method were significantly improved. The maximum tensile strength was 243 MPa, which was equivalent to 90 % of Cu base metal and 54 % of Al base metal. Furthermore, the evolution of IMCs across the transition layer was analyzed in depth. The results indicated that, with an increase in the rotation speed, the IMCs layer gradually became thicker. However, when the thickness reached a certain level, it promoted the generation of micro-cracks on IMCs and reduced the strength of the joint. According to thermodynamic and kinetic analysis, IMCs were formed with respect to Al2Cu-Al4Cu9 sequence, which was consistent with transmission electron microscopy results.

Effects of rotation tool-induced heat and material flow behaviour on friction stir lapped Al/steel joint formation and resultant microstructure

Reliable joining of Al/steel via friction stir lap welding (FSLW) is strongly dependent on interfacial macro-/micro-structures. However, how the underlying thermo-mechanical process affects them and how they can be controlled remain unclear. In this study, a 3D coupled Eulerian–Lagrangian finite element model was integrated with a tracer particle technique to simulate the FSLW of Al alloy 5052 and high-strength DP590 steel, to elucidate the role of tool-induced heat and material flow. The results showed that the material flow recirculated near the shoulder and pin, which mainly originated from the advancing side of the Al and the retreating side of the steel. Increasing the rotational velocity intensified the overall material flow, resulting in increased migration on the steel side. Insufficient steel migration around the pin at lower rotational velocities was mainly responsible for the micro-voids and non-bonding defects at the lap interface. The asynchronous convergence of Al and steel flowing from the advancing and retreating sides, respectively, refilled the instantaneous gap, thereby normally bonding the lapped interface behind the pin. The rotational pin affected the hook structure and steel fragment formation through the shearing and squeezing of the steel migration flow. Material inter-migration produced an intercalated structure at the lapped Al/steel interface. The extremely high temperature, approximately above Al 5052 solidus temperature, under the pin bottom caused the formation of a thicker intermetallic compound (IMC), thereby considerably reducing the interfacial strength. Multi-scale mechanical strength assessments indicated that an intercalated interfacial structure with a thickness of Al-rich IMC layer less than ∼1.0 μm was desirable because it exhibited a higher local interfacial strength than the Al matrix.

Interfacial Reaction between SAC3807 Lead-Free Solders and Different Copper Substrate via Reflow Soldering Process

The different composition material of copper substrate significantly affects the intermetallic compound (IMC) formation and the solder joints durability. This study was conducted on the interfacial reaction between lead-free solder and the different copper substrates via reflow soldering. The selected substrate is copper (Cu) and copper-beryllium (Cu-Be). The lead-free solder involved is Sn-3.8Ag-0.7Cu (SAC3807) solder ball with a diameter of 700 μm. All the samples were subjected to the isothermal aging process. The material characterization and analysis on the IMC formation were examined by scanning electron microscopy (SEM), optical microscope (OM), and energy dispersive X-ray analysis (EDX). After the reflow process, the result revealed that Cu3Sn, Cu6Sn5 IMC layer formed at SAC3870/Cu and SAC3870/Cu-Be interface. The changes to a rod-like shape Cu6Sn5 and irregular needle-shaped Cu3Sn4 occur after the aging treatment on SAC3870/ Cu. Meanwhile, the IMC layer for SAC3870/Cu-Be shows a rod-like shape transformed into a blocky-like shape Cu6Sn5 and Cu3Sn4 diamond-shape. This result indicates that Ag3Sn nanosized was formed on the intermetallic surface during the aging process for both SAC3807/Cu and SAC3807/Cu-Be. The Ag3Sn nanosized element at SAC3807/Cu-Be is many compared to SAC3807/Cu. In addition, IMC thickness for SAC3807/Cu-Be shows a thicker layer than SAC3807/Cu. Lastly, in this research, the element of Be in SAC3807/Cu-Be cannot be defined because the beryllium element is not easily detected as the percentage was very low.

