Growth Of Intermetallic Compound Layer Research Articles

Dissimilar linear friction welding of AZ31 magnesium alloy and AA5052-H34 aluminum alloy

The intermetallic compound (IMC) layer, tensile properties, and fracture behavior of dissimilar Mg/Al joints and their relationship during linear friction welding (LFW) are investigated to develop a strategy to obtain high-strength Mg/Al dissimilar materials. The thickness of the Mg/Al-based IMC layer decreases as the applied pressure increases and the frequency decreases. The IMC layer is mainly composed of Mg17Al12 and Mg2Al3 at the weld interface. The tensile strength of the joints fabricated at an appropriate frequency of 50 Hz and a high pressure of 200 MPa during LFW is 235 MPa, which is 94 % the tensile strength of AZ31 and is attributed to the effective suppression of the Mg2Al3 IMC layer growth. At a lower frequency, large defects and pores are formed near the weld interface edge on the Mg side owing to the low welding temperature. The joint fabricated at a higher frequency exhibits a thick and brittle Mg2Al3 IMC layer at the weld interface because of the high growth rate; thus, the dissimilar joints fractured primarily at the Mg2Al3 IMC layer. The inhibition of the Mg2Al3 IMC layer growth yields superior tensile properties in Mg/Al dissimilar materials.

Growth mechanism of intermetallic compound in SnAg/Cu interface of micro-bumps under extremely low-temperature by phase field method

Scientific investigation will increasingly focus on deep space exploration. Spacecraft will be subjected to extremely low-temperature, changing internal microstructure and micro-bumps mechanics, reducing reliability. Thus, micro-bumps must be tested in extremely low temperatures. This research examines the impact of low-temperature storage on IMC (Intermetallic Compound) growth and micro-bumps crystallography at −196 °C. Secondly, a diffusion-weak coupled phase field theory is summarized, and the COMSOL multi-physics simulation platform simulates the growth of IMC layer in micro-bumps developing during extremely low-temperature storage. Finally, microhardness and elastic modulus of various phases were studied. Experimental data indicate that holding Sn at −196 °C for 1000 h produces recrystallization, resulting in tiny grains with diverse orientations. Micro-bumps with Sn/IMC interfaces have highest von Mises equivalent stress. Strain gradient thickens IMC layer at low temperatures with storage time, and edge IMC layer is thinner than axis IMC layer. The diffusion-force weak coupling phase field model's driving force curve indicates that stress gradient, not phase separation, drives IMC growth at extremely low temperatures. Low-temperature storage enhances Sn microhardness and elastic modulus through compressive stress and grain refining. IMC microhardness and elasticity decrease with tensile stress.

Tailoring interfacial structure and achieving excellent strength-ductility synergy of Al/Mg/Al composite via porthole die co-extrusion and post-annealing

Porthole die co-extrusion (PDCE) is an effective strategy for fabricating high-performance laminated bimetal composites. In this study, PDCE and post-annealing treatment were employed to tailor the interfacial structure and matrix microstructure of Al/Mg/Al composite, and the ensuing evolution in the fracture behaviors and mechanical properties were systematically investigated. A mechanical bond without the formation of intermetallic compounds (IMCs) at Al/Mg interface, strip-like substructure in Al layer, and bimodal structure composed of fine recrystallized grains coexisting with coarse deformed grains in Mg layer were achieved by PDCE and maintained after annealing at 200 °C. Increasing the annealing temperature or time caused the formation and growth of IMCs (γ-Mg17Al12 and β-Al3Mg2) layers, with the growth mode transforming from a combination of grain boundary and lattice diffusion at 300 °C to the predominant lattice diffusion at 400 °C. For Al layer, the static recrystallization (SRX), normal, and abnormal grain growth could not be triggered until the temperature higher than 400 °C. However, the SRX and grain growth in Mg layer were extremely boosted as the temperature increased to 300 °C. The differences in the plasticity and strength between Al and Mg layers resulted in the multi-step fracture of Al/Mg/Al composite without IMCs. With increasing of annealing temperature, early-stage delamination of Al and Mg layers took place due to the rupture of brittle IMCs, followed by independently deformation of each constituent layers. Al/Mg/Al composite annealed at 200 °C for 1 h show superior tensile strength of 191 MPa and maximal ductility of 22.7%.

