Copper Interface Research Articles

Plasma facing component with built-in tungsten wires and a W-Cu functionally graded layer: A finite element assessment

A new model for a plasma-facing component with built-in tungsten wires and a W-Cu functionally graded layer is proposed and investigated. Using ABAQUS software on the basis of finite element method, the distributions of temperature and thermal stress in different first wall models under normal ITER operation condition are simulated. The result shows that W-Cu functionally graded layer instead of Cu layer can significantly reduce the high thermal stress at the interface of tungsten and copper. Inclusion of W wires further decreases the thermal stress in W-Cu functionally graded layer. A variety of comparative simulations are performed to achieve the optimal design of this model, especially the diameter and spacing of tungsten wires.

Copper laminated composites reinforced with Al2O3 nanoparticles by suspension method and hot pressing

Laminated composite of copper with alumina nanoparticle reinforcements has application such as electrical industries. Electrical junctions should have high electrical, thermal conductivity with good mechanical strength. In this research the layers interface of pure copper were reinforced by alumina nanoparticles. For the production of the composite, first alumina nanoparticles were dispersed on Cu layers by suspension method and then the layers were hot pressed at 950°C under 20 MPa pressure. After composite making, the microstructure, the tensile and impact of these composite were studied. The results showed that by increasing amount of alumina nanoparticles up to 0. 5 wt %, tensile and impact strength were increased and for the composites with more than 0.5 wt % because of agglomeration of nanoparticles, these properties were decreased.

Interfacial charge-transfer process in nanosemiconductor- N -benzylpiperidine phenanthroimidazole (BDPI)-metal heterostructure: A combined experimental and theoretical studies of BDPI-(FeO) n composites

Abstract The interfacial electron-hole recombination at the interface of zinc copper ferrite/zinc oxide composite nanosemiconductor: 1-(1-benzylpiperidin-4-yl)-2-(3, 4-dimethoxyphenyl)-1H-phenanthro[9,10-d]imidazole (BDPI) in the fabricated Cu-ZnO-BDPI-Ag heterostructure have been studied. In which Ag-BDPI HIB is higher than ZnO-BDPI HIB and ZnO-BDPI EIB is lower than Cu-ZnO-BDPI EIB. Therefore electrons flow from Ag into the ZnO CB is possible until reaching the lowest energy state since ZnO has high electron mobility and hence Ag-to-BDPI-to-ZnO charge transfer direction is the dominant one. X-ray photo electron spectroscopy (XPS) shows doped iron and copper existed as Fe2+ and Fe3+ and Cu2+, respectively, in zinc copper ferrite/zinc oxide composite. Scanning electron microscope (SEM) image of zinc copper ferrite/zinc oxide composite show that they appear to be cocoon-like shape and the selected area electron diffraction (SAED) pattern supports the nano crystalline character of the synthesized material. The faster interfacial charge transfer of zinc copper ferrite/zinc oxide composite was analyzed by Nyquist plot. The near zero remanence magnetic indicates the superparamagnetic behavior of zinc copper ferrite/zinc oxide composite. The binding energy and energy gap of the benzylpiperidine phenanthrimidazole–iron oxide composites dependent on nature of iron oxide cluster and the charge transfer in BDPI–Fe3O4 composite is faster than the same in other composites. Molecular docking technique has also been carried out to understand the BDPI–DNA interactions.

Stability analysis of interfacial Richtmyer-Meshkov flow of explosion-driven copper interface

