Shear Strength Of Solder Joints Research Articles

Thermomigration Microstructure and Properties of Ni Nanoparticle-Reinforced Sn58Bi Composite Solder/Cu Solder Joint

A Sn58Bi composite solder reinforced by Ni nanoparticles was prepared using a mechanical mixing technique, and the thermomigration microstructure and properties of the solder joints were studied. The findings indicate that incorporating an appropriate quantity of Ni nanoparticles can enhance the microstructure of the composite solder and mitigate the coarsening of Bi-phase segregation. At 0.75 weight percent Ni nanoparticle content, the composite solder’s tensile strength is 59.7 MPa and its elongation is 54.6%, both of which are noticeably greater than those of the base solder. When the thermal loading time is 576 h, the shear strength of the composite solder joint is 25.5 MPa, which is 30.1% higher than that of the base solder joint. This study reveals that the shear fracture path shifts from the boundary region between the solder seam and the IMC layer to the IMC layer itself. Concurrently, the fracture mode evolves from a mix of brittle–ductile fracture, characterized by quasi-cleavage, to a predominantly brittle fracture, marked by numerous “rock candy-like” cross-sectional features and secondary cracking. Adding Ni nanoparticles to the Sn58Bi composite solder/Cu solder junction can significantly extend its service life.

SnPbInBiSb high-entropy solder joints with inhibited interfacial IMC growth and high shear strength

The rapid advancements in microelectronic devices towards miniaturization and multifunctionality have led to an increasing demand for solder joints that exhibit enhanced mechanical properties and reliability. This study focuses on investigating the high-shear strength of SnPbInBiSb/Cu high-entropy solder joints. The analysis encompasses the microstructure evolution, interfacial reactions, and shear behavior of these solder joints after reflowing at 180 °C. The study reveals the formation of very thin intermetallic compound (IMC) layers, specifically Cu6Sn5 and Cu3Sn, at the SnPbInBiSb/Cu interface with an average thickness of about 1.04 μm following a 10min reflow. Transmission electron microscopy (TEM) analysis illustrates the presence of nanoscale precipitates of InSn3 or Sn3Sb phases dispersed within the Cu6Sn5 IMC. The high mixing entropy of the SnPbInBiSb solder contributes to the suppression of the interfacial IMC growth rate during the reflow process. Notably, the shear strength and fracture behavior of the SnPbInBiSb high-entropy solder joints are significantly influenced by the thickness of the interfacial IMC. In particular, solder joints reflowed at 180 °C for 10 min exhibit a high shear strength of 102.4 MPa with a ductile fracture mode.

Effects of Minor Zn Dopants in Sn-10Bi Solder on Interfacial Reaction and Shear Properties of Solder on Ni/Au Surface Finish.

Sn-10Bi low-bismuth-content solder alloy provides a potential alternative to the currently used Sn-Ag-Cu series due to its lower cost, excellent ductility, and strengthening resulting from the Bi solid solution and precipitation. This study primarily investigates the interfacial evolution and shear strength characteristics of Sn-10Bi joints on a Ni/Au surface finish during the as-soldered and subsequent isothermal aging processes. To improve the joint performance, a 0.2 or 0.5 wt.% dopant of Zn was incorporated into Sn-10Bi solder. The findings demonstrated that a 0.2 or 0.5 wt.% Zn dopant altered the composition of the intermetallic compound (IMC) formed at the interface between the solder and Ni/Au surface finish from Ni3Sn4 to Ni3(Sn, Zn)4. The occurrence of this transformation is attributed to the diffusion of Zn atoms into the Ni3Sn4 lattice, resulting in the substitution of a portion of the Sn atoms by Zn atoms, thereby forming the Ni3(Sn, Zn)4 IMC during the soldering process, which was also verified by calculations based on first principles. Furthermore, a 0.2 or 0.5 wt.% Zn dopant in Sn-10Bi significantly inhibited the Ni3(Sn, Zn)4 growth after both the soldering and thermal aging processes. Zn addition can enhance the shear strength of solder joints irrespective of the as-soldered or aging condition. The fracture mode was determined by the aging durations-with the brittle mode occurring for as-soldered joints, the ductile mode occurring for aged joints after 10 days, and again the brittle mode for joints after 40 days of aging.

