Evolution Of Intermetallic Compounds Research Articles

Abnormal Intermetallic Compound Evolution in Ni/Sn/Ni and Ni/Sn-9Zn/Ni Micro Solder Joints Under Thermomigration

Interfacial reactions in Ni/Sn/Ni and Ni/Sn-9Zn/Ni micro solder joints during thermomigration (TM) have been studied by reflowing solder joints on a hot plate. Asymmetrical growth and transformation of interfacial intermetallic compounds (IMCs) were clearly observed. The growth of the Ni3Sn4 IMC in the Ni/Sn/Ni solder joints was always fast at the cold end and relatively slow at the hot end. Only asymmetrical growth of the Ni5Zn21 IMC in the Ni/Sn-9Zn/Ni solder joints occurred at the beginning because Zn was the dominant TM species; however, asymmetrical transformation of the Ni5Zn21 IMC also occurred under the combined effect of Zn depletion and Ni dissolution and migration, resulting in formation of a thin τ-phase layer at the hot end and a thick τ-phase/Ni5Zn21/τ-phase sandwich structure at the cold end. TM of Ni and Zn atoms was identified towards the cold end, being responsible for the abnormal IMC evolution. Addition of Zn was found to slow the TM-induced IMC growth and Ni dissolution.

Study on Evolution of Ti-containing Intermetallic Compounds in Alloy 2618-Ti during Homogenization

Abstract Dispersive Al3Ti particles introduced into alloy 2618-Ti are enclosed gradually by ternary Al18Mg3Ti2 phase during homogenization, which can be described as a “peritectic reaction”. This reaction is sensitive to homogenization temperature and time within 24 h but not so sensitive to homogenization time after 24 h because of its special growth pattern. The evolution of the intermetallic compounds during homogenization process of alloy 2618-Ti is further confirmed by means of diffusion couple of (Al-25Mg)/(Al-10Ti). After homogenization, much Al3Ti particles coexist with Al18Mg3Ti2 which depends on the composition of Al-Mg-Ti system and only a few single Al18Mg3Ti2 appear. The occurrence of single Al18Mg3Ti2 phase, within which Al3Ti disappears, can be attributed to the local fluctuation of alloy compositions.

Microstructural Evolution of Intermetallic Compounds in TCNCP Cu Pillar Solder Joints

This study investigated the microstructure, especially intermetallic compounds (IMCs), formed between a Cu pillar and Cu trace joined by thermal compression bonding with nonconductive paste (NCP). Continuous, uniform layers of Cu3Sn formed on the surface of both the Cu pillar and Cu trace. However, the growth of Cu6Sn5 was suppressed, forming nonuniformly on the Cu trace due to NCP filler entrapment at the Cu–solder interface that hindered Sn diffusion flux. Multireflow induced rapid growth of IMCs within the Cu pillar solder joint. The combination of multireflow and thermal cycle testing gave rise to asymmetric growth of IMCs between the chip side and substrate side as a result of stress migration induced by thermal cycling.

Spreading Behaviour and Joint Reliability of Sn–0.3Ag–0.7Cu Lead-Free Solder Alloy on Nickel Coated Copper Substrate as a Function of Reflow Time

Solder joint directly interfaces electrically, mechanically and thermally with numerous electronic components in electronic assemblies. Sn–Ag–Cu lead-free solder alloys for electronic assembly are being driven by the environmental issues concerning the toxicity of lead. In the present study, spreading behaviour, evolution of intermetallic compounds during solidification of Sn–0.3Ag–0.7Cu solder alloy on Ni coated Cu substrate and the related joint strength were studied as a function of reflow time. Experiments were carried out for various reflow times of 10, 100, 300 and 500 s at a reflow temperature of 270 °C. The solder alloy exhibited improvement in wettability on the substrate at longer reflow times. An increase in the IMC (CuNi)6Sn5 thickness was observed for samples reflowed up to 300 s and the thickness decreased for samples reflowed for 500 s. IMC layer formed were about 0.3, 1.15, 2.03, 1.94 μm during 10, 100, 300 and 500 s of reflow time respectively. The joint shear test was performed to assess the integrity of the Sn–0.3Ag–0.7Cu solder solidified on Cu substrates. The maximum joint strength was observed for samples reflowed for 100 s.

