Interfacial Intermetallic Compounds Research Articles

Interface characteristics and fracture mechanism of laser-arc hybrid welded Al-Ti dissimilar butt-joint through beam oscillation

Two laser oscillating patterns including circle and inscribed double-circle were adopted for the laser-arc hybrid welding of Al-Ti dissimilar butt-joint, and compared with the none-oscillating hybrid welding. The results showed that a two-layer intermetallic compounds (IMCs) including Al3Ti and Al2Ti was formed at the Al-Ti interface without laser oscillation, and the thickness (τ) of IMCs layer reached up to 5.56 μm. The IMCs layer was transferred to a single-layer Al2Ti with decreased the τ to 1.18 μm by the optimized inscribed double-circle oscillating hybrid welding. The optimized laser oscillation benefited to form local turbulences inside the molten pool, which optimized the composition of interface IMCs layer and effectively reduced its thickness. Due to the combined improvements, the ultimate tensile strength of Al-Ti dissimilar butt-joint was increased by 18% from 182.6 to 215 MPa. The corresponding tensile fracture of welded joint changed from the two-layer IMCs layer to the base metal. Because no orientation relationship between them along the Al3Ti/ Al2Ti was formed, the tensile crack preferentially propagated between the Al3Ti and Al2Ti IMCs at the interface, resulting in the poor tensile properties.

Cu–Cu joint with great strength using In/Sn–58Bi hybrid soldering at low temperature (90 °C)

This study investigates Cu single-sided solder joints using hybrid soldering (In + Sn58Bi) at reflow temperatures ranging from 80 to 130 °C. The wetting angles of 27° at 90 °C and 22° at 130 °C demonstrated good wettability. The hybrid solders were composed of γ-In(Sn, Bi) and Bi(In, Sn)2 phases, forming Cu6(In, Sn)5 interfacial intermetallic compounds (IMCs). Thermodynamic calculations proved that the hybrid soldering possessed a low liquid temperature of 86.8 ° C, making it suitable for low-temperature applications. The hybrid solders demonstrated notable mechanical performance, with microhardness values exceeding 10 HV—higher than Sn–52In solder (6 HV). Sandwich hybrid-solder joints, reflowed at 90 and 130 ° C, outperformed Sn–52In soldering strength (30.1 and 35.5 MPa) by over 135% and 175%. Additionally, the hybrid solder contains only 41.9 wt% In, lower than Sn–52In, reducing material costs. This study reveals the hybrid solder system offers a promising low-cost and good-strength solution for low-temperature soldering applications.

Microstructure of ternary Sn-Bi-xCu alloy on mechanical properties, current endurance and corrosion morphology via cycling corrosion test

Low melting temperature of Sn-58 wt.% Bi (SB) solders adding 0.5wt.% Cu (SB05C) and 1.7wt.% Cu (SB17C) concentrations were evaluated for the signal transmission in the 3D IC package. Microstructure combined with phase analysis and Pandat simulation were together with to explain the relationship among the mechanical property, electrical endurance and corrosion resistance. By Cu decoration, the presence Cu6Sn5 intermetallic compound (IMC) acts as heterogeneous nucleation sites to reduce surface free energy and generate fine Bi grain that resulted in higher hardness value. The power-law was used to explain the mechanism of interfacial IMC growth, both Cu6Sn5 and Cu3Sn formation were speculated to be volume diffusion control and surface reaction domination, respectively. The fracture morphology by shear testing indicates that earliest plastic deformation accompanied with brittle rupture were major factors due to the intergranular fracture and Cu6Sn5 compound induced bulk fracture. By cycling corrosion test (CCT), the lump shape of SnO2 by-product was found among solders at three cycling. After seven cycling, Sn phase has been completely corroded and Cu6Sn5 IMC began to be corroded forming circle shape of Cu2O but Bi phase still not be corroded among solders. In the electrical endurance, dense Cu6Sn5 dispersed in solder bulk and fine grain size were feasible to induce current crowding and joule heating, thus Cu deteriorated SB solders is easily failed.