Effect of Mo and ZrO2 nanoparticles addition on interfacial properties and shear strength of Sn58Bi/Cu solder joint

The influence of Mo and ZrO2 nanoparticles addition on the interfacial properties and shear strength of Sn58Bi solder joint was investigated. The interfacial microstructures of Sn58Bi/Cu, Sn58Bi + Mo/Cu and Sn58Bi + ZrO2/Cu solder joints were analysed using a scanning electron microscope (SEM) coupled with energy dispersive X-ray (EDX) and the X-ray diffraction (XRD). Intermetallic compounds (IMCs) of MoSn2 are detected in the Sn58Bi + Mo/Cu solder joint, while SnZr, Zr5Sn3, ZrCu and ZrSn2 are detected in Sn58Bi + ZrO2/Cu solder joint. IMC layers for both composite solders comprise of Cu6Sn5 and Cu3Sn. The SEM images of these layers were used to measure the IMC layer’s thickness. The average IMC layer’s thickness is 1.4431 µm for Sn58Bi + Mo/Cu and 0.9112 µm for Sn58Bi + ZrO2/Cu solder joints. Shear strength of the solder joints was investigated via the single shear lap test method. The average maximum load and shear stress of the Sn58Bi + Mo/Cu and Sn58Bi + ZrO2/Cu solder joints are increased by 33% and 69%, respectively, as compared to those of the Sn58Bi/Cu solder joint. By comparing both composite solder joints, the latter prevails better as adding smaller sized ZrO2 nanoparticles improves the interfacial properties granting a stronger solder joint.

Effects of soldering temperatures and composition on the microstructures and shear properties of Sn58Bi-xSAC0307/ENIG solder joints

PurposeThis paper aims to systematically study the effects of reflow temperature and SAC0307 (SAC) content on the micromorphology and mechanical properties of Sn58Bi-xSAC0307 composite solder joints to meet the requirements of high integration and low-temperature packaging of devices and provide references for the application of composite solder joints.Design/methodology/approachSn58Bi and SAC0307 solder paste was mechanically mixed in different proportions to prepare Sn58Bi-xSAC0307/ENIG solder joints. The thermal properties, microstructure and mechanical properties of the composite solder joints were studied.FindingsAs SAC content in the solder increases, the balling temperature of SnBi-SAC solder gradually increases. The addition of SAC alloy reduces the grain size of large Bi-rich phase, and there are small-sized dispersed Bi and Ag3Sn particles in the bulk solder. The intermetallic compounds composition of the SnBi-xSAC/ENIG solder joint changes from Ni3Sn4 to (Ni, Cu)3Sn4 and (Cu, Ni)6Sn5 with SAC increasing. As the soldering temperature increases, the strength of all solder joints shows a rising trend. Among them, the shear strength of SnBi-20SAC solder joints at a reflow temperature of 150°C is approximately 37 MPa. As the reflow temperature increases to 250°C, the shear strength of solder joints increases to approximately 67 MPa.Originality/valueThis study provides a reference for the optimization of low-temperature solder composition and soldering process under different package designs.

Effect of electron irradiation on microstructural evolution and mechanical properties of Sn3Ag0.5Cu solder joints

Power electronic devices face harsh radiation environments in deep space exploration. It is significant to study the reliability of solder joints of electronic devices in radiation environments. The effect of electron irradiation on the microstructure and mechanical properties of Sn3Ag0.5Cu (SAC305) Ball Grid Array (BGA) solder joints was investigated in this work. The results show that the central position of the SAC305 solder joint surface was damaged after electron irradiation. Then the surface of the solder joints was remelted. The shear strength of solder joints increases as the electron irradiation dose rises. When the electron irradiation dose reaches 80 Mrad, the shear strength of the solder joint is enhanced by 8.62% compared with that of the unirradiated sample. After irradiation, the number of dimples on the fracture surface of solder joints increases and the depth of dimples decreases. Geant4 simulation results show that the surface of solder joint is subject to more severe electron impact than the inside of solder joint is. The interaction between electrons and solder joints is the primary reason for the surface remelting of solder joints.