The size effect on intermetallic microstructure evolution of critical solder joints for flip chip assemblies

Purpose – The purpose of this paper is to study the intermetallic compound (IMC) thickness, composition and morphology in 100-μm pitch and 200-μm pitch Sn–Ag–Cu (SAC305) flip-chip assemblies after bump reflow and assembly reflow. In particular, emphasis is placed on the effect of solder joint size on the interfacial IMCs between metal pads and solder matrix. Design/methodology/approach – This work uses 100-μm pitch and 200-μm pitch silicon flip chips with nickel (Ni) pads and stand-off height of approximately 45 and 90 μm, respectively, assembled on substrates with copper (Cu) pads. The IMCs evolution in solder joints was investigated during reflow by using 100- and 200-μm pitch flip-chip assemblies. Findings – After bump reflow, the joints size controls the IMC composition and dominant IMC type as well as IMC thickness and also influences the dominant IMC morphology. After assembly reflow, the cross-reaction of the pad metallurgies promotes the dominant IMC transformation and shape coarsened on the Ni pad interface for smaller joints and promotes a great number of new dominate IMC growth on the Ni pad interface in larger joints. On the Cu pad interface, many small voids formed in the IMC in larger joints, but were not observed in smaller joints, combined with the drawing of the IMC growth process. Originality/value – With continued advances in microelectronics, it is anticipated that next-generation microelectronic assemblies will require a reduction of the flip-chip solder bump pitch to 100 μm or less from the current industrial practice of 130 to150 μm. This work shows that as the packaging size reduced with the solder joint interconnection, the solder size becomes an important factor in the intermetallic composition as well as morphology and thickness after reflow.

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.

겹치기 마찰교반접합 된 Al6061/HT590 합금의 기계적 특성 평가

This study was carried out to evaluate mechanical properties of the jointed Al6061/HT590 alloys by friction stir welding (FSW). FSW was conducted under the conditions with tool rotating speed of 500 RPM and traveling speed of 300 mm/min., where Ar gas was introduced to prevent the materials from corrosion during the welding process. Electron back-scattering diffraction (EBSD) was used to characterize microstructures such as grain size, misorientation angle and crystal orientation. Evolution of intermetallic compounds in Al6061 during the process were examined in terms of morphology, size and aspect ratio at three distinct zones Al base material, heat affected zone and stir zone, where transmission electron microscope (TEM) was used. It was revealed that FSW gave rise to refinement of grains as well as growth of intermetallic compounds in Al6061. The morphological changes of intermetallic compounds exerted an influence on mechanical properties, resulting in occurrence of fracture in the part of the base material instead of the jointed parts (heat affected zone and stir zone). This study systematically evaluated the microstructural evolutions during the FSW for joining Al6061 with HT590 and their effect on mechanical properties.

Formation and evolution of intermetallic compounds at interfaces of Cu/Al joints by ultrasonic-assisted soldering

The formation and evolution of Cu–Zn intermetallic compounds (IMCs) and Al–Cu–Zn ternary IMCs of Cu/Sn–9Zn/Al joint interfaces by ultrasonic-assisted soldering without flux in air were investigated. Aluminum particulates dissolved from the base metal and migrated into the solder by ultrasonic action. As the duration of ultrasonic action increased to 60s, the contents of Al in the solders reached 7.85wt%, which is significantly higher than the equilibrium solubility limit. The formation of Cu5Zn8 was prevented, and the IMC layers of the copper–solder surface changed from Cu5Zn8 to the Al4.2Cu3.2Zn0.7 (T′), because of the additional aluminum present in the solder. The Al–Cu–Zn ternary IMCs exhibited a slower growth rate and considerably thinner thickness than the Cu–Zn IMCs. The effect of the ultrasonic action on the thickness of the IMC layers and tensile strength of the joints was investigated. As duration of ultrasonic action increased from 2s to 60s, the thickness of the IMC layer increased from 1μm to 20μm, and the tensile strength of the joints decreased from 77MPa to 39MPa. The critical thickness of T′ was approximately 5μm.

