Interfacial Void Formation Research Articles

Inhibiting the formation of interfacial voids in Cu/In/Cu microbump via Zn doping into Cu substrate

To address warpage issues in 3D-IC, low temperature soldering technology such as Cu/In bonding has been developed in recent years. However, the formation of Kirkendall voids at the original Cu/In interface would lead to degradation of joint reliability. By adding Zn, the diffusional flux of Cu was inhibited, and the numbers of interfacial voids larger than 50 nm decreased substantially by 66% at top interface and 58% at bottom interface, respectively. In this study, Cu-15Zn/In/Cu system was investigated and could be regarded as a promising option for advanced electronic packaging in the future.

Kinetics of voids evolution during diffusion bonding of dissimilar metals on consideration of the realistic surface morphology: Modeling and experiments

A comprehensive model for analyzing the kinetics of void evolution and shrinkage during dissimilar diffusion bonding is proposed based on the sinusoidal profile. The model incorporates atom accumulation at void tip to determine the curvature radius of void neck, and integrates the local effect of surface diffusion to quantify the contribution of surface diffusion, thus avoiding the unrealistic void evolution observed in previous models. Furthermore, the model utilizes a combined diffusion coefficient for multicomponent alloys under the effect of stress and concentration gradients, to determine the interfacial diffusion coefficient for dissimilar joints. In contrast to previous models, the current model demonstrates significant improvements in predicted accuracy, efficiently depicting the realistic void evolution and interpreting the formation of various interfacial voids, which can be applied in various bonding cases, including for the dissimilar base metals with different surface conditions. Simulation results from bonding between austenitic steel and ferritic steel with different surface roughness reveal that interfacial voids predominantly form on the side of the base metal with the rougher bonding surface. Additionally, as surface roughness decreases, the prevailing surface source diffusion and interface source diffusion mechanisms promote void evolution and shrinkage, resulting in a significant reduction of the final bonding time. To achieve a high-quality bonding joint, it's suggested to place the smoother bonding surface on the higher creep-resistant base metal, which can accelerate the void closure process.

Interfacial characteristics, interfacial oxide evolution and bonding mechanism of 2219 aluminum alloy joints manufactured by hot-compression bonding

The bonding joints of 2219 aluminum alloy with different deformations of 30%, 45% and 55% were fabricated using hot-compression bonding, and subsequent subjected to homogenization treatment. The interfacial microstructure and interfacial oxide evolution of the bonding joints were systematically investigated. The results showed that increasing deformation can effectively reduce the formation of interfacial voids and promote the interfacial grain boundary migration (IGBM). As the deformation increased from 30% to 55%, the flat bonding interface transformed into curved grain boundaries, and ultimately being occupied by dynamically recrystallized (DRXed) grains. The development of IGBM and interfacial DRXed grains is crucial for ensuring high-quality bonding joints. At 55% deformation, the interface bonding strength reached 156.2 MPa, corresponding to 98.1% of the matrix bonding strength. In addition, the residual interfacial oxide film Al2O3 reacted with MgO and transformed into MgAl2O4 spinel. The final evolution products at the bonding interface were the mixture of MgO, Al2Cu, Al2O3, and MgAl2O4. The bonding interface at 55% deformation successfully achieved relatively clean atomic bonding after homogenization. Based on interfacial void closure, interfacial oxide film fragmentation and evolution, and interfacial recrystallization, the bonding mechanism of 2219 aluminum alloy joints was proposed. These findings contribute to our understanding of the interfacial bonding process in metal solid bonding.