The Evolution of Interfacial Intermetallic Compound Growth and Solder Joint Strength of Sn-40Pb/Cu under Thermal Aging

The Evolution of Interfacial Intermetallic Compound Growth and Solder Joint Strength of Sn-40Pb/Cu under Thermal Aging

A Cu/Ni/Cu/Sn1.8Ag microbump structure for void-free interface under long time high-temperature storage

Microbumps play a crucial role in interlayer interconnections for advanced packaging. Among the prevalent microbump structures are Cu/Sn and Cu/Ni/Sn configurations. However, as the bump size continues to shrink, excessive Kirkendall voids tend to form in Cu/Sn microbumps, leading to potential reliability issues. While Cu/Ni/Sn structures can suppress Kirkendall void formation, Ni3Sn4 intermetallic compound (IMC) exhibits inferior physical properties compared to Cu3Sn and Cu6Sn5. In this study, a novel Cu/Ni/Cu/Sn1.8Ag (CNCT) Sn-rich microbump structure with controlled Cu thickness is proposed to suppress Kirkendall void formation while promoting Cu6Sn5 and Cu3Sn as interfacial IMCs. A Ni barrier layer is inserted to partition the Cu pillar and impede Cu atom replenishment from the bottom side. The remaining Cu pillar at the top is designed to be 3μm thick, which is intended to be fully consumed by 8μm Sn1.8Ag solder while simultaneously serving as redundant protection for the bottom Cu pillar against unexpected Sn spillage. The effects of high temperature storage (HTS) at 150°C on IMC evolution in CNCT microbump bonding were investigated for 1500 hours. No significant voids were observed at the bonding interface during HTS. Interfacial positions recorded from 0 to 500 hours show that the Cu3Sn IMC grows unidirectionally toward the Cu side but not toward the Sn side, indicating a greater diffusion flux of Sn atoms compared to Cu atoms. The diffusion coefficients of Cu in Cu3Sn (DCu,ε), Cu6Sn5 (DCu,η), and Sn in Cu3Sn (DSn,ε), Cu6Sn5 (DSn,η) at 150°C were calculated as 1.36×10−18 m2/s, 5.01×10−19 m2/s, 9.53×10−19 m2/s and 1.10×10−18 m2/s, respectively. The dramatic decrease of DCu,η suggests that the diffusion capacity of Cu atoms into Sn is significantly suppressed. The notable transformation of Cu3Sn to Cu6Sn5 occurred after 500 hours. By 1500 hours, Cu3Sn was greatly consumed, and the bonding interface tended to form a stable Cu/Ni/Cu6Sn5/Ni/Cu structure. Diffusion models were established and discussed to elucidate the mechanisms governing both stages.

Evolution mechanism of interfacial multi-layer intermetallic compounds and failure behavior in the Al–Au wire bonding

Evolution mechanism of interfacial multi-layer intermetallic compounds (IMCs) and their impact on failure behavior in Al–Au wire bonding after thermal storage and thermal cycle process are investigated. Microstructural analysis shows that multi-layer IMCs form between the Al wire and barrier layer. After thermal storage and thermal cycle process, the Au8Al3 layer transforms into AuAl2, and Au pad transforms to a thicker layer containing Au2Al and AuAl. Thermodynamic analysis indicates that Au8Al3, Au2Al, AuAl, and AuAl2 have increasing stability. Small-size, equiaxed AuAl2 grains form due to high stored energy, while large-size, columnar Au2Al and AuAl grains result from slower reaction rate and limited recrystallization. The stack-like formation of AuAl2 grains is attributed to the balance between driving force and interfacial energy resistance. During thermal storage, thicker IMC layers cause cracking between IMC layers and Au pad, and micro voids form near the IMC layers/barrier layer interface due to Kirkendall effect. Thermal stress results show that plastic deformation of the Al layer slightly affects the thermal stress in other layers during the thermal cycle process. The cyclic stress at the interface with initial cracks ranges from −157 MPa to 114 MPa, facilitating crack propagation. Additionally, micro void grows under cyclic thermal input, weakening interface adhesion. Therefore, bond strength decreases and frequency of bonding lift-off with cracking along the IMC layers/barrier layer interface increases after thermal storage and thermal cycle process. These results provide the guidance for regulating the interfacial IMCs and predicting the thermal stress in Al–Au wire bonding.

