Growth Of Intermetallic Layer Research Articles

The effect of multiple reflow on intermetallic layer of Sn- 4.0AgCu/Cu by using microwave and reflow soldering

Soldering method is a general trend in demand that can be used to analyse different process parameter and their relationship in faster and easier way. Different soldering methods will influence the growth of intermetallic layer. This study investigates the effect of multiple reflow on intermetallic layer of Sn-4.0Ag-0.5Cu with diameter 700 μm solder size and Cu substrate by using microwave soldering. As comparison, reflow soldering was conducted. The material characteristic was characterised by using optical microscope, emission scanning (SEM) and energy dispersive X-ray analysis (EDX). The results revealed that only Cu6Sn5 intermetallic compound (IMC) was formed on solder joint. Meanwhile, Cu3Sn layer was detected after second and third reflow. The results also indicated that the soldering method could influence the IMC growth, where the microwave soldering produced a thinner IMC layer than reflow soldering. Besides, the morphology of IMC was observed as smaller circle bumps and scallop shapes. Moreover, the grain sizes of IMC for reflow soldering presented a larger, denser and rounder compared to microwave soldering.

A method of integrating CALPHAD data into phase-field models using an approximated minimiser applied to intermetallic layer growth in the Al-Mg system

This article describes an approach to combine single phase thermodynamic potentials into a multiphase composite potential suitable for integration in a multicomponent phase-field model. The composite potential avoids implicit interfacial energy contributions by starting from a grand potential formulation. The method is made explicit by expanding the minimiser resulting from the Legendre transform between grand and Helmholtz potentials about a known equilibrium state. The resulting composite function is explicit, reproduces the equilibrium states exactly, and is smooth such that it can be differentiated to provide the driving forces for mass transport and phase change in a thermodynamically self-consistent manner. The model is demonstrated by simulating a sequence of phase transformations for intermetallic growth in Al-Mg interdiffusion for advanced nuclear research reactor fuel.

38 - Enasidenib (AG-221), A Selective Oral Inhibitor of Mutant Isocitrate Dehydrogenase 2 (IDH2) Enzyme, In Patients with Myelodysplastic Syndromes (MDS)

Different types of Sn coatings are widely used in the electronics industry. However, they are susceptible to spontaneous whisker formation which can cause reliability issues. In this paper, whisker growth from submicron Sn thin films was studied at room temperature for 150 days. For this purpose, 99.99% pure Sn was vacuum evaporated onto 1.5 mm thick Cu and ceramic substrates, with an average thickness of 400 nm. It was found that the submicron thick Sn layers on a Cu substrate can generate intense whiskering directly after layer deposition. The microstructure, composition and grain orientation of the whiskers and the areas underneath were studied with a Scanning Ion Microscope (SIM) and a Transmission Electron Microscope (TEM). It was proven that the whisker growth was induced by Cu6Sn5 intermetallic layer growth between the Cu substrate and the Sn thin film which resulted in large stress within the film. We found the first evidence in a tin-copper layer system that the high stress due to the intermetallic formation itself can initiate the interfacial flow mechanism (without a direct mechanical load) between the Sn layer and the intermetallic layer. This phenomenon can explain the intense whisker growth from submicron Sn thin films.

On the growth of intermetallic phases by heat treatment of friction stir welded aluminum steel joints

Multi-material components made from aluminum and steel sheet metal are an innovative approach for weight reduction in automotive applications. However, lightweight components made from aluminum and steel require suitable joining technologies. A promising solid-state welding technology for producing dissimilar steel aluminum joints is Friction Stir Welding, which minimizes the formation of Fe-Al intermetallic phases due to process temperatures lower than the melting temperatures of the base material. The results obtained show a comparison of steel aluminum joints made by FSW using DC04 mild steel with the strain hardened aluminum alloy AA5754-H22 on the one hand and the precipitation hardened aluminum alloy AA6082-T6 on the other hand. The difference between achieved maximum tensile strengths of the joints in relation to those from both base materials is investigated. Due to the stirring and heat input of the welding process, the temper condition of the precipitation hardened aluminum alloy is changed. To improve the mechanical properties of the welded joints, post weld heat treatments are performed. The post weld heat treatments of the produced multi-material specimens from AA6082-T6 aluminum alloy and mild steel at various heat treatment conditions show substantial growth of intermetallic phase layer, which is characterized in detail within the present work. Tensile tests show a degradation of the mechanical properties resulting in a decreased tensile strength and insufficient connection of both materials. Investigations using a scanning electron microscope (SEM) show a distinct increase of the thickness of intermetallic phases in the transition between aluminum and steel.