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

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

Linear growth behaviour of intermetallic compound layer in electronic interconnections

We observed a linear behaviour of intermetallic compound (IMC) layer growth in electronic metallurgical interconnections, although the time required was twice that of commercial reliability standards for electronic packaging. This finding contradicts the classical parabolic growth law, which is widely reported to represent growth behaviour. We suggest that the parabolic growth law may be inadequate to thoroughly explain the IMC layer's growth by considering (a) one-directional growth and (b) reactions between elements for formation and growth. Further analysis has been carried out to analyse the logical judgment of the parabolic growth law and support our finding over linear IMC layer growth behavior.

Effect of Sn Plating Thickness on Wettability, Solderability, and Electrical Connections of Electronic Lead Connectors for Surface Mount Technology Applications

The wettability of solder is important to achieve good solderability between the electronic component and printed circuit board (PCB). Tin (Sn) plating is widely used to promote the wettability of the solder on the substrates. However, an adequate amount of Sn plating thickness must be taken into consideration to acquire good wettability and solderability. Thus, this study investigates the Sn plating thickness of the electronic lead connector and their effect on the wettability and electrical connection. Two types of Sn plating thicknesses, ~3 μm, and 5 μm were applied on the electronic lead connector surface. It was found that the thin Sn plating thickness of ~3 μm has shown failure in electrical connections and lack of solder joint wettability and solderability properties. A thicker Sn plating thickness of 5 μm, has shown better wettability and solderability properties. In addition, the electrical connections also passed which implies that the thicker Sn plating thickness provides good solder joint establishment leading to good electrical connections. It is also observed that the better wettability of solder has been achieved for thicker Sn plating thickness. The finding from the field emission scanning electron microscope (FESEM) shows that the intermetallic compound (IMC) layer growth in the lead connector surface is regarded as abnormal for thin Sn plating thickness (~3 μm), in which the IMC layer was consumed and penetrating up to the surface of Sn-coating. This has led to poor solderability of the thin Sn plating with the solder to establish solder joint. The findings from this study have shed some light upon a better understanding of the importance of considering the adequate amount of Sn coating thickness to avoid IMC consumption at the Sn plating, better wettability properties, solderability, and solder joint quality for surface mount technology (SMT) especially for electronic lead connector applications.

Formation of columnar grains during diffusional growth of Nb3Sn layer and its suppression

The manufacturing process of multifilamentary Nb3Sn superconducting wire includes annealing for diffusional growth of the Nb3Sn intermetallic compound layer. During the process, the formation of columnar Nb3Sn grains should be suppressed to maximize the flux pinning effect. However, the detailed mechanism underlying the formation of columnar Nb3Sn grains has not been clarified yet, and is an obstacle to finding optimal process conditions. In the present work, we investigated the fundamental reason for the columnar grain formation, using a novel Monte Carlo Potts model which can simultaneously predict grain growth and interfacial reactions. We found that a decrease in thermodynamic driving force due to insufficient Sn at the interface causes the formation of columnar Nb3Sn grains. Accordingly, columnar grain formation is expected to be suppressed when abundant Sn atoms are supplied rapidly to the reaction front. Based on the fundamental understanding of columnar grain formation, possible ways to suppress columnar grain formation are suggested. We especially focused on the difference in the columnar grain fraction depending on the wire strand type (bronze processed wire vs. internal-tin processed wire). Based on simulations and experimental analyses, we suggest a brief guideline for the design of wire strand geometry to avoid columnar grain formation.

