Thin Copper Foil Research Articles

Evaluation of glued-diaphragm fibre optic pressure sensors in a shock tube

Glued-diaphragm fibre optic pressure sensors that utilize standard telecommunications components which are based on Fabry–Perot interferometry are appealing in a number of respects. Principally, they have high spatial and temporal resolution and are low in cost. These features potentially make them well suited to operation in extreme environments produced in short-duration high-enthalpy wind tunnel facilities where spatial and temporal resolution are essential, but attrition rates for sensors are typically very high. The sensors we consider utilize a zirconia ferrule substrate and a thin copper foil which are bonded together using an adhesive. The sensors show a fast response and can measure fluctuations with a frequency up to 250 kHz. The sensors also have a high spatial resolution on the order of 0.1 mm. However, with the interrogation and calibration processes adopted in this work, apparent errors of up to 30% of the maximum pressure have been observed. Such errors are primarily caused by mechanical hysteresis and adhesive viscoelasticity. If a dynamic calibration is adopted, the maximum measurement error can be limited to about 10% of the maximum pressure. However, a better approach is to eliminate the adhesive from the construction process or design the diaphragm and substrate in a way that does not require the adhesive to carry a significant fraction of the mechanical loading.

Silicon-on-insulator cantilevers as charge collectors for radioisotope micropower sources: design, fabrication and characterization

A silicon-on-insulator cantilever is proposed as a potential charge collector for radioisotope micropower sources. The conversion efficiency can be improved by directional control of the radiated particles. A two-dimensional microfluidic modeling was successfully generated to analyze the performance of the radiated particles as a quick proof of concept using ANSYS™. The mounting of the radiation source and the release of charged particles in this novel approach are simple and practical from the point of view of fabrication and operation. Prototype cantilevers were fabricated at the millimeter scale to increase the amount of collected charge and obtain a higher fabrication yield. A processing technique, using a thin copper foil as a gap protector, was successfully created to resolve the stiction issues for freestanding silicon-on-insulator cantilevers with their length and width at the millimeter scale and their thickness at tens of micrometers. The vibration of these prototypes was characterized through a self-made feedback interferometer. The difference between the measured natural frequency and the finite-element analysis is less than 0.4%, an extremely high accuracy pertaining to the nanofabrication tolerances in device dimensions. The proposed self-made feedback interferometer presents an efficient solution to calibrate the vibration of microdevices with their dimensions at the millimeter scale. The analytical deflection of the silicon-on-insulator cantilevers with charged particles was rigorously derived, which shows only a 1.5% difference from the three-dimensional electromechanical coupled-field simulation using ANSYS™, an excellent accuracy and an extremely simple solution.

High SNR flexible top hat monopole probe for 1.5 T MRI

In this paper, design principles and application of a thin and flexible intravascular top hat monopole probe with increased signal-to-noise ratio (SNR) and improved longitudinal and radial coverage are described and compared with the conventional monopole probe. The top hat probe is constructed by removing a segment of the shield of a coaxial cable. A flexible thin copper foil in contact with the inner conductor of the cable is added to the end section of the cable. The copper foil acts as an antenna top hat load increasing the uniformity of the current distribution on the probe and establishes a uniform region of SNR distribution around the probe. Improvement of the SNR distribution of the top hat probe relative to the conventional monopole probe is evaluated using quantitative indices. Experimental results show that for the top hat probe, the ratio of the maximum image SNR to its relative standard deviation (SR) is 2.73 times higher than that of a conventional probe.