In this paper, a stability analysis is given to study the unstable mechanism of the Richtmyer-Meshkov flow of explosion-driven copper interface. The Richtmyer-Meshkov flow refers as an interfacial instability growth under shockwave incident loading. Numerical investigations are performed to check the applicability of the two-dimensional hydrocode, which is named AFE2D, and the physical models of detonation waves propagating in the high explosives, equations of state and the constitutive behaviors of solids in the analysis of Richtmyer-Meshkov flow problems. Here we theoretically analyze the two key issues of the unstable mechanism in Richtmyer-Meshkov flow in solids. The unstable mechanism includes temperature related melting mechanism and the plastic evolution related tensile fracture mechanism. In the analysis of the temperature related unstable mechanisms, the calculated temperature increase during the shockwave compression from the shock Hugoniot data in the shockwave physics is not enough to melt the material near the perturbed interface. On the other hand, the temperature increase from the translation of plastic work during perturbation growth which relats to the distribution of the cumulative effective plastic strain is also not enough to supply the thermal energy which is needed to melt the crystal lattice of solid, either. Therefore, the temperature related melting mechanism is not the main factor of the unstable growth of copper interface under explosion driven. In the analysis of the plastic tensile fracture related unstable mechanism, a scaling law between the maximum cumulative effective plastic strain and the scaled maximum amplitude of spikes is proposed to describe the relationship between the plastic deformation of material and the perturbation growth of interface. Combined with a critical plastic strain fracture criterion, the unstable condition of the scaled maximum amplitude of spikes is given. If the spikes grow sufficiently to meet the unstable condition, the interfacial growth will be unstable. Numerical simulations with varying initial configurations of perturbation and yield strength of materials show good agreement with the theoretical stability analysis. Finally, a criterion to judging whether the growth is stable is discussed in the form of competition between the temperature related unstable mechanism and the tensile fracture unstable mechanism.

Analysis of electrical discontinuity problem in MLB using Ishikawa model

Purpose The purpose of this study/paper is regarding analysis of electrical discontinuity in penultimate layer of a few batches of Multilayer Boards (MLB) fabricated and supplied by a vendor. The ever-increasing demand of miniaturization in launch vehicle and spacecraft electronics systems has led to the usage of multilayer printed circuit boards (PCBs) for realizing high-performance electronics circuitry. Multilayer boards (MLBs) fabricated by qualified agencies based on the customer requirement are being used in the critical launch vehicle/spacecraft systems after evaluating the preliminary test results supplied by the vendor. However, a few batches of MLBs fabricated and supplied by a particular vendor (“A”) showed a discontinuity problem in a few PCB tracks connected by soldering pads. As these MLBs are part of Flight critical systems of both launch vehicle and spacecraft, a malfunction in the board may lead to fatal errors during fight or on-orbit, thereby jeopardizing the mission. Design/methodology/approach A systematic approach was followed to have a thorough understanding of the problem, and major tests such as inspection, continuity measurement, microsection of the plated through hole (PTH) and Scanning Electron Microscopy–Energy Dispersive X-ray Analysis tests were conducted on identified test boards based on Ishikawa model. Emphasis was given for horizontal microsection, as it has got a clear edge in detecting defects at any point of PTH barrel to inner-layer copper interface. Findings Systematic testing and evaluation on specimen revealed the presence of unwanted material at the bonding area of inner-layer copper and PTH copper due to inadequate fabrication process. The un-cleaned epoxy materials present at the bonding area creates a weak bond between barrel and inner-layer copper. Electrical strength of the MLB is the strength of this link. This weaker interconnection leads to electrical discontinuity of inner-layer tracks. Originality/value MLBs are part of Flight critical systems of both Launch Vehicle and Spacecraft; a malfunction in the board may lead to fatal errors during fight or on-orbit, thereby jeopardizing the mission. Case study of an original failure observed in MLBs helped to achieve normal functioning of systems and avoided failures at later stage of mission.

Strengthening effect of reduced graphene oxide in steel clad copper rod

Reduced graphene oxide has been extensively used as reinforcing agent owing to their high mechanical properties. In this work, an attempt is made to synthesize steel clad copper rod reinforced with reduced graphene oxide (RGO) by the combination of powder-in-tube and intermediate annealing (IA). Experiments show that the Fe/RGO/Cu composites manifest better mechanical properties than Fe/Cu composites. In the process of groove rolling, RGO acts as effective binder, which can greatly improve the adhesive strength of copper scrap and two metals. Moreover, the strengthening effect of RGO is tightly related to its dispersion state. The RGO diffuses much more uniformly on the metallic substrate under the IA temperature of 1100 °C than 800 °C, which can be characterized by less deformation twins appearing at the interface of core copper and the formation of Fe–RGO–Cu transition belt at the bonding interface. In this case, the peak hardness, tensile strength and shear strength of Fe/RGO/Cu composites are 52 HV, 125 and 41 MPa higher than those of the Fe/Cu composites, respectively. The difference of strengthening effect and mechanisms of RGO under 800 and 1100 °C of IA are systematically discussed by referring to experimental results.