Reliability and prediction of Sn36Pb2Ag solder joints under thermal aging test

In this work, the capacitor solder joints were aged at 50 °C, 75 °C, 100 °C, 125, and 150 °C from 100 h to 1000 h. The intermetallic compounds (IMCs) layer growth of Sn36Pb2Ag on hot air solder leveled (HASL) pad and electroless nickel/immersion gold (ENIG) pad was measured. Based on the empirical power-law of the IMC growth and the Arrhenius relationship between diffusion coefficient and aging temperature, a method to predict the IMC growth at a selected temperature was developed. The mechanical property of capacitor solder joints after thermal aging was investigated through the shear test. Through analysis of the fracture surface, the mixed fracture mode of ductile and brittle was exhibited. The porous structure of the Cu coating on the capacitor electrode was determined to be the origin of the crack.

Effect of Ni-modified reduced graphene oxide on the mechanical properties of Sn–58Bi solder joints

Sn–58Bi solder has great research value as a low-temperature solder. However, it still requires strengthening due to a lot of brittle Bi-phase, which reduces mechanical reliability. In this study, Ni-modified reduced graphene oxide (rGO@Ni) was prepared by heat reduction, and mechanical stirring was used to manufacture rGO@Ni-reinforced Sn–58Bi composite solder. The distribution, phase composition, and structural changes of graphene and Ni nanoparticles during enhancer synthesis were characterized in detail by Scanning Electron Microscope, Energy Dispersive Spectroscopy Raman and Fourier Transform Infrared spectra, X-ray Photoelectron Spectroscopy, X-ray Diffraction, and Transmission Electron Microscope. Besides, the morphology of intermetallic compound (IMC) layers of the composite solder/Cu interface was investigated. The thickness of the IMC layer decreases with the increase of rGO@Ni content. The microstructure analysis demonstrated that the rGO@Ni distributed near the IMC layer, which limits the diffusion of metal atoms and decreases the IMC layer's growth rate during the reflowing process. Besides, compared with Sn–58Bi solder alloys, the addition of 0.01 wt% rGO@Ni can increase the shear strength by up to 15%. However, when the content of rGO@Ni is more than 0.05 wt%, it agglomerates inside the composite solder, resulting in a decrease in the shear strength of the composite solder joint.

Influence of SiC reinforcement on microstructural and thermal properties of SAC0307 solder joints

The effect of SiC nano-phases (nano-particles and nano-fibers) addition into SAC0307 solder paste was investigated on the thermal and microstructural properties of the composite solder joints. The nano-phases were used between 0.125 and 1 wt%, and they were mixed into the solder paste by ball milling process. For the study power MOSFET (metal oxide semiconductor field effect transistor) components were soldered onto metal core printed circuit boards (MCPCBs). The thermal impedance Zth(t) and thermal resistance Rth of MOSFETs were measured by an indirect electrical method. Furthermore, the void formation and the microstructure of solder joints were also studied. The solderability and voiding properties of the composite solder alloys were acceptable. It was found that in 0.5 wt% amount, SiC nano-particles have positive effects on the thermal parameters of the solder joints, which could be explained by the IMC (intermetallic compound) layer growth suppression effect of the nano-phases. The microstructural analysis revealed that the microstructural refinement of the composite solder joints differs in the case of nano-particles and nano-fibers.

Ultrasonic vibration-induced thinning of intermetallic compound layers in friction stir welding of dissimilar Al/Mg alloys

Frictions stir welding (FSW) and ultrasonic vibration enhanced FSW (UVeFSW) of dissimilar Al/Mg alloys were conducted, and the intermetallic compounds (IMCs) layers formed at Al/Mg interface in welds were characterised by TEM. It was found that the IMCs thickness was significantly reduced in UVeFSW, and the IMCs were generated by solid-state atomic diffusion in butt joints under the used welding conditions since the measured temperature at the tool/workpiece interface was far below the eutectic points. The EBSD characterisation showed that ultrasonic vibration improved the degree of grain recrystallization on both sides of the IMCs layers and promoted the consumption of dislocations, which resulted in a reduced diffusion rate of atoms. Therefore, the growth of IMC layer was suppressed in UVeFSW.