Effect of Si3N4 nanoparticles on IMC as well as mechanical properties of Sn58Bi/Cu solder joints during thermal aging

This paper investigated the changes in microstructure, intermetallic compounds (IMC), and mechanical properties of Sn58Bi/Cu and Sn58Bi-0.6 Si3N4/Cu solder joints in the thermal aging process at 125 °C. With the increase of the thermal aging time, the Bi-phase was gradually coarsened, but the coarsening of the Bi-phase was suppressed after adding Si3N4 NPs. The thickness of the IMC increased continuously, and some areas even detached into the solder matrix, accompanied by gradual grain growth. For the samples with Si3N4 NPs, the IMC thickness significantly decreased, and the grain size was finer. Fractures mainly occur in the Bi-rich phase of the solder matrix following a brief period of thermal aging. However, as the aging time increases, the fracture location gradually shifts from the solder matrix to the IMC, resulting in intergranular and transgranular fractures. However, the shear strength of solder joints with added Si3N4 NPs was higher during the same aging period.

Thermal Cycling Performance of Heterogeneous Solder Ball Joints with Sn-3.0Ag-0.5Cu and Sn-0.75Cu(-Ni,Bi) Solder Ball Composition for BGA Package

Sn-3.0Ag-0.5Cu (SAC305) is one of the most commonly used Pb-free solder composition nowadays. A minor alloying element addition can improve mechanical properties and thermal reliability of the solder joint. Minor amount of Bithmuth (Bi) or Nickel (Ni) addition can improve mechanical properties of solder by solid solution strengthening, or ensure the structural stability of the intermetalllic compounds. Also, low melting temperature solder with Bithmuth can reduce the cost of soldering process and keep components from deterioration. In this study, reliability of heterogeneous and homogeneous solder joint in the ball-grid-array (BGA) package solder joint were investigated. Using Sn-3.0Ag-0.5Cu (SAC305) solder paste and two kinds of solder balls, we have investigated which combination of solder joint improves the thermo-mechanical reliability. SAC305 and SCN (Sn-0.75Cu-Ni,Bi) balls were used for homogeneous and hetrogeneous joints. Solder balls were attached in BGA package. To examine the solder joint reliability, thermal cycling test was conducted after reflow soldering. Shear strength measurement and cross-sectional analysis of the BGA package solder joints were carried out before and after 2000 cycles of the test. The shear strength of homogeneous solder joint decreased to 68.2% and heterogeneous decreased to 43.5%. The cross-sectional analysis using scanning electorn microscopy (SEM) and electorn back-scattered diffraction (EBSD) showed the (Ni,Cu)<sub>6</sub>Sn<sub>5</sub> and Cu<sub>6</sub>Sn<sub>5</sub> IMCs which were generated in the solder joint, and the crack propagated longer in the homogeneous solder joint of SAC305 after the thermal cycling test. IPFM showed the grain refinement effect of the SCN solder joint after thermal cycling. The minor addition of Bi had played a role as dislocation pinning site and became to equiaxied grain, so that the lifetime of heterogeneous SCN solder joint was superior than that of the SAC305.

Comparing the Solderability of Different SA C0307 Composite Solder Pastes

In the present study, the effect of four oxide ceramics (TiO2, ZnO, ZrO2, and CuO) as reinforcements were investigated on the soldering parameters of the SAC 0307 solder alloy. The oxide ceramics were used in nano-powder format. Composite solder pastes were composed by the standard ball milling process of the nano-particles into the SAC 0307 solder paste in 0.25wt% weight fraction. The wettability, shear strength, and microstructure of the composite solder joints were studied and compared. The ceramic nano-particles did not have a major effect on the wettability of the solder. Shear strength increases were observed at the composite joints, except in the case of ZnO. Generally, Sn grain refinement was found in the Sn-matrix which could be the reason for the shear strength increase.

