Intermetallic Growth Research Articles

Interfacial Reactions between Ga and Cu-10Ni Substrate at Low Temperature.

Ga alloys have been attracting significant renewed attention for low-temperature bonding applications in electronic packaging. This study systematically investigates the interfacial reaction between liquid Ga and Cu-10Ni substrates at 30 °C. In addition to CuGa2 formed from binary Ga/Cu couples, a layer of nanocrystalline Ga5Ni and CuGa2 formed between the Cu-10Ni substrate and the blocklike micrometer scale CuGa2 layer. The growth of interfacial intermetallics (IMCs) on the Cu-10Ni substrate was substantially accelerated compared to the IMC growth in binary Ga/Cu couples. Reaction kinetics study shows the IMC growth from the Cu-10Ni substrate was controlled by reaction and volume diffusion, while the IMC growth from the Cu substrate was controlled by volume diffusion. It is also found that the presence of Ni within the CuGa2 phase resulted in improved thermal stability and a smaller coefficient of thermal expansion during heating from 25 to 300 °C, using synchrotron XRD analysis. There was least thermal expansion anisotropy among most of the IMCs that form in conventional Sn-based solder alloys, including Cu6Sn5 and so forth. It is concluded that using a Cu-10Ni substrate as opposed to a Cu substrate could achieve sufficient metallurgical bonding within shorter processing time. The results have implications for broadening the application temperatures when using Ga as a low-temperature joining material.

Four dimensional (4D) microstructural evolution of Cu6Sn5 intermetallic and voids under electromigration in bi-crystal pure Sn solder joints

Electromigration (EM) causes intermetallic and void growth that decreases the reliability and lifetime of solder joints. As a diffusion-controlled process, EM is highly dependent on the fastest diffusion pathways in a structure. In anisotropic β-tetragonal Sn those pathways are along high angle grain boundaries and along the c-axis of the Sn grains. A bicrystal sample with two major grain orientations and two major grain boundary types was EM tested for 100 h. EM was interrupted at intervals for x-ray microtomography to reveal the 3D evolution of intermetallic compounds (IMCs) and voids within the joint. Quantitative IMC growth along high angle grain boundaries and twins was captured for the first time and related to the effective Cu diffusivity of multiple grains. Using a correlative approach that combined scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD) mapping, IMC growth and morphology were linked to the evolution of the Sn grain structure. Unusual void shrinkage and void splitting behavior were connected to uneven cathode interface consumption and thermal compression.

A Model for Intermetallic Growth in Thin Sn Joints Between Cu Substrates: Application to Solder Microjoints

Thin Sn-based solder microjoints, typically less than 25 μm thick, attached to Cu bond pads on both sides in three-dimensional electronic packages are often converted completely into intermetallic compounds (IMC) during service or accelerated testing. The rate of IMC growth and the proportions of the IMCs relative to the unreacted Sn in the joint have strong implications on solder joint reliability, and hence on the performance of the entire package. Although IMC growth at the interface between two semi-infinite slabs of different components (e.g., Cu and Sn) has been previously modeled, to date, no analytical treatment of intermetallic growth at the interfaces of a thin joint (Sn) sandwiched between two massive substrates (Cu), with concurrent growth of two different intermetallics (Cu6Sn5 and Cu3Sn) at each interface, has been proposed. In this work, a multicomponent diffusion-based model is developed for IMC growth in a thin joint between two semi-infinite substrates, with each interface possessing a multiphase structure. Because the Sn layer is thin, after prolonged aging, Sn may be completely depleted by reaction with Cu from the substrates, with the entire joint becoming IMC. Considering the joint as a finite source of Sn and the substrates as semi-infinite sources of Cu, general solutions of Fick’s second law of diffusion were applied to obtain the concentration of Cu within each phase. Values of interdiffusion coefficients available in literature were used to solve for the interfacial position parameters in the multiphase system, and thence to determine the instantaneous thicknesses of Cu6Sn5 (η), Cu3Sn (e), and Sn. The predictions of the model were validated against experimental data on the growth of IMCs in thin solder joints at 180°C and 210°C. Finally, the model was used to simulate the effects of aging temperature, joint thickness, and initial IMC thicknesses on the growth kinetics of IMCs during isothermal aging.