Impact of Ni-coated carbon fiber on the interfacial (Cu,Ni)6Sn5 growth of Sn-3.5Ag composite solder on Cu substrate during reflow and isothermal aging

In this work, a novel composite solder was fabricated by mechanically incorporating Ni-coated carbon fiber (Ni-CF) into the Sn-3.5Ag solder paste in an effort to improve the overall service capability, where the intermetallic compound (IMC) formation and growth is a fundamental issue for consideration. General findings indicated that the addition of Ni-CF did not significantly impact the processing properties of the base alloy, such as melting temperature and wettability, when the reinforcement fraction was less than 2 wt%. Isothermal aging tests were carried out to study the formation and growth of interfacial IMC layers between the composite solder and Cu substrate. The addition of Ni-CF into Sn-3.5Ag solder could effectively promote the formation of interfacial (Cu, Ni)6Sn5 phase during reflow but retard its growth in the solid-state aging. The addition of 1 wt% Ni-CF was believed to be more effective to restrict and reduce the subsequent growth rate of the IMCs during solid-state aging due to the initial formation of a thicker (Cu, Ni)6Sn5 layer after reflow.

Contribution of Mechanical Activation on the Growth of Intermetallic Compound Layers at the Cu/Al Interface During Vacuum Hot Pressing

Contribution of Mechanical Activation on the Growth of Intermetallic Compound Layers at the Cu/Al Interface During Vacuum Hot Pressing

The self-healing of Kirkendall voids on the interface between Sn and (1 1 1) oriented nanotwinned Cu under thermal aging

The self-healing of Kirkendall voids (KVs) was observed on the interface between Sn and (111) oriented and nanotwinned Copper ((111)nt-Cu) during aging. Around 85 % of KVs healed up after 288 h aging, while the interfacial Cu3Sn intermetallic compound (IMC) layer decreased its thickness noticeably. This is mainly due to the high Cu diffusivity on (111) plane. In addition, the wettability of Sn on (111)nt-Cu was higher than those of conventional polycrystalline Cu (C-Cu) and (110) textured Cu ((110)Cu), since (111)nt-Cu was less prone to be oxidized during reflow. For (110)Cu, the IMC layer growth was restrained after reflowing and thermal aging, which is strongly related to the slow Cu diffusivity along the (110) plane.

Formation and Growth of Intermetallic Compounds in Lead-Free Solder Joints: A Review.

Recently, research into the factors that influence the formation and growth of intermetallic compounds (IMCs) layer in lead-free solders has piqued interest, as IMCs play an important role in solder joints. The reliability of solder joints is critical to the long-term performance of electronic products. One of the most important factors which are known to influence solder joint reliability is the intermetallic compound (IMC) layer formed between the solder and the substrate. Although the formation of an IMC layer signifies good bonding between the solder and substrate, its main disadvantage is due to its brittle nature. This paper reviews the formation and growth of IMCs in lead-free solder joints detailing the effect of alloying additions, surface finishes, aging time, aging temperature and solder volume. The formation and growth of the brittle IMCs were significantly affected by these factors and could be possibly controlled. This review may be used as a basis in understanding the major factors effecting the IMC formation and growth and relating it to the reliability of solder joints.