Extending the Life-Time of Low Cost Fuel Cells

Extending the bipolar plate lifetime of low-cost fuel cell. Energy conversion sources that offer lower carbon emissions, increased efficiency and reduced environmental impact at a competitive cost are a key requirement for future low carbon transport and stationary power generation applications.Fuel cells are promising candidates but widespread uptake has so far been hindered by the high cost of materials and manufacturing in addition to limited durability under realistic operating conditions. There is a clear need for a lower cost approach but without sacrificing performance or durability. Bipolar plates are responsible for collecting current, supplying the fuel to the MEA as well as exhausting water produced at the cathode side1. Metallic bipolar plates must be resilient, non-porous, conductive with a low contact resistance and obviously cheap for mass market penetration2. The US Department of Energy (DoE) has introduced target cost plans for 2020 on different PEM fuel cell components, including bipolar plates3. The technical plan states that the corrosion rate must be below 1 µA.cm-2 and that an interfacial contact resistance must be below 10 mΩ.cm2 at a compaction pressure of 140 N.cm-2. These condition has to be attained with a cost below 3 $kW-1. Bipolar plates account for 45-60 % of the stack cost, 80 % of the weight, and almost all the volume of the PEM fuel cell stack. The flexiplanar approach uses a metallic substrate mounted on a printed circuit board (PCB) in order to produce a low cost cell. Copper is a strong candidate for this purpose: it is robust, has a high conductivity and a low contact resistance as well as a possibility of scalable hydroforming or stamping4, which is an important feature in order to produce a flow field plate. However, due to the harsh conditions within the fuel cell stack such as a high potential and temperature, the copper interface must be protected by a coating. Coatings applied on the flow field plate must have a good electrical conductivity, a low contact resistance and also have to be resilient to fuel cell operating conditions i.e. 120 °C and 1.2 V. In recent years, there has been an increasing amount of literature on carbon polymer blend used as metallic substrate protector19 , 20 , 21. Carbon-polymer mixtures are commercially available at reasonably affordable prices. Nevertheless, they are also likely to be corroded due to carbon micro-particles dispersed in the polymer. Hence further investigation needs to be done in this poorly understood area. 1 Polymer Fuel Cells - Cost reduction and market potential, C. Trust, 2012. 2 C. Spiegel, Designing and Building Fuel Cells, 2007. 3 T. Plan and F. Cells, 2015, 1–49. 4 ASM International, Copper and Copper Alloys, ASM International, 2001. 5 W. L. Wang, S. M. He and C. H. Lan, Electrochim. Acta, 2012, 62, 30–35. 6 Y. Show and K. Takahashi, J. Power Sources, 2009, 190, 322–325. 7 Y. B. Lee and D. S. Lim, Curr. Appl. Phys., 2010, 10, S18–S21.

Soda Lime Silicate Glass-Copper Metal Joining by Controlled Heat Treatments in Air

Metal–glass joints are needed to improve efficiencies of heat collecting units used in linear parabolic sun collector systems. Soda lime silicate glass–copper metal joints were prepared at 800 ◦C for 5, 10 and 20 min by furnace treatment in air. Cu is rapidly oxidized with heat treatment in air, reacted with glass and formed some bubbles at reaction interface. Scanning electron microscope investigation suggested copper oxide formation at copper interface, reaction between copper oxide and glass and formation of bubbles at joining interface and some microcracking for the studied glass disk on Cu disk sample profiles. ANSYS14 software simulations suggested joined glass experienced complicated and high residual stress levels due to big thermal expansion coefficient difference and bubble formation at the joining interface. The residual minimal principal stress levels were at the order of −400 MPa for joined glass at interface produced microcracking in glass starting from joined interface growing into glass layer.

Molecular Engineering of Aluminum–Copper Interfaces for Joining by Plastic Deformation

Interface modification based on ultra‐thin mercapto‐propyl(trimethoxy)silane (MPTMS) films is shown to promote joining of copper and aluminum by plastic deformation followed by a heat treatment. The surface morphology and the surface chemistry of the metal substrates were analyzed by means of FE‐SEM, XPS, and FT‐IRRAS. The spectroscopic data show that the MPTMS film is crosslinked via Si–O–Si bonds and that stable Cu–S and Si–O–Al interfacial bonds are formed. The shear‐force tests of the joints led to force displacement curves that are characteristic for a covalently bonded interface. Complementary cross sectional SEM and EDS analysis of the joint proved that a defect‐free interface was formed without any measureable interdiffusion of metals across the interface or cracking of an oxide films.

