Cu6Sn5 Intermetallic Compounds Research Articles

Controlling the distribution of porosity during transient liquid phase bonding of Sn-based solder joint

The rapid growth of (Cu,Ni)6Sn5 intermetallic compounds (IMCs) when Sn reacts with Cu containing 6 wt%Ni (Cu-6Ni) offers huge potential for resolving the lengthy transient liquid phase (TLP) processing time. However, the uncontrolled formation of voids at the centre of the joint remains a serious issue. Therefore, we have studied the influence of different Ni concentrations (0, 2 and 6 wt%) in the Cu substrate and the relative location of the porosity when reacting with Sn-0.7Cu solder in the sandwich structure of the joint. Through in-situ X-ray microradiography, the changes in the void positions and the reaction time required to form the IMC joints was interpreted with reference to growth kinetics equations. The results indicate that the different growth rates of (Cu,Ni)6Sn5 and Cu6Sn5 IMCs due to the different Ni concentrations of the Cu-Ni substrates can control the location of the porosity and influence the shear strength of the TLP lap joint. This discovery is a potential gateway to developing reliable electronic interconnects for the power device industry.

Investigation of interfacial reactions between Sn–Ag–Bi–In solder and (Cu, electroless Ni–P/Cu) substrate

Abstract The growth kinetics of intermetallic compound layers formed between Sn–3Ag–8Bi – 5In solder and (Cu, electroless Ni – P/Cu) substrate were investigated at temperatures between 70 and 170 °C for 1 to 60 days. The layer growth of the intermetallic compounds in the Sn–Ag– Bi – In/Cu and Sn–Ag –Bi – In/electroless Ni –P systems satisfied the parabolic time law. As a whole, because the values of time exponent have approximately 0.5, the layer growth is mainly controlled by diffusion. The apparent activation energies for the growth of the Cu6Sn5 and Ni3Sn4 intermetallic compounds are 81.4 and 67.1 kJ/mol, respectively.

Interfacial Reaction between SAC3807 Lead-Free Solders and Different Copper Substrate via Reflow Soldering Process

The different composition material of copper substrate significantly affects the intermetallic compound (IMC) formation and the solder joints durability. This study was conducted on the interfacial reaction between lead-free solder and the different copper substrates via reflow soldering. The selected substrate is copper (Cu) and copper-beryllium (Cu-Be). The lead-free solder involved is Sn-3.8Ag-0.7Cu (SAC3807) solder ball with a diameter of 700 μm. All the samples were subjected to the isothermal aging process. The material characterization and analysis on the IMC formation were examined by scanning electron microscopy (SEM), optical microscope (OM), and energy dispersive X-ray analysis (EDX). After the reflow process, the result revealed that Cu3Sn, Cu6Sn5 IMC layer formed at SAC3870/Cu and SAC3870/Cu-Be interface. The changes to a rod-like shape Cu6Sn5 and irregular needle-shaped Cu3Sn4 occur after the aging treatment on SAC3870/ Cu. Meanwhile, the IMC layer for SAC3870/Cu-Be shows a rod-like shape transformed into a blocky-like shape Cu6Sn5 and Cu3Sn4 diamond-shape. This result indicates that Ag3Sn nanosized was formed on the intermetallic surface during the aging process for both SAC3807/Cu and SAC3807/Cu-Be. The Ag3Sn nanosized element at SAC3807/Cu-Be is many compared to SAC3807/Cu. In addition, IMC thickness for SAC3807/Cu-Be shows a thicker layer than SAC3807/Cu. Lastly, in this research, the element of Be in SAC3807/Cu-Be cannot be defined because the beryllium element is not easily detected as the percentage was very low.

Systematic investigation of the effect of Ni concentration in Cu-xNi/Sn couples for high temperature soldering

High temperature solders have experienced a marked increase in demand due to the boom of high power interconnects in electric vehicles and the miniaturisation of electronic devices. Transient liquid phase (TLP) bonding is a promising technology for these applications. Alloys from the Cu-Sn system widely used in conventional soldering processes have potential for high temperature applications if the relatively low melting point Sn phase can be consumed in a TLP process. This process results in a joint composed of Cu6Sn5 or Cu3Sn intermetallic compounds (IMCs) which have higher melting points than Sn. Alloying Ni to the Cu substrate promotes the growth rate of the (Cu,Ni)6Sn5 IMCs, significantly reduces the TLP processing time and costs, while suppressing the formation of (Cu,Ni)3Sn. However, the properties of the (Cu,Ni)6Sn5 formed also change significantly depending on the Ni concentration in the system. In this work, the composition, morphology, grain sizes and crystal structure of the (Cu,Ni)6Sn5 formed via the reaction of Sn and Cu-xNi substrates of different Ni concentrations are studied in detail via electron microscopy and synchrotron powder X-ray diffraction to provide a basis for further understanding of the physical, electrical and mechanical properties. The findings are further verified by density functional theory calculations. Additionally, the complex interplay of grain boundary diffusion rates and the IMC nucleation rate which accelerate with increasing Ni concentration, along with the Cu-xNi dissolution rate and the crystal growth rate which decrease with increasing Ni concentration are identified to be the main factors affecting the IMC growth rates.

