Growth Behavior Of Interfacial Intermetallic Compound Research Articles

Influence behavior and mechanism of crystal orientation of Cu6Sn5 coating on interfacial intermetallic compounds growth in Sn-0.7Cu/Cu solder joint

Herein, the Cu6Sn5 coatings with principal crystal orientations were prepared on the Cu substrate using magnetron sputtering to inhibit the growth of interfacial intermetallic compounds (IMCs) in Sn-0.7Cu/Cu solder joint. The effect of sputtering parameter on the principal crystal orientation of Cu6Sn5 coating was researched firstly, followed by the investigation on the influence of Cu6Sn5 coating principal orientation on the interfacial IMCs growth kinetics. The influence mechanisms were studied using molecular dynamics simulations and first-principles calculations. The results revealed that the increasing sputtering power from 40 W to 60 W and 80 W can not only improve the bonding property between the prepared Cu6Sn5 coating and Cu substrate, but also promote the transformation of the coating principal orientation from (132) to (132)/(22-1) and (132)/(22-1)/(42-2). Moreover, the three prepared Cu6Sn5 coatings can inhibit IMC growth at SC07/Cu solder joint, and the Cu6Sn5 coatings with (132)/(22-1) and (132)/(22-1)/(42-2) principal orientations exhibit more significant inhibitory effects on IMC growth than that with (132) principal orientation. It can be proved in this work that the growth of interfacial IMCs in Sn-0.7Cu/Cu solder joint at aging stage is mainly caused by the diffusion of Cu from Cu substrate toward Cu6Sn5 phase. The difference in the growth behavior of IMCs can be attributed to the fact that when the Cu atoms diffuse across Cu6Sn5 (22-1) and Cu6Sn5 (42-2), the bonding strength between the Cu atom at the saddle point and its surrounding atoms is significantly larger than when diffusing across Cu6Sn5 (132), leading to the smaller diffusion coefficients and a slower interfacial IMCs growth rate.

Insight into the improvement of service performance of Sn/Cu solder joint by Pt doping in Cu6Sn5 interfacial intermetallic compound

The effects of Pt doping on the mechanical properties of (Cu,Pt)6Sn5 interfacial intermetallic compound (IMC), bonding properties of the (Cu,Pt)6Sn5/Cu interface, and growth behavior of (Cu,Pt)6Sn5 IMC during the aging stage were investigated using first-principles calculations. The results indicate that Pt doping improves both the deformation resistance and ductility of the (Cu,Pt)6Sn5 phase, and that Cu2Pt4Sn5 demonstrates the highest ductility, as indicated by the maximum B/G value (3.14) and Poisson’s ratio (0.356). This phenomenon can be attributed to the smallest standard deviation of the charge density of 0.097 e/Å3. Comparisons of the interfacial work of adhesion and tensile strength of the Cu2Pt4Sn5/Cu and Cu6Sn5/Cu interfaces show that Pt doping enhances interfacial atomic interaction. Based on semi-classical Boltzmann theory, the electrical conductivity of the Cu2Pt4Sn5/Cu interface is smaller than that of the Cu6Sn5/Cu interface, with an amplitude of 9.26%, owing to the enhanced electron localization after Pt doping and resulting in a slight increase in the service temperature. Nevertheless, Pt doping still significantly suppresses the diffusion of Cu atoms, as evidenced by the millions of times reduction in the diffusion coefficient of Cu atoms across the Cu2Pt4Sn5/Cu interface compared to that across the Cu6Sn5/Cu interface because of the latter interface’s larger diffusion activation energy (3.52 eV > 2.08 eV), which was investigated by climbing image nudged elastic band methods. Therefore, Pt doping not only strengthens the mechanical properties of the (Cu,Pt)6Sn5 phase and improves the bonding strength of the (Cu,Pt)6Sn5/Cu interface, but also suppresses the growth of IMC during the aging stage, playing a positive role in obtaining a highly reliable Sn/Cu solder joint.

Growth behavior and reliability of interfacial IMC for Sn58Bi/Cu and Sn58Bi–AlN/Cu solder joints applied in IGBT modules

The IMC (interfacial intermetallic compound) produced by the metallurgical reaction between the solder and the Cu plate enables the packaging of IGBT (insulated gate bipolar transistor) modules. In this paper, the growth behavior of IMCs of Sn58Bi/Cu and Sn58Bi-0.05AlN/Cu at different times (10, 30 and 60 min) and temperatures (200, 250 and 300 °C) was investigated, which can provide a reference for the connection of IGBT. It was shown that the interfacial IMC thickness of both solders increased with time and temperature, but the growth of interfacial IMC was suppressed for Sn58Bi solder containing 0.05 wt% AlN. The effect of AlN on the inhibition of grain growth was also observed by EBSD testing. Because of the adsorption effect of AlN nanoparticles, they can adhere to the surface of IMC layer and decrease the effective the diffusion path of unreacted Cu atoms, thereby inhibiting the growth of interfacial IMC. And the effect of AlN particles on interfacial IMC was analyzed via phase field simulation. In addition, under the heating conditions with high temperature and long time, there were fewer cracks in the solder joints containing AlN particles, compared to the Sn58Bi solder. Therefore, AlN nanoparticles can enhance the reliability of Sn58Bi/Cu solder joints.