Process optimization for enhancing interconnect performance of large-size BGA component during vibration loading

A series of problems such as failure solder at SnAgCu large-size BGA component and Pb-rich phase at SnPb component are always found during mixed lead-free/tin-lead assembly. In order to give a better reflow process window of assembled printed circuit board, process optimization was carried out to satisfy a favourable reflow time for all the components. Numerical simulation according to the Box-Behnken design method was carried out to monitor the effective reflow time of mixed lead-free/tin-lead and tin-lead components, and a mathematical response model between the effective reflow time and the process curve was developed by multivariate quadratic regression analysis. An optimal reflow process curve was established by simulated annealing algorithm. According to the optimal process parameter, numerical simulation was carried out to observe the temperature distribution and residual stress, and the experimental researches including the vibration test and micro structure analysis were conducted on the mixed lead-free/tin-lead assembled component to monitor the dynamic resistance and deformation and characterize the reaction product at the interface. It is shown that the corner BGA component still suffers from both a higher residual stress (about 32 MPa) after reflow process and a larger deformation (about 64 μm) at the first order modality during random vibration test. However, a continuous intermetallic compound layer with the thickness of 1.2–1.5 μm containing the reaction products Ni3Sn4 and (Au,Ni)Sn4 is well generated, and no cracks and voids are observed.

Evolution of interfacial IMCs and mechanical performance of joints of Mg/Al dissimilar metals soldered by using Ga-coating protection

The soldering of Al/Mg dissimilar metals by using Sn–9Zn solder at a low temperature of 230 °C was investigated. A liquid gallium layer was coated on the faying surface of the base metals to avoid secondary oxidation and contact between Mg and Sn-based filler metal before soldering. The growth and distribution of intermetallic compounds (IMCs) at the interface of Mg/solder was focused on. The interface was composed of scattered large and dense small blocky IMC layers. The discontinuous Mg2Sn layer was found to be the key factor dominating the mechanical performance of the joints. The highest shear strength of 38 MPa was reached at a reasonable holding time of ∼10 min. An over long holding time would cause the segregation of gallium which would deteriorate the water resistance of the joints.

Microstructure Evolution and Shear Strength of the Cu/Au80Sn20/Cu Solder Joints with Multiple Reflow Temperatures.

In order to present the multiple reflow process during electronic packaging, the influence of the different short-time reheating temperatures on the microstructure and shear strength of the Cu/Au80Sn20/Cu solder joints was studied and discussed. The results showed that high-quality Cu/Au80Sn20/Cu solder joints were obtained with 30 °C for 3 min. The joints were mainly composed of the ζ-(Au,Cu)5Sn intermetallic compound (IMC) with an average thickness of 8 μm between Cu and solder matrix, and (ζ-(Au,Cu)5Sn +δ-(Au,Cu)Sn) eutectic structure in the solder matrix. With an increase in the multiple reflow temperature from 180 °C to 250 °C, the microstructure of the joint interface showed little change due to the barrier effect of the formed ζ IMC layer and the limitation of short-time reheating on the element diffusion. The eutectic structures in the solder matrix were coarsened and transformed from lamellar to the bulk morphology. The shear strength of the as-welded joint reached 31.5 MPa. The joint shear strength decreased slightly with reheating temperatures lower than 200 °C, while it decreased significantly (by about 10%) with reheating temperatures above 250 °C compared to the as-welded joint. The shear strength of the joints was determined by the brittle solder matrix, showing that the joint strength decreased with the coarsening of the δ phase in the eutectic structure.

Highly reliable Cu[sbnd]Cu low temperature bonding using SAC305 solder with rGO interlayer