Interface reactions between copper and 50In-50Pb (wt%) alloy by solid-state aging

This study investigated the interface microstructure that developed between 50In-50Pb (wt%) solder and copper (Cu) base material as a function of solid-state aging. The aging temperatures and times were in the range of 55°C – 170°C and 1 – 350 days, respectively. The analysis examined the intermetallic compound (IMC) layer compositions; the rate kinetics of IMC layer growth; and the role of the IMC layer on solder joint shear strength. The IMC layer transitioned from pseudo-equilibrium compositions towards an equilibrium composition of Cu11In9 (φ phase) with an increased degree of aging, illustrating the non-equilibrium nature of the interface. The rate kinetics for solid-state IMC formation exhibited a time exponent, n, of 0.47±0.09, which indicated a diffusion-controlled reaction. The relatively low, apparent activation energy, ΔH, of 23±4 kJ/mol implied an anomalously-fast diffusion mechanism. The shear stresses were 22±2 MPa and 19±1 MPa for the 0.190 mm and 0.380 mm joint clearances, respectively, representing the as-fabricated condition; the difference reflected the plane strain effect. The crack path remained in the In-Pb solder so that the In-Pb microstructure, not the thickness, composition, or morphology of the IMC layer, controlled shear strength for either joint clearance. The shear strength trends differed between joint clearances due to competing processes in the In-Pb solder. Precipitation and re-solutionization of Cu dissolved in the In-Pb solder controlled the effects of aging on the shear strength of the 0.190 mm joint clearance while traditional recovery and recrystallization mechanisms determined the aging response of the 0.380 mm solder joints.

Improvement of Solder Joint Shear Strength under Formic Acid Atmosphere at A Low Temperature.

With the continuous reduction of chip size, fluxless soldering has brought attention to high-density, three-dimensional packaging. Although fluxless soldering technology with formic acid (FA) atmosphere has been presented, few studies have examined the effect of the Pt catalytic, preheating time, and soldering pad on FA soldering for the Sn-58Bi solder. The results have shown that the Pt catalytic can promote oxidation-reduction and the formation of a large pore in the Sn-58Bi/Cu solder joint, which causes a decrease in shear strength. ENIG (electroless nickel immersion gold) improves soldering strength. The shear strength of Sn-58Bi/ENIG increases under the Pt catalytic FA atmosphere process due to the isolation of the Au layer on ENIG. The Au layer protects metal from corrosion and provides a good contact surface for the Sn-58Bi solder. The shear strength of the Sn-58Bi/ENIG joints under a Pt catalytic atmosphere improved by 44.7% compared to using a Cu pad. These findings reveal the improvement of the shear strength of solder joints bonded at low temperatures under the FA atmosphere.

Strong composite SnAgCu solder joints with internal aligned carbon fibers by magnetic field

Lightweight carbon fibers with high mechanical performance are referred to as an ideal reinforcement for an extensive variety of composite materials. However, the addition of carbon fibers into electronic interconnection solders is extremely limited so that the expected reinforcement in the mechanical properties of the composite solder joints has not been completely realized. Here, we used magnetic fields to align Ni-coated carbon fibers in the Sn-3.0Ag-0.5Cu solder vertically with the Cu substrate and prepared the oriented composite solder joints. We achieved a further improvement in the shear performance of composite solder joints (∼58 MPa) with a small addition of Ni-coated carbon fibers (0.5 wt%), which is 25% higher than that of pristine joints. It is found that these vertically oriented carbon fibers changed the propagation path of shear cracks and thus increased the shear resistance. Ni-coated carbon fibers also promoted nucleation of interfacial Cu6Sn5 in the solder joints during reflow, but prevented the formation of brittle Cu3Sn phase during isothermal aging, thus ensuring the high shear strength of composite solder joints after isothermal aging. This success provides a new pathway to fabricate a strong composite solder joint with a limited addition of reinforcements by aligning their orientation.

A strategy to improve the thermal fatigue resistance of solder joints based on amorphous Co-P coating to spontaneously build skeleton of CoSn3 laths

Integrated circuit systems are always suffering the temperature cycling environment caused by frequent power on and off. Mismatch in thermal expansion coefficients among chip package components will cause severe cyclic stress to the solder joints. During thermal fatigue, β-Sn grains tended to generate thermal fatigue cracks at the grain boundaries. This work proposed a strategy of using amorphous Co-15 at.% P coating as the interface layer to inhibit the initiation and propagation of thermal fatigue cracks and improve the shear strength of solder joints by numerous endogenous CoSn3 laths. Mechanistically, based on the amorphous structure of the Co-P coating, Co atoms would massively and rapidly diffuse into the molten solder during the liquid-solid diffusion stage of reflow soldering, and the eutectic solidification together with β-Sn spontaneously precipitated numerous laths of CoSn3 intermetallic compounds (IMC), which were evenly distributed and became the skeleton of the solders. The skeleton-like CoSn3 laths with high elastic modulus were the reinforcing phase of Sn-based solder, but also refined the grains of β-Sn. The refinement of β-Sn grains and the strengthening of CoSn3 laths played an important role in inhibiting the initiation and propagation of thermal fatigue cracks. In addition, a discontinuous Co-Sn IMC layer was formed between the amorphous Co-P and the solder. The alternating appearance of CoSn3 and relatively soft β-Sn at the interface avoided the generation of cracks at the interface during temperature cycling.