Development of a cavitation erosion model

A study of visual and erosion effects of cavitation on simple single hydrofoil configurations in a cavitation tunnel was made. A thin copper foil, applied to the surface of the hydrofoils, was used as an erosion sensor. The cavitation phenomenon on hydrofoils at different flow conditions (system pressure, water gas content, flow velocity) was observed. Results that showed a significant relationship between cavitation erosion and the visual effects of cavitation made it possible to use these information to develop a cavitation erosion model. The model is based on the physical description of different phenomena (cavitation cloud implosion, pressure wave emission and its attenuation, micro-jet formation and finally pit formation), which are involved in the process of pit formation. It is capable to predict the influence of significant parameters as flow velocity and gas content of water. The model that was developed on the basis of measurements of cavitation on a single hydrofoil was later tested on an actual hydraulic machine in the form of a radial pump. The predicted magnitude and distribution of cavitation damage relates well to the experimentally measured one.

Lubrication for Micro Forming of Ultra Thin Metal Foil

The objective of the present investigation is to establish lubrication technique in micro forming operation. Conventional lubricant, in general, cannot be applied directly to micro forming process, since the lubricant thickness is similar to the dimensions of feature size in micro forming operations. In present investigation, the Octadecyltrichlorosilane (OTS) self-assembled monolayer (SAM) was chosen as a potential lubricant because it sticks to Si wafer die and can be applied to surface with uniform thickness of several nanometer thick. Friction coefficient and adhesion force were measured for OTS SAM coated wafer. It is shown that OTS SAM coated Si wafer offers substantially lower friction and lower adhesion than bare Si wafer. Micro channel wafer die was coated with OTS SAM and channel forming operation with 1μm thick copper foil was carried out. Experimental results show that OTS SAM coated wafer die improves forming characteristic of ultra thin copper foil substantially. These results show that SAM coating can be used as a lubricant in micro forming successfully.

Size effects in tensile testing of thin cold rolled and annealed Cu foils

Thin copper foils of varying thickness were tested in tension at room temperature. The thickness of the samples was between 10 and 250 μm, length and width were scaled according to the thickness. Two types of samples were tested: as-received samples and annealed samples. The microstructure of the foils was determined in detail by means of several methods. If samples of the same processing condition were compared, there was a clear dependence of the mechanical behavior on the thickness of the foils in the tensile test. When the thickness was reduced from 250 to 10 μm, the fracture strain decreased for the as-received foils from approximately 20% to 0.2% and for the samples with heat treatment from 35% to 15%. It has to be stressed that this size effect occurred in the absence of considerable strain gradients and for samples with a comparable microstructure.

Influence of titanium oxide films on copper nucleation during electrodeposition

Copper electrodeposition has an important industrial role because of various interconnects used in electronic devices such as printed wire boards. With an increasing trend in device miniaturization, in demand are void-free, thin copper foils of 10 μm thick or less with a very low surface profile. In accordance, nucleation kinetics of copper was studied with titanium cathodes that were covered with thin, passive oxide films of 2–3 nm. Such an insulating oxide layer with a band gap of 3 eV is supposed to nearly block charge transfer from the cathode to the electrolyte. However, significant nucleation rates of copper were observed. Pipe tunneling mechanism along a dislocation core is reasoned to account for the high nucleation kinetics. A dislocation core is proposed to be a high electron tunneling path with a reduced energy barrier and a reduced barrier thickness. In supporting the pipe tunneling mechanism, both ‘in situ’ and ‘ex situ’ scratch tests were performed to introduce extra dislocations into the cathode surface, that is, more high charge paths via tunneling, before electrodeposition.

Three-Dimensional Microstructure of Thin Copper Foils Revealed by Ion Beam Cutting and Electron Backscatter Diffraction (EBSD)

Tensile testing of thin rolled copper foils with thickness ranging from 10 to 250 µm shows a dependence of the fracture strain with respect to the thickness of the foils [G. Simons et al., in Solid Mechanics and its Applications, Vol. 114 (2004), pp. 89-96]. To understand the influence of the microstructure in the foils on this phenomenon the microtexture is investigated by orientation mapping through electron backscatter diffraction (EBSD). As the samples are rather small standard preparation techniques do not apply. Two methods are described which allow the investigation of different section cuts of the samples: Cross sections of the samples were produced by ion beam cutting with a wide beam of 7 keV Kr ions. Internal planes parallel to the specimen surface were made accessible by wet etching. The as-received material possesses a very strong texture consisting mostly of the cube component and some remnants of a previous rolling texture. Specimens tested in a tensile test do not show major microstructural changes compared to virgin samples. After a heat treatment at 300°C the cube texture has significantly weakened in favour of revived rolling components, and the fracture strain increased about ten times relative to the as-is material.