Suppression of selective surface oxidation in DP steels by effective shielding of copper — Kinetic simulation and experimental validation

Abstract The high strength steels have become essential for the auto body parts owing to the combination of high strength as well as better crash resistance. The galvanizing and galvannealing of these high strength steels are required for longer performance life of the steels. The constituent alloying elements in the high strength steel e.g. manganese, silicon and chromium have a tendency to oxidize at the steel surface during the continuous annealing of the steel. The oxides greatly inhibit the wettability of steel with molten zinc during galvanizing. In the present study the application of prior copper coating on Dual Phase (DP) steel was shown to act as a diffusion barrier for the alloying elements during annealing. The kinetic simulation for diffusion of manganese and oxygen through the copper layer having an initial thickness of 200 nm showed that the oxidation front can be arrested at the sub-surface region near the steel–copper interface. The simulation results were verified with experimental annealing simulation and subsequent depth profiling by Glow Discharge Optical Emission Spectroscopy (GDOES) and Transmission Electron Microscopy (TEM)/Energy Dispersive Spectroscopy (EDS) line scanning. The copper coating was able to suppress the surface segregation and selective oxidation of manganese as oppose to the conventional DP steels. The galvanizing of the copper coated DP steels exhibited defect free zinc coating as compared to the regular DP steels having high number of bare spots. The simulation technique can be further extended to determine the thickness and type of pre-coating layers for high strength steels.

Neural network molecular dynamics simulations of solid-liquid interfaces: water at low-index copper surfaces.

Solid-liquid interfaces have received considerable attention in recent years due to their central role in many technologically relevant fields like electrochemistry, heterogeneous catalysis and corrosion. As the chemical processes in these examples take place primarily at the interface, understanding the structural and dynamical properties of the interfacial water molecules is of vital importance. Here, we use a first-principles quality high-dimensional neural network potential built from dispersion-corrected density functional theory data in molecular dynamics simulations to investigate water-copper interfaces as a prototypical case. After performing convergence tests concerning the required supercell size and water film diameter, we investigate numerous properties of the interfacial water molecules at the low-index copper (111), (100) and (110) surfaces. These include density profiles, hydrogen bond properties, lateral mean squared displacements and residence times of the water molecules at the surface. We find that in general the copper-water interaction is rather weak with the strongest interactions observed at the Cu(110) surface, followed by the Cu(100) and Cu(111) surfaces. The distribution of the water molecules in the first hydration layer exhibits a double peak structure. In all cases, the molecules closest to the surface are predominantly allocated on top of the metal sites and are aligned nearly parallel with the oxygen pointing slightly to the surface. The more distant molecules in the first hydration layer at the Cu(111) and Cu(100) surfaces are mainly found in between the top sites, whereas at the Cu(110) surface most of these water molecules are found above the trenches of the close packed atom rows at the surface.

Nondestructive Characterization of Molecular Structures at Buried Copper/Epoxy Interfaces and Their Relationship to Locus of Failure Analysis

Delamination at heterogeneous metal/polymer interfaces during reliability testing of packaged devices continues to be a reliability issue in microelectronic packaging. Although interfacial adhesion properties are largely determined by molecular structures at buried interfaces, structure-property relationships at buried metal/polymer interfaces are not well understood due to a lack of nondestructive interface sensitive analytical techniques. In this paper, methodology was developed to nondestructively characterize the molecular structure at buried copper/epoxy interfaces in situ using infrared-visible sum-frequency generation (SFG) vibrational spectroscopy. The methodology was applied to elucidate the relationship between molecular structure at the buried copper/epoxy interface and delamination behavior by correlating molecular structure with the locus of failure analysis. SFG and locus of failure analysis suggest that molecular ordering and silane behavior at the copper interface both contribute to a gradient in network structure and mechanical properties near the copper interface which was correlated with a locus of failure at an interfacial weak zone. The combined destructive and nondestructive characterization methodology developed here is general and can be directly applied to selectively characterize relationships between molecular structure at buried metal/polymer interfaces and interfacial properties such as adhesion, delamination, and interfacial moisture transport during Joint Electron Device Engineering Council qualification testing.