Simulation for Cu Atom Diffusion Leading to Fluctuations in Solder Properties and Cu6Sn5 Growth during Multiple Reflows

The multiple reflows process is widely used in 3D packaging in the field of electronic packaging. The growth behavior of interfacial intermetallic compound (IMC) is more important to the reliability of solder joints. In this paper, experimental measurement combined with simulation calculation were preformed to investigate the evolution of Cu concentration in solders during multiple reflows, as well as its effects on the growth behavior of IMC and solder properties. The concentration of Cu in solder fluctuated, increasing with the increase of reflow times, which led to the fluctuation in the growth rate of the IMC. Furthermore, the Vickers hardness and melting point of the solder fluctuated during the multiple reflow processes due to the fluctuation in the Cu concentration. The data generated during this study could help to develop machine learning tools in relation to the study of interfacial microstructure evolution during multiple reflows.

Effect of Electromigration on the Type of Drop Failure of Sn–3.0Ag–0.5Cu Solder Joints in PBGA Packages

Board-level drop tests of plastic ball grid array (PBGA) packages were performed in accordance with the Joint Electron Devices Engineering Council standard to investigate the effect of electromigration (EM) on the drop reliability of Sn–3.0Ag–0.5Cu solder joints with two substrate surface finishes, organic solderability preservative (OSP) and electroless nickel electroless palladium immersion gold (ENEPIG). In the as-soldered state, drop failures occurred at the substrate sides only, with cracks propagating within the interfacial intermetallic compound (IMC) layer for OSP solder joints and along the IMC/Ni–P interface for ENEPIG solder joints. The drop lifetime of OSP solder joints was approximately twice that of ENEPIG joints. EM had an important effect on crack formation and drop lifetime of the PBGA solder joints. ENEPIG solder joints performed better in drop reliability tests after EM, that is, the drop lifetime of ENEPIG joints decreased by 43% whereas that of OSP solder joints decreased by 91%, compared with the as-soldered cases. The more serious polarity effect, i.e., excessive growth of the interfacial IMC at the anode, was responsible for the sharper decrease in drop lifetime. The different types of drop failure of PBGA solder joints before and after EM, including the position of initiation and the propagation path of cracks, are discussed on the basis of the growth behavior of interfacial IMC.

A study on the interfacial reaction of Sn58Bi/Cu soldered joints under various cooling and aging conditions

As one of the important factors affecting the quality of soldered joints, the interfacial intermetallic compound (IMC) formed at the solder/substrate interface is of increasing concern to researchers. Thus, the growth behavior of interfacial IMC in Sn58Bi/Cu solder joints was investigated as different cooling methods-quenched water, cooling in air, and cooling in a furnace during reflowing were used. In this work, the effect of cooling rate on interfacial IMC growth is studied in Sn58Bi/Cu system. Morphology and growth kinetics of the interfacial Cu–Sn IMC under various cooling rates were studied. It was found that only scallop-like Cu6Sn5 IMC layer was observed between solder and Cu substrate in cases of water cooling and air cooling, while bi-layer composed of scallop-like Cu6Sn5 and planar Cu3Sn was detected under furnace cooling due to sufficient reaction time to form Cu3Sn between Cu6Sn5 IMC and Cu substrate which resulted from slow cooling rate. Samples with different reflow cooling rate were further thermal aged at 373 and 393 K, respectively. The results showed that the morphology of interfacial Cu–Sn IMC layer would transform from scallop-like to planar-like with increasing aging time, and the thickness of IMC increased linearly with square root of aging time. The growth constants of interfacial IMC layer were obtained and compared for different cooling rates and aging temperatures, indicating that the IMC layer thickness increased faster in samples under slow cooling rate than the fast cooling ones under the same aging condition, and higher aging temperature could result in faster growth of IMC layer. The interfacial Cu6Sn5 grains gradually transformed to facet prismatic shape as the cooling rate decreased, and the grain size increased dramatically as the samples were cooled in furnace, comparing with that of samples cooled in water and air.