The immoderate growth of intermetallic compounds (IMCs) and the transformation of benign IMCs to malignant IMCs are the main causes for the decrease of the mechanical properties and reliability in the CuSn joints. In this study, a 14 nm thickness reduced graphene oxide (rGO) interlayer was directly prepared between Cu and Sn-3.0 Ag-0.5 Cu (SAC305) solder to inhibit the immoderate growth of IMCs and malignant IMCs formation at the bonding interface. The highly reliable CuCu bonding was realized at 150 °C under the external pressure of ~8.3 MPa. The bonded samples were aged at 150 °C for 0 h–72 h for reliability tests. After aging for 72 h, the thickness of the IMCs layer at the Cu/rGO/solder interface decreases by more than 30%, and the average projected area of IMCs grains decreases by more than 80% compared with that at the Cu/solder interface. Furthermore, the decreasing rate of shear strength with rGO interlayer is lower than that without rGO interlayer for long time aging. For the Cu/rGO/solder bonding structure, after 72 h aging, the shear strength is higher and the contact resistance is lower compared with the Cu/solder bonding structure. For this low temperature bonding process using the rGO interlayer, the immoderate growth of IMCs at the bonding interface was inhibited, which can delay the decrease of shear strength due to aging of the bonding interface.

The Effect of Multiple Thermal Process on Microstructural Evolution and Mechanical Properties of Additive Manufactured Al/Steel Structure

Wire and arc additive manufacturing (WAAM) provides a convenient solution for the integrated design and manufacturing of Al/steel structures. The multiple thermal cycles inherent in WAAM can affect the Al/steel interface and ultimately the overall performance of the Al/steel structure. Herein, the evolution behavior of the Al/steel interface microstructure under different WAAM modes, number of thermal cycles, and interpass temperature is investigated. The results show that the process of heat accumulation plays an important role in the evolution of Al/steel interface. As the number of thermal cycles increases, the intermetallic compounds layer gradually transforms from the mainly τ5‐Al8Fe2Si phase to (Al, Si)13(Fe, Cr)4 phase. The rise of interpass temperature significantly aggravates the microstructural evolution process, but the final interface structure can be manipulated employing temperature control. When the interpass temperature is lower than 250 °C, the formation of the brittle Fe2Al5 phase is avoided. With the increase of thermal cycles, the shear strength of Al/steel additive specimens increases first, then decreases, and finally tends to be stable. The changes in shear strength are closely related to the interface microstructures.

Evolution of IMC layer and its reinforcing effect in 2024/MB8 dissimilar joints using a multi-interlayer of Cu/Zn via U-TLP bonding

2024/MB8 dissimilar alloys can be joined in atomsphere using ultrasonic-assisted transient liquid phase (U-TLP) bonding with multi-interlayers made of copper and zinc foil. These multi-interlayers not only prevent the formation of Al3Mg2 and Al12Mg17 but also offer high efficiency and defect-free joining at 380 °C. The results show that the copper foil functions as a “physical barrier”. The zinc foil lowers the bonding temperature and balances the consumption of copper foil via base metals (BMs). Mechanical properties of these joints can be improved by adjusting the type of intermetallic compounds (IMCs) on the surface of copper foil. When utilizing Cu interlayer, the fracture route of the joints occurred on the Al2Cu layer between Al BM and copper foil. When utilizing Cu/Zn multi-interlayer, the fracture route shifted to the Mg2Cu layer along the surface of copper foil on the Mg BM side as the IMCs layer between Al BM and copper foil changed from Al2Cu to AlZnCu2 +Al2Cu, improving bonding. When utilizing Zn/Cu/Zn multi-interlayer, the IMCs layer along the surface of copper foil on the Mg BM side changed from MgZn2 (1.5 s) to Mg4Zn7 + MgZnCu (3 s) to MgZnCu (11 s) to Mg2Cu (24 s) with longer ultrasonic treatment time. The MgZnCu layer increased the shear strength of the joints to a maximum value of 59.92 MPa, which is about threefold that of the Cu interlayer and was about twofold that of the Cu/Zn multi-interlayer.

Shear performance of microscale ball grid array structure Cu(Ni)/Sn–3.0Ag–0.5Cu/Cu(Ni) solder joints at low temperatures

In this study, the shear performance of microscale ball grid array structure Cu/Sn–3.0Ag–0.5Cu (SAC305)/Cu, Cu/SAC305/Ni, Ni/SAC305/Cu, and Ni/SAC305/Ni solder joints was investigated at decreasing temperatures (25 °C, 0 °C, −25 °C, −50 °C, −75 °C, −100 °C, and −125 °C). The results showed that the shear performance of the solder joints was considerably influenced by both the temperature and substrate materials. The shear strength of the Cu/SAC305/Cu solder joint monotonically increased with decreasing temperature, whereas the shear strength first increased and then decreased for the other solder joints. The fracture positions of all solder joints shifted from the solder matrix to the interface between the solder matrix and intermetallic compound layer when the temperature decreased, and the fracture mechanism changed from ductile to brittle with a ductile-to-brittle transition temperature of approximately −75 °C. Moreover, the interfacial fracture of the Cu/SAC305/Ni and Ni/SAC305/Cu solder joints was prone to occur at the Ni substrate side.