Applicability of Non-Destructive Examination to Iter TF Joints

The Iter TF joints are of a twin-box design and the critical parameters of the overall resistance are 1) the contact between cable and termination, and 2) the resistance between two terminations. This paper describes applicability of non-destructive examination (NDE) to these joints. The TFEU joint was adapted to make the joint demountable and the contact area was artificially degraded. The TFEU Joint was measured in the range 30-70 kA, 0-6 T. With no artificial degradation, the resistance of the TFEU Joint was measured to be better than the inter-pancake criterion of 3 nΩ at 2 T, 68 kA. At high fields (6 T) the voltage-current (V I) characteristic of the joint is nonlinear and the resistance is higher than expected. The nonlinearity is worse when the joint is artificially degraded. An FEA model was used to demonstrate that the magneto-resistant copper's contribution to the overall joint resistance is low (<; ~1 nΩ) and does not explain the high field behavior. The nonlinear V I behavior is due to poor current redistribution within the joint, which is related to the resistance of the strand-bundle to copper interface. CRPP is developing a room temperature NDE technique based on resistance profiles to investigate this interface. Resistance measurements at low current and field, or high current and low field, do not guarantee performance at high field; joint tests under the operating conditions are required. Tests on the upper terminations of the TFEU Joint showed that large defects in the contact area between two terminations could be tolerated, when the joint has a good strand-bundle to copper contact resistance and effective current redistribution.

Cu/Cu direct bonding by metal salt generation bonding technique with organic acid and persistence of reformed layer

In this study, the effect of the metal salt generation bonding technique on the strength of a direct-bonded copper–copper interface was investigated. Copper surfaces were modified by boiling in several types of organic acids, and direct bonding was performed at a bonding temperature of 423–673 K under a load of 588 N (for a bonding time of 0.9 ks). As a result of the surface modification, bonded joints were obtained at bonding temperatures of 150 K (after treatment with formic acid) and 100 K (after citric acid treatment) lower than that required for the unmodified surfaces. In addition, the duration of the modification effects was investigated by exposing the modified surface to an air atmosphere furnace kept at 323 K. The bonding strength of the citric acid-modified surface remained unchanged even after 168 h, whereas that of the surface modified with formic acid decreased within 6 h.

Faceting Transition at the Oxide–Metal Interface: (13 13 1) Facets on Cu(110) Induced by Carpet-Like Ceria Overlayer

Structural transitions affect electronic structure of materials and consequently their catalytic properties. We report the observation of faceting of a low index metal surface at an oxide–metal interface in a catalytically relevant system of ceria on Cu(110). We observe formation of (13 13 1) facets on the Cu(110) surface covered by ceria upon annealing above 500 °C. The faceting transition occurs in spite of a weak adsorbate–substrate interaction, which manifests itself in ceria adopting a carpet-like growth mode. We rationalize the surface faceting under such conditions by oxide overlayer-induced modification of the roughening temperature of Cu(110). We describe the carpet-like ceria film in terms of elasticity theory and show that the specific structure of the ceria supported on Cu(13 13 1) can lead to a periodic modulation of the electronic structure of the ceria–copper interface. The reported structural transition indicates that surface faceting of metal can occur at the oxide–metal interface at relatively low temperatures with possible consequences for the catalytic properties of the interface. The oxide overlayer induced faceting transition can be expected to occur for other oxide–metal combinations and, as such, has perspective applications in preparation of functional oxide–metal nanostructures.