Adhesive copper films for an air-breathing polymer electrolyte fuel cell

A design for an air-breathing and passive polymer electrolyte fuel cell is presented. Such a type of fuel cell is in general promising for portable electronics. In the present design, the anode current collector is made of a thin copper foil. The foil is provided with an adhesive and conductive coating, which firstly tightens the hydrogen compartment without mask or clamping pressure, and secondly secures a good electronic contact between the anode backing and the current collector. The cathode comprises a backing, a gold-plated stainless steel mesh and a current collector cut out from a printed circuit board. Three geometries for the cathode current collector were evaluated. Single cells with an active area of 2 cm 2 yielded a peak power of 250–300 mW cm −2 with air and pure H 2 in a complete passive mode except for the controlled flow of H 2. The cells’ response was investigated in steady state and transient modes.

The effect of growth parameters on the aspect ratio and number density of CuOnanorods

We have studied how different growth conditions, namely, oxygen flow rate, annealingtemperature and annealing time affect the diameter, aspect ratio and number density ofCuO nanorods using scanning and transmission electron microscopy. CuO nanorods aresynthesized by thermal annealing of thin copper foil. It is observed that while the diameterand number density of nanorods depend critically on the oxygen flow rate and annealingtemperature, the aspect ratio and dispersion in diameter of nanorods can mostly beimproved by thermal annealing for extended time periods. The growth mechanism of thenanorods is inferred from the evolution of observed microstructural changes. It is proposedthat the growth of nanorods takes place from triangular shaped pyramids due to therelaxation of stress accumulated in oxide film during the process of oxidation andannealing.

Grain structure of thin electrodeposited and rolled copper foils

Planar and cross-section light optical and transmission electron microscopy (TEM) and X-ray diffraction analysis have been used to characterize the technologically relevant thin copper films and foils. The grain structure and grain orientation of (i) 1–15 μm deposit on the polyimide (PI) substrate, (ii) 5–35 μm free-standing foil and (iii) 200 μm sheet prepared by the industrial scale rolling or electrodeposit process have been examined. It is shown that the rolled foil structure is highly anisotropic due to grain stretching during rolling; the pancaked grains circumscribe a dislocation cell substructure. Thermal exposure in the 423–453 K range results in full anneal softening, while initiating the polygonization of cellular substructure, the formation of new large grains by discontinuous recrystallization and the transformation of the near 〈111〉 deformation textures into the near 〈100〉 anneal textures. The texture transformation is facilitated when the oxygen content of copper is reduced from the normal 100–400 ppm level or when a low level silver (∼200 ppm) addition is made to copper. Depending upon the electrodeposition conditions or the nature of additives introduced in the electrolyte, it is possible to develop an electrodeposit with (a) a truly equiaxed, fine, twin-free, randomly oriented grain structure or (b) a relatively coarse grain structure, accompanied by extensive twinning, z (growth)-direction grain extension, columnar grain morphology and strong 〈220〉 crystallographic texture. Between (a) and (b), it is possible to tailor the processing to obtain a mix of fine and coarse grains, a large fraction of random orientation component (weak near 〈220〉 textures), moderate twinning, and vestiges of columnar grain morphology and z-direction grain extension. The anneal softening is not accompanied by significant grain structure modification or by texture change; somewhat above the softening temperature, an in situ grain growth ensues. For both rolled and electrodeposited (ED) foils, at 100 K or more above the softening temperature, grain growth is impeded by the foil surfaces.