Formation of Cu-=SUB=-6-=/SUB=-Sn-=SUB=-5-=/SUB=- intermetallic in Cu/Sn thin films

The study of the formation of the Cu6Sn5 intermetallic compound in Sn(55 nm)/Cu(30 nm) thin bilayer films was carried out directly in the column of a transmission electron microscope (electron diffraction mode) by heating the film sample from room temperature to 300oC and recording the electron diffraction patterns. The thin films formed as a result of a solid state reaction were monophase and consisted of the eta-Cu6Sn5 hexagonal phase. The temperature range for the formation of the eta-Cu6Sn5 phase was determined. The estimate of the effective interdiffusion coefficient of the reaction suggests that the main mechanism for the formation of the Cu6Sn5 intermetallic is diffusion along the grain boundaries and dislocations. Keywords: thin films, Cu6Sn5 intermetallic compound, transmission electron microscopy, electron diffraction.

Kinetics of Cu6sn5 and Cu3sn Intermetallic Compounds Growth and Isothermal Solidification During Cu-Sn Transient Liquid Phase Sintering Process

Kinetics of Cu6sn5 and Cu3sn Intermetallic Compounds Growth and Isothermal Solidification During Cu-Sn Transient Liquid Phase Sintering Process

Sn-Cu intermetallic compound laminated film with excellent friction coefficient, contact resistance, and solder wettability

ABSTRACT The connector used for electronic parts of automobiles is a type with Sn plating on the copper surface. In recent years, as the number of connector pins has increased and the insertion force has increased, problems have arisen in the insertion and removal operations. In addition, the reliability of the connection in high temperature environments needs to be improved. Various Sn plating alternative processes have been developed to meet these demands. Tha authors have previously reported on Sn-Cu plating processes that can provide more stable properties. 1 Using Sn-Cu plating and Sn plating, a Cu6Sn5 intermetallic compound layer with low roughness formed just below the surface. A pure Sn layer is formed on it. The authors have previously reported that the formation of a pure Sn layer with high connection reliability and a stable hard intermetallic compound layer can be expected to improve various properties. In this study, as a result of investigating the solder wettability of this plating film, which has excellent low friction coefficient and low contact resistance, it was clarified that good connector characteristics can be obtained.

The Mechanical Properties and Elastic Anisotropy of η′-Cu6Sn5 and Cu3Sn Intermetallic Compounds

Full intermetallic compound (IMC) solder joints present fascinating advantages in high-temperature applications. In this study, the mechanical properties and elastic anisotropy of η′-Cu6Sn5 and Cu3Sn intermetallic compounds were investigated using first-principles calculations. The values of single-crystal elastic constants, the elastic (E), shear (G), and bulk (B) moduli, and Poisson’s ratio (ν) were identified. In addition, the two values of G/B and ν indicated that the two IMCs were ductile materials. The elastic anisotropy of η′-Cu6Sn5 was found to be higher than Cu3Sn by calculating the universal anisotropic index. Furthermore, an interesting discovery was that the above two types of monocrystalline IMC exhibited mechanical anisotropic behavior. Specifically, the anisotropic degree of E and B complied with the following relationship: η′-Cu6Sn5 > Cu3Sn; however, the relationship was Cu3Sn > η′-Cu6Sn5 for the G. It is noted that the anisotropic degree of E and G was similar for the two IMCs. In addition, the anisotropy of the B was higher than the G and E, respectively, for η′-Cu6Sn5; however, in the case of Cu3Sn, the anisotropic degree of B, G, and E was similar.

