Growth Of Intermetallic Layer Research Articles

Morphological Effect on the Intermetallic Compound Layer Growth Kinetics of Metallurgical Joining

Evaluating the growth kinetics is one of the most important characteristic in assessing the quality and reliability of metallurgical joining, especially in electronics packaging such as soldering and wire bonding technology. The growth kinetics is normally assessed using Arrhenius equation that involves diffusion activities due to thermally activated process. The well-known factors of thermal and time together with generally accepted growth exponent have been widely used for this assessment. The intermetallic compound layer which is the by-product of metallurgical reaction during soldering process has been exposed to high temperature to accelerate its growth. The cross-section of the joining was observed using optical microscope to quantify the layer of intermetallic compound. Morphological effect and shape factor of the layer have been analysed in complement with the effect of temperature and time on the growth behaviour. Directional growth and irregularities shape of the intermetallic layer show some inconsistency on the selection of growth exponent. The effect of initial size of intermetallic layer must also be considered in this assessment. This study suggests that the morphological effect must be analysed prior to the selection the growth exponent in assessing growth behaviour and kinetics of intermetallic layer in metallurgical joining.

Modelling of intermetallic layers formation during solid-liquid joining of dissimilar metallic materials

Joining of dissimilar metallic materials gives rise to the production of components with improved properties. At the joint interface, the formation of brittle intermetallic layers might deteriorate the component application. Therefore, its formation and growth must be well understood and carefully controlled. Numerical simulations assist in the determination of processes parameters to obtain the desired bond characteristics. In solid-liquid joining processes, the melt movement plays an important role und must be accounted in the simulations. In this paper, a mathematical model at the continuum scale is used for the description of the interface formation during solid-liquid joining. The description of convection and advection of the molten alloy and the dissolution of the solid substrate are of interest. The substrate dissolution into the melt alters the local composition of the molten alloy, leading to precipitation of intermetallic compounds on the substrate surface during the solidification process. To account for these phenomena, convection heat transfer with phase transformation and diffusion and reaction at the solid-liquid interface are considered in the mathematical model that is based on conservation equations of mass, momentum, energy and species. The different scale problem is solved by applying a dynamic mesh refinement at the interface to accurately solve the intermetallic layer growth. The model was implemented in OpenFoam® and simulation results for the intermetallic layer thickness as a function of solid substrate temperature (Ts) for compound casting between initially liquid Al and a solid Cu substrate are presented. In general, for Ts initial value ranging from 400 to 700 °C while keeping the initial Al melt temperate at 750 °C, the intermetallic layers thickness increases as Ts increases.

Phase-field study of IMC growth in Sn–Cu/Cu solder joints including elastoplastic effects

In this article, we aim to study the problem of the growth of intermetallic phases in solder joints undergoing mechanical deformation, using a phase-field model for multi-phase systems that can treat diffusion, elastic and plastic deformation. A suitable model is formulated and applied to Sn–Cu/Cu lead-free solder joints. The growth of the intermetallic layers during solid-state annealing is simulated for different strain states. We assess the values of stiffness tensors available in literature and perform ab initio calculations to support the selection of reasonable values from literature. We also perform a parametric study with different eigenstrain values and applied strains. We find that there is a significant effect of the considered eigenstrains and applied strains on the growth kinetics of the system and parabolic growth kinetics is followed in cases where the intermetallic layers grow. We thereby establish the importance of strain in the growth of intermetallic layers and the need for more targeted experiments on the role of strain in the reliability of the solder joint.