Relationship between cavitation structures and cavitation damage

A study of visual and erosion effects of cavitation on simple single hydrofoil configurations in a cavitation tunnel was made. A two-dimensional hydrofoil with circular leading edge was used for the experiments. In addition, the hydrofoil geometry was modified to obtain some three-dimensional cavitation effects. A thin copper foil, applied to the surface of the hydrofoil, was used as an erosion sensor. Cavitation phenomenon above hydrofoils at different flow conditions (system pressure, water gas content) was observed. Images of vapour cavities from above and from side view were taken. A statistical evaluation of cavitation structures was made. Images of damaged copper coated hydrofoil surface were taken under sufficient magnification. A pit-count method, based on computer-aided image processing, was used for direct measurement of the cavitation erosion by evaluating the damage of the surface of the hydrofoil. A relation between characteristics of cavitation structures and cavitation damage was established.

Metal to ceramic joining via a metallic interlayer bonding technique

The lack of suitable joining techniques for dissimilar materials such as metal and ceramic for high-temperature applications and devices is a major hindrance to the utilization of their outstanding properties and lower costs. This paper presents the results of joining between the high-temperature and corrosion resistant iron–chromium–aluminium alloy (Fecralloy) with silicon nitride by use of metallic interlayer. The primary objectives were to produce joints for high-temperature applications (above 500 °C) and to observe the effects of processing parameters with regards to joint strength. Joining by use of a thin (12.5 μm) and non-remaining copper foil produced joints with an average maximum shear strength of 67.5 MPa (±5) at 1100 °C, 30 min dwell time at 9.5 MPa, under vacuum. The processing conditions were found to play a very important role in the joining process and effected joint strength. The results suggest that a thin aluminium nitride, AlN, reaction product layer was present on the silicon nitride interface in the joined samples. This is an indication that reactive wetting was occurring. Iron, chromium, aluminium and copper were found to infiltrate the silicon nitride, whilst silicon and nitrogen diffused into the Fecralloy. Joining was also attempted using a Ti/Cu/Ti multilayer and its variations. Joining was not possible due to the formation of a brittle reaction product layer, highlighting that wetting and joining are not synonymous.

Elastic and elastoplastic response of thin copper foil

The tensile elastic, elastoplastic and low strain plastic parameters of the 12–35 μm thick rolled (R) and electrodeposited (ED) copper foils have been characterized between 296 and 573 K and after an anneal exposure at up to 1173 K. At 296 K, all parameters are inversely proportional to grain size but the thermal effects dominate at the higher temperatures. For the R foils, the temperature coefficient of elastic modulus (E) is more or less identical to that for the bulk copper. For the ED foils, the coefficient increases with decreasing grain size; this effect is presumably related to the characteristic point defect structure generated during deposition. A significant grain growth ensues upon annealing but the post-anneal grain size has little effect on E; for the R foil, however, E decreases sharply with the anneal induced emergence of new crystallogrpahic textures with orientations near (100). The tangent modulus (E t) in the elastoplastic regime decreases with strain and with temperature, a very large drop in E t with anneal temperature suggests that both the diminution of dislocation activity and the texture modification are the contributory factors. It is argued that the strain hardening parameter (n) in the elastoplastic regime, and the strain rate hardening parameter (m) and the flow stress in the low strain plastic regime influence the handling damage to the thin foil.

Application of Imaging Plate to Measurement of Radiation Spatial Distribution

An imaging plate (IP) was applied to 1) detecting of low-level contamination that was difficult to detect by a conventionalway, 2) measurement of spatial distributions of thermal neutrons and 3) profile measurement of fast neutronsand proton beam of low intensity. For 1), a large-size IP (BAS-Ills) was disposed to the sample, and the position andintensity of the contamination was identified unambiguously by scanning IP. For 2), activation foils were combinedwith IP to avoid 7-rays from neutron sources and radioactive accelerator components. We placed small gold activationfoils at many points of interest in an accelerator room and disposed them on IP after irradiation. This method enables tomeasure neutron spatial distribution in a single scanning. We extended this method to profiling of fast neutron by usingan aluminum plate and proton beams with intensity too low to measure by beam current but too strong to measure bypulse counting by using a thin copper foil.

