Thick Copper Foil Research Articles

Microstructural development and mechanical properties of wide gap and conventional transient liquid phase bonds between Ti-48Al-2Cr-2Nb substrates

An investigation of microstructural development and structure-property relationships in a transient liquid phase bonded Ti-48Al-2Cr-2Nb at.- alloy abbreviated here to 48-2-2 is presented. The use of copper containing interlayers is examined. The primary focus of the paper is wide gap composite interlayers consisting of copper as a liquid former, plus a TiAl alloy binary TiAl or 48-2-2 as a non-melting diffusional sink. However, bonds employing commercial purity copper foils of thickness 5 and 50 m are also examined. Bond microstructures are characterised by edge-on transmission electron microscopy, plus scanning electron microscopy and light microscopy. Mechanical properties are determined through the use of room temperature shear and bend testing, supplemented by both room and elevated temperature tensile testing. The formation of copper containing intermetallics at the bond line and the formation of gamma-TiAl by both epitaxial growth and non-epitaxial precipitation are discussed. The microstructure of the bonds is compared with that of the parent 48-2-2 material. The influence of both the main bond line microstructure and the fillets on the mechanical properties of transient liquid phase bonded 48-2-2 is determined.

In-Situ Studies of X-Ray Diffraction Line Profiles from Strained Copper Foils

The development of an in-situ tensometer is described along with preliminary results of x-ray line profiles from copper foils under tensile stress. The tensometer was designed and constructed on the high resolution diffraction instrument, Station 2.3 at the synchrotron radiation source (SRS) Daresbury Laboratory, and is capable of collecting data in either symmetric or asymmetric geometry including transmission and reflection modes. Experiments were carried out using 18 J..Lm thick copper foil up to strain levels of 5 % using both symmetric reflection and symmetric transmission diffraction. All profiles displayed diffraction broadening and asymmetry which increased with strain. In addition, the asymmetry observed in symmetric transmission was associated with extended tails on the low angle side of the profiles, but in symmetric reflection data the opposite asymmetry was observed. In the analysis, the measured profiles were fitted using the software TOPAS, a fundamental parameters approach to profile fitting. The instrumental profile function was characterised and modelled using annealed LaB6 powder. The diffraction broadening was then determined by refining the convolution of a Voigt function, an asymmetric exponential function and a fixed instrument function to reproduce the observed broadened profiles. The integral breadth and asymmetry results display a strong order dependence and increase almost linearly with strain. The results were interpreted by assuming crystallite size broadening in combination with dislocation broadening arising from fcc a/2( 110) {Ill } dislocations.

Microfabrication of thermoelectric generators on flexible foilsubstrates as a power source for autonomous microsystems

A flexible thermoelectric generator with overall dimensions of16×20×0.05 mm has been fabricated using a unique low-costprocedure as part of our ongoing research efforts on developing economicaland reliable energy sources for autonomous microsystems. The generatorconsists of a multiplicity of micro Sb-Bi thermocouple strips embedded ina 50 µm thick flexible epoxy film and is capable of generating avoltage of 0.25 V at a temperature difference of 30 K. Its fabricationinvolves only a few steps, such as foil lithography, electroplating,embedding and wet chemical etching. The exposure of aqueous photoresist onflexible foil substrates is carried out using a specially constructed maskaligner by Karl Süss GmbH. The thermocouple strips, with a crosssection of 40×10 µm and a length of 20 mm, are electroplatedgalvanostatically from their associated acidic electrolytes into thepatterned AZ 111XFS template on a 50 µm thick copper foil. After atop-over embedment of the electroplated structures with an epoxy film, theoriginal copper substrate is removed completely by wet chemical etching,leaving the generator module to be embedded in the epoxy film. Thisprocess is proven to be cost-effective, easily manageable and highlyreliable. It is now being applied to our current fabrication of moreefficient thermoelectric generators based on n- and p-type Bi2Te3compound materials.