Ceramic-to-metal bonding using rare-earth containing Sn–Bi solder

With the increasing miniaturization and power of optoelectronic devices, direct bonding of optical substrates like semiconductors and ceramics to metal heat sinks using low melting-point solder has gained significant interest. In this study, we demonstrated the bonding of glass to copper using Sn-58 wt% Bi solder (SB solder) doped with a small amount of rare earth (RE) elements. The RE elements act as active agents that facilitate the bonding to glasses without glass metallization. By optimizing the bonding parameters, such as reflow temperature and time, and employing an inert gas atmosphere to prevent solder or RE oxidation, we successfully achieved the highest shear strength in glass-copper solder joints using SB-RE solder, without the need for ultrasonic-assisted soldering (UAS). These results demonstrate the potential of using RE-containing solder for bonding unmetallized glass and ceramics in optoelectronic devices with metals at low soldering temperatures (< 200 °C). Furthermore, analysis of the shear strength and failure morphology of solder joints revealed only small degradation, primarily originating from the bulk solder region rather than the solder-glass interface, after both thermal aging (100 h) and cycling tests (100 cycles). The establishment of low-melting point RE-containing solders opens the possibility of direct jointing ceramic optoelectronic substrates to metal heat sinks for more efficient heat dissipation. In the meantime, our work also suggests that further optimization studies are necessary to explore its performance under more extreme working conditions.

Preparation, characterization and mechanical properties analysis of SAC305-SnBi-Co hybrid solder joints for package-on-package technology

The development of hybrid solder for chip packing is a major 3D packaging research topic. The incorporation of with low melting points into solder materials has been used in low-temperature packaging. Hybrid solder struggles to enhance low-temperature solder efficiency and mechanical properties. This work examined the effects of Co elements on microstructure and intermetallic compound (IMC) morphology of SAC305-SnBi-Co hybrid solder generated by reflow welding on electroless nickel immersion gold (ENIG) substrate at various temperatures. Moreover, mechanical characteristics and failure behavior of joints were extensively explored. The results show that the addition of 0.05% Co reduced the melting range of the solder and improved the wettability of SnBi solder. According to transmission electron microscopes (TEM) and electron diffraction spots (EDS), the crystal structure of the grains is (Cu, Co)6Sn5 basic-centered monoclinic crystal. Fourier analysis of high-resolution images yields deformed lattice fringes, indicating that Co atoms fill Cu6Sn5's lattice gap in IMC. The shear strength of SAC305/SnBi hybrid solder joints with Co rises and then decreases with temperature. The highest shear strength of solder joints with 0.05% Co (40 nm) is 73.2 MPa at 220 °C, whereas joints with 0.1%Co are 67.5 MPa. Combined with the fracture morphology, the proportion of IMC fracture mode decreased after adding Co element.

Effect of Ni-deposited carbon nanotubes on morphology and shear strength of lead-free solder joints

Effect of Ni-deposited carbon nanotubes on morphology and shear strength of lead-free solder joints

Effect of Nano-Cu6Sn5 upon development mechanism of Cu–Ni–Sn compounds and mechanical characteristics for mixed solder joints

