Interfacial Intermetallic Layer Research Articles

Growth kinetics of interfacial intermetallic layer of In-48Sn/Cu solder joint by transient liquid phase bonding

Growth kinetics of interfacial intermetallic layer of In-48Sn/Cu solder joint by transient liquid phase bonding

Coupling influence of laser-Nb interlayer on microstructure and performance of Ti/Al joint

Laser fusion welding of TC4 titanium (Ti) alloy and aviation 7075 aluminum (Al) alloy was conducted with the assistance of a niobium (Nb) interlayer. The effect of laser heat input and the alloying effect of Nb on the interfacial layer was analyzed. The study also investigated the coupling influence of the laser-Nb interlayer on the microstructure and performance of the Ti/Al joint. By utilizing a 0.1 mm-thick Nb interlayer and a welding velocity of 1800 mm/min, the results reveal an initial increase in tensile-shear force followed by a decline with the increase of laser power. The tensile-shear force reached a peak of 1663 N at 1.2 kW, representing a 36.76 % improvement over the 1 kW levels. Under appropriate laser power, the enhancement in joint performance is dominated by the controlled heat input and the effective Nb-alloying effect, which reduce the thickness and brittleness of the interfacial intermetallic layer, respectively. However, metallurgical regulation of Nb will be restricted by the insufficient Nb melting amount resulting from the low laser power, leading to a decrease in joint properties. Excessive laser power can lead to the formation of hot cracks and an excessive amount of Ti-Al intermetallic compounds, which can decrease the Nb content, thereby restricting the metallurgical regulation of Nb and the overall joint performance.

Effect of Al2O3 and NiO Nanoparticle Additions on the Structure and Corrosion Behavior of Sn—4% Zn Alloy Coating Carbon Steel

The application of a higher corrosion resistance coating modified with nano additions can effectively decrease or prevent corrosion from occurring. In the present work, a novel method is successfully developed for the modification of carbon steel surfaces aiming for high corrosion resistance using Sn—4% Zn alloy/nanoparticle composite (NiO+ Al2O3) coating. Sn—4% Zn alloy/nanoparticle composite (NiO+ Al2O3) coatings were deposed on carbon steel using a direct tinning process that involved a power mixture of Sn—4% Zn alloy along with a flux mixture. Regular coating and interface structures were achieved by individual Al2O3 and both NiO and Al2O3 nanoparticle combined additions in the Sn-Zn coating. The maximum coating thickness of 70 ± 1.8 µm was achieved for Al2O3 nanoparticles in the Sn-Zn coating. Interfacial intermetallic layer thickness decreased with all used nanoparticle additions in individual and hybrid conditions. The minimum intermetallic layer thickness of about 2.29 ± 0.28 µm was achieved for Al2O3 nanoparticles in the Sn—Zn coating. Polarization and impedance measurements were used to investigate the influence of the incorporated Al2O3, NiO, and hybrid Al2O3/NiO nanoparticles on the passivation of the low-carbon steel (LCS) corrosion and the coated Sn—Zn LCS in sodium chloride solution. It was found that the presence of Al2O3, NiO, and Al2O3/NiO nanoparticles remarkably improved the corrosion resistance. The corrosion measurements confirmed that the corrosion resistance of the coated Sn-Zn carbon steel was increased in the presence of these nanoparticles in the following order: Al2O3/NiO > NiO > Al2O3.

Additive manufacturing of nano-oxide decorated AlSi10Mg composites: A comparative study on Gd2O3 and Er2O3 additions