Hillock formation in β-Sn films during high frequency cyclic bending at low strains

Cyclic bending of ß-Sn films with 1μm thickness on atomic force microscopy silicon cantilevers was performed at resonance in both first and second mode vibration. The stress response as a function of position along the cantilever at very small strain amplitudes was examined by changes in surface morphology. Hillock formation and growth, the dominant responses observed, were measured using scanning electron microscopy as a function of the number of cycles and the strain distribution along the cantilever. New hillocks formed with increasing numbers of cycles, with their morphologies similar to the pre-existing hillocks observed before cycling. However, all hillocks exhibited a constant diameter-to-height ratio observed of 1: (1–1.2), with both pre-existing and new hillocks reached a limiting height which did not grow with further cycling. A saturation in the number of hillocks was observed with increased cycling, with the cycles to saturation depending on the vibration mode. The hillock density along the cantilever was found to be proportional to the local strain amplitude in both the first and second vibration modes. These results demonstrate that even the small maximum strain amplitudes in these experiments are sufficient to drive the nucleation and growth of hillocks as a stress relaxation response. Comparisons between these experiments and prior studies of whisker and hillock formation on β-Sn films due to Cu-Sn intermetallic compound growth and thermal mismatch stresses in thermal cycling are made in terms of morphologies, densities, and time dependence of nucleation and growth.

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.

Effects of amorphous Co W and Ni W barrier layers on the evolution of Sn/Cu interface

In advanced microelectronic packaging, a high-performance diffusion barrier layer is urgently required for Sn/Cu joint, to hinder the formation of CuSn intermetallic compounds (IMCs). In this work, the barrier performance of electrodeposited Ni, Co, amorphous NiW and amorphous CoW were studied. During 150 °C aging test, amorphous CoW exhibited the best barrier performance among the four barrier layers with the slowest IMC growth rate. Compared with the reaction-controlled IMCs in Sn/Co/Cu sample, the IMCs' growth rates in the other three samples were limited by different diffusion species. Due to the larger diffusion flux of Ni diffusing from NiW layer than that of Co from CoW layer, IMCs in Sn/Ni-W/Cu sample grew faster than Sn/Co-W/Cu sample. The nanoindentation test indicated that the IMCs formed in Sn/Co-W/Cu sample were less sensitive to brittle fracture than Sn/Ni-W/Cu sample. This research provides a scientific basis for the selection of barrier layers with excellent barrier performance and mechanical properties in electronic packaging.

Rapid fabrication of Cu/40-μm thick full Cu3Sn/Cu joints by applying pulsed high frequency electromagnetic field for high power electronics

With the application of wide bandgap semiconductors for high power electronics, the joints are inevitably faced with a trade-off between withstanding high temperature environments and remaining low bonding temperatures. In this study, a full Cu3Sn intermetallic compounds layer with thickness of 40 μm, which can survive at 679 °C, were obtained between Cu plates using pulsed High Frequency Electromagnetic Field (HFEF) within 10 min at ambient temperature. Output power and frequency of the HFEF was 6 kW and 530 kHz, respectively. In contrast to common Sn-based solder joints, the joints prepared through HFEF consisted predominately of Cu3Sn, because both the horizontal and vertical temperature gradients and the eddy currents within the joints strongly promoted the 3D diffusion of copper atoms. With increasing HFEF exposure time, the Cu3Sn changed from an irregular needle-like to smoothly scalloped or columnar morphology. The HFEF approach enabled Cu3Sn joints to achieve a superior shear strength (>56 MPa) and a greater stand-off height (>30 μm), which are useful to mitigate the coefficient of thermal expansion (CTE) mismatch problems; thereby yielding higher reliability. We envision that these full Cu3Sn joints prove useful in a wide range of applications in high-temperature and high-power electronics.

Molecular dynamics simulation of the interfacial evolution and whisker growth of copper-tin coating under electrothermal coupling

With the development of lead-free electronic devices, the failure caused by the growth of tin whiskers poses a potential threat to the reliability of electronic products. In this study, the modified embedded atomic potential proposed by Baskes was used to simulate the interfacial evolution and the whisker growth of copper and tin coatings under electrothermal coupling by using molecular dynamics. Numerical results show that the increase in electric field intensity and temperature can promote the diffusion of Cu atom to Sn atom, and the intermetallic compounds Cu6Sn5 and Cu3Sn are formed successively at the interface of the coating. Compression stress is formed in the coating, and the whisker is shaped at the weak part of the oxide film on the tin layer surface. The increase in electric field intensity and temperature can accelerate the growth of the whisker. This condition is because the increase in electric field intensity or temperature promotes the formation of intermetallic compounds, providing a greater driving force for the growth of tin whiskers. The results can provide a theoretical basis for the growth mechanism of tin whiskers.