Influence of Ag-modified graphene nanosheets addition into Sn–Ag–Cu solders on the formation and growth of intermetallic compound layers

In this study, varying amounts of Ag-modified graphene nanosheets (Ag-GNSs) were added to Sn–Ag–Cu (SAC) solders to synthesize composite solders. Then, the morphology and thickness of the intermetallic compound (IMC) layers were investigated during the liquid–solid reactions and isothermal aging. The test results revealed that the IMCs were scallop-shaped after soldering, but they changed from scallop-shaped to an irregular shape with increasing aging time. The IMC thickness and diffusion coefficients of the composite solders were both found to be lower than those of the plain solders. Moreover, it is worth noting that with the same amount of reinforcement, the composite solders reinforced with Ag-GNSs exhibited thinner IMC layers and lower diffusion coefficients than the solders reinforced with GNSs alone. Furthermore, Ag-GNSs prepared using ball milling yielded thinner IMC layers and lower diffusion coefficients than the same amount of Ag-GNSs prepared via mechanical mixing using a blender. Our results indicate that Ag-GNSs are more influential on delaying the growth of IMC layers than GNSs alone and that ball milling has advantages over mechanical mixing using a blender for the preparation of Ag-GNS composite solders.

Whisker growth from vacuum evaporated submicron Sn thin films

Different types of Sn coatings are widely used in the electronics industry. However, they are susceptible to spontaneous whisker formation which can cause reliability issues. In this paper, whisker growth from submicron Sn thin films was studied at room temperature for 150days. For this purpose, 99.99% pure Sn was vacuum evaporated onto 1.5mm thick Cu and ceramic substrates, with an average thickness of 400nm. It was found that the submicron thick Sn layers on a Cu substrate can generate intense whiskering directly after layer deposition. The microstructure, composition and grain orientation of the whiskers and the areas underneath were studied with a Scanning Ion Microscope (SIM) and a Transmission Electron Microscope (TEM). It was proven that the whisker growth was induced by Cu6Sn5 intermetallic layer growth between the Cu substrate and the Sn thin film which resulted in large stress within the film. We found the first evidence in a tin-copper layer system that the high stress due to the intermetallic formation itself can initiate the interfacial flow mechanism (without a direct mechanical load) between the Sn layer and the intermetallic layer. This phenomenon can explain the intense whisker growth from submicron Sn thin films.

Laser welding of dissimilar metallic materials with use of diffractive optical elements

A use of laser technology it is progressive in the welding of dissimilar materials. Pulsed laser welding of an aluminum alloy AK4 and a titanium alloy VT5-1 was performed. Processing conditions were determined, the realization of which during melting of materials in the heat-affected zone makes it possible to obtain a homogeneous structure without voids and shells, potentially producing sufficiently sound welded joints. To create the required power density distribution across the laser beam, it was found expedient to use diffractive optical elements. Aluminum and copper were welded by continuous laser beam. It is determined that laser action with its well-defined and precise localized heat input makes it possible to significantly reduce the growth of intermetallic compound layers.

Intermetallic compounds in solar cell interconnections: Microstructure and growth kinetics

The microstructure and intermetallic phase growth in solder joints of photovoltaic modules are investigated because of their significance for interconnection reliability. Interconnector ribbons with Sn60Pb40, Sn62Pb36Ag2, Sn43Bi57, Sn41Bi57Ag2 and Sn91Zn9 are soldered on the front busbars of industrial crystalline silicon solar cells. Cross sections are inspected using microscopy, SEM and EDX. The interconnections are isothermally aged, whereas the intermetallic layer thickness is determined successively. The microstructural changes in the bonds are characterized. Grain coarsening, volume increase of intermetallic compounds, Sn-penetration into the metallization and growth of grain boundaries between the phases are found. The composition of the intermetallic phases within Sn91Zn9-bonds is discussed. A diffusion model is used to simulate the intermetallic layer growth after 3000h at 85°C and thermal cycling from −40°C to 85°C for 600 cycles. A prognosis of the phase growth within the photovoltaic module after 25 years at the location Freiburg in Germany is made. It is found that the Ag3Sn-phase using Sn43Bi57 extends to 6.6µm after 3000h at 85°C as compared to 2.6µm for Sn60Pb40. After 25 years in Freiburg the Ag3Sn-layer within Sn43Bi57 joints is predicted to be 2.4µm whereas within Sn60Pb40-bonds only 2.2µm.