Characterization of Ni-P and Fe-P by X-ray absorption spectroscopy

Due to the lack of long range order and hence the absence of grain boundaries, amorphous alloys have unusual physical properties. For example, they have excellent corrosion resistance. The presence of metalloids such as P and C lead to the formation of amorphous or glassy structure. In a previous study, Lalvani et al. [1] have studied the structure of these alloys by X-ray absorption spectroscopy (XANES). The energy level used in these structures was quite low (less than 2200 eV) which enabled the investigation of P K-edge. Their research indicated both a metalloid-P character in amorphous Ni-P and the transfer of charge from the Ni to the P-p orbitals in this material. They also showed that scratching of the sample leads to a p5+oxidized feature. The Fe-P sample (relative to the NiP) appeared to indicate a stronger transition of metal-P hybradization. The XANES technique is superior to the ones employing X-ray photoelectron microscopy and angleresolved XPS since the latter suffer from a number of deficiencies. They are not able to quantitatively describe the chemical composition of the passive films formed on the surface. In addition, the data obtained on the valency of species present is not clear. One of the major problems in studying the corrosion behavior of amorphous alloys in aqueous solutions is that the passive oxide layers formed are usually very thin (typically a few nanometers), and are formed under the presence of a high electric field [2]. Generally, ex situ surface analysis methods are used for investigation which involve vacuum conditions and beams of electrons or ions in the absence of electric field and electrolyte which could significantly alter the passive layers. Raman spectroscopy on the other hand could be employed in situ, however it has certain limitations as well [3]. XANES probes electron transmissions from core levels (the 1s level for the K edge) to unoccupied levels and is thus sensitive to the valance and coordination of the absorbing atom. In addition, the height of the absorption edge is proportional to the total amount of the absorbing element present in the beam (irrespective of valence) and thus can be used to monitor dissolution of elements from thin films [4]. Fe-P and Ni-P samples were produced by electrodeposition. Electrodeposition was carried out under constant current from acidic solutions on 25 micron thick copper foil. The bath composition is given in Table I. 500 ml of electrolytic solution was used in each case. Significant agitation was provided to the bath during deposition with a magnetic stirrer. The anode and cathode were placed parallel to each other at a distance of 4 cm. The current densities and temperature conditions were: 0.05–0.23 A/cm2 and 50–65 ◦C for Ni-P and 0.02– 0.1 A/cm2 and 40–50 ◦C for Fe-P deposition. The elemental composition of the deposits was found by atomic absorption spectroscopy. Additional experimental details are also provided elsewhere [5, 6]. The EXAFS spectrum (absorption vs. energy) and Fourier transformation (amplitude) of the signal vs. distance (Angstrom) are plotted for both, FeP and Ni-P samples in Figs 1–3. For the Fe-P sample, a peak is observed at the energy level of about 7100 eV which gradually decreases over higher energy levels. The spectrum corresponds to the Fe-K edge. XAS measurements are sensitive both to the atomic site electron states and the near shell coordination number/types. Using one shell data analysis, the bond length for Fe-P sample was estimated to be about 2–3A and the disorder parameter was found to be approximately 0.0066. The Fourier transformation (Fig. 2) shows one single major peak at about 2A which is significant in that it shows that there is no long distance order and only short distance order is possible. Hence, it is concluded that the sample is

Interactions between laser-activated nucleation sites in pool boiling

A technique of activating nucleation sites by heating them with laser beams has been developed to enable direct measurements of interactions between active nucleation sites. Interactions between two, three and four simultaneously active nucleation sites in various arrangements on 25 μm thick copper and titanium foil in saturated water pool boiling were studied experimentally. The experiments were performed with heated spot diameters ranging from 1.66 to 5.23 mm and heat fluxes up to 560 kW/m 2. The interaction between two laser activated nucleation sites occurs as a net decrease of activity of both sites. It is possible that the activity of both decreases simultaneously, or the activity of one increases, while the activity of the other nucleation site decreases simultaneously. Similar behaviour was also observed in the experiments involving three and four active nucleation sites. In the extreme case, one nucleation site can deactivate the other. Local surface characteristics can play an important role in the interaction between the nucleation sites.

Measurement of Induced Radioactivity in Copper Exposed to High Energy Heavy Ion Beam

The residual radioactivities produced by high energy heavy ions have been measured using the 290MeV/u and 400MeV/u 12C ions and 400MeV/u 20Ne ion beams of the Heavy Ion Medical Accelerator in Chiba (HIMAC) at National Institute of Radiological Sciences. During the irradiation experiment, the beam intensities were measured with a transmission-type ionization chamber. We used the natural copper target of 100mm x 100mm size and 5mm thickness which had total thickness of 3.5cm, 5.5cm and 10cm to stop the projectile heavy ion beams, 290 and 400MeV/u-C ion beams and 400MeV/u-Ne ion beam, respectively. Additional activation foils of copper, aluminum, iron and stainless steel were inserted at every 5mm to 20mm interval in the copper target to measure the spatial distribution of residual nuclei in the copper target. The spatial distribution of residual nuclei was obtained by measuring the gamma-ray activities of 0.5mm thick copper, aluminum, iron and stainless steel foils inserted in the target with a high purity Ge detector after about lhr to 6 hrs irradiation. From the irradiation experiments, we identified the residual nuclei induced in these activation foils and obtained the spatial distributions of 61Cu, 60Cu, 62mCo, 61Co, 56Mn, 49Cr, 44Sc and 38Cl in the copper target.

Pool boiling CHF on a laser heated thin plate

The technique of laser heating a thin metal foil was used to experimentally observe local phenomena in pool boiling CHF on a small flat surface. The experiments were performed with saturated water boiling on 25 μm thick copper and titanium foils with heating surface diameters ranging from 2.27 to 9 mm. The number of simultaneously active nucleation sites depends on the heat flux and the size and material of the laser heated surface. A reduction in the heating surface diameter D H moves the transition between one and several simultaneously active nucleation sites towards higher heat fluxes. CHF for small heating surfaces is lower than that for entirely heated surfaces. The variation of the ratio of bubble/vapour mass diameter to the heating surface diameter, D B/ D H, with D H is similar to the variation of CHF with D H. CHF is significantly influenced by the number of simultaneously active nucleation sites. The influence of heating of the surrounding surface on decreasing D H, which was observed using two laser beams with different diameters was more intense at higher D H on Cu foil than on Ti foil.