Effect of nano-Ag3Sn additions on wettability, interfacial intermetallic growth and mechanical properties of Zn–30Sn–1Ge solders on Cu substrates

The influences of different addition (0, 0.2, 0.4, 0.6, 0.8, and 1.0 wt%) of Ag3Sn on the wettability, the morphology of interfacial intermetallic compounds (IMCs), and the mechanical properties of Zn30Sn1Ge (ZSG) solder on Cu substrate were investigated. The Ag3Sn nanoparticles with an average particle size of approximately 30–45 nm were dispersed in the α-Zn phase and IMC layer. The added Ag3Sn nanoparticles can remarkably improve the wettability of ZSG solder and inhibit the formation and growth of the interfacial IMCs between the nanocomposite solders and Cu substrates. The enhancement of wettability and inhibition of interfacial IMC increased with the increase of nano-Ag3Sn addition amount under low concentration. However, the excessive addition of Ag3Sn nanoparticles in ZSG solder will degrade the wettability and inhibition of interfacial IMCs. When the amount of Ag3Sn nanoparticles is 0.6 wt%, the ZSG–0.6Ag3Sn solders possess the best wettability. In addition, the ZSG–0.4Ag3Sn solder exhibits the most prominent effect in retarding the formation and growth of interfacial IMCs. Meanwhile, the addition of Ag3Sn nanoparticles increases the shear strength and Vickers hardness of the solder joint. When the amount of Ag3Sn nanoparticles is 0.4 wt%, the shear strength of the welded joint is increased by 13.3%. Moreover, the macroscopic hardness of ZSG–0.6Ag3Sn solder is 49.507 HV, which is 57.5% higher than that of the solder without added nanoparticles (31.38 HV). Results show that the addition of Ag3Sn nanoparticles plays an important role in the interfacial reaction and mechanical properties between the ZSG solder and Cu substrate.

Microfluidics revealing formation mechanism of intermetallic nanocrystals

Insightful understanding of the reaction mechanisms that control both growth and phase formation is one of the most challenging issues in ordered intermetallic catalysts. In this study, we developed a microfluidic system with a millisecond time resolution for the synthesis of PtSn intermetallic nanocrystals, with which the complex formation mechanism of intermetallic phase was enabled to investigate. The result revealed that the formation of PtSn nanocrystals occurs in four stages: increasing monomer, burst nucleation of monomers and intermetallic phase formation, growth and particle attachment, and sintering stage. The products in the range of milliseconds to seconds can be obtained by different lengths of reaction microchannels. This setup allowed control of the phases of the PtSn nanocrystal growth and thereby tuned the catalytic performance of the ethanol oxidation reaction. Such an understanding of the growth of pathways is significant for the design of ordered intermetallic nanocatalysts.

Interfacial reactions and structural properties of explosively welded titanium/copper plates

In this study, the effect of post-processing heat treatment on the interface morphology and kinetics of intermetallic phase growth in titanium/copper bimetallic sheets were analyzed using a scanning electron microscopy and mechanical testing. Ti/Cu composite was fabricated by explosive welding. Then, clads were subjected to the post-welded annealing at 973 K for times ranging between 15 min and 100h. In the as-bonded state, the interface shows a wavy character with a limited number of melted zones, which are mostly composed of phases that are not observed in the Ti-Cu equilibrium phase diagram. Short-term annealing is shown to transform non-equilibrium phases into equilibrium ones, such as TiCu4 and Ti3Cu4. For longer annealing times, the growth of four intermetallic sublayers (Ti2Cu, TiCu, Ti3Cu4, and TiCu4) distributed along the entire interface is detected. However, the growth kinetics of particular sublayers was different. Volume fraction estimation of intermetallic phases at annealing times under study revealed the largest thickness for TiCu and TiCu4 phases. The nano-hardness of intermetallic sublayers was found to drop with the Ti content.