Microstructure evolution and shear fracture behavior of aged Sn3Ag0.5Cu/Cu solder joints

The effect of isothermal aging on the microstructure and shear strength of Sn3Ag0.5Cu/Cu (SAC305/Cu) solder joints were studied systematically. The single-lap shear samples of SAC305/Cu solder joint were prepared and aged up to 456h at 150 and 180°C, respectively. The interfacial intermetallic compound layer of the aged solder joint gradually thickened with increasing both aging time and aging temperature, while, the interfacial intermetallic compound layer morphology transformed from scallop-type to layer-type after the aging treatment. The growth of the interfacial Cu-Sn interfacial intermetallic compounds layer of aged SAC305/Cu solder joints exhibited a linear function of the square root of aging time, indicating that the formation of the interfacial Cu-Sn interfacial intermetallic compounds during aging treatment was mainly controlled by the diffusion mechanism. The diffusion coefficient (D) values of interfacial intermetallic compound layer were 4.64×10−17 and 1.06×10−16m2s−1 for aging temperatures of 150°C and 180°C, respectively. Single-lap shear tests results revealed that the shear strength of SAC305/Cu solder joints decreased continuously with an increase in interfacial intermetallic compound layer thickness and aging time. The main reason for these characteristics was the excessive increase in the interfacial intermetallic compound thickness of solder joints, causing a change in the stress concentration of the shear load from the protruding region to the inside of the interfacial intermetallic compound layer at the same tested condition. In addition, the shear fractures in as-reflowed and short time aged solder joints were shown to be ductile in nature and confined in the bulk solder rather than through the interfacial intermetallic compound layer. However, the shear fracture locations transferred from the solder bulk to the interfacial Cu-Sn interfacial intermetallic compound layer, and finally to the Cu3Sn/Cu interface with increasing aging time.

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.

Effect of Si on the growth of Fe-Al intermetallic layer in Zn-11%Al-3%Mg coating

Abstract Pure iron specimens were immersed in Zn-11%Al-3%Mg-x%Si baths containing different amount of Si at 510 °C for different time. The effect of Si in Zn-11%Al-3%Mg bath on phase constitution and the growth of Fe-Al intermetallic layer in Zn-11%Al-3%Mg-x%Si coatings were investigated by scanning electron microscope (SEM) and energy dispersive spectrometer (EDS). The results show that the existence of Si in Zn-11%Al-3%Mg bath could affect the phase constitution of Fe-Al intermetallic layer and restrain remarkably the growth of the layer. The thickness of Fe-Al intermetallic layer is minimum when Si content in Zn-11%Al-3%Mg was 0.2 wt.%. The growth of Fe-Al intermetallic layer in Zn-11%Al-3%Mg and Zn-11%Al-3%Mg-0.2%Si coatings is controlled by diffusion mechanism. 0.2 wt.% Si in Zn-11%Al-3%Mg bath decreases obviously the growth-rate index n and the growth rate constant k of Fe-Al intermetallic layer in coating.

Comparative study of Au–Sn and Sn–Ag–Cu as die‐attach materials for power electronics applications

A comparative study of Sn–3.0Ag–0.5Cu (SAC305) and Au–20Sn solders as die‐attach materials for high‐temperature power electronic applications was performed. The solid‐state interfacial reactions of SAC305 and Au–20Sn solders with a Ni‐plated Si chip and a direct‐bonded‐copper substrate, as well as the growth of interfacial intermetallic compound layers and interfacial stability, were investigated and compared during aging at 150 and 200 °C for up to 2000 h. The SAC305 solder exhibited a higher interfacial intermetallic compound growth rate and a higher consumption rate of the Ni layer than the Au–20Sn solder. The Au–20Sn solder had a superior interfacial stability for high‐temperature power electronic applications. Copyright © 2016 John Wiley & Sons, Ltd.

Improving shear strength of Sn-3.0Ag-0.5Cu/Cu joints and suppressing intermetallic compounds layer growth by adding graphene nanosheets

This study investigated the effects of adding 0.1wt% of graphene nanosheets (GNSs) into Sn-3.0Ag-0.5Cu solder matrix on the growth of intermetallic compounds (IMC) layer with Cu substrates during isothermal aging at temperatures of 100, 125, 150 and 175°C for up to 7 days. The results indicated that the GNSs could provide huge diffusion barrier for the diffusion of Sn and Cu atoms in solder matrix, and the activation energy for IMC layer growth was calculated as 46.20 and 59.72kJ/mol for Sn-3.0Ag-0.5Cu solder and Sn-3.0Ag-0.5Cu-0.1GNSs composite solder, respectively. Compared with Sn-3.0Ag-0.5Cu solder joints, the IMC layer morphology transformation from scallop-type to layer-type and the IMC layer growth for composite solder joints were suppressed. After aging 7 days at 175°C, the shear strength of composite solder joints, whose IMC layer was comparatively thin, was 30% higher than that of Sn-3.0Ag-0.5Cu solder joints.