Effect of intermetallic compounds on the mechanical property and corrosion behaviour of aluminium alloy/steel hybrid fusion-brazed welded structure

Al alloy/steel joint was produced by fusion-brazing welding with different heat inputs to obtain intermetallic compounds (IMCs) layer with different thicknesses. Following by enhancing heat input, not only the FeAl binary IMCs (Fe2Al5 and Fe4Al13) became thicker at the interface, the formation of Fe-Al-Si ternary IMCs, such as Fe2Al8Si, also became evident. Nevertheless, the joint strength was maintained at a high level. An increase of corrosion current density with three orders of magnitude was identified when the joint was welded under a high heat input (>632 J/cm) due to the appearance of enhanced tunnelling corrosion caused by ternary IMCs with weld seam. Binary IMCs became less corroded with the increase of heat input arising from the cathodic corrosion protection. Therefore, a low heat input should be utilised to preserve the corrosion resistance of the joint, while keeping its mechanical performance.

Microstructure and mechanical performance of dissimilar metal joints of aluminium alloy and stainless steel by cutting-assisted welding-brazing

The 5052 aluminium alloy and 304 stainless steel were successfully joined by cutting-assisted welding-brazing (CAWB) method without using flux. Dual-scale interfacial structures were achieved by designing the geometry of cutting tool. Results indicated that the macroscale self-locking interface was produced when the taper step-shape cutting tool was adopted. Especially when the cutting tool step was increased to 6 steps, the microscale interface took on a micrometre-sized self-locking morphology and a layer of wavy intermetallic compound (IMC) with an average thickness of 3.3 μm was formed at the interface. The τ4 IMC particles and the FeAl6 phases on a small scale were dispersed homogeneously in the welded seam. The maximum tensile strength of the joints reached 152.3 MPa, 75% that of the 5052 aluminium base metal. The robust Al/steel dissimilar joints were attributed to the particle-reinforced weld metal and the macro- and microscale dual self-locking structure at the interface.

Abnormal Shear Performance of Microscale Ball Grid Array Structure Cu/Sn–3.0Ag–0.5Cu/Cu Solder Joints with Increasing Current Density

The shear performance and fracture behavior of microscale ball grid array structure Cu/Sn–3.0Ag–0.5Cu/Cu solder joints with increasing electric current density (from 1.0 × 103 to 6.0 × 103 A/cm2) at various test temperatures (25 °C, 55 °C, 85 °C, 115 °C, 145 °C, and 175 °C) were investigated systematically. Shear strength increases initially, then decreases with increasing current density at a test temperature of no more than 85 °C; the enhancement effect of current stressing on shear strength decreases and finally diminishes with increasing test temperatures. These changes are mainly due to the counteraction of the athermal effect of current stressing and Joule heating. After decoupling and quantifying the contribution of the athermal effect to the shear strength of solder joints, the results show that the influence of the athermal effect presents a transition from an enhancement state to a deterioration state with increasing current density, and the critical current density for the transition decreases with increasing test temperatures. Joule heating is always in a deterioration state on the shear strength of solder joints, which gradually becomes the dominant factor with increasing test temperatures and current density. In addition, the fracture location changes from the solder matrix to the interface between the solder matrix and the intermetallic compound (IMC) layer (the solder/IMC layer interface) with increasing current density, showing a ductile-to-brittle transition. The interfacial fracture is triggered by current crowding at the groove of the IMC layer and driven by mismatch strain at the solder/IMC layer interface, and the critical current density for the occurrence of interfacial fracture decreases with increasing test temperatures.