Interfacial IMC growth behavior of Sn-3Ag-3Sb-xIn solder on Cu substrate

PurposeThe reliability of solder joints is closely related to the growth of an intermetallic compound (IMC) layer between the lead-free solder and substrate interface. This paper aims to investigate the growth behavior of the interfacial IMC layer during isothermal aging at 125°C for Sn-3Ag-3Sb-xIn/Cu (x = 0, 1, 2, 3, 4, 5 Wt.%) solder joints with different In contents and commercial Sn-3Ag-0.5Cu/Cu solder joints.Design/methodology/approachIn this paper, Sn-3Ag-3Sb-xIn/Cu (x = 0, 1, 2, 3, 4, 5 Wt.%) and commercial Sn-3Ag-0.5Cu/Cu solder were prepared for bonding Cu substrate. Then these samples were subjected to isothermal aging for 0, 2, 8, 14, 25 and 45 days. Scanning electron microscopy and transmission electron microscopy were used to analyze the soldering interface reaction and the difference in IMC growth behavior during the isothermal aging process.FindingsWhen the concentration of In in the Sn-3Ag-3Sb-xIn/Cu solder joints exceeded 2 Wt.%, a substantial amount of InSb particles were produced. These particles acted as a diffusion barrier, impeding the growth of the IMC layer at the interface. The growth of the Cu3Sn layer during the aging process was strongly correlated with the presence of In. The growth rate of the Cu3Sn layer was significantly reduced when the In concentration exceeded 3 Wt.%.Originality/valueThe addition of In promotes the formation of InSb particles in Sn-3Ag-3Sb-xIn/Cu solder joints. These particles limit the growth of the total IMC layer, while a higher In content also slows the growth of the Cu3Sn layer. This study is significant for designing alloy compositions for new high-reliability solders.

Microstructure Modification and Enhancement in Mechanical Properties Cu/Sn-Ag/Cu Microbump Joints with 5-Micron Bonding Height Via Alloying of Zn and Ni in Cu Ubm

With the rise of artificial intelligence (AI) and the 5G era, advanced microelectronic packaging is gaining attention, shifting towards high-density interconnection and downsizing packaging structures. In response to increasing demands for high power density, low energy consumption, and low latency, 3-dimensional chip stacking technology (3D-IC) has emerged. In 3D-IC structures, Pb-free microbump solder joints, notably with diameters potentially below 10μm, are widely used, exhibiting sizes 10 times smaller than traditional flip chip joints. However, this miniaturization poses challenges, leading to interfacial Intermetallic Compound (IMC) overgrowth and high internal stress due to volume shrinkage and natural brittleness. To address this, Cu-Zn-based substrates are employed, forming a Zinc-rich layer that efficiently reduces IMC thickness. The transition of hexagonal η-Cu6Sn5 to monoclinic η'-Cu6Sn5 and the formation of porous Cu3Sn under certain conditions impact mechanical reliability. The addition of Ni and Zn in solder joints is reported to enhance phase stabilization and mechanical properties. Considering the influence of solder alloy composition on melting points, adding Zn and Ni in substrates is suggested to ensure a stable source of dopants and stabilize molten behavior. Co-doping Zn and Ni in substrates aids in Cu-Sn IMC suppression. Previous work on double-sided Cu-26Zn-18Ni substrates soldering with Sn-3.5Ag solder optimized IMC thickness, inhibiting the brittle Cu3Sn phase and Kirkendall voids, while inducing the tough γ-Cu5Zn8 phase. This phase exhibits favorable toughness and shear modulus, enhancing mechanical strength.This study investigates the microstructure evolution, elemental distribution, and mechanical reinforcement of Cu-26Zn-18Ni/Sn-3.5Ag/Cu-26Zn-18Ni microbumps with a bond height below 10μm. A field emission electron probe micro-analyzer (FE-EPMA) was utilized to examine microstructures and elemental distribution. Additionally, transmission electron microscopy with energy dispersive spectroscopy (TEM/EDS) was employed for detailed voiding formation and phase identification. Electron backscatter diffraction (EBSD) confirmed the presence of highly randomly oriented (Cu,Ni)6(Sn,Zn)5 with a submicron grain size. Fracture modes of the microbumps were characterized through shear tests and correlated with microstructures. In comparison to Cu/Sn-3.5Ag/Cu microbumps, the alternative Cu-Zn-Ni substrates significantly improved shear strength (19.6% to 97.8%) and failure toughness (10.6% to 132.1%) under different reflow times. The microstructure of Cu-26Zn-18Ni/Sn-3.5Ag/Cu-26Zn-18Ni microbumps, featuring solid solution strengthening and refined (Cu,Ni)6(Sn,Zn)5 along with tough bulk (Cu,Ag)5(Sn,Zn)8, demonstrated remarkable toughness.These findings offer valuable insights into the design of microbumps with a bonding height in the sub-10-micron scale. Keywords: Microbump, Shear strength, Microstruture, Intermetallic compounds Figure 1