A review of geopolymer ceramic as a potential reinforcement material in solder alloys

Nowadays, lead-free solder has been currently used in electronic packaging technology as part of soldering material. Since SnPb was detected to produce toxicity and might harm the consumers, the usage of Pb solder has been banned by WEE and RoHS. Therefore, various studies have been developed as alternatives to replace the usage of SnPb. Since lead-free solder might not perform as well as their traditional SnPb, researchers suggested to add some elemental reinforcement particles in matrix alloy. Previously, addition of ceramic reinforcement has been widely known in enhancing the properties of solder-substrate. This paper reviews about the presence studies of ceramic as solder reinforcement, the characteristics of geopolymer ceramic as potential solder reinforcement, and their properties in providing a superior solder joint. In this review, the characterization is divided into two stages; 1) characterization of geopolymers in terms of microstructural and crystallographic; 2) characterization of solder properties in terms of intermetallic layer growth (IMC), wettability, and its mechanical properties

The Effect of Multi-Walled Carbon Nanotubes Reinforcement and Multiple Reflow Cycles on Shear Strength of SAC305 Lead-Free Solder Alloy

Abstract In this study, the effect of multi-walled carbon nanotubes (MWCNT) reinforcement on joint shear strength and microstructural development of tin-3.0silver-0.5copper (SAC305)/copper solder joint subjected to multiple reflow cycles was investigated. The MWCNT-reinforced SAC305 solder systems (SAC305-x MWCNT; x = 0.01, 0.05, 0.1, and 0.5 wt.%) were developed by a mechanical dispersion method. The microstructural, mechanical, and melting properties of SAC305 composite solders were evaluated as a function of different wt.% of MWCNT addition. The melting behavior of composite solders was analyzed using differential scanning calorimetry. The morphology and intermetallic compound growth at the solder joint interface were studied using scanning electron microscopy. The copper/solder/copper micro-lap-shear solder joint specimens reflowed for multiple reflow cycles were systematically characterized to evaluate the joint shear strength. The results showed that the reinforcement in the range of 0.01–0.05 wt.% of MWCNT resulted in the improvement of joint shear strength and better wettability compared to plain SAC305 solder alloy. Amongst all compositions analyzed, SAC305-0.05MWCNT nanocomposite suppressed the intermetallic compound layer growth effectively leading to improvement in the joint shear strength under multiple reflow cycles.

Fabrication of Novel Geopolymer Reinforced Tin Copper Solder in Suppressing Intermetallic Layer Growth

Currently, lead-free composite solder technology system is the new approach that have been considered as a promising replacement for toxic SnPb solder alloy. Sn-0.7Cu was used as matrix solder alloy while fly ash geopolymer and kaolin geopolymer with different compositions (0.5 wt.%, 1.0 wt.%, and 1.5 wt.%) was added as a reinforcement to increase the properties of solder alloy. The solder composite was prepared by using powder metallurgy method which consist of mixing, compaction, and sintering process via microwave oven. Microwave sintering approach results in more uniform heating, lower pore coarsening with cost-effective and energy efficiency. The chemical composition and morphology of geopolymer reinforcement was analysed by using X-ray Flourescene and Scanning Electron Microscope. The influences of the geopolymer particulates in the monolithic matrix solder on the interfacial intermetallic compound thickness and wettability were investigated by using optical microscope, while the specific value was measured by using J-image software. The melting point temperature were investigated by using differential scanning calorimeter (DSC). The influences of adding types of geopolymer particulates into Sn-0.7Cu lead free solder were investigated in terms of interfacial intermetallic compounds (IMCs) and thermal properties. It is noted that several addition of fly ash geopolymer and kaolin geopolymer particles can remarkably supressed the thickness of intermetallic layer between composite solder and the substrate and thus gives higher melting temperature but somehow certain composition resulted low in mechanical properties. Overall, the addition of 0.5 wt.% of kaolin geopolymer reinforcements into Sn-0.7Cu lead-free improved all the listed properties of the solder materials.

Abnormal effect of temperature on intermetallic compound layer growth at aluminum-titanium interface: The role of grain boundary diffusion

The Al3Ti intermetallic compound (IMC) layer growth kinetics at Al-Ti interface was investigated. Surprisingly an abnormal effect of temperature was observed with a thicker IMC layer formed at lower annealing temperature due to the much faster Al3Ti grain coarsening at a higher temperature, the IMC layer growth at 630 °C became slower than that at 600 °C after a certain annealing time. The quantitative influence of grain size on effective diffusion coefficient was analysed. Calculations showed that the lattice diffusion makes little contribution to the effective diffusion coefficient. Grain boundary diffusion, therefore, dominates for all the annealing conditions studied.