Investigation on mechanical properties of the green synthesis bamboo fiber/eggshell/coconut shell powder-based hybrid biocomposites under NaOH conditions

Abstract This research delves into the effects of different alkalization treatment approaches on the mechanical characteristics of epoxy matrix composites that are reinforced with natural bamboo fibers and enriched with egg and coconut shell powders as fillers. Various weight ratios of fibers and fillers were investigated, specifically at 5%, 10%, 15%, 20%, 25%, and 30%. The study assessed mechanical properties such as tensile strength, flexural behavior, microhardness, and impact resilience. Findings indicate that composites with alkali-treated fibers demonstrate superior mechanical performance (49.28 MPa of tensile, 57.33 MPa of flexural 89 HV of hardness, and 1.3 kJ·m−2 of impact) compared to untreated counterparts. Particularly noteworthy is the significant improvement in fracture toughness observed with the inclusion of 20% hybrid laminates, surpassing the performance of existing biomaterial-based composites. This heightened toughness is attributed to the optimized composition of fibers and enhanced water absorption capabilities. Conversely, the incorporation of 25% and 30% hybrid composites led to a decrease in mechanical strength (38.65 MPa of tensile, 46.7 MPa of flexural, 72 HV of hardness, and 1.19 kJ·m−2 of impact) due to the formation of additional interfacial contacts, pores, and voids within the polymeric matrix.

Void Growth Dynamics in Solid-State Batteries

Solid-state batteries (SSBs) can potentially offer improved energy density and safety, when compared to current lithium-ion batteries. Despite their irrefutable theoretical promise, further advancement of SSBs relies on developing a comprehensive understanding of various fundamental aspects including electro-chemo-mechanics, transport interactions, morphological evolution and related failure modes at solid-solid interfaces. Amongst the wide range of challenges, the formation and evolution of interfacial voids at the lithium-metal/solid-electrolyte interface during stripping is critical, due to its associated effect on internal short-circuit and cell failure during subsequent plating. The void growth phenomenon in SSBs is jointly determined by different factors such as the self-diffusion kinetics and mechanical response of lithium, reaction distribution at the solid-solid interface, and operating conditions such as external pressure and temperature. In this presentation, the pivotal role of reaction heterogeneity on the contact evolution process, along with key descriptors such as the lithium microstructure, surface morphology and contact percolation are discussed. The underlying asymmetry in terms of the competing electrochemical/mechanical processes and contact evolution during plating and stripping is highlighted. Lastly, the influence of non-uniformities in external pressure and temperature on the occurrence of disparate void growth patterns and electrochemical response is examined in this presentation.

(Industrial Electrochemistry and Electrochemical Engineering Division H. H. Dow Memorial Student Achievement Award) Mechanistic Analysis of Interface Stability in Solid-State Batteries

Solid-state batteries (SSBs) utilizing lithium metal anodes are promising next-generation energy storage systems, capable of offering enhanced energy density and power density when compared to conventional lithium-ion batteries. However, the morphological instability of the lithium anode continues to be a major challenge, resulting in filamentous lithium growth and internal short circuit across a wide range of inorganic solid electrolytes. In addition, the formation and growth of interfacial voids during stripping is a critical mechanism that limits the rate performance of SSBs. A coupled set of electrochemical-transport-mechanics processes governs the dynamic evolution and stability of the solid electrolyte/lithium interface. This interaction is affected by various factors including the mechanical properties and microstructure of the solid electrolyte and lithium metal, external pressure, operating temperature, and interfacial heterogeneities. In this presentation, the competing nature of interfacial mechanisms including electrodissolution, lithium mechanics and lithium diffusion kinetics on the origin of voids during stripping will be discussed. The coupled electrochemical-mechanical processes governing the evolution of lithium filaments, especially driven by microstructural heterogeneities such as grain boundaries will be delineated. An analysis pertaining to the dependence of such failure mechanisms on the external temperature, temperature and current density will be presented. Lastly, the role of underlying electrochemical interactions at the solid-solid interface on the onset of thermal instability in SSBs will be evaluated.