Formation mechanisms of Ni–Al intermetallics during heat treatment of Ni coating on 6061 Al substrate

The formation mechanisms and growth kinetics of Al3Ni and Al3Ni2 in Ni–Al diffusion couple prepared by electrodeposition of Ni on Al substrate were investigated. The nickel coating with 20 µm thickness was applied on 6061 aluminum alloy by direct current electroplating. The samples were then heat-treated for different durations at 450, 500 and 550 °C under argon atmosphere. The intermetallic phases were identified by means of scanning electron microscopy (SEM), energy dispersive spectrometry (EDS) and X-ray diffraction (XRD). The results showed that the formation of intermetallic phases consisted of two important steps. The first step was the lateral growth of intermetallic phase from separate sites, resulting in the formation of a continuous layer. The second step was the growth of the continuous intermetallic layer in the direction perpendicular to the interface. However, excessive increase in thickness of intermetallic phases led to the detachment of reaction products, i.e., Al3Ni and Al3Ni2, from the substrate. It was also observed that aluminum was the dominant diffusing element during Al3Ni growth, while nickel diffusion was dominant during Al3Ni2 growth. The growth kinetics of both Al3Ni and Al3Ni2 phases obeyed a parabolic law.

Interfacial reactions between Cu substrate and Sn–1Ag–0.5Cu solder containing 0.1 wt% Al by dipping method

Effects of 0.1 wt% Al addition to Sn–1Ag–0.5Cu (SAC105) on the structure of solder/copper interface have been studied. The solder/copper joint assembly was prepared by dip soldering process at 250 °C for 10 s and then aged thermally at 150 °C for 500 h for an accelerating aging test. Results show that the addition of Al does not change the type of the reaction product with the Cu substrate. The reaction product is always Cu6Sn5 and Cu3Sn phases formed at the solder/copper interface. However, it is found that the addition of Al retards the interfacial reaction and suppresses the growth of interfacial intermetallic layer(s). Potential mechanisms are proposed to explain the effects of Al addition on the solder/copper interfacial reactions.

Formation and evolution of intermetallic compounds between the In-3Ag solder and Cu substrate during soldering

The formation and growth of intermetallic compounds (IMCs) have an important effect on the reliability of the solder. In this paper, formation and evolution of IMCs between the In-3Ag solder and Cu substrate were systematically explored for different soldering time ranged from 1 to 30 min. The interface soldered for 1 or 2 min was only composed of (Ag,Cu)In2 IMCs. When the soldering time extended to 4 min, a new (Cu,Ag)11In9 IMCs layer appeared under the (Ag,Cu)In2 IMCs layer. When the soldering time exceeded 5 min, the (Ag,Cu)In2 layer was completely decomposed and replaced by the (Cu,Ag)11In9 layer. Meanwhile, the growth of (Ag,Cu)In2 and (Cu,Ag)11In9 intermetallic layers during jointing were all diffusion-controlled and the growth rates of them are 0.398 and 0.507 µm2/s, respectively. Furthermore, shear strength results showed that the shear strength of solder joints decreased with soldering time extending, and those decrease from 5.64 MPa after soldered for 1 min to 3.07 MPa when the soldering time extended to 30 min. The fracture mode also changed from typical ductile fracture mode to mixed ductile–brittle fracture mode with soldering time extending.

Effect of Ti on Morphology and Growth of Zn–Fe Intermetallic Phases

The effect of Ti in Fe substrate on the morphology and growth of Zn–Fe alloy phases in (Zn–0.2 wt.%Al)/Fe diffusion couples was investigated using optical and scanning electron microscopy. It is shown that ζ phase layer does not exist in (Zn–0.2 wt.%Al)/Fe couple, but it can be clearly observed in (Zn–0.2 wt.%Al)/(Fe–Ti) diffusion couples. Increasing of dissolved Ti in Fe substrate delays the disappearance of the ζ phase and promotes the formation of δk phase. The δp phase grows toward the ζ phase layer in the form of arborescence. The growth of total intermetallic phase layers in all diffusion couples is controlled by diffusion of Zn and Fe atoms within the layers at 380 °C. The thickness of total intermetallic layer increases with increasing of dissolved Ti in Fe substrate and reaches the maximum when Ti content is 0.4 wt.%.