Suppression of the Growth of Intermetallic Compound Layers with the Addition of Graphene Nano-Sheets to an Epoxy Sn⁻Ag⁻Cu Solder on a Cu Substrate.

This study investigated the suppression of the growth of the intermetallic compound (IMC) layer that forms between epoxy solder joints and the substrate in electronic packaging by adding graphene nano-sheets (GNSs) to 96.5Sn–3.0Ag–0.5Cu (wt %, SAC305) solder whose bonding characteristics had been strengthened with a polymer. IMC growth was induced in isothermal aging tests at 150 °C, 125 °C and 85 °C for 504 h (21 days). Activation energies were calculated based on the IMC layer thickness, temperature, and time. The activation energy required for the formation of IMCs was 45.5 KJ/mol for the plain epoxy solder, 52.8 KJ/mol for the 0.01%-GNS solder, 62.5 KJ/mol for the 0.05%-GNS solder, and 68.7 KJ/mol for the 0.1%-GNS solder. Thus, the preventive effects were higher for increasing concentrations of GNS in the epoxy solder. In addition, shear tests were employed on the solder joints to analyze the relationship between the addition of GNSs and the bonding characteristics of the solder joints. It was found that the addition of GNSs to epoxy solder weakened the bonding characteristics of the solder, but not critically so because the shear force was higher than for normal solder (i.e., without the addition of epoxy). Thus, the addition of a small amount of GNSs to epoxy solder can suppress the formation of an IMC layer during isothermal aging without significantly weakening the bonding characteristics of the epoxy solder paste.

Phase-Field Study of IMC Growth in Sn–Cu/Cu Solder Joints Including Elastoplastic Effects

Lead-free solders are being researched over the last decade in order to replace the lead-tin solder which was used as a connecting material in electronic devices. During the solid-state annealing processing step and during service in electronic devices, solder joints experience stresses that lead to elastoplastic deformation. These stresses influence the kinetics and morphology of the brittle intermetallic compounds that are formed, in turn affecting there liability of the joint. In this article, we aim to study the problem of the growth of intermetallic phases in solder joints undergoing mechanical deformation, using a phase-field model for multi-phase systems that can treat diffusion, elastic and plastic deformation. A suitable model is formulated and applied to Sn–Cu/Cu lead-free solder joints. The growth of the intermetallic layers during solid-state annealing is simulated for different strain states.The stiffness tensors required as input are calculated by ab initio methods to corroborate the values available in literature. We find that the growth rate of the Cu3Sn intermetallic layer increases with applied tensile strain but decreases with applied compressive strain, as also observed in experiments. We thereby establish the importance of strain in the growth of intermetallic layers and the need for more targeted experiments on the role of strain in the reliability of the solder joint.

Microstructural evolution of Ti–6Al–4V/UD-Cf/LAS composites joint brazed by graphene nanosheets reinforced composite filler

A graphene nanosheets reinforced Ag-Cu composite filler (Ag-Cu + GNSs) was developed by introducing GNSs into Ag-Cu powder filler. Unidirectional carbon fiber reinforced lithium aluminosilicate matrix composites (UD-Cf/LAS composites) and Ti–6Al–4V alloy were brazed with Ag-Cu + GNSs composite filler. The typical interfacial microstructure of joint was Ti–6Al–4V/Ti(s,s)/Ti2Cu/TiCu/Ag(s,s)/Ti3Cu4/Cu(s,s)+TiCu + TiC/Ti3Cu4/TiC + TiSi2/UD-Cf/LAS composites. The in situ synthesized TiCu + TiC composite from the reaction between Ti and GNSs had the following benefits: 1) refined the microstructure of the joint; 2) reinforced the joint; 3) alleviated the thermal stress of the joint by constraining the growth of continuous Ti3Cu4 intermetallic layers. Moreover, with the increase of GNSs content, the amount of TiCu + TiC phases increased. Ag(s,s) and Ti3Cu4 became uniform and fine in the interlayer. Both the thickness of reaction layers and the size of granular Ti3Cu4 and TiCu + TiC phases firstly increased and then decreased with the rise of the brazing temperature. On the contrary, the content of Ag based composite decreased at first and then increased. The highest shear strength of joints reached 45.5 MPa with 0.5% GNSs addition when brazed at 900 °C for 10 min. Based on the experimental results, the interface evolution mechanism of the Ti–6Al–4V/Ag-Cu + GNSs/UD-Cf/LAS composites joint was investigated.