The effect of Ag on the growth of intermetallics at the interface of Sn5Zn/Cu interconnects

The reliability of electronic packages is primarily affected by the growth of the intermetallic compound (IMC) between the solder and the copper interconnection. It is therefore necessary to study the effect of element addition on the growth of the IMC interface with respect to an improvement in the package reliability. In this study, the influence of Ag on the growth of intermetallic compounds in the Sn5Zn solder/copper interconnection interface was investigated. The results revealed that in comparison with Sn5Zn/Cu, the interfacial IMC thickness decreased initially and then increased in accordance with an increase in the doping amount of alloying elements in the solder. Further, it was observed that the doping of the alloying element (Ag) can significantly reduce the IMC growth rate at the interface. Compared with the Cu5Zn8 unit cell formation energy (-0.632eV), one dopant atom and two dopant atoms of Ag can reduce the formation energy of a Cu5Zn8-based unit cell to the minimum values of -0.636 eV and –0.640 eV, respectively; consequently, the stability is increased. The maximum diffusion activation energies of Cu atoms and Zn atoms in a Cu5Zn8-based unit cell are 3.419 eV and 1.692 eV, which increase to 3.512 eV and 1.971 eV, respectively, after doping with Ag.

Inhibition of intermetallic compounds growth at Sn–58Bi/Cu interface bearing CuZnAl memory particles (2–6 μm)

In total, 0.5 wt% CuZnAl memory particles with the diameters (2–6 μm) were added into Sn–58Bi solder in order to enhance the properties of solder joints in electronic packaging. The interface reaction and the growth kinetics of intermetallic compounds at Sn–58Bi/Cu interface and Sn–58Bi–0.5CuZnAl/Cu interface were studied systematically at 250 °C, 230 °C and 210 °C, the results indicate that the growth rate of intermetallic compounds (IMC) at both interfaces at 250 °C was higher than that at 230 °C, the addition of CuZnAl memory particles can reduce the diffusion coefficient of interfacial IMC, and however, at 210 °C the inhibition effect of CuZnAl particles was so small. Based on the transient liquid phase bonding, it is demonstrated that Cu/Sn–58Bi–0.5CuZnAl/Cu-bonded joints can achieve the chip stacking in 3D packaging with 10 μm thickness with obvious superiority.

An analytical model to predict diffusion induced intermetallic compounds growth in Cu-Sn-Cu sandwich structures

A mass diffusion model is developed to describe the growth kinetics of Cu6Sn5 intermetallic compounds (IMC) in the Cu-Sn-Cu sandwich structure. The proposed model is based on the local interfacial mass conversation law where interfacial Cu/Sn reactions and atomic diffusion are considered. Theoretical analysis shows that the IMC thickness growth is proportional to the square root of the product of the diffusion coefficient and time. The proposed model can explain the polarity effect of electromigration on kinetics of IMC growth where all the parameters have clear physical meaning. The theoretical predictions are compared with experimental results and show reasonable accuracy.

Simulation of the Ni3Al intermetallic inclusion growth process during direct laser deposition using Ni-based superalloy powder

The mechanical properties of Ni-based superalloys are based on the hardening γ′-phase which is mainly Ni3Al intermetallic compound with an ordered structure (Ll2). A mathematical model of γ′-phase inclusions growth during direct laser deposition was developed to predict parameters of the hardening phase. The subject of the study is the assessment of the applicability of the model as well as its adjustment if it is necessary. A series of experiments on growing thin walls were carried out to confirm the operability of this model. The power of the laser source was changed (450, 600, 900 and 1200 W) at constant values of the processing speed (1.2 mm/s), powder feed rate (45 g/min) and the beam diameter in the processing region (1.2 mm) in these experiments. The average size of γ′-phase inclusions was determined by means of a metallographic study and amounted to 10.74, 15.19, 25.62 and 24.49 nm, respectively. A comparison of the calculated and experimental values of the inclusions size showed that the proposed model gives satisfactory results in a limited range of cooling rates. Probably, it is connected with the fact that the growth of grains due to formation of a new phase stops due to a decrease of the concentration of components involved in the chemical reaction in the adjacent zone and the growth due to the absorption of neighboring grains does not have enough time to occur.