Factors Controlling the Defect Formation in Cu-Sn Micro Joints in 2.5D and 3D Interconnects

The Cu-Sn reaction upon soldering has been thoroughly studied and the sporadic formation of Kirkendall voids within the intermetallic bonds between ball grid array (BGA) or surface mount technology (SMT) solder joints and Cu pads has been demonstrated as well-known concern. However, in the realm of ever developing device miniaturization, there is very limited information on the impact of space confinement on the dynamics of the Cu/solder joint interface. It is known that no voiding has been found in solder joints with high-purity Cu but this phenomenon presents itself, albeit to a different extent, when the joint is realized with electroplated Cu. Also, it is believed, that the voiding propensity in the Cu3Sn intermetallic compounds (IMC) is more likely to be higher in micro joints than in BGA/CSP scale (macro) joints for a given quality of electroplated Cu. Along with that it has been shown that the IMCs on Cu surfaces seem to grow much faster when the solder becomes very thin, and this is accompanied with a greatly enhanced risk of Kirkendall void nucleation.The emphasis of this work is on understanding the voiding behavior within the intermetallic bonds of Cu-Sn micro joints (5 – 30 µm) with the eventual goal of learning how it can be controlled or prevented. Our systematic studies have corroborated the association of voiding with the incorporation of small concentrations of impurities resulting from organic additives degradation during the Cu electroplating as already illustrated for macro joints. Our results also show lack of any voiding not only in macro- but also in micro joints when the interconnection is realized with high purity Cu, likely because no organic impurities are present in sufficient amount to prompt defect nucleation and growth. Our research further demonstrates that the IMC growth rate varies with factors and parameters such as solder volume to pad area ratio, solder composition, pad finish, initial assembly process parameters, subsequent heat treatments, and specifics of the further thermomechanical history, thus impacting differently the overall voiding level. Following this lead, the analysis of micro joints subjected to different synthetic and processing treatments clearly demonstrates the propensity for voiding to be substantially higher, for a given quality of electroplated Cu, in very small solder joints (5 – 30 µm), such as those found in 3D assemblies, unlike in macro joint counterparts. The risk and severity of voiding in these thinner joints is confirmed to depend on the type and amount of incorporated organic impurities in the electroplated Cu. Therefore, in the present report we show how the bath additive chemistry and various Cu electroplating parameters play a systematic role in the type and quantity of impurity incorporation, and thus the propensity for voiding. Approaches to control the electroplating Cu quality in a way that leads eventually to void-free micro joints are also discussed.

Microstructural and shear strength properties of GNSs-reinforced Sn-1.0Ag-0.5Cu (SAC105) composite solder interconnects on plain Cu and ENIAg surface finish

In this study, the combined effect of GNSs (graphene nanosheets) and ENIAg (Electroless Nickel Immersion Silver) surface finish on the formation of intermetallic compounds (IMCs) and shear strength of the Sn-1.0Ag-0.5Cu (SAC105) solder system was studied. Both plain and composite solder systems (SAC105-xGNS; x = 0, 0.01, 0.05 and 0.1 wt%) were successfully prepared using the powder metallurgy technique and thereafter soldered on the plain Cu and ENIAg surface finish substrates. From the microstructural analysis, the Cu6Sn5 IMC was observed at the solder/substrate interface of the SAC105-xGNS/Cu solder joints. Moreover, the Ni3Sn4 and (Cu,Ni)6Sn5 IMC phases were observed at the solder/substrate interface of the SAC105-xGNS/ENIAg counterparts. The GNSs and ENIAg surface finish provided huge barrier for Sn and Cu atoms diffusion required for IMC formation. The interfacial IMC layer thickness decreased with increasing addition of GNSs for both sample grades. The SAC105-xGNS/ENIAg demonstrated lower IMC thicknesses that ranged between 2.98 and 2.53 μm relative to the 5.23–3.35 μm exhibited by the SAC105-xGNS/Cu. In general, the strengthening potential of the GNSs was well marked in both sample grades, with the SAC105-0.01GNS/Cu and SAC105-0.01GNS/ENIAg demonstrating the highest shear strengths of 11.2 MPa and 12.1 MPa, respectively.

A Study of Transient Liquid Phase Bonding Using an Ag-Sn3.0Ag0.5Cu Hybrid Solder Paste

The feasibility of transient liquid phase (TLP) bonding technology for high-temperature endurable power electronics packaging has been evaluated in this study. An Ag-Sn3.0Ag0.5Cu hybrid solder paste was fabricated and used as a bonding material. The bonding reactions between chip/substrate and hybrid solder paste and die shear strengths of the TLP-bonded joints were evaluated during conventional soldering and vacuum soldering processes. Compared to the conventional soldering, the vacuum-soldered joints had fewer voids and relatively good metallurgical microstructures. After TLP bonding, (Cu,Ni)6Sn5, Ag3Sn, and Cu6Sn5 intermetallic compounds formed at the chip interface, in the middle of the joint, and at the bottom interface, respectively. It was confirmed that the vacuum soldering process could create good interfacial uniformity with minimal voids in the Si chip/ceramic substrate joints. The formation of voids during TLP bonding significantly affected the mechanical shear strength of the TLP-bonded joints. The vacuum-soldered joints had high shear strength values of approximately 40 MPa. To ensure the high joint strength and long-term reliability of Sn-based TLP-bonded joints, critical void control in the joints is needed.