AlSi10Mg-based nanocomposites were fabricated by laser powder bed fusion (LPBF) additive manufacturing with the addition of 1 wt% Gd 2 O 3 and Er 2 O 3 nanoparticles. The effect of different process parameters and supplementary remelting on the densification of the samples was evaluated. Results showed that remelting the printed layers could improve the densification. According to the microstructural observations, stacking the nanoparticles on uneven surfaces of irregular AlSi10Mg particles beside van der Waals's attractive force between the adjacent particles eventually forms coarsened clusters in printed samples. The XRD patterns disclosed the partial reaction between the nano-oxides and the aluminum matrix and the formation of some interfacial intermetallic layers, which were also validated by SEM characterization. The measurement of grain size and microhardness implied that the addition of Er 2 O 3 played a more effective role in grain refinement and enhanced the hardness more uniformly compared to Gd 2 O 3 . Overall, the acquired average hardness for both nano-oxide reinforced specimens was greater than the reported values for LPBF-fabricated AlSi10Mg-matrix composites in the past. EBSD analyses revealed that due to the pinning effect of the nanoparticles, particle-rich zones demonstrated higher KAM and grain orientation spread (GOS) values which were attributed to the formation of more GNDs at the matrix/particles interfaces. • The effect of laser remelting on the compactness of the samples was evaluated. • The distribution of the nanoparticles in Al matrix was characterized by the SEM. • Refinement impact of nano-oxide powders on microstructure studied by the EBSD. • Correlation of the microstructural changes with hardness distribution surveyed.

Design, fabrication, microstructure, and mechanical properties of interlayer-free vacuum diffusion bonding Mg/Ti composites

The light weight and complementary properties of Mg and Ti give Mg/Ti composites great development potential. The design and exploitation of high-quality and low-cost fabrication technologies support the advancement of Mg/Ti composites. In this study, Mg/Ti composites were fabricated without interlayer by reaction-diffusion between Al and Ti in AZ91 and TA2 alloys, respectively. The formation order of the interfacial intermetallic was deduced by thermodynamics calculations. The feasibility of interlayer-free diffusion bonding Mg/Ti composites held for 1–3 h was scrutinized by observing the microstructural evolution of the Mg/Ti interface and testing the mechanical properties of the Mg/Ti composites. The results indicated that with increasing holding time, diffusion bonding became more compact and joint quality improved. A high-quality bond formed between the Mg and Ti held for 3 h. The interfacial intermetallic layer formed a continuous and compact Al3Ti + Ti3Al duplex structure. The contents of the Al3Mn nanophase and Mg17Al12 decreased gradually with increasing holding time. Owing to the highest volume of Mg attached to the Ti side and the formation of a few dimples, the tensile strength and elongation of the Mg/Ti composite were increased by 88.8 and 99.6%, respectively, by extending the holding time to 3 h.

Effect of Ni on the Suppression of Sn Whisker Formation in Sn-0.7Cu Solder Joint.

The evolution of internal compressive stress from the intermetallic compound (IMC) Cu6Sn5 growth is commonly acknowledged as the key inducement initiating the nucleation and growth of tin (Sn) whisker. This study investigates the effect of Sn-0.7Cu-0.05Ni on the nucleation and growth of Sn whisker under continuous mechanical stress induced. The Sn-0.7Cu-0.05Ni solder joint has a noticeable effect of suppression by diminishing the susceptibility of nucleation and growth of Sn whisker. By using a synchrotron micro X-ray fluorescence (µ-XRF) spectroscopy, it was found that a small amount of Ni alters the microstructure of Cu6Sn5 to form a (Cu,Ni)6Sn5 intermetallic layer. The morphology structure of the (Cu,Ni)6Sn5 interfacial intermetallic layer and Sn whisker growth were investigated by scanning electron microscope (SEM) in secondary and backscattered electron imaging mode, which showed that there is a strong correlation between the formation of Sn whisker and the composition of solder alloy. The thickness of the (Cu,Ni)6Sn5 IMC interfacial layer was relatively thinner and more refined, with a continuous fine scallop-shaped IMC interfacial layer, and consequently enhanced a greater incubation period for the nucleation and growth of the Sn whisker. These verification outcomes proposes a scientifically foundation to mitigate Sn whisker growth in lead-free solder joint.