Intermetallic growth kinetics in gold ball bonds on Al-1%Si-0.5%Cu bond pads at 175∘C

Purpose The purpose of this study is to demonstrate that isothermal intermetallic growth data for gold ball bonds can be non-parabolic with explanations of why deviation from parabolic kinetics may occur. Design/methodology/approach Intermetallic thickness measurements were made at the centre of cross-sectioned ball bonds that were isothermally annealed at 175°C. Intermetallic growth kinetics were modelled with a power law expression(x(t) − x0)2 = α1tα2. The parameters of the power law model were obtained by transformation of the response and explanatory variables followed by data fitting using simple linear regression (SLR). Findings Ball bonds made with 4 N (99.99%Au) and 3 N (99.9%Au) gold wires exhibited two consecutive time regimes of intermetallic growth denoted Regime I and Regime II. Regime I was characterised by reactive diffusion between the gold wire and the aluminium alloy bond pad, during which Al was completely consumed in the formation of Au–Al intermetallics with non-parabolic kinetics. In Regime II, the absence of a free supply of Al to sustain intermetallic growth led to the conclusion that thickening of intermetallics was caused by phase transformation of Au8Al3 to Au4Al. Ball bonds made with 2 N (99%Au) wire also exhibited non-parabolic kinetics in Regime I and negligible intermetallic thickening in Regime II. Research limitations/implications The analysis of intermetallic growth is limited to total intermetallic growth at a single temperature (175°C). Originality/value The value of this study lies in showing that the assumption that only parabolic intermetallic growth is observed in isothermally aged gold ball bonds is incorrect. Furthermore there is no need to assume parabolic growth kinetics because with an appropriate data transformation, followed by fitting the data to a power law model using SLR and with the use of statistical diagnostics, both the suitability of the kinetic model and the nature of the growth kinetics (parabolic or non-parabolic) can be determined.

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

A prediction of Fe-Al IMC layer thickness in TIG-assisted hybrid friction stir welded Al/steel dissimilar joints by numerical analysis

In joining aluminum alloy to steel, excessive growth of Fe-Al intermetallics (IMC) can deteriorate the joint quality with its brittleness by low solubility of liquid aluminum in iron. This problem can be fixed by adopting a solid-state welding such as friction stir welding (FSW), but lack of plastic flow and excessive tool wear are limitations during the process. In this study, joining 2.5 mm thick Al5052 aluminum alloy to 1.4 mm thick DP590 high strength steel was proceeded by TIG-assisted hybrid friction stir welding (HFSW) to improve the plastic flow and to decrease plunging force on the FSW tool. The purpose of this study is to realize the effect of preheating source on the growth of IMC layer thickness based on the 3D heat transfer numerical model. Thermal characteristics and IMC layer thickness on the welded joints were estimated and validated with experimental results. Consequently, HFSW adopting 20 A TIG current achieved the highest average tensile strength as 184 MPa with 2.39 μm IMC layer thickness, and the numerical result showed a fair agreement to the experimental results. It is realized that the heat generation per unit length of the time significantly influences on the maximum temperature and the growth of IMC layer thickness.

Activation energy for Cu-Sn intermetallic in CNT-reinforced Sn-1.0Ag-0.5Cu solder

Purpose The purpose of this study is to investigate the addition of 0.05 Wt.% carbon nanotube (CNT) into the Sn-1.0Ag-0.5Cu (SAC) solder on the intermetallic (IMC) growth. Lead-based solders play an important role in a variety of applications in electronic industries. Due to the toxicity of the lead in the solder, lead-free solders were proposed to replace the lead-based solders. Sn-Ag-Cu solder family is one of the lead-free solders, which are proposed and considered as a potential replacement. Unfortunately, the Sn-Ag-Cu solder faces some reliability problems because of the formation of the thick intermetallic compounds. So the retardation of intermetallic growth is prime important. Design/methodology/approach The solder joint was aged under liquid state aging with soldering time from 1 to 60 min. Findings Two types of intermetallics, which are Cu6Sn5 and Cu3Sn were observed under a scanning electron microscope. The morphology of Cu6Sn5 intermetallic transformed from scallop to planar type as the soldering time increases. The addition of carbon nanotube into the SAC solder has retarded the Cu6Sn5 intermetallic growth rate by increasing its activation energy from 97.86 to 101.45 kJ/mol. Furthermore, the activation energy for the Cu3Sn growth has increased from 102.10 to 104.23 kJ/mol. Originality/value The increase in the activation energy indicates that the growth of the intermetallics was slower. This implies that the addition of carbon nanotube increases the reliability of the solder joint and are suitable for microelectronics applications.