Anode‐Less All‐Solid‐State Batteries Operating at Room Temperature and Low Pressure

AbstractAnode‐less all‐solid‐state batteries (ASSBs) are being targeted for next‐generation electric mobility owing to their superior energy density and safety as well as the affordability of their materials. However, because of the anode‐less configuration, it is nontrivial to simultaneously operate the cell at room temperature and low pressure as a result of the sluggish reaction kinetics of lithium (de)plating and the formation of interfacial voids. This study overcomes these intrinsic challenges of anode‐less ASSBs by introducing a dual thin film consisting of a magnesium upper layer with a Ti3C2Tx MXene buffer layer underneath. The Mg layer enables reversible Li plating and stripping at room temperature by reacting with Li via a (de)alloying reaction with a low reaction barrier. The MXene buffer layer maintains the electrolyte‐electrode interface by inhibiting the formation of voids even at low pressure of 2 MPa owing to the high ductility of MXene. This study highlights the importance of a combined chemical and mechanical approach when designing anode‐less electrodes for practical adaptation for anode‐less ASSBs.

A comparative study on the oxidation behavior of Y-, Hf- and YHf-doped NiCoCrAl alloys: Effect of reactive elements

This study investigates the effect of Y, Hf and Y/Hf addition on oxidation behavior of NiCoCrAl alloys at 1100 °C. It is demonstrated that Hf is most effective in reducing the oxide growth rate, while co-doping Y and Hf doesn’t result in a synergistic effect in slowing down oxidation rate. Formation of interfacial voids is inhibited in NiCoCrAlY and NiCoCrAlYHf, suggesting that Y is more effective in improving the resistance to oxide spallation. A new model based on the ionic radii of reactive elements (REs) and bonding strength of RE-O is proposed to guide alloy design for improved oxidation resistance.

The void formation behaviors in working solid-state Li metal batteries.

The fundamental understanding of the elusive evolution behavior of the buried solid-solid interfaces is the major barrier to exploring solid-state electrochemical devices. Here, we uncover the interfacial void evolution principles in solid-state batteries, build a solid-state void nucleation and growth model, and make an analogy with the bubble formation in liquid phases. In solid-state lithium metal batteries, the lithium stripping-induced interfacial void formation determines the morphological instabilities that result in battery failure. The void-induced contact loss processes are quantified in a phase diagram under wide current densities ranging from 1.0 to 10.0 milliamperes per square centimeter by rational electrochemistry calculations. The in situ-visualized morphological evolutions reveal the microscopic features of void defects under different stripping circumstances. The electrochemical-morphological relationship helps to elucidate the current density- and areal capacity-dependent void nucleation and growth mechanisms, which affords fresh insights on understanding and designing solid-solid interfaces for advanced solid-state batteries.

Non-destructive monitoring of incipient corrosion in reinforced concrete with top-bar defect using a combination of electrochemical and ultrasonic techniques

Top-bar defect in reinforced concrete (RC) leads to the formation of interfacial voids underneath the reinforcements at an elevation of 300 mm or more. Rebars with top-bar defects show earlier corrosion initiation, faster corrosion rate and a different pattern of corrosion, compared to those without. This paper proposes combined electrochemical and ultrasonic methods for monitoring incipient corrosion in RC. An RC wall structure is cast vertically aiming to create top-bar defect. The specimens were subjected to accelerated chloride-induced corrosion. Simultaneously, they have been monitored with half-cell potential method (HCP), linear polarisation resistance method (LPR), ultrasonic guided waves (GW) and ultrasonic imaging (UI). The pros and cons of the four techniques are determined and discussed. The results are correlated and calibrated with the state of corrosion. Key milestones of the corrosion mechanism such as corrosion initiation and crack initiation can be successfully identified and the progression of bar deterioration, steel-concrete interfacial debonding and cracking propagation have been traced.

Forming mechanism and growth of Kirkendall voids of Sn/Cu joints for electronic packaging: A recent review

For the common Cu-Sn interconnection system in microelectronics packaging, a significant concern is the sporadic interfacial void formation within the Cu–Sn interface and intermetallic compound (IMC) layer during the service. The existence of these voids affects the electrical and mechanical properties of the joint and thus deteriorates reliability. Most scholars simply attribute the Kirkendall voids problem to the Kirkendall effect caused by the difference in Cu/Sn inter-diffusion coefficients. However, Kirkendall voids are formed for a combination of many reasons. The plating additives, current density, surface roughness, coating thickness, and substrate types affect the formation of Kirkendall voids. We believe that among the many factors affecting the formation of voids, the unbalanced diffusion of elements (Kirkendall effect) is the root cause, and impurities and Cu microstructure are the dominant factors. The addition of alloying elements to the solder affects the formation of voids by changing the unbalanced diffusion of elements. This paper releases the possible mechanism of Kirkendall voids and gives the perspective summary from three steps of void formation, and the available suppression method is given based on the final solution.