This investigation aimed to examine the development mechanism of Cu–Ni–Sn compounds and analyze the mechanical properties of mixed solder (MS) joints. Results show that an intermetallic compound (IMC) layer was formed in an SAC305 solder joint prepared herein comprising (Ni, Cu)3Sn4 and (Cu, Ni)6Sn5 phases following the reflow process. The morphology of the (Cu, Ni)6Sn5 grains was identified to be dodecahedral. Meanwhile, the IMC layer of the prepared MS joints contained only the (Cu, Ni)6Sn5 phase, which exhibited a hexagonal prism morphology. The lattice characteristics of Cu6Sn5 changed after Ni dissolution, forming (Cu, Ni)6Sn5 crystals with an X-shaped morphology in the MS joints that exhibited a high Cu content during the aging process. After reflow, the MS joints exhibited slightly higher shear strength than the SAC305 solder joint. After aging at 165 °C for 1000 h, the shear strength of the SAC305 solder joint reduced by 21.72% compared to its value after reflow owing to the annexation of Sn grains. However, the number of Sn grains in the MS joints did not considerably decrease after aging. Further, the grain boundaries of β-Sn and (Cu, Ni)6Sn5 particles contributed to the strengthening of the MS joints. The shear strength of the MS joints decreased by 11.06%–18.35% after aging.

Dynamics of corrosion on mechanical and electrical reliability of SAC305 solder joints during salt spray test

This paper, concerns the impact of a corrosion evolution on mechanical and electrical reliability of solder joints during salt spray tests. Focus is made in test vehicle resistors (1210) soldered with a SAC305 lead-free solder. Solder joints resistors were electrically and mechanically tested and aged from 24 to 96 h in a salt spray chamber with one salinity of 5 % NaCl at five temperatures ranging from 25 °C to 45 °C. The shear strengths of SAC305 solder joints decreased with increasing temperature and corrosion time. No electrical failure was observed. However, the solder joints deterioration is visible by cross-section after 72 h at 25 °C, 60 h at 30 °C, 48 h at 35 °C, 36 h at 40 °C and 24 h at 45 °C. Moreover, the corrosion has a significant effect on the mechanical strength of lead-free solder joints. A relationship between the mechanical behaviour and the dynamics of corrosion of the solder joints has been established. In addition, although the corrosion product remains the same, the corrosion dynamics of the solder material (alloy) and the solder joint (assembly) are very different: the corrosion kinetics is significantly less in the solder material than in the solder joints.

Study on the properties of epoxy-based Sn[sbnd]58Bi solder joints

In electronic packaging technology, Sn58Bi alloy solder has the advantages of low-temperature soldering and high shear strength of solder joint. It has a wide range of application in the electronics industry for low-temperature soldering, especially for temperature-sensitive substrates. Epoxy-based Sn58Bi solder paste is a mixture of curable flux and Sn58Bi solder powder. During the soldering process, the curable flux, in addition to the functions of a conventional flux, forms a cured epoxy shell around the periphery of the solder joint, which can effectively improve the shear strength and thermal stability of the solder joint. In this study, a self-made epoxy-based Sn58Bi solder paste was prepared and the properties of the solder joints were investigated. The results show that epoxy-based Sn58Bi solder paste has better wettability than traditional Sn58Bi solder paste without epoxy resin. And the shear strength of epoxy-based Sn58Bi solder joint is about 25 % higher than that of traditional Sn58Bi solder joint. Furthermore, the electrical conductivity of epoxy-based Sn58Bi solder joint has the same order of magnitude as that of traditional Sn58Bi solder joint, which means that non-conductive epoxy resin has no effect on the electrical conductivity of the epoxy-based Sn58Bi solder joint.

Minor Ag inducedshear performance alternation in BGA structure Cu/SnBi/Cu solder joints under electric current stressing

In this work, the effect of minor Ag addition on shear performance of ball grid array (BGA) structure Cu/SnBi/Cu solder joints under electric current stressing was investigated. The results show that the shear strength of solder joints decreased with increasing current density, and the effect of Ag addition on shear strength changed from an elevating state to a deteriorating state. The elevating effect of Ag addition was due to the dominance of Sn/Bi phase refinement and Ag3Sn dispersion, which was weakened gradually with the increase in current density. The deteriorating effect of Ag addition was attributed to the more inhomogeneous distribution of current density and higher thermal gradient induced by the finer phase of the solder matrix as well as the consequent severer strain mismatch at the Sn/Bi phase interface. The finer Sn/Bi phase was also conductive to easier lattice atom migration under current stressing, resulting in a rapid decrease in shear strength. Moreover, the dominant factor on the shear strength reduction tended to change from Joule heating to athermal effect of current stressing. The fracture of solder joints indicated an insignificant influence by the Ag addition, which all occurred in the solder matrix in a ductile mode.