Enhancement of mean-time-to-failure of Sn3.0Ag0.5Cu solder bump joint under current stressing via controlling bump shape

In this research, two different Sn3.0Ag0.5Cu solder bump joints with barrel shape and hourglass shape respectively were fabricated by controlling solder process, and evolution of intermetallic compounds (IMC) between different solder joint and Cu substrate under 4 × 103 A/cm2 current stressing at 60 °C were investigated. The results indicate that both the decrease of IMC layer thickness in the cathode and the increase of IMC layer thickness in the anode of the hourglass-shaped solder bump joint were obviously slower than that of barrel-shaped solder bump joint, and the formation of the voids at cathode interface was observed in the barrel-shaped solder bump joint after current stressing for 240 h. The mean-time-to-failure (MTTF) of solder joint with hourglass-shaped bump is efficiently improved compared to that with barrel-shaped bump. Compared to that of the solder joint with barrel-shaped bump, enhancement of MTTF of the solder joint with hourglass-shaped bump is attributed to relieve current crowding in entrance and outlet of electric current.

Confinement Effects on Evolution of Intermetallic Compounds During Metallurgical Joint Formation

In this work, we compare the microstructural evolution of Sn/Cu/Sn and Cu/Sn/Cu ‘sandwich’ configurations under metallurgical bonding conditions. These simulations are relevant in explaining experimental observations that suggest that the resulting dominant intermetallic compound in Cu-Sn systems depends on the relative supply of Cu and Sn. Through the analysis of morphological evolution and growth rate, it is shown that the Cu6Sn5 layer becomes dominant in the Sn/Cu/Sn structure, while the Cu/Sn/Cu structure is dominated by Cu3Sn after extended reaction periods.

The effect of reflow time on reactive wetting, evolution of interfacial IMCs and shear strength of eutectic Sn–Cu solder alloy

In the present work, the effect of reflow time on wetting behaviour, microstructure and shear strength of the eutectic Sn–0.7Cu lead-free solder on Cu substrate were studied. The reflow time was varied from 10 to 10,000 s. The contact angle decreased with the increase in reflow time. The growth of intermetallic compounds (IMCs) increased with the reflow time. The thickness of the Cu6Sn5 IMC layer formed during a reflow time of 10 s was about 3.76 μm and its thickness increased to 3.89, 6.2, 6.68, 7.6 and 19.83 μm during 100, 300, 500, 1,000 and 10,000 s reflow time respectively. The joint shear test was performed to assess the integrity of Sn–0.7Cu solder solidified on copper substrate surfaces. The shear strength decreased with increase in reflow time after an optimum value.

Behavior of intermetallics formation and evolution in Ag–8Au–3Pd alloy wire bonds

Ag–8Au–3Pd alloy wire has shown promise as an economical substitute for gold wire interconnects from integrated circuits to substrates. This work is undertaken to gain a better understanding on the intermetallic compounds (IMC) formation and evolution at the interface between Ag–8Au–3Pd wire and Al metallization pad. Longitudinal cross-section of bond interface was prepared by dual-beam focused ion beam (FIB) micro-machining for transmission electron microscopy (TEM) analysis. Two intermetallic regions formed at interface were crystallochemically identified as AuAl2+(Au, Ag)4Al and Ag2Al respectively. Interface evolution tracking by back scattered electron (BSE) imaging showed that IMC initially formed at periphery of bonding area. After short-term annealing treatment (175°C for 24h), the voids in the center of the bonding interface shrank and vanished, due to the Ag diffusion played dominant part in IMC growing. The mechanism of IMC formation and evolution at interface was finally elaborated on the basis of thermodynamics and diffusion kinetics respectively.

The Influence of Sn Orientation on Intermetallic Compound Evolution in Idealized Sn-Ag-Cu 305 Interconnects: an Electron Backscatter Diffraction Study of Electromigration

Previous research showed the relationship between Sn grain orientation and the intermetallic growth rate in Sn-Ag-Cu (SAC)305 interconnects. Samples with the Sn c-axis aligned parallel to the current flow have an intermetallic compound growth rate significantly faster than samples with the c-axis perpendicular to the current flow. This study continues the previous research by investigating intermetallic growth in polygranular joints and in joints that have a thin Ni layer at the cathodic or anodic interface of the interconnect. Planar SAC305 interconnects were sandwiched between two Cu pads (sometimes incorporating a thin Ni layer at the interface) and subjected to uniaxial current. The crystallographic orientation of Sn in these samples was characterized with electron backscatter diffraction before and after electromigration testing. The results show that polycrystalline joints have relatively slow intermetallic growth rates, close to those found in single-crystal joints with the c-axis perpendicular to the current. When a Ni layer was present on the anode side, the intermetallic grew at a rate comparable to that in samples without a Ni layer. However, when the Ni layer was on the cathode side, the intermetallic growth was significantly retarded. The measured growth rates of the intermetallic, combined with literature values for the diffusion of Cu in Sn, were used to calculate values for the effective charge, z*, which is significantly smaller for samples with current parallel to the c-axis than for either polycrystalline samples or samples with the c-axis perpendicular to the electron flow.