Influence of Copper Substrate Roughness on the Growth of Intermetallic Compounds Layer in SAC305 Solder Joints

This study aimed to evaluate the effect of surface morphology of copper (Cu) substrate on the intermetallic compound (IMC) growth and interfacial reactions when soldered with SAC305 lead-free solder during a thermal aging process. The surface morphology conditions of the Cu substrate influence the growth activity of the IMC layer. This study used different grits of silicon carbide (SiC) abrasive paper (400, 800 and 1200) to grind the Cu substrate to produce different surface roughness. The resulting Cu surface morphologies were examined using an infinite focus microscope (IFM), and the parameters used in this stereometric analysis were profile roughness. Hand soldering was used to melt the SAC305 solder on the Cu substrates with different surface roughness. Subsequently, the samples were subjected to an aging temperature of 150 °C for 800 hours to grow the IMC layers. Thermal aging increased the IMC thickness at the Cu-SAC305 interfaces. After thermal aging, the IMC layer thickness and related parameters were measured and analyzed with the IFM. The growth of the IMC layer thickness depended on the different surface morphology of the substrate when the aging temperatures and Cu materials were maintained in this study. In general, the IMC morphology for the rougher Cu substrate had a scallop-shaped and uniformed layer compared to those IMC from the smooth Cu substrate. The Cu substrate ground surface roughness with 400 grit SiC abrasive paper produced an average roughness, Ra of 505.02 nm; this roughness produced the thinnest IMC layers compared to the different Cu substrates ground by SiC abrasive paper of different grits.

Effect of Zn and in to microstructure of aged SAC305/Cu joint

In this project, Sn-3.0Ag-0.5Cu (SAC305) solder was alloyed with Indium (In) and Zinc (Zn) at 0.5–1.5 wt%, and the aim was to reduce growth rate of IMC layer at interface of solder joint during thermal exposure. Five samples were prepared via casting; SAC305, SAC/1In, SAC/1In-0.5Zn, SAC/1In-1Zn and SAC/1In-1.5Zn. Solders were characterized via SEM equipped with EDX for the bulk microstructure, and the IMC layer after reflow and aging at 150 °C for 100 h. Reflow was done on bare copper (Cu) substrate at 270 °C for 10 s. Among the percentages evaluated, microstructural analysis revealed that addition of 1.0% Zn not only refined the Ag3Sn and Cu6Sn5 particles, but also increased the eutectic area and promoted the formation of small (Cu,Ag)5Zn8 intermetallic compound (IMC). This would potentially increase the strength of solder, and at the same time, provide blocking mechanism for atomic diffusion during thermal aging and could lead to lower IMC growth. With increasing Zn content up to 1.0 wt%, the reaction phase (Cu,Ag)5Zn8 becomes larger and its morphology changed from a strip-like shape into flower-like or dendritic shape. Highest addition of Zn at 1.5 wt% gave slowest growth indicating that addition of Zn did suppress growth of IMC in SAC305. This could be because Cu was being used to form (Cu,Ag)5Zn8 which was observed at vicinity of the Cu6Sn5 layer. The results showed great potential of Zn alloying to suppress growth of IMC layer during thermal aging of solder joint, and this could lead to higher reliability of solder joint in electronic packaging.

Effect of SiO2 nanoparticle addition on growth of interfacial Ag3Sn intermetallic compound layers between lead-free solder and silver conductor

This study investigated the effects of silver powder modification on intermetallic compound (IMC) formation and silver leaching during soldering at high temperatures. Silica nanoparticles (NPs) were deposited onto a silver powder surface to inhibit silver leaching, which can lead to soldering joint failure during high-temperature soldering. The NPs were deposited through hydrolysis and a condensation reaction of tetraethyl orthosilicate (TEOS) based on the Stöber method. Fourier transform infrared spectroscopy and scanning electron microscopy were used to observe the microstructures of silver powders after the deposition of silica NPs with various TEOS concentrations and various deposition times. As the deposition time increased, the amount of silica NPs on the surface of the silver powder increased. The transmission electron microscopy results show that silica NPs were located at the IMC grain boundaries, which can hinder the dissolution of IMCs by lead-free solder melt along grain boundaries during soldering, retarding silver leaching. The growth kinetics and mechanism of IMCs during soldering were investigated. The results show that the growth of IMCs is mainly dominated by bulk diffusion. The activation energy for IMC growth increased and the growth rate decreased with increasing silica NP addition and deposition time.