Effects of Zr Distribution on High‐Temperature Oxidation Resistance of a FeCrAlZr Alloy

Two FeCrAlZr alloys are fabricated by twin‐roll strip casting (TRSC) and ingot casting (IC), and different Zr distributions are formed. After cyclic oxidation tests at 1200 °C for 200 h in air, it is found that the scale spallation resistance in the FeCrAlZr alloy is improved by homogenizing the Zr distribution by TRSC. To understand the improvement in oxidation resistance, the composition and microstructure of the thermally grown scales are investigated. During oxidation, Zr diffuses toward the scale and forms ZrO2 particles in the scale and at the surface of the oxide scale. Meanwhile, the outward diffusion of Zr inhibits the formation of interfacial voids and S segregation regardless of Zr distribution. However, the TRSC sample with a more uniform Zr distribution can form the high‐density oxide penetrations, keying the scale to the matrix and improving scale adhesion. The Zr fluxes toward the scales are calculated to explain the difference in the distribution of oxide penetrations in the TRSC and IC samples during oxidation.

Current status and future directions of all-solid-state batteries with lithium metal anodes, sulfide electrolytes, and layered transition metal oxide cathodes

All-solid-state batteries (ASSBs) offer great promise as a next-generation energy storage technology with higher energy density, wider operating temperature range, and improved safety for electric vehicles. ASSBs employing lithium metal anodes (Li), sulfide-based solid-state electrolytes (SSE), and Ni-rich layered transition metal oxide cathodes (LiMO 2 , M = Ni, Mn, Co, Al) are particularly promising due to its superior electrochemical performance compared to other solid-electrolyte systems. However, the battery cycle life at high cathode mass loading and high current is still limited because the failure mechanism is not fully understood. Lithium dendrite growth at the anode or inside a solid electrolyte still represents as a serious risk of cell failure. Interfacial resistance increases attributed to electrolyte decomposition and interfacial void formation at both cathode−electrolyte and anode−electrolyte interfaces lead to gradual capacity fading. In this Review, we present the fundamental challenges and recent scientific understandings of each component in ASSBs. The novel diagnostic tools for these components, especially the interfaces buried under the surface that are often hard for characterization are mainly examined. Finally, we offer a perspective for future research directions. We hope this Review will provide a timely snapshot of state-of-the-art research progress in ASSBs to accelerate the development of ASSBs. • Progress and challenges of lithium metal anodes, sulfide electrolytes, and layered ternary oxide cathodes in solid-state batteries. • Origins of the failures in lithium metal anodes, Li-electrolyte interface, sulfide electrolytes, electrolyte-cathode interface, and layered metal oxide cathodes. • Summarize the state-of-the art diagnostic tools for investigating interfaces buried under the surface. • Future research directions for the solid-state battery architectures.

Modified Zeolite/Polysulfone Mixed Matrix Membrane for Enhanced CO2/CH4 Separation.