Effects of steel type and sandblasting pretreatment on the solid-liquid compound casting characteristics of zinc-coated steel/aluminum bimetals

Effects of zinc-coated steel type and steel surface sandblasting pretreatment in the solid-liquid compound casting of layered type steel/aluminum bimetals were investigated. The Zn coating behavior and its effects on interfacial microstructure evolution and fracture mechanism were also discussed. The aluminum fluidity in thin plate type flow channels formed by the steel insert and the mold wall primarily depended on the insert surface roughness and secondarily on the wettability. As-galvanized (GI) steel/aluminum bimetal joints showed the bonding strength of 20 MPa and more, while galvannealed (GA) steels showed poor bonding. The interfacial bonding zone consisted of most Al13Fe4, Al8Fe2Si, Al4.5FeSi intermetallic phases, as well as some Si phases. A low temperature and short time of the bonding reaction coupled with a high silicon content of the aluminum alloy suppressed the formation of Al5Fe2 phase. Oxide scales on the GA steel surface prevented the molten Zn coating from mixing with the aluminum melt. The Zn coating of GI steels was rapidly disappeared from the steel surface by the chemical affinity and surface energy-driven fluid flow as well as the diffusion, resulting in the formation of Zn-free intermetallic phases. The Zn coating of GI steels played a role in retarding the onset of bonding reaction. A long time sandblasting caused an excessive growth of intermetallic layers and the formation of Kirkendall voids on the steel side, resulting in the shift of main fracture sites and a slight decrease of the bonding strength.

Geometrical effects on growth kinetics of interfacial intermetallic compounds in Sn/Cu joints reflowed with Cu nanoparticles doped flux

In this study, Cu nanoparticles prepared by chemical reduction method, were doped into flux (0–2 wt%) and disseminated to the pure Sn solder ball at 250. The enhanced spreading rate due to use of nanoparticles, increased the base diameter (W) and decreased the height (H) of the solder at constant volume. The finite element analysis for Cu concentration, temperature and velocity; in relation to the magnitudes of W and H show that larger W is responsible for enhancement of supersaturation and radial thermal gradient, whereas smaller H is responsible for reduction in flow velocity. The growth kinetics of interfacial Cu 6Sn 5 film during isothermal reflow is proportional to W 2/3 during isothermal reflow whereas linearly dependent on H during air cooling. As the ripening at isothermal stage and precipitation at cooling stage contribute to the gross growth behavior of Cu 6Sn 5 intermetallic compounds layer growth, the combined geometrical effect of base diameter and height of the solder specimen renders solder corresponding to flux with 2.0 wt% nanoparticles to have the overall thickest intermetallics.

Effect of silicon and manganese on the kinetics and morphology of the intermetallic layer growth during hot-dip aluminizing

Hot dip aluminizing (HDA) of low carbon steel in aluminum bath containing various amounts of silicon and manganese was studied in this work. The effect of bath alloying elements on the morphology and growth kinetics of intermetallic layer during the reaction of steel substrate and aluminum bath was investigated by scanning electron microscope equipped with EDS. Results showed that Fe2Al5 (η) and FeAl3 (θ) layers are detectable when pure aluminum bath is used. In contrast, when the bath contains 6 and 12 wt% silicon, new intermetallic layer Fe2Al7Si (τ5) has appeared adjacent to the topcoat aluminum layer. Moreover, dispersed Fe2Al7Si particles were observed in the topcoat. Presence of silicon in the compound layer had a significant effect on the growth kinetics and intermetallic layer thickness. The inhibiting effect of silicon on the growth of compound layer is possibly due to silicon placement inside the compound layer which retards the diffusion. However, in the bath with 3 wt% manganese, no changes were observed in the composition of the intermetallic layers. Phases of Fe2Al5 (η) and FeAl3 (θ) were the dominant intermetallic layers with no traces of manganese. Although, dispersed intermetallic particles of the topcoat revealed amounts of manganese. Existence of manganese in the bath indicated no significant effect on the growth rate of the layer and its morphology. Furthermore, a method for evaluating roughness intensity of the compound layer has been developed in this work. Investigations on the tongue-like morphology and roughness of the intermetallic layer revealed that the interface roughness increases linearly with the thickness of the layer. Presence of 3 wt% manganese in the aluminum bath indicated a negligible effect on the thickness and roughness of the layer. However, silicon eliminated the tongue-like morphology of the interface by retarding the rate of the growth.