Stable SnAgCu solder joints reinforced by nickel-coated carbon fiber for electronic packaging

Today’s 3D electronic packaging is characterized by smaller size and higher functional density, which generally require multiple reflow cycles. However, due to the Ostwald ripening process of the interfacial intermetallic compound (IMC), the solder joint’s strength would decrease as the number of reflow cycles increases. To address this, we developed a novel composite solder by incorporating nickel-coated carbon fiber (Ni@CF) into the Sn–3.0Ag–0.5Cu (SAC305) solder connection. The study showed that Ni@CF effectively enhanced the stability and reliability of solder joints during multiple reflow processes. Compared with Ni@CF-free equivalents, Ni@CFs promoted the nucleation of interfacial IMC during the solid–liquid reaction and inhibited Ostwald ripening, leading to a refinement of the interfacial IMC grains. As a result, the interface was strengthened, and the shift of shear fracture to the brittle interface seen in the SAC305 solder joint with multiple reflows did not occur in the composite solder joint. Furthermore, carbon fiber strengthened the solder matrix through the load transfer and shear-off mechanisms, depending on its inclination angle with the shear plane. Consequently, the Ni@CFs-reinforced solder joints maintained a shear strength of over 42 MPa throughout ten reflow cycles, while the pristine SAC305 solder joint exhibited decreased shear strength to 33 MPa. This study provides new insights into composite solder joints’ stability and reinforcement characteristics when subjected to multiple reflows.

Mechanical property of intermetallic compounds in Zn–Al solder interconnects by nanoindentation and first-principles calculations

Presently, interfacial intermetallic compounds play a vital role in determining the reliability of solder joints due to their intrinsic mechanical property. Especially for Zn–Al solder joints, the interfacial Cu–Zn IMCs grow significantly without diffusion barriers. This work comprehensively investigated the mechanical properties of interfacial IMCs in Zn–Al solder joints with and without the Ni–W–P diffusion barrier by nanoindentation tests and first-principles calculations. The nanoindentation results show that the elastic moduli of CuZn4, Cu5Zn8, CuZn and Al3Ni2 were 68.45 ± 1.4 GPa, 142.6 ± 2.3 GPa, 94.7 ± 1.16 GPa, and 221 ± 18.9 GPa, respectively. Their corresponding hardness were 1.03 ± 0.04 GPa, 5.98 ± 0.23 GPa, 1.38 ± 0.16 GPa, and 17.7 ± 0.16 GPa. Through first-principles calculations, the bulk modulus of CuZn and Cu5Zn8 exhibits isotropic behaviour, while CuZn4 and Al3Ni2 demonstrate anisotropy. In addition, the bulk modulus, shear modulus, Young's modulus and hardness values of Al3Ni2 are considerably higher when compared to those of Cu–Zn intermetallic compounds.

Power modulation and its effect on microstructural evolution during laser oscillating welding of steel to aluminum alloy

The control of intermetallic compounds (IMCs) poses a challenge in welding Al–Fe joints. To tackle this issue, power-modulated laser welding was utilized to join 6061 aluminum (6061Al) and AISI-304 stainless steel (304SS) in an overlap configuration. This research compares the impacts of two power modes: constant power (CP) and gradient power (GP) on weld formation and interface IMCs to demonstrate the superior performance of the GP mode. The GP mode alters the energy distribution pattern, resulting in distinct weld formation and interface microstructures compared to the CP mode. Notably, the research confirms that the GP mode enhances the tensile shear strength of the joints, highlighting the effectiveness of the GP mode.