Spatial and spectral behavior of the optical near field studied by a terahertz near-field spectrometer

We have developed a technique to obtain spectroscopic information in the optical near field. The spectrometer operates in the frequency range from 30 GHz to 1.5 THz using highly monochromatic and coherent radiation which can be continuously tuned. Small pinholes (λ/100–λ/10) in thin copper foils serve as near-field probes. For an accurate, fast, and contact-less control of the probe–sample distance a confocal microscope is employed. We experimentally test the diffraction theory of electromagnetic waves on subwavelength pinholes. Based on our findings we formulate requirements for near-field spectroscopy at THz frequencies.

Nuclear reactions in copper induced by protons from a petawatt laser-foil interaction

High-intensity (>1019 W cm−2) laser-plasma interactions have been shown to produce large quantities of protons with energies up to several tens of MeV. A range of laser-driven proton-induced reactions in copper have been investigated and the observed reactions quantified. The energy spectrum of the accelerated protons was determined from the reactions in a single thin copper foil and found to be in agreement with that deduced from (p,n) reactions measured in a stack of copper foils. The potential applications of this diagnostic technique are discussed.

Thermal effects in thin copper foil

The anneal response and high-temperature ductility for four commercial-grade 35-µm rolled (R: GR5) and electrodeposited (ED: GR1, GR3, and TCAM) copper foils, used for rigid and flexible printed circuits, are investigated. Using tensile and microhardness monitors, the anneal response is examined to 900°C for up to 300 min, and the high-temperature ductility is characterized to a 200°C test temperature. For comparison, the ED “control” foils, using deposition parameters identical to those for the commercial foils but without the additives usually introduced in the electrolyte, are also examined. The ED control foils thermally soften readily; the temperature range of softening decreases with the electrodeposition overvoltage (η). For the commercial-grade foils, the proprietary additives help tailor thermal softening but cause severe disruption of anneal kinetics (TCAM) and embrittlement at (TCAM) and above (GR1, GR3) 23°C.

Transmission electron microscopy study of the interaction between a glide dislocation and a dislocation node

Using in-situ tensile straining in conjunction with stereo imaging in a transmission electron microscope, real-time observations have been made in thin copper foils of the interaction of glide dislocations with a dislocation node. A mechanism is observed by which a dislocation approaching the node effectively bypasses the node by exchanging segments with one of the dislocations constituting the node.

Thin copper foil heater for measuring the thermal conductivity of polymers

AbstractA new and rather simple apparatus is described for measuring the thermal conductivity of insulating materials. The technique employs a double‐sided, copper‐coated plastic sheet, known as a printed circuit board, to generate a nearly uniform wall heat flux. Heating is achieved by passing an electrical current through the copper coating. Identical sample slabs are placed against opposite sides of the heater, and the combination is placed in a bath having constant and uniform temperature. When thermal equilibrium is reached, the temperature drops across the central portions of the sample slabs are measured with thermocouples. The one‐dimensional form of Fourier heat transfer equation is used to compute thermal conductivity from the observed quantities. In preliminary tests with polymer materials, equilibrium is reached within half an hour. It is estimated that the apparatus is capable of giving measurements accurate to within 5%, and experimental results are consistent with this estimate. Thermal conductivity values are reported for pure polyethylene (PE) and PE mixed with aluminum powder and carbon black. Also reported is the thermal conductivity of pure polycarbonate (PC) and PC mixed with carbon black. The results obtained with the present apparatus are consistent with previous findings. The characteristics of the apparatus make it especially suitable for academic laboratory instruction and for low temperature thermal conductivity measurements. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 12: 2823–2827, 2003