In Situ Study on Current Density Distribution and Its Effect on Interfacial Reaction in a Soldering Process

The interfacial reaction in Cu/Sn/Cu solder joint during liquid–solid eletromigration (EM) was in situ studied using synchrotron radiation real-time imaging technology. The current density distribution in the solder joint was analyzed with the finite element method (FEM). The relationships among solder shape, current density distribution, Cu dissolution, and the formation and dissolution of interfacial intermetallic compound (IMC) were revealed. The current promoted dissolution of the cathode IMC and growth of the anode IMC and suppressed the dissolution of anode Cu. The change of interfacial IMC had little effect on the current density distribution; however, the dissolution of cathode Cu, which changed the solder shape, had a significant effect on the current density distribution. The dissolution of cathode Cu under forward current and cathode IMC under reverse current and the growth of anode IMC under forward current was faster where the current density was higher. The synchrotron radiation real-time imaging technology can not only in situ observe the change of solder shape, the dissolution and growth behavior of interfacial IMC and the dissolution behavior of substrate in a soldering process but also provide data needed for numerical simulation of current density distribution in a solder joint.

Investigation of the Growth of Intermetallic Compounds Between Cu Pillars and Solder Caps

In flip chip applications, Cu pillars with solder caps are regarded as next-generation electronic interconnection technology, because of high input/output density. However, because of diffusion and reaction of Sn and Cu during the high-temperature reflow process, intermetallic compounds (IMC) are formed, and grow, at the interface between the cap and the pillar. Understanding the growth behavior of interfacial IMC is critical in the design of solder interconnections, because excessive growth of IMC can reduce the reliability of connections. In this study, the growth of IMC during thermal cycling, an accelerated method of testing the service environment of electronic devices, was studied by use of focused ion beam–scanning electron microscopy. Under alternating high and low-temperature extremes, growth of Cu6Sn5 (η-phase) and Cu3Sn (e-phase) IMC was imaged and measured as a function of the number of cycles. The total IMC layer grew significantly thicker but became more uniform during thermal cycling. The Cu3Sn layer was initially thinner than the Cu6Sn5 layer but outgrew the Cu6Sn5 layer after 1000 cycles. It was found that, with limited Cu and Sn diffusion, consumption of Cu6Sn5 for growth of the Cu3Sn layer can result in a thinner Cu6Sn5 layer after thermal cycling.

Effect of Isothermal Aging and Thermal Cycling on Interfacial IMC Growth and Fracture Behavior of SnAgCu/Cu Joints

The growth behavior of interfacial intermetallic compounds (IMCs) of SnAgCu/Cu soldered joints was investigated during the reflow process, isothermal aging, and thermal cycling with a focus on the influence of these parameters on growth kinetics. The SnAgCu/Cu soldered joints were isothermally aged at 125°C, 150°C, and 175°C while the thermal cycling was performed within the temperature ranges from −25°C to 125°C and −40°C to 125°C. It was observed that a Cu6Sn5 layer formed, followed by rapid coarsening at the solder/Cu interface during reflowing. The grain size of the interfacial Cu6Sn5 was found to increase with aging time, and the morphology evolved from scallop-like to needle-like to rod-like and finally to particles. The rod-like Ag3Sn phase was formed on the solder side in front of the previously formed Cu6Sn5 layer. However, when subject to an increase of the aging time, the Cu3Sn phase was formed at the interface of the Cu6Sn5 layer and Cu substrate. The IMC growth rate increased with aging temperature for isothermally aged joints. During thermal cycling, the thickness of the IMC layer was found to increase with the number of thermal cycles, although the growth rate was slower than that for isothermal aging. The dwell time at the high-temperature end of the thermal cycles was found to significantly influence the growth rate of the IMCs. The growth of the IMCs, for both isothermal aging and thermal cycling, was found to be Arrhenius with aging temperature, and the corresponding diffusion factor and activation energy were obtained by data fitting. The tensile strength of the soldered joints decreased with increasing aging time. Consequently, the fracture site of the soldered joints migrated from the solder matrix to the interfacial Cu6Sn5 layer. Finally, the shear strength of the joints was found to decrease with both an increase in the number of thermal cycles and a decrease in the dwell temperature at the low end of the thermal cycle.

Isothermal and thermal cycling aging on IMC growth rate in lead-free and lead-based solder interface

The growth of interfacial intermetallic compounds (IMC) between Pb-free and Pb-based solders with different surface finish (Cu and Ni/Au) metallization is a major concern for long-term solder joint reliability performance in electronic assemblies. The growth rate of the IMC layer can affect the solder joint reliability. Analysis of solid-state diffusion mechanism for the growth of IMC between solder-to-substrate interface for Pb-free and Pb-based solders subject to isothermal and thermal cycling aging were conducted. Experimental study of IMC layer growth between Sn3.8Ag0.7Cu and Ni/Au surface finish by isothermal aging versus thermal cycling (TC) aging was investigated to develop a framework for correlating IMC layer growth behavior. An integrated model for IMC growth was derived to describe the Ni-Cu-Sn IMC growth behavior subject to TC aging. Comparison of modeling and test results showed that IMC layer growth rate under TC aging was accelerated. It is noted that IMC layer growth study from various references showed different experimental data and growth kinetic parameters for both liquid-state and solid-state reactions.