Corrosion Behavior and Mechanical Property of 5182 Aluminum/DP780 Steel Resistance Spot Welding Joints.

Corrosion behavior is critical to the application of lightweight aluminum/steel joints using new resistance spot welding (RSW) technology. The study investigated the corrosion mechanism and the shear strength of RSW joints comprising 1.2 mm 5182 aluminum and 1.5 mm DP780 galvanized steel. Electrochemical corrosion tests were conducted on the base materials and various positions of the welds in a 3.5% NaCl solution. This result revealed that the corrosion susceptibility of the interfacial intermetallic compound (IMC) layer was not accelerated by the aluminum nugget because of the noble corrosion potential. Subsequently, the spray acceleration test was employed to investigate the corrosion mechanism. It is noteworthy that microcracks, as well as regions enriched with silicon and oxygen at the interface front, are preferential to corrosion during salt spray exposure, instead of the IMC layer. Moreover, the shear strength of the joints decreases with the reduction in the effective joint area after the salt spray exposure of the weld joints. This research systematically explored the corrosion behavior and its relationship with the mechanical properties of Al alloy/steel RSW joints.

An innovative high-entropy alloy solder for high-reliability low-temperature bonding in 3D electronic packaging–based on nano InSnBiZnAg particles

To address the demand for multilevel package, a low-melting-point high entropy alloy (HEA) solder was developed. It consists of 43In28Sn14Bi9Zn6Ag micro- and nano-particles with a melting point of about 62.80 °C. We obtained 43In28Sn14Bi9Zn6Ag nanoparticles by combining ultrasonic heating interaction with a "hot shock" process. Upon reflowing at 115 °C for 5 min, a Cu/Zn/Ag ternary intermetallic compound (IMC) formed at the interface between the solder and the copper substrate, leading to a shear strength of 40 MPa. The microstructure of this joint exhibits a complex composition with at least three phases, including Bi3In5 phase, Ag5Zn8 phase, and In0.2Sn0.8 solid solution. The stable Ag5Zn8 phase not only enhances the overall strength of the alloy matrix but also impedes the diffusion of In and Bi atoms, thereby preventing the segregation of the Bi3In5 phase. The high mixing entropy and pronounced lattice distortion in this high entropy alloy hinder the diffusion of elements within the solder matrix, mitigating the issue of excessive interfacial IMC growth. Consequently, the solder joints exhibit little degradation even after a high-temperature aging test. This high-entropy alloy solder has promising potential for multi-level chip stacking in 3D packaging.

Investigating the impact of cobalt incorporation on the transformation of Cu6Sn5 layer to (Cu, Co)6Sn5: Microstructural and mechanical insights

In this study, cobalt (Co) particles were incorporated as reinforcing agents into the Sn58Bi solder. The solderability of the solder and the strength of the solder joints were investigated. The results indicated that adding Co particles did not alter the low melting point characteristics of the Sn58Bi solder, yet its undercooling was reduced, and the wettability was enhanced. In the Sn58Bi/Cu solder joint, adding Co led to forming free (Cu, Co)6Sn5 intermetallic compound (IMC) and generating the CoSn2 phase through microalloying. The interfacial IMC was gradually transformed from a fan-shaped Cu6Sn5 to a flatter layer-like (Cu, Co)6Sn5 IMC, eventually exhibiting a coral-like structure with increased Co content. Adding Co particles increased the thickness of the IMC layer, but at low levels, the Co could refine the IMC grains. Simultaneously, implementing grain refinement and Orowan strengthening resulted in heightened microhardness and shear strength. In the shear test, the fracture of solder joints predominantly transpired within the solder matrix. Excessive Co particles were prone to aggregating within the solder, forming irregular block-shaped (Cu, Co)6Sn5. Concurrently, the coral-like IMC at the interface led to a decline in the mechanical performance of the solder joints, with some interfacial IMC being exposed in the fracture region.