Junction growth and interdiffusion during ultrasonic additive manufacturing of multi-material laminates

Ultrasonic additive manufacturing is a promising approach for making net-shaped multi-material laminates from material combinations difficult to process with fusion-based additive manufacturing techniques. The properties of these multi-material laminates depend sensitively on the interface between the constituents, which can be decorated with pores as well as thin intermetallic layers. Here, we develop process models for junction growth and interdiffusion during ultrasonic additive manufacturing of dissimilar metals. These process models are validated against published experimental data, then used to generate process diagrams which reveal that high normal loads and high sonotrode velocities can reduce intermetallic growth while maintaining strong interlayer bonding.

無電解Ni/Pd/Auめっきにおけるはんだボール接続信頼性-金属間化合物の成長に及ぼす電解Pdめっき膜厚の影響

無電解Ni/Pd/Auめっきにおけるはんだボール接続信頼性-金属間化合物の成長に及ぼす電解Pdめっき膜厚の影響

Effect of surface roughness on void formation and intermetallic growth in electrodeposited Cu-Sn stacks

Abstract Effect of surface roughness on the void formation and intermetallic compounds (IMCs) growth in the Cu-Sn diffusion layers is reported. Different samples having varying surface roughness of the electrodeposited copper were obtained by using different current densities, i.e., 5 mA/cm2 (type-I) and 50 mA/cm2 (type-II). Electrodeposited copper samples having higher surface roughness showed the formation of larger voids than the samples having a lower surface roughness, which was attributed to the larger peaks and lower availability of copper at the peaks. The mechanism for void formation and growth was also proposed with the experimental validation. The IMC growth was hampered in samples having higher copper surface roughness due to larger voids at Cu-Cu3Sn interface. The direct influence of underlying copper surface roughness on the void size, void fraction, and the IMC growth is experimentally demonstrated.

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.

Modeling of the Formation Process of the Coherent Intermetallides in Nickel Alloys during Laser Treatment

A solution for new phase inclusion growth is suggested for the case of the Ni-based alloys. This solution takes into account a chemical composition of the alloy and conditions of the laser treatment process. A method for calculation of the chemical reaction rate constant is also suggested for the Ni3Al formation in the Ni-Al alloy. Modeling is fulfilled for the laser cladding process. Time dependences for the reacting component concentration is obtained as well as for intermetallic inclusion growth and thermal cycle.

An in-situ study on the diffusion growth of intermetallic compounds in the Al–Mg diffusion couple

Study on the diffusion growth of intermetallic compounds in the Al–Mg based light-weight metal materials is important due to its close interrelation with property. The current work aims at solving the existing problems of estimating interdiffusivities of intermetallic compounds, such as the early-stage effect on the accurate determination of parabolic growth constant and the simultaneous calculation of composition- and temperature-dependent interdiffusion coefficient. We present the first usage of High-Temperature Laser-Scanning Confocal Microscopy for effective in-situ observation of the time-dependent intermetallic compound growth in the Al–Mg diffusion couples. The method is verified by successfully recording the growth of Al3Mg2 and Al12Mg17 phases in diffusion couples annealed at 380 °C, 400 °C and 420 °C, and the accurate parabolic growth constant of intermetallic compound are estimated without early-stage effect. The experimental data are then subject to a numerical inverse methods to generate a set of self-consistent interdiffusivities, which can reproduce the observed diffusion growth behavior of intermetallic compounds in the Al–Mg diffusion couples. The applicability of current method to other alloy systems is also discussed.