Impact of different aging conditions on the IMC layer growth and shear strength of Ni-modified MWCNTs reinforced Sn-Ag-Cu composite solder

PurposeThe purpose of this paper is to develop a new composite solder to improve the reliability of composite solder joints. Nano-particles modified multi-walled carbon nanotubes (Ni-MWCNTs) can indeed improve the microstructure of composite solder joints and improve the reliability of solder joints. Although many people have conducted in-depth research on the composite solder of Ni-MWCNTs. However, no one has studied the performance of Ni-MWCNTs composite solder under different aging conditions. In this article, Ni-MWCNTs was added to Sn-Ag-Cu (SAC) solder, and the physical properties of composite solder, the microstructure and mechanical properties were evaluated.Design/methodology/approachIn this study, the effect of different aging conditions on the intermetallic compound (IMC) layer growth and shear strength of Ni-modified MWCNTs reinforced SAC composite solder was studied. Compared with SAC307 solder alloy, the influence of Ni-MWCNTs with different contents (0, 0.1 and 0.2 Wt.%) on composite solder was examined. To study the aging characteristics of composite solder joints, the solder joints were aged at 80°C, 120°C and 150°C.FindingsThe experimental results show that the content of Ni-MWCNTs affects the morphology and growth of the IMC layer at the interface. The microhardness of the solder increases and the wetting angle decreases. After aging at moderate (120°C) and high temperature (150°C), the morphology of the Cu6Sn5 IMC layer changed from scallop to lamellar and the grain size became coarser. The following two different phase compositions were observed in the solder joints with Ni-MWCNTs reinforcement: Cu3Sn and (Cu, Ni)6Sn5. The fracture surface of the solder joints all appeared ductile dents, and the size of the pits increased significantly with the increase of the aging temperature. Through growth kinetic analysis, Ni-modified MWCNTs in composite solder joints can effectively inhibit the diffusion of atoms in solder joints. In short, when the addition amount of Ni-MWCNTs is 0.1 Wt.%, the solder joints exhibit the best wettability and the highest shear strength.Originality/valueIn this study, the effects of aging conditions on the growth and shear strength of the IMC layer of Ni modified MWCNTs reinforced SAC307 composite solder were studied. The effects of Ni MWCNTs with different contents (0, 0.1 and 0.2 Wt.%) on the composite solder were examined.

Investigation of microstructure, thermal properties, and mechanical performances of Ni-added Sn-5.0Sb-0.5Cu/Cu solder joints

Small amounts of Ni were added to Sn-5.0Sb-0.5Cu (SSC505) solder alloy. The added Ni slightly increased the melting temperature and slightly reduced the melting range of the alloy. The microstructure of the SSC505 solder included a β-Sn phase, and SbSn and Cu6Sn5 intermetallic compound (IMC) phases distributed in the solder matrix. The addition of Ni produced a new (Cu0.7,Ni0.3)6Sn5 IMC phase with a mixed morphology comprising hexagonal and flake-shaped phases. The addition of 0.1wt.%Ni increased the ultimate tensile strength (UTS) and hardness of the SSC505 solder to 43.31 MPa and 17.52 HV, respectively, but the addition of 0.2wt.%Ni increased the size and number of the IMC phases, which weakened both properties. The interfacial layers of SSC505/Cu solder joints were composed of Cu6Sn5 and Cu3Sn IMC layers. The addition of Ni inhibited the growth of the Cu3Sn IMC layers, but produced a new, thicker, dendritic IMC layer identified by energy dispersive X-ray spectroscopy (EDS) as (Cu0.96,Ni0.04)6Sn5. As a result, the shear strength of the SSC505-0.2Ni/Cu solder joint was low. This work showed that the microstructure and mechanical performances of both a SSC505 solder alloy and SSC505/Cu solder joint were improved by the addition of 0.1wt.%Ni.