Microstructural evaluation of interfacial intermetallic compounds between Sn58Bi and ENEPIG

BackgroundLow carbonization and Restriction of Hazardous Substances (RoHS) regulations have promoted the development of low-temperature lead-free solder. The solder and substrate are critical entities of joint connections. MethodsSn58Bi has been considered a promising low-temperature solder. Electroless nickel/electroless palladium/immersion gold (ENEPIG) is a good surface finish that prevents solder joints from oxidizing and extends the shelf life of the substrates. In this study, the interfacial reactions between the Sn58Bi solder and ENEPIG surface finish were systematically analyzed. Findings(Au,Pd,Ni)(Sn,Bi)4 was observed after reflow at 160 °C. Au and Pd dissolved into solder rapidly in the beginning. NiSn4 and Ni3Sn4 with small amounts of Au and Pd dissolution formed at the interface after aging. The morphology of NiSn4 evolved from block-like to needle-shaped and finally to a layered configuration as the aging temperature and time increase. Ni3Sn4 was observed between NiSn4 and substrate above 100 °C. This study established the growth mechanism of intermetallic compounds (IMCs) in the reaction between Sn58Bi and ENEPIG for low-carbon emitting processes.

Microstructural response characteristics of SAC305/Cu column joint under friction embedded welding conditions

The friction welding method for macro-scale weldments was introduced into the manufacturing of electronic products. Without mold assistance, the positioning and connection of micro copper columns in column grid array packaging (CGA) devices were achieved. The average connection strength of 40.6 N and the intermetallic compound interface layer meant that effective connections were achieved. In the poorly identified stirring-mixing zone (SMZ) in scanning electron microscopy (SEM) images, electron backscatter diffraction (EBSD) results showed that this region was composed of recrystallized grains, twin grains, and Ag3Sn and Cu6Sn5 particles distributed inside or at the grain boundaries. The grain size was about 2 μm, and the Ag3Sn and Cu6Sn5 particle sizes were broken to 250 nm and 120 nm due to stirring. The SMZ at the bottom of the copper column only underwent deformation-induced dynamic recrystallization, while the SMZ on the side was discharged from the bottom of the copper column, so it underwent dynamic recrystallization through the process of cutting crushing-extruding and flow-bonding-deformation. Therefore, the hardness of SMZ was significantly reduced after welding. Unlike traditional friction welding, in the thermo-mechanical affected zone (TMAZ), the solder not only underwent deformation but also formed 47.8% recrystallization microstructure and 14.6% recovery microstructure. Therefore, the effect of deformation strengthening was weakened and recrystallization led to a decrease in hardness. Recovery was the main response behavior in the micro-deformation zone (MDZ). Combined with the numerical simulation results, the temperature and stress driving conditions of the microstructure of each micro-region in instantaneous friction embedded welding (FEW) were also discussed.

Influence behavior and mechanism of crystal orientation of Cu6Sn5 coating on interfacial intermetallic compounds growth in Sn-0.7Cu/Cu solder joint

Herein, the Cu6Sn5 coatings with principal crystal orientations were prepared on the Cu substrate using magnetron sputtering to inhibit the growth of interfacial intermetallic compounds (IMCs) in Sn-0.7Cu/Cu solder joint. The effect of sputtering parameter on the principal crystal orientation of Cu6Sn5 coating was researched firstly, followed by the investigation on the influence of Cu6Sn5 coating principal orientation on the interfacial IMCs growth kinetics. The influence mechanisms were studied using molecular dynamics simulations and first-principles calculations. The results revealed that the increasing sputtering power from 40 W to 60 W and 80 W can not only improve the bonding property between the prepared Cu6Sn5 coating and Cu substrate, but also promote the transformation of the coating principal orientation from (132) to (132)/(22-1) and (132)/(22-1)/(42-2). Moreover, the three prepared Cu6Sn5 coatings can inhibit IMC growth at SC07/Cu solder joint, and the Cu6Sn5 coatings with (132)/(22-1) and (132)/(22-1)/(42-2) principal orientations exhibit more significant inhibitory effects on IMC growth than that with (132) principal orientation. It can be proved in this work that the growth of interfacial IMCs in Sn-0.7Cu/Cu solder joint at aging stage is mainly caused by the diffusion of Cu from Cu substrate toward Cu6Sn5 phase. The difference in the growth behavior of IMCs can be attributed to the fact that when the Cu atoms diffuse across Cu6Sn5 (22-1) and Cu6Sn5 (42-2), the bonding strength between the Cu atom at the saddle point and its surrounding atoms is significantly larger than when diffusing across Cu6Sn5 (132), leading to the smaller diffusion coefficients and a slower interfacial IMCs growth rate.