On the interfacial phase growth and vacancy evolution during accelerated electromigration in Cu/Sn/Cu microjoints

In this work, we integrate different computational tools based on multi-phase-field simulations to account for the evolution of morphologies and crystallographic defects of Cu/Sn/Cu sandwich interconnect structures that are widely used in three dimensional integrated circuits (3DICs). Specifically, this work accounts for diffusion-driven formation and disappearance of multiple intermetallic phases during accelerated electromigration and takes into account the non-equilibrium formation of vacancies due to electromigration. The work compares nucleation, growth, and coalescence of intermetallic layers during transient liquid phase bonding and virtual joint structure evolution subjected to accelerated electromigration conditions at different temperatures. The changes in the rate of dissolution of Cu from intermetallics and the differences in the evolution of intermetallic layers depending on whether they act as cathodes or anodes are accounted for and are compared favorably with experiments. The model considers non-equilibrium evolution of vacancies that form due to differences in couplings between diffusing atoms and electron flows. The significance of this work lies in understanding the vacancy transport due to the difference in intrinsic diffusion of elements in different features of the microstructure, and the severe unidirectional convective flux of atoms due to the enforced electron wind that ultimately paves the road to study nucleation of microvoids.

High-Temperature Oxidation Resistance of NiAl Intermetallic Formed In Situ by Thermal Spraying

An Al/Ni composite coating was deposited on the surface of a pure Ti substrate by arc spray technology and plasma spray technology. In order to enable the in-situ reaction between the Al/Ni composite coating and the specimen, they were heated under different conditions. In addition, oxidation testing was conducted to test the oxidation-resistant property of the coating. The phase transition regulation of the coating after heating, the influence of heating at different temperatures and time on the reaction depth, and the correlated theory of the in-situ formation of the NiAl intermetallic compounds were studied and analyzed. The results showed that after the heat treatment, a ragged wave-like morphology was exhibited in the diffusion front of Al, and a small amount of the Ni in the diffusion region did not participate in the reaction. The growth of the NiAl intermetallic layer in the diffusion region of the Al/Ni/Ti specimen was obviously slower compared with the Al/Ni specimen.

Effect of silicon, manganese and nickel present in iron on the intermetallic growth at iron - aluminum alloy interface

Recent interest in joining aluminum to steel necessitates a critical understanding of growth kinetics of various intermetallic phases that form across the mixed material interface. In order to understand the individual effect of ternary alloying elements present on iron side, growth kinetics of intermetallic layers formed at the interface between iron and aluminum alloy 6061 were studied by dipping pure iron and binary Fe-X alloys in the melt of AA6061, where X was Mn, Ni and Si. The immersion experiments were performed at 750 °C for various time durations from 90 s to 2400 s. The intermetallic layers formed at the interface were Fe2Al5 and FeAl3 in all cases. It was found that the presence of all the three ternary alloying elements in iron reduced the growth of intermetallic layer. Silicon was found to be the best for reducing the growth kinetics of the intermetallics followed by Ni and Mn in that order. The growth of Fe2Al5 layer was found to be diffusion controlled. Thickness of FeAl3 layer was found to increase with time at the beginning and to decrease with time at later stages. This behavior of FeAl3 was attributed to the two competitive processes that are simultaneously occurring at the FeAl3/AA6061 interface during liquid-solid diffusion viz. dissolution and formation of the FeAl3. The effect of the alloying elements on the growth kinetics of the intermetallic layer is explained based on velocity of interface in terms of interdiffusion fluxes and concentration gradients across the interface.