Phase-field simulations of intermetallic compound evolution in Cu/Sn solder joints under electromigration

In this work, we present a preliminary model based on the multiphase-field formalism that is used to investigate the evolution of intermetallic compound (IMC) layers in the Cu/Sn solder system under electromigration conditions. The simulation considers the concurrent evolution of the Cu3Sn and Cu6Sn5 IMC layers under electrochemical driving forces. We use CALPHAD descriptions for the thermodynamics of the bulk phases (Cu, Sn and both IMCs) and incorporate electrochemical contributions to the total free energy of the microstructure in order to simulate the evolution of the interfacial microstructure due to mass–current couplings. The simulation considers grain-boundary diffusion as the dominant mechanism for chemical-potential-driven mass flux. The simulation considers the effect of current density and polarity on the growth of IMCs. The simulations are in turn compared to experimental measurements of growth rates, morphology of IMC grains and evolution of interface roughness. The analysis of experiments and simulations suggest that back-stress resulting from the non-equilibrium vacancy generation due to diffusive flux imbalance among the individual diffusants (Cu and Sn) plays a fundamental role in the evolution of the IMC layers. Overall, the simulations and experiments show good qualitative agreement.

Spreading Behavior and Evolution of IMCs During Reactive Wetting of SAC Solders on Smooth and Rough Copper Substrates

The effect of surface roughness of copper substrate on the reactive wetting of Sn-Ag-Cu solder alloys and morphology of intermetallic compounds (IMCs) was investigated. The spreading behavior of solder alloys on smooth and rough Cu substrates was categorized into capillary, diffusion/reaction, and contact angle stabilization zones. The increase in substrate surface roughness improved the wetting of solder alloys, being attributed to the presence of thick Cu3Sn IMC at the interface. The morphology of IMCs transformed from long needle shaped to short protruded type with an increase in the substrate surface roughness for the Sn-0.3Ag-0.7Cu and Sn-3Ag-0.5Cu solder alloys. However, for the Sn-2.5Ag-0.5Cu solder alloy the needle-shaped IMCs transformed to the completely scallop type with increase in the substrate surface roughness. The effect of Ag content on wetting behavior was not significant.

Aging and Cu concentration effects on Sn–9Zn–xCu/Au couples

Aging and Cu concentration effects on the interfacial reactions between Sn–9wt%Zn–xwt%Cu (SZ–xCu) alloys and the Au substrate were investigated in this study. The Au3Zn7/AuZn2/AuZn and Au3Zn7/AuZn phases were formed in the SZ/Au and SZ–1Cu/Au couples aged at 160°C for 24h. Only the AuSn phase was found in the SZ–4Cu/Au couple aged at 160°C for 24h. When the aging time was extended to 800h the Sn atoms became the dominant diffusion element. Binary Au–Sn phases and the metastable Au–Zn–Sn ternary phase were formed at the interface in the SZ–xCu couples when the Cu content was 1–4wt%. When the Cu content was increased to 7–10wt% AuSn and (Cu, Au)Sn phases were observed at the alloy/Au interface aged at 160°C for 24h. After 800-h heat treatment the SZ–xCu systems were transformed completely into the Cu–Sn/Au systems. The (Cu, Au)SnAuSn and Cu6Sn5/AuSn were formed in the SZ–7Cu/Au and SZ–10Cu/Au couples. The results indicate that the evolution of intermetallic compounds (IMCs) was very sensitive to the Cu concentration in the SZ solders and the heat treatment period.

Computational Investigation of the Evolution of Intermetallic Compounds Affected by Microvoids During the Solid-State Aging Process in the Cu-Sn System

In this work, the impact of microvoids on the microstructural evolution of η-Cu6Sn5 and ɛ-Cu3Sn in the Cu-Sn system is evaluated numerically. Through the use of the multiphase-field method, the systems of interest are allowed to evolve using a solid-state aging temperature of 453 K in conjunction with material parameters and reaction conditions adopted from previous research. The simulation results are then analyzed and compared with previous experiments in terms of the morphological evolution of the intermetallic compounds (IMCs), the IMC layer thicknesses, and the corresponding interfacial roughness. It is shown that the presence of microvoids at the ɛ/Cu interface interferes with the flow of mass throughout the phases, impeding phase transformations and grain coarsening. This ultimately affects the IMC coarsening rate and overall IMC layer thicknesses. Additionally, it was observed that the presence of microvoids at the ɛ/Cu interface affects the formation of both IMC layers and their corresponding interfaces, and the changes in roughness for the interfaces are quantitatively provided. Overall, the simulations are found to be within the range of accepted experimental values for the morphology of the IMC grains, the evolution of IMC layer thicknesses, and the evolution of interface roughness.