Achieving outstanding mechanical property after long-cycle thermal shock of reflow/ultrasonic-assisted Kovar/SnSb10 interfaces

The present study analyzed the microstructure evolution corresponding to the mechanical properties of reflow/ultrasonic-assisted Kovar/SnSb10/Fe joints after long-cycle thermal shock (TS). The results indicate that the thickness of interfacial intermetallic compounds (IMCs) at Kovar/SnSb interface with ultrasonication was less than 1 μm even after 2000 cycles, and almost no defects were detected, exhibiting superior microstructure stability. The ultimate shear strength with and without ultrasonication reached 58 MPa and 45 MPa, respectively. From TEM analysis, the nanoprecipitates inside Sn or IMC region primarily consisted of Ni3Sn4 and Ni3Sn phases. The ultimate outstanding mechanical property after long-cycle TS was attributed to dispersed strengthening and dislocation strengthening. This work provides valuable insights into the stability and reliability of the Kovar/SnSb10 system.

Effect of Al-Si Coating on the Interfacial Microstructure and Corrosion Resistance of Dissimilar Laser Al Alloy/22MnB5 Steel Joints

This investigation employed different laser powers to conduct the laser welding–brazing process of 5052 aluminum alloy to both Al-Si coated and uncoated 22MnB5 steel. The flux-cored Zn-Al22 filler metal was employed during the procedure. The influence of Al-Si coatings on the microstructure and corrosion resistance of Al/Steel welded joints was investigated using microstructural characterization and electrochemical tests. It was noted that the interfacial microstructure of the laser Al/steel joints was significantly altered by the Al-Si coating. Moreover, the Al-Si coating suppressed the formation and growth of the interfacial reaction layer. Electrochemical corrosion tests showed that the impact of Al-Si coating on the corrosion resistance of laser joints depended on the laser powers and thickness of the interfacial intermetallic compound (IMC) layer. The research suggests that galvanic corrosion occurs due to the differences in corrosion potential between fusion zone (FZ), steel, and Fe-Al-Zn IMCs, which accelerate the corrosion of the joint. The IMC layer acts as a cathode to accelerate the corrosion of the FZ and as an anode to protect the steel from corrosion.

Improved shear property of Sn-3.0Ag-0.5Cu/Ni micro solder joints under thermal shock between 77 K and 423 K by adding TiO2 nanoparticles

The rapid development of space exploration technology was intensifying the desire for lead-free solders with high performance and reliability under extreme temperature environments. In this study, the influence of TiO2 nanoparticle addition on the microstructure, growth behavior of interfacial intermetallic compounds (IMCs) and shear property of Sn-3.0Ag-0.5Cu (SAC305)/Ni micro solder joints under thermal shock from 77 K to 423 K was systematically investigated. The results indicated that the grain size of β-Sn, IMC (Ag3Sn and (Cu,Ni)6Sn5) particles inside the solder was refined by adding 0.05 and 0.1 wt% TiO2 nanoparticles. Due to the spalling of interfacial IMCs into the solder occurring in all micro joints during thermal shock, the thickness of interfacial IMCs did not show a monotony increasing trend with increasing thermal cycles. However, the micro composite solder joint added with 0.05 and 0.1 wt% TiO2 nanoparticles always exhibited thinner interfacial IMC thickness and higher shear force compared with the plain micro joints during thermal shock. The inhibiting effect of TiO2 nanoparticles on the interfacial IMC growth could be explained by the adsorption theory and grain boundary pinning theory. The improvement in shear property of micro composite solder joints was primarily induced by the refinement of IMC particles in the solder and the reduced growth rate of interfacial IMCs by adding TiO2 nanoparticles.