Dissimilar gas tungsten arc weld-brazing of Al/steel using Al-Si filler metal: Microstructure and strengthening mechanisms

In this paper gas tungsten arc welding (GTAW) was applied to dissimilar lap joining of Al6061 and Zn-coated galvanized low carbon steels using Al-5 wt% Si filler metal. The joining mechanism was based on a hybrid brazing/welding mechanism. Three factors contributed to the joint strength including (i) low heat input rate of GTAW process which reduce the intermetallic compound layer growth during joining, (ii) the special role of Si in the filler metal which was able to change the nature of reaction layer from predominantly η-Al5Fe2 phase to predominately less brittle Al-Fe-Si phase and (iii) the flux-like action of Zn-coating which ensures complete wetting of steel surface by Al melt. It was found that there is a critical heat input which when exceeded caused degradation of the mechanical strength of the joint due to increased intermetallic compound growth.

Microstructural effects of isothermal aging on a doped SAC solder alloy

Abstract An Sn–Ag–Cu based solder alloy, including Ni, Bi and Sb additives, is investigated in this study under isothermal aging conditions. Shear creep tests are conducted on different aged solder joints with copper substrate, giving the creep resistance evolution with aging time. Microscopy analyses reveal the limited growth of the Cu-rich intermetallic layer due to the Ni content and allow for determination of the time-dependent growth of the Sn-rich intermetallic layer. The aged specimens also exhibit a partial dynamically recrystallized microstructure after creep deformation and a brittle-to-ductile fracture transition is found with occurrence of intergranular cracking in the joint.

Growth of inter-metallic compound layers on CLAM steel by HDA and preparation of permeation barrier by oxidation

Hot-dip aluminizing (HDA) on China Low Activation Martensitic (CLAM) steel and followed by oxidation to obtain an Al2O3/FexAly layer covering was considered to be a promising method to resist the harsh environments in fusion reactors. In the present study, CLAM steel was coated in molten pure Al and Al-0.3Ce (wt.%) melt. The growth behavior of the inter-metallic compound (IMC) layers after different immersion time and temperature was investigated and described. The IMC layer mainly consists of Fe2Al5 and FeAl3 after hot-dipping. And the addition of Ce in the molten pure Al could promote the growth of IMC layers, which provided the idea of obtaining a certain thickness of the IMC layer at a lower temperature. After two independent oxidation processes (normalized heat-treatment and 760°C for 15h) in air, the Fe2Al5 and FeAl3 of IMC layers had been transformed into ductile phases (FeAl2 and FeAl), and Al2O3 layers were detected on the coating surface. The oxidation of 760°C for 15h was considered to form a denser Al2O3 film. However, cracks and pores were observed in the IMC layer after oxidation due to the heat-treatment and cooling methods

Growth of Interfacial Intermetallic Compound Layer in Diffusion-Bonded SAC–Cu Solder Joints During Different Types of Thermomechanical Excursion

The effects of mechanical strain on the growth kinetics of interfacial intermetallic compounds (IMCs) sandwiched between Cu substrate and Sn-1.0 wt.%Ag-0.5 wt.%Cu (SAC105) solder have been investigated. Isothermal aging (IA) at 70°C and 125°C, and thermal cycling (TC) as well as thermomechanical cycling (TMC) with shear strain of 12.8% per cycle between −25°C and 125°C were applied to diffusion-bonded solder joints to study the growth behavior of the interfacial IMC layer under various types of thermomechanical excursion (TME). The microstructure of the solder joint tested under each TME was observed at regular intervals. It was observed that the growth rate of the IMC layer was higher in the case of TMC compared with TC or IA. This increased growth rate of the IMC layer in the presence of mechanical strain suggests an additional driving force that enhances the growth kinetics of the IMC. Finite element analysis was performed to gain insight into the effect of TC and TMC on the stress field in the solder joint, especially near the interface between the solder and the substrate. Finally, an analytical model was developed to quantify the effect of strain on the effective diffusivity and express the growth kinetics for all three types of TME using a single expression.