Preliminary study on the effect of Ni addition on tin (Sn) whisker growth from lead-free solder coating

It has been widely confirmed that alloying significantly can mitigate the formation of tin (Sn) whiskers and consequently became a possible candidate as a lead-free alloys coating material in the microelectronics industry. In this study, the effect of 0.05 wt.% Ni addition on the formation and growth of Sn whisker in Sn-0.7Cu solder coatings have been investigated under continuous mechanically stress induced at room temperature. It is clearly found that Ni addition have significantly enhanced stress relaxation by reducing the growth rate of formation Sn whiskers in Sn-0.7Cu solder coatings. The morphology of (Cu,Ni)6Sn5 interfacial IMC was more refine and thinner with a fine scallop-shaped interfacial intermetallic layer purposely to lower the compressive stress of Sn coating and extend the nucleation period, thus mitigating the formation and growth of Sn whiskers.

Influence of processing window on laser welding-brazing of Al to press-hardened 22MnB5 steel

Laser welding-brazing of AA6061 alloys and press-hardened 22MnB5 steel in lap configuration was carried out with Zn-Al15 filler metal. The processing window in different defocused distances was investigated and its influence on microstructure and mechanical properties of Al/steel dissimilar joints was explored. The results revealed that good appearances could be acquired in different processing windows with variation of defocused distances. The processing window was enlarged with increase of laser spot diameters, from laser power of 2.1–2.3 kW in defocused distance of +20 mm (laser spot diameter of 1.4 mm) to 2.8–3.6 kW in defocused distance of +40 mm (laser spot diameter of 2.4 mm). The thickness of interfacial intermetallic layer increased gradually from 0.47 to 1.86 μm for defocused distance of +20 mm to 3.76–11.03 μm of +40 mm. The newly formed phase at the interface at defocused distance of +20 mm was identified as Fe2(Al, Zn)5 and those were identified as the mixture of Fe2(Al, Zn)5 and FeZn10 when the defocused distances were +30 mm and +40 mm. The tensile-shear test of laser welded-brazed joints produced in various processing windows showed two types of fracture modes occurred. The interfacial failure appeared with the defocused distance less than +30 mm. The maximum fracture load reached 2793 N, representing 84.6% joint efficiency in regard to aluminum alloys. However, when the defocused distance increased to +40 mm, the maximum tensile-shear force decreased to 2242 N and failure occurred in the softening region of HAZ in aluminum alloy caused by effect of large laser irradiation. At larger defocused distance, the weak position of the dissimilar joints would transfer from the interface to the HAZ of the aluminum alloy, resulting in a bottleneck to improve mechanical property of joints.

Retardation Effect of Tin Multilayer on Sn-3.0Ag-0.5Cu (SAC305)-Based Solder Joint Interface

Transient liquid phase-like soldering technique has been successfully applied to prepare lead-free solder joints at 230 °C. Multiple interlayers of tin thin films in combination with a Sn-3.0Ag-0.5Cu (SAC305) solder paste have been used as filler for joining. Microstructural analysis was carried out by electron microscopy and energy-dispersive spectroscopy. For interlayer containing samples (Cu-Sn-SAC305-Sn-Cu), interfacial intermetallics layers found to be more homogeneous compared to the samples without interlayers (Cu-SAC305-Cu). Quality of the joints has been investigated nondestructively by ultrasonic method. On measuring the electrical resistivity by four-probe method, Cu-Sn-SAC305-Sn-Cu solder joint shows lower electrical resistivity compared to that of the Cu-SAC305-Cu solder joint, wherein nonlinear ultrasonic parameters confirm the superiority of former over later.

The Growth of Interfacial IMC Layer in SAC0307 Solder Joints with Specific Grain Orientation Under Electrical and Thermal Coupling Fields