The effect of intermetallic compound evolution on the fracture behavior of Au stud bumps joined with Sn-3.5Ag solder

The microstructure and joint properties of Au stud bumps joined with Sn-3.5Ag solder were investigated as functions of flip chip bonding temperature and aging time. Au stud bumps were bonded on solder-onpad (SOP) at bonding temperature of 260°C and 300°C for 10 s, respectively. Aging treatment was carried out at 150°C for 100 h, 300 h, and 500 h, respectively. After flip chip bonding, intermetallic compounds (IMCs) of AuSn, AuSn2, and AuSn4 were formed at the interface between the Au stud bump and Sn-3.5Ag solder. At a bonding temperature of 300°C, AuSn2 IMC clusters, which were surrounded by AuSn4 IMCs, were observed in the Sn-3.5Ag solder bump. After flip chip bonding, bonding strength was approximately 220.5mN/bump. As aging time increased, the bonding strength decreased. After 100 h of aging treatment, the bonding strength of the joint bonded at 300°C was lower than that bonded at 260°C due to the fast growth rate of the AuSn2 IMCs. The main failure modes were interface fractures between the AuSn2 IMCs and AuSn4 IMCs, fractures through the AuSn2 IMCs and pad lift. Initial joint microstructures after flip chip bonding strongly affected the bonding strengths of aged samples.

Phase-field simulations of intermetallic compound growth in Cu/Sn/Cu sandwich structure under transient liquid phase bonding conditions

The microstructural evolution of η(Cu6Sn5) and ε(Cu3Sn) in a Cu/Sn/Cu structure under transient liquid phase bonding conditions is numerically investigated through the use of the multiphase-field method. The material parameters and reaction conditions were adopted from relevant experimental research. Simulation results were then analyzed and compared with the experiments in terms of morphology of intermetallic compound (IMC) grains, growth ratio of the η layer with respect to the ε layer, evolution of each layer and roughness of each interface. Additionally, it is shown through the use of simulation data that, while liquid Sn is present, the growth of the η IMC layers is dominant and that, upon the exhaustion of liquid Sn, the η grains of the upper and lower layers impinge on one another, at which time the larger grains continue to coarsen at the expense of the smaller grains. Concurrently, the growth of the ε layers becomes significant and continues to increase until the η layer is fully consumed or the reaction is thermally arrested. Overall, the simulations were found to be in good qualitative agreement with experiments for morphology of the IMC grains, while showing good quantitative agreement, in spatial extent and elapsed time frames, for the evolution of each of the IMC layers and the derived growth ratio of the η layer with respect to the ε layer. Furthermore, it is shown that the results corresponding to different thickness values for the initial Sn layer suggest that the IMC evolution can be reasonably predicted in advance of experimental studies.

Effect of trace Al on growth rates of intermetallic compound layers between Sn-based solders and Cu substrate

This paper reports the effect of the addition of 1wt% Al into 100Sn, 96.5Sn–3.5Ag (SA) and 95.5Sn–3.8Ag–0.7Cu (SAC) solders, on growth rates of intermetallic compound (IMC) layers between the solders and a Cu substrate. During reflow at 260°C under 2%H298%N2 forming gas for 5–120min, the most pronounced reduction in IMC growth was observed in the SAC–1Al/Cu system. This was accompanied with the evolution of a layer of η2 (AlCu) IMC which was first formed within the bulk of the solder, then migrated towards and gradually replaced the previously formed η (Cu6Sn5) and ε (Cu3Sn) IMCs at the solder/Cu interface, and was finally transformed into δ (Al2Cu3) IMC and dispersed into the bulk of the solder again. A similar reduction in growth and associated evolution of IMCs was observed in the SAC–1Al/Cu samples subjected to thermal ageing at 170°C under air for 24–2096h.