In recent years, mixed matrix membranes (MMMs) have received worldwide attention for their potential to offer superior gas permeation and separation performance involving CO2 and CH4. However, fabricating defect-free MMMs still remains as a challenge where the incorporation of fillers into MMMs has usually led to some issues including formation of undesirable interfacial voids, which may jeopardize the gas separation performance of the MMMs. This current work investigated the incorporation of zeolite RHO and silane-modified zeolite RHO (NH2–RHO) into polysulfone (PSf) based MMMs with the primary aim of enhancing the membrane’s gas permeation and separation performance. The synthesized zeolite RHO, NH2–RHO, and fabricated membranes were characterized by X-ray diffraction (XRD) analysis, Fourier transform infrared-attenuated total reflection (FTIR-ATR), thermogravimetric analysis (TGA) and field emission scanning election microscopy (FESEM). The effects of zeolite loading in the MMMs on the CO2/CH4 separation performance were investigated. By incorporating 1 wt% of zeolite RHO into the MMMs, the CO2 permeability and ideal CO2/CH4 selectivity slightly increased by 4.2% and 2.7%, respectively, compared to that of a pristine PSf membrane. On the other hand, a significant enhancement of 45% in ideal CO2/CH4 selectivity was attained by MMMs incorporated with 2 wt% of zeolite NH2-RHO compared to a pristine PSf membrane. Besides, all MMMs incorporated with zeolite NH2-RHO displayed higher ideal CO2/CH4 selectivity than that of the MMMs incorporated with zeolite RHO. By incorporating 1–3 wt% zeolite NH2-RHO into PSf matrix, MMMs without interfacial voids were successfully fabricated. Consequently, significant enhancement in ideal CO2/CH4 selectivity was enabled by the incorporation of zeolite NH2–RHO into MMMs.

Evolution Kinetics of Voids in Electroplated Cu-Cu Wafer Bonding

Cu-to-Cu direct bonding implemented in three-dimensional (3D) integrated circuits (ICs) has been widely studied. Formation of interfacial voids occurs in the absence of atomically smooth surfaces when wafers are mated together at room temperature. At elevated temperature, interfacial voids undermine the reliability of devices. Cu-Cu bonding usually accompanies oxide-oxide bonding to form hybrid bonding. Compressive stress can occur at Cu-Cu bonded interface. This study introduces artificial voids at bonded interfaces by bonding an etched Cu sample to an unetched Cu sample. The evolution and the healing kinetics of interfacial voids at temperatures from 120 °C to 250 °C were examined. Results revealed no sample bonding at temperatures below 120 °C (B120) and that healing of samples B150, B200 and B250 occurred only with compressive stress.

A review of intermetallic compound growth and void formation in electrodeposited Cu–Sn Layers for microsystems packaging

In recent years, Cu–Sn solid–liquid interdiffusion (SLID) bonding has been used in semiconductor packaging, die-attach, fine-pitch interconnection, and through-silicon vias (TSV)-based 3D stacking applications. Due to its specific advantages such as lower cost, less stringent surface uniformity requirements, higher thermal bond stability, and relatively lower processing temperatures, electrodeposited Cu–Sn-based bonding is explored to achieve wafer-level hermetic encapsulation of miniaturized sensors; however, the overall reliability of Cu–Sn bonds remains a challenge. The voids formed in the electrodeposited Cu–Sn layers and the brittle nature of the formed intermetallic compounds (IMC) affects the long term reliability of the Cu–Sn SLID bonds. A significant concern is the sporadic interfacial void formation within the Cu–Sn layers during the bonding process and high-temperature applications. This review article summarizes the different mechanisms of the IMC formation and their growth and explores the reasons behind the interfacial voids formed in the electrodeposited Cu–Sn layers when these are annealed at different temperatures ranging from 150 to 300 °C. A detailed description of the IMC and void formation and their subsequent growth in the thick electrodeposited Cu–Sn layers is presented, along with the various design parameters affecting the IMC growth during the bonding process. Various remedies to minimize these interfacial voids are also suggested. Higher bonding pressure, lower processing temperature, and reduced surface roughness are the key factors affecting the void size and voids density. The chemical impurity in the copper electrolyte and the resultant surface roughness affect the interfacial void formation in the electrodeposited Cu–Sn layers. This review will help minimize the interfacial voids and, thus, obtain higher bond reliability.