We reported the reliability of Sn0.3Ag0.7Cu (SAC0307) solder joints under electrical and thermal coupling fields, where the c-axes of Sn grains were all nearly parallel to the direction of current and thermal flows. In these studies, individual electromigration (EM), individual thermomigration (TM), and thermoelectric coupling migration behaviors were investigated by applying a current density of 104 A/cm2, and a temperature gradient of 103°C/cm at Cu/SAC0307/Cu solder joints, respectively. The SEM and EBSD were utilized to characterize the morphologies and crystal orientations of each solder joint. The results indicated that the Cu atoms tended to migrate to the anode side under EM. The thickness of an interfacial intermetallic (IMC) layer at the anode increased 3.93 μm. In addition, the Cu atoms diffused toward the lower temperature side under TM, and the thickness of the IMC layer at cold side increased 1.72 μm. When the solder joints were experiencing the coupling fields with the same directions of current and thermal flows, the thickness of IMC layer at anode side (cold side) could increase up to 7.67 μm. The results showed that the effect of thermal flow could assist to accumulate the IMC at the anode side, and accelerate the migration of Cu atoms. This research could help to further understand the reliability behaviors of SAC0307 solders under the service environment.

Effect of heat treatment on bonding mechanism and mechanical properties of high strength Cu/Al/Cu clad composite

The present study is aimed at fabricating Cu/Al/Cu tri-layered clad composite with one pass heavy reduction roll bonding and subsequent heat treatment. High strength clad composite was designed via introducing 7075 alloy. The interface bonding mechanism was discussed under different conditions. The mechanical properties of the Cu/Al/Cu clad composites were also studied. The results showed that thick interfacial intermetallic layer could be formed after certain heat treatments (annealing at 500 °C or T6 treatment). The peeling behavior was affected by the intermetallic layer. The interfacial bonding behavior was related with the state of Cu/Al/Cu clad composite. Peel strength could reach 78.1 or 62.2 N/cm after annealing at 500 °C or T6 treatment, respectively. Lamellar delamination traces were remained on the peel surface after peel process. The thickness of interfacial compounds was in proportional with the altitude of delamination remaining. During the peel process, peel gap sheared through the interfacial layer and transformed between two matrix layers periodically. The mechanical properties of present clad composite could reach a best comprehensive value after T6 treatment with strength of 458 MPa and elongation of 15.2%. The strength level increased clearly as compared with pure aluminum and copper “sandwich” clad composite.

Effects of Ga Additives on the Thermal and Wetting Performance of Sn-0.7Cu Solder

The effects of Ga additions on thermal behavior, wettability, microstructure and properties of Sn-0.7Cu solder were investigated. The addition of Ga influences the surface tension of the solder and improves the wetting performance. The best wetting was achieved when the Ga content approached 0.5% (by weight), but further increases of Ga did not improve the wettability of the Sn-0.7Cu solder. The most uniform and refined grain structure was obtained with ∼ 0.5% Ga. The interfacial intermetallic (IMC) layer was also refined and reduced in thickness with the addition of Ga. Also, the hardness increases with increases in Ga content compared to SnCu solder without Ga. This is likely due to the refinement of grain structure and the uniform distribution of IMC phases in the solder.

The Interfacial Intermetallic and Shear Strength of Ni Nanoparticle‐Decorated Reduced Graphene Oxide Reinforced Sn2.5Ag0.5Cu Lead‐Free Composite Soldering Joints

The Ni nanoparticle‐decorated reduced graphene oxide (Ni‐rGO) reinforced Sn2.5Ag0.5Cu lead‐free composite solder, as well as the interfacial intermetallic (IMC) and the shear strength of soldering joints, are investigated with scanning electron microscopy (SEM), X‐ray diffraction (XRD), and transmission electron microscope (TEM). The results show that Ni‐rGO can be synthesized by the thermal decomposition method, and the adsorption type between Ni atoms and rGO is chemisorption. When the amount of Ni‐rGO addition reaches 0.05 wt%, the high strength and toughening Ni‐rGO reinforced lead‐free composite solder is obtained, with a tensile strength and elongation of 58.0 MPa and 32.3%, respectively. The growth of the interfacial IMC layers is restrained by the addition of Ni‐rGO, and the highly reliable soldering joints are obtained accordingly. When the amount of Ni‐rGO addition reaches 0.05 wt%, the shear strength of the Ni‐rGO reinforced lead‐free composite solder is 28.1 MPa, which is 26.6% higher than that of the plain Sn2.5Ag0.5Cu soldering joints. With the increase in the amount of Ni‐rGO, the fracture pattern is transforme from a ductile‐brittle mixed fracture to a ductile fracture. Additionally, the fracture pathway shifts from a transition zone, consisting of soldering seam and interfacial IMC, to the direction of the soldering seam.