Characterization and growth kinetics of the formation of intermetallic compounds in the liquid state during soldering with lead-free solders

The research described in this paper developed the experimental techniques necessary for promoting intermetallic layer growth throughout the melting and solidification cycle of the solder and then measuring the thickness of these layers. Most of the literature to date reported on aged soldered joints to investigate in-service intermetallic layer growth. To observe intermetallic compound (IMC) growth during the liquid state of soldering required an experimental setup that quickly raises the temperature of the solder joint followed by fast cooling (comparable to the actual joint conditions). Temperatures at increments of 25° above the soldering temperature and times of 2, 5, and 8 s for growth were carefully controlled. After the experiments, the copper substrate/solder alloy interface was examined using light microscopy, scanning electron microscopy (SEM), and SEM-EDS (energy dispersive spectroscopy). As expected, intermetallic phases such as Cu6Sn5, Cu3Sn, and Ag3Sn were observed, with Cu6Sn5 being the major phase. Statistical analysis was performed for the IMC thickness data obtained from the long profile analysis. Empirical equations capable of predicting the IMC layer thicknesses were determined. Using Arrhenius analysis, the activation energy for intermetallic layer growth was calculated to be approximately 7 kCal/mol. This value is significantly lower than the value of approximately 24 kCal/mol reported in the literature for Cu6Sn5. Even considering the presence of Cu3Sn (counted together with Cu6Sn5) which has about 15 % higher activation energy of formation than Cu6Sn5, the experimentally measured values were still lower. The discrepancy was attributed to the fact that the values reported in the literature were mostly based on solid-state transformations while the measurements and calculations in this work were limited to the intermetallic layer formation from liquid state followed by growth.

Effects of metallic nanoparticle doped flux on the interfacial intermetallic compounds between lead-free solder ball and copper substrate

Lead free solders currently in use are prone to develop thick interfacial intermetallic compound layers with rough morphology which are detrimental to the long term solder joint reliability. A novel method has been developed to control the morphology and growth of intermetallic compound layers between lead-free Sn–3.0Ag–0.5Cu solder ball and copper substrate by doping a water soluble flux with metallic nanoparticles. Four types of metallic nanoparticles (nickel, cobalt, molybdenum and titanium) were used to investigate their effects on the wetting behavior and interfacial microstructural evaluations after reflow. Nanoparticles were dispersed manually with a water soluble flux and the resulting nanoparticle doped flux was placed on copper substrate. Lead-free Sn–3.0Ag–0.5Cu solder balls of diameter 0.45mm were placed on top of the flux and were reflowed at a peak temperature of 240°C for 45s. Angle of contact, wetting area and interfacial microstructure were studied by optical microscopy, field emission scanning electron microscopy and energy-dispersive X-ray spectroscopy. It was observed that the angle of contact increased and wetting area decreased with the addition of cobalt, molybdenum and titanium nanoparticles to flux. On the other hand, wettability improved with the addition of nickel nanoparticles. Cross-sectional micrographs revealed that both nickel and cobalt nanoparticle doping transformed the morphology of Cu6Sn5 from a typical scallop type to a planer one and reduced the intermetallic compound thickness under optimum condition. These effects were suggested to be related to in-situ interfacial alloying at the interface during reflow. The minimum amount of nanoparticles required to produce the planer morphology was found to be 0.1wt.% for both nickel and cobalt. Molybdenum and titanium nanoparticles neither appear to undergo alloying during reflow nor have any influence at the solder/substrate interfacial reaction. Thus, doping of flux with appropriate metallic nanoparticles can be successfully used to control the morphology and growth of intermetallic compound layers at the solder/substrate interface which is expected to lead to better reliability of electronic devices.

Investigation on the intermetallic compound layer growth of Sn–0.5Ag–0.7Cu–xGa/Cu solder joints during isothermal aging

This work was focused on the influence of Ga on the thermal properties, microstructural evolution and interfacial morphology with aging treatment at 150 °C of low-silver Sn–0.5Ag–0.7Cu (SAC) lead-free solder. The melting temperature of the SAC–Ga solder was decreased owing to the low melting point element Ga and the formations of intermetallic compound (IMC) and growth at the interfaces of SAC/Cu and SAC–0.5Ga/Cu were studied for different aging time ranging from 0 to 720 h. The results indicated that for both solders, the thickness of the IMC increased with aging time prolonging. However, compared with the interface of SAC/Cu, the thickness of the interface of SAC–Ga/Cu was obviously suppressed and the growing speed was slowed down, which may be attributed to the decreased activity of copper atoms by Ga addition, so that the SAC–Ga solder showed relatively planar-like IMC instead of scallop-like at the interface.