Non-destructive electrochemical graphene transfer from reusable thin-film catalysts

We demonstrate an electrochemical method – which we term oxidative decoupling transfer (ODT) – for transferring chemical vapor deposited graphene from physically deposited copper catalyst layers. This copper oxidation-based transfer technique is generally applicable to copper surfaces, and is particularly suitable where the copper is adhered to a substrate such as oxidized silicon. Graphene devices produced via this technique demonstrate 30% higher mobility than similar devices produced by standard catalyst etching techniques. The transferred graphene films cover more than 94% of target substrates – up to 100mm diameter films are demonstrated here – and exhibit a low Raman D:G peak ratio and a homogenous and continuous distribution of sheet conductance mapped by THz time-domain spectroscopy. By applying a fixed potential of −0.4V vs. an Ag/AgCl reference electrode – significantly below the threshold for hydrogen production by electrolysis of water – we avoid the formation of hydrogen bubbles at the graphene–copper interface, preventing delamination of thin sputtered catalyst layers from their supporting substrates. We demonstrate the reuse of the same growth substrate for five growth and transfer cycles and prove that this number is limited by the evaporation of Cu during growth of graphene. This technique therefore enables the repeated use of the highest crystallinity and purity substrates without undue increase in cost.

Study of the UBM to copper interface robustness of solder bumps in flip chip packages

Shear tests on SnAg solder bumps were performed with a reduced height to the surface for a high shear force on the under bump metallurgy (UBM) to redistribution layer (RDL) copper interface. By this the failure mechanism of UBM–RDL delamination after stress tests simulating several assembly reflows could be reproduced. A design of experiment was done with corner wafers at worst case conditions for topography and interface clean. TEM cross sections confirmed nano scale carbon residues in the interface when reducing the clean efficiency. This results in a mechanically weakened interface with a present electrical contact. The shear test with reduced height is a more severe test beyond the JEDEC test to verify the bump robustness. This is important when existing bump technologies are used for flip chip package solutions with increased solder reflow requirements.

Cu/Cu Direct Bonding by Metal Salt Generation Bonding Technique with Formic Acid and Citric Acid

The effect of formic acid and citric acid surface modification on the bonded strength of the solid-state direct bonded interface of copper was investigated by SEM observations of interfacial microstructures and fractured surfaces. Copper surfaces were modified by boiling in 98% formic acid for 0.6 ks and 17% aqueous solution of citric acid for 0.96 s. Solid-state bonding was performed in a vacuum chamber at bonding temperature of 423 ~ 673 K under a pressure of 588 N (bonding time of 0.9 ks). As a result of surface modification by formic acid and citric acid, bonded joints were obtained at a bonding temperature 150 K (formic acid) and 100 K (citric acid) lower than that required for non-modified surfaces, and the bond strength was comparable to that of the maximum load.

Removal of copper in leachate from mining residues using electrochemical technology

This research is related to a laboratory study on the performance of a successive mining residues leaching and electrochemical copper recovery process. To clearly define the experimental region for response surface methodology (RSM), a preliminary study was performed by applying a current intensity varying from 0.5 A to 4.0 A for 60 min. By decreasing the current intensity from 4.0 A to 0.5 A, a good adhesion and a very smooth and continuous interface of copper was formed and deposited on the cathode electrode. However, the removal rate of Cu decreased from 83.7% to 37.9% when the current intensity passed from 4.0 A to 0.5 A, respectively. Subsequently, the factorial design and central composite design methodologies were successively employed to define the optimal operating conditions for copper removal in the mining residues leachate. Using a 23 factorial matrix, the best performance for copper removal (97.7%) was obtained at a current intensity of 2.0 A during 100 min. The current intensity and electrolysis time were found to be the most influent parameters. The contribution of current intensity and electrolysis time was around 65.8% and 33.9%, respectively. The treatment using copper electrode and current intensity of 1.3 A during 80 min was found to be the optimal conditions in terms of cost/effectiveness. Under these conditions, 86% of copper can be recovered for a total cost of 0.56 $ per cubic meter of treated mining residues leachate.

Numerical modeling and experimental verification of through silicon via (TSV) filling in presence of additives

Copper electro-chemical deposition (ECD) of through silicon via (TSV) is a key challenge of 3D integration. This paper presents a numerical modeling of TSV filling concerning the influence of the accelerator and the suppressor. The diffusion–adsorption model was used in the simulation and effects of the additives were incorporated in the model. The boundary conditions were derived from a set of experimental Tafel curves with different concentrations of additives, which provided a quick and accurate way for copper ECD process prediction without complicated surface kinetic parameters fitting. The level set method (LSM) was employed to track the copper and electrolyte interface. The simulation results were in good agreement with the experiments. For a given feature size, the current density for superfilling could be predicted, which provided a guideline for ECD process optimization.