Accelerated temperature cycling induced strain and failure behaviour for BGA assemblies of third generation high Ag content Pb-free solder alloys

In severe operation environments where extreme thermal cycles and long dwells are common, such as the engine compartment of motor vehicles, solder alloys resistant to fatigue under thermomechanical stimuli are required. With this in mind, new third generation lead free alloys are being designed to enhance the toughness of interfacial intermetallic layer (IML), and solid solution strengthening is introduced to compensate for the strength loss due to Ag3Sn particle coarsening. In this paper, the reliability of ceramic Ball Grid Array (BGA) assemblies using third generation lead-free alloys under various strain levels and Accelerated Temperature Cycling (ATC) profiles, 0/100 °C and −40/125 °C, are presented. Failure analysis was conducted and cracking along the IML at the solder/package interface was determined to be the root failure mechanism. The ATC test results indicate that the induced fatigue strain on each ring of the BGAs is a function of maximum dwell temperature, alloy choice and temperature change (ΔT) within the thermal cycle, and this is noted to have a significant influence on characteristic lifetimes. Results correlate well with the Coffin-Manson model, and activation energies (EA) were determined to predict the reliability of the electronic on the premise of the same predominant failure mechanism.

Influence of Bi Addition on Wettability and Mechanical Properties of Sn-0.7Cu Solder Alloy

The effect of bismuth (Bi) micro-alloying additions on wettability and mechanical properties of Sn-0.7Cu lead-free solder were explored. This paper also investigates the influences of various Bi percentages on the suppression of intermetallic compound formation. Scanning electron microscope (SEM) was used to observe the microstructure evolution of solder joint including the thickness of interfacial intermetallic layers. Overall, with the addition of Bi to Sn-0.7Cu solder, the size of primary Cu6Sn5become smaller and suppresses the thickness of interfacial intermetallic compound between solder and the Cu substrate. Microhardness value and wetting properties also increased with Bi addition which resulted in smaller size of β-Sn and Cu6Sn5.

Study on the Reliability of Carbon Nanotube-Reinforced Sn-58Bi Lead-Free Solder Joints

The wettability, microstructure and mechanical properties of multi-walled carbon nanotube (CNT)-reinforced Sn-58Bi composite solder joints were investigated. The results indicate that the wettability of the Sn-58Bi solder is improved and the growth of interfacial intermetallic (IMC) compounds for solder joints is restrained by CNTs. The thickness of the IMC layers is decreased with increasing CNTs concentration. The microstructure of the Sn-58Bi composite solders is refined, the maximum tensile strength and shear strength are obtained by adding the optimum CNTs content about 0.01 wt.%. However, excessive content of CNTs addition can deteriorate the properties. The creep rupture life of Sn-58Bi solder joint and Sn-58Bi-0.01CNTs solder joint is decreased with increasing load, temperature and current density. The average creep rupture life of Sn-58Bi-0.01CNTs composite solder joint is 60% higher than that of the plain solder joint.

Effect of heat treatment on the interfacial microstructure and properties of Cu-Al joints

The purpose of this article is to study the effect of heat treatment on the interfacial microstructure and properties of the Cu-Al contact reaction brazed joint, and compare the results with a similar study performed on flash welding. The results show that the interfacial intermetallics in Cu-Al joint change from original two layers (Cu9Al4/CuAl2) to three layers (Cu9Al4/CuAl/CuAl2) both in contact reaction brazing and in flash welding. Some Kirkendall voids form during the growth of interfacial intermetallics. The voids in the contact reaction brazed joint form in the middle of interfacial intermetallic layer and lead a discontinuous crack after 500 h heat treatment. The voids in the flash welded joint form between copper and interfacial intermetallics and lead to a continuous crack after 500 h heat treatment. The growth rate of interfacial intermetallics conforms to the parabolic law for both joints. The relation between joint properties and the interfacial intermetallic thickness can be described by a linear function. The joint properties of contact reaction brazing are better than that of flash welding during the heat treatment. Therefore, contact reaction brazing is more preferred to maintain electrical stability and mechanical integrity of Cu-Al joint.