Quasi-in-situ observation on diffusion anisotropy dominated asymmetrical growth of Cu-Sn IMCs under temperature gradient

Quasi-in-situ method was carried out to observe the growth behavior of intermetallic compounds (IMCs) in Cu/Sn-3.0Ag-0.5Cu/Cu micro solder joints with single β-Sn grain during aging with and without temperature gradient (TG). The bilayer IMCs of Cu6Sn5 + Cu3Sn showed symmetrical growth at both interfaces without TG, proving that β-Sn grain orientation had no effect on interfacial IMC growth during isothermal aging. Many Kirkendall voids were detected due to the dominated growth of Cu3Sn. However, during aging under TG, the IMCs in the joints with different β-Sn grain orientations showed quite different growth behavior and Cu6Sn5 was always the dominant IMC phase with little Cu3Sn and no Kirkendall voids formation. In the joints with small or medium θ angle β-Sn grains, remarkably asymmetrical IMC growth with thick Cu6Sn5 at the cold end and thin discontinuous Cu6Sn5 at the hot end was clarified. Meanwhile, the cold end Cu6Sn5 in medium θ angle joints also presented step-like morphology. The diffusion anisotropy of Cu atoms in β-Sn was responsible for the asymmetrical growth and step-like morphology. In the joints with large θ angle β-Sn grains, the Cu6Sn5 presented similar symmetrical growth to the isothermal aging cases. The different mechanisms of inhibiting Cu3Sn and Kirkendall voids formation at the cold and hot ends were revealed based on TG-induced Cu flux. Finally, a method was proposed to predict the IMC morphology and thickness considering β-Sn grain orientation, which could be helpful for reliability assessment and may also be suitable for IMC growth analyzes under current stressing.

Influences of silicon carbide nanowires’ addition on IMC growth behavior of pure Sn solder during solid–liquid diffusion

In this paper, various mass fractions (0, 0.2, 0.4, 0.6, 0.8, 1.0 wt%) of silicon carbide nanowires (SiC NWs) were incorporated into pure Sn solder to enhance the performances of Sn solder joint. The wetting behavior, shear strength, and intermetallic compound (IMC) growth mechanism of Sn–xSiC/Cu solder during solid–liquid diffusion at 250 °C were investigated systematically. The experimental results demonstrated that the wettability of Sn–xSiC/Cu solder had a significant improvement when the addition of SiC NWs was up to 0.6 wt%, and excessive additives would degrade the wettability of the composite solder. The formation of the Cu6Sn5 IMC layer was observed at the Sn–xSiC solder/Cu interface. Meanwhile, SiC NWs as additives were conducive to restraining the growth of interfacial IMC during soldering process and the IMC thickness overtly fell down after doping 0.8 wt% SiC NWs into Sn solder. Moreover, SiC NW addition would contribute to enhancing the mechanical performance of Sn solder joint. The fracture mechanism of solder joint changed from a mix of brittle and ductile fracture to a characteristic of typical ductile fracture.

Convolutional neural network model for synchrotron radiation imaging datasets to automatically detect interfacial microstructure: An in situ process monitoring tool during solar PV ribbon fabrication

Designing means and methods to detect the presence of interfacial bubbles and intermetallic compounds (IMCs) during hot dipping solder coating of Cu ribbon, can help in the production of defect-free PV ribbons. A mechanistic study of Cu6Sn5 IMC grain growth and bubble morphology evolution at the solder-substrate interface is performed with phase field simulation. A machine learning model is utilized to identify the occurrence of bubble(s) and IMC at the material interface of liquid solder and solid Cu. The datasets for the microstructural images consisting of bubble(s), IMC and planar solder/Cu interface are generated using in situ synchrotron radiation (SR) imaging experiment techniques. The integration of in situ SR radiography based non-destructive testing experiments with convolutional neural network model to intelligently detect the interfacial microstructures paves the path for potential industrial application of this technique in the smart manufacturing of defect free and reliable PV ribbon material.