Effect of Annealing-Induced Tensions on the Mechanical Failure of Copper/Copper Interface in Wafer-to-Wafer Hybrid Bonding

The copper/copper (Cu/Cu) interface has an important role in wafer-to-wafer hybrid bonding for 3D integration applications. Reports indicate the possibility of the formation of post-bonding interfacial voids and cracks which must be avoided. Here, we use molecular dynamics simulations to investigate the effect of annealing-induced tensions on the strength and deformation mechanisms of Cu/Cu interfaces. We perform tensile tests on the pristine and defective Cu/Cu interfaces including a prototypical interfacial grain boundary in two defective limits: the presence of a single (isolated) void, and an array of multiple voids. The latter resembles interfacial nanoscale roughness as a result of weak sample preparation and bonding conditions. We show that in the limit of isolated voids, the strength of the system is lower than that of the pristine interface. The corresponding deformation mechanism is ductile and through dislocation activities which could be accompanied by void growth. In contrast, multiple interfacial voids lead to a ductile-to-brittle transition in the failure mechanism accompanied by a drastic reduction of the system strength. Our findings shed light on the importance of process control to assure the integrity and reliability of the bonded components.

Enhanced gas permeation performance of mixed matrix membranes containing polysulfone and modified mesoporous MCM-41

The aim of this study was the development of mixed matrix membranes (MMMs) based on silica MCM-41 dispersed in polysulfone (PSf) for the separation of carbon dioxide from methane. For this purpose, MCM-41 was synthesized by a hydrothermal method and was modified with 3-aminopropyltrietoxysilane (APTES). SEM, FTIR, BET and XRD analyses were used for characterization of the modified and unmodified particles. Then, various MMMs containing PSf at different weight percents (5, 10, 15 and 20) of modified and unmodified particles were prepared and the morphology and structure of the prepared membranes were studied using SEM and XRD analyses. Regardless of the particle type, the addition of MCM-41 to PSf caused an increase in gas permeability compared to a neat PSf membrane. Adding unmodified particles to PSf matrix resulted in undesirable effects, including particle agglomeration and/or the formation of interfacial voids. The MMMs with modified MCM-41 showed relatively better separation performance compared to MMMs with unmodified MCM-41. As a result, the MMM of PSf with 20 wt. % modified MCM-41 showed a significant increase in selectivity of carbon dioxide/methane and the value of selectivity reached 25.24.

Thin-film nanocomposite membranes containing tannic acid-Fe3+ modified MoS2 nanosheets with enhanced nanofiltration performance

The development of thin-film nanocomposite (TFN) membranes for water treatment is of immense scientific interest. In this work, MoS2 nanosheets modified with tannic acid (TA)-Fe3+ coordination complexes were embedded within the polyamide (PA) layer to construct TFN nanofiltration (NF) membranes. The incorporation of modified MoS2 nanosheets into the PA matrix facilitates the formation of a bumpy surface with the appearance of scattered protuberances. Besides, the introduced covalent bonding between phenol groups and unreacted acid chloride groups during interfacial polymerization contributes to an enhanced crosslinking degree of the PA layer, simultaneously avoiding the formation of non-selective interfacial voids. The optimal TFN NF membrane with the addition of 0.01 wt% modified MoS2 nanosheets demonstrates 1.6-fold water permeance of the TFC membrane, along with increased salt rejection. The improved permeance of the TFN membrane is mainly due to the crumpled surface architecture with high roughness, which increases the permeable area for water transport. Overall, our study suggests that the employment of TA-MoS2 nanosheets for the construction of TFN membranes can be a promising method to develop high-performance NF membranes.

Suppressing interfacial voids in Cu/In/Cu microbump with Sn and Cu addition

To overcome the reliability and manufacturing drawbacks in 3D-IC, such as warpage and low thermal budget, low temperature solder alloys are increasingly studied. Although Indium-rich solder has a beneficial low melting point of 156 °C, the formation of interfacial voids after bonding has raised concerns for reliability. By introducing Cu and Sn, the solder retained low melting points and the interfacial voids in microbumps were significantly reduced. The melting point of Cu-Sn-In alloys were measured to ensure that there is no additional phase transformation at higher temperature. In addition, the interfacial IMCs phases were characterized.