Effect of Cobalt Doping on the Microstructure and Tensile Properties of Lead Free Solder Joint Subjected to Electromigration

Rapid Cu diffusion is one of the main causes of electromigration (EM) failure in lead-free solder joints. In this study, an effort has been made to investigate the detrimental effects of EM on microstructure and mechanical performance of solder joint by introducing Co nanoparticles (NP) doped flux at the interface between SAC305 solder and copper substrate. EM tests were conducted on un-doped SAC305 and Co-doped SAC305 solder joints for different time intervals, with the maximum duration of 1128 h. A DC current was applied to the both types of solder joints to achieve a current density of 1 × 104 A/cm2. EM tests were performed in an oil bath maintained at a constant temperature of 80 °C. It is found that Co-doped flux significantly reduced the formation of cracks and voids at the cathode interface. Co atoms entered into the lattice of Cu6Sn5 leading to the formation of (Cu, Co)6Sn5. This thermodynamically stabilized the interfacial intermetallic (IMC) layers both at the anode and cathode sides and suppressed the change in their thickness. The average anodic growth rate of (Cu, Co)6Sn5 interfacial IMC in the doped sample was about one order of magnitude lower compared with that of Cu6Sn5 in the un-doped samples. Co-NP also improved the tensile strength considerably before and after EM. The report suggests that the reliability of solder joint during EM can be improved by using Co-NP doped flux.

Microstructural influences on thermomechanical fatigue behaviour of third generation high Ag content Pb-Free solder alloys

New third generation lead free alloys are being targeted for use in harsh environments requiring resistance to both thermal and mechanical loading. In applications such as the engine compartment of motor vehicles where extreme thermal cycles and long dwell are common, it has been necessary to look for strengthening mechanisms that better survive extremes of temperature and strain. Alloys are being designed to improve toughness of interfacial intermetallic layers and provide solid solution strengthening to compensate for the loss of strength once the Ag3Sn particles coarsen. Results show that while solid solution-strengthening by additions of Sb is effective, it is not sufficient, and other strengthening options through the introduction of additional precipitates and solid solution strengthening using Bi is most desirable. The role of Ni is difficult to discern but it is most concentrated in the Cu6Sn5 intermetallic phase located at the interface between the solder and the copper substrate. This presumably has a toughening effect on the intermetallic thereby inhibiting crack formation and growth.

Microstructural Evolution and Mechanical Properties in (AuSn)eut-Cu Interconnections

The interfacial reactions between the widely employed solder Au-20wt.%Sn and the common contact metallizations (e.g. Ni, Cu and Pt) are normally complex and not well determined. In order to identify the proper contactor for Au-20wt.%Sn solder, the present study focuses on (1) rationalizing the interfacial reaction mechanisms of Au-20wt.%Sn|Cu as well as (2) measuring the mechanical properties of individual intermetallics formed at the interface. The evolution of interfacial reaction products were rationalized by using the experimental results in combination with the calculated Au-Cu-Sn phase diagram information. It was found that the growth of the AuCu interfacial intermetallic layer was diffusion-controlled. The diffusion path of Au-20wt.%Sn|Cu at 150°C was proposed. The hardness and indentation modulus of the interfacial reaction products were measured using nanoindentation tests. The results revealed a significant influence of the Cu solubility on the mechanical properties of (Au,Cu)Sn and (Au,Cu)5Sn, i.e. their hardness and contact modulus increased with the increase in the amount of Cu. Furthermore, results obtained here for the Au-20wt.%Sn|Cu joints were compared to those from Au-20wt.%Sn|Ni in order to assess the similarities and differences between these widely used interconnection metallization systems.