Mechanical fatigue of thin copper foil

The electrodeposited and the rolled 12 to 35 µm thick copper foils are subjected to the bending/unbending strain-controlled flex fatigue over a wide range of strain amplitudes. The fatigue life is associated with an increase in electrical resistance of the specimen beyond a preassigned threshold. For each foil type, in the rolled or as-deposited as well as in the (recrystallization-like) annealed conditions, the inverse Coffin-Manson (C-M) relationship between strain amplitude (Δe/2) and fatigue life (Nf) is established in the high Δe/2 (low Nf) and the low Δe/2 (high Nf) regimes. The Nf, Δe/2, and C-M slopes (c,b) are utilized to calculate the cyclic strain hardening (n′) and fatigue ductility (Df) parameters. It is shown that for a given foil thickness, an universal relationship exists between Df and the strength (σ) normalized fatigue life (Nf/σ). The propagation of fatigue crack through the foil thickness and across the sample width is related to the unique fine grain structure for each foil type: pancaked grains for the rolled foil and equiaxed grains for the electrodeposited foil. The fatal failure corresponds to convergence of the through-thickness and the across-the-width fatigue cracks. The variations in (i) electrical resistance, (ii) mid-thickness microhardness and grain structure and (iii) dislocation configurations with fatigue are monitored. Except for a small but significant fatigue induced softening (or hardening), no convincing evidence of strain localization (and the associated dislocation configurations generally observed for the bulk samples) has been found.

Specifics of the process of explosive cladding by foils

The specific features of explosive cladding of St. 3-steel plates and shells by copper and aluminum foils of thickness 20 and 50 μm are investigated. It is shown that the cladding is reliable if the foil thickness is comparable with the height of microroughness of a clad surface. The quality of the joint is worsened when the degree of surface finish is improved. The quality of the joint can be improved if the duration of loading is increased. The microroughness of the surface decreases during cladding.

18 μm electrodeposited copper foil for flex fatigue applications

The strain‐based flex fatigue of 18 μm thick copper foil is evaluated over a wide range of strain amplitudes. Seven electrodeposited foils, four commercial grades and three experimental foils, and a commercial grade rolled foil are characterized. The fatigue life versus cyclic strain amplitude curve in the high strain amplitude (low cycle) and low strain amplitude (high cycle) regimes is developed for each foil. On the basis of fatigue life (Nf) and fatigue ductility (Df), the low cycle fatigue performance of eight foils is ranked. Universal correlations of Nf and Df with the uniaxial tensile strength are established. Two electrodeposited foils, experimental foil DF 8 in the high strain amplitude regime and commercial foil DF 9 in the low strain amplitude regime, have been shown to display fatigue performance comparable to that of the commercial rolled GR 8 foil.

Transient liquid phase bonding of a Hf bearing single crystal nickel aluminide to MM247 superalloy

An investigation of transient liquid phase bonding of single crystal NiAl to a conventional polycrystalline nickel base superalloy MM247 is presented here. The NiAl substrate material employed was cast single crystal NiAl (B2 compound, β phase) with 1·5 at.-% hafnium (Hf) as an alloying element. The interlayers employed in the bonds were 50 μm thick pure copper foils. Based on investigations employing transmission electron microscopy and scanning electron microscopy with energy dispersive X-ray spectrometry, the microstructural changes in the joint region and the adjacent substrates were examined as a function of bonding time at a temperature of 1150°C. The results indicated that hafnium as an alloying element in single crystal NiAl had a strong effect on the microstructure of joints. In particular, attention is focused on the formation of Hf bearing phases and the suppression of σ phase precipitation during bonding.

Hydraulic Bulge Test of Electrodeposited Copper Foil

SUMMARYThe 18 pm to 72 μ thick commercial electrodeposited copper foils GR I and GR 3, the experimentalfoil TCAM and the commercial rolled foil GR 8 are tested in bulge and in tension at temperatures up to 300°C. Utilizing the bulge data, pressure and deflection at rupture, the through-thickness fracture stress (σ,) and fracture strain (€) are calculated and compared to the corresponding average tensile values σav and €av. The effects of foil thickness, orifice size and test temperature on σ1 and €1 are characterized. In many instances approximately one-to-one correspondence exists between σ1, €ε and σav; €avthere are, however, significant exceptions due to texture hardening, thermal embrittlement and grain pancaking. The extent of embrittlement is greatest for the GR 1 foil, increasing with the foil thickness: it is virtually- non-existent for the (rolled) GR 8 foil. Thermal annealing overshadows the embrittlement effects for the GR 3 foil. The TCAM foil embrittles modestly but displays poor resistance to thinning at room temperature; however, the resistance improves markedly with increasing test temperature.

Planar integrated magnetic component with transformer and inductor using multilayer printed wiring board

A new planar integrated magnetic component using multilayer printed wiring board (ML-PWB) technology has been developed for use in switching power supplies. This component integrates a transformer and a choke coil. The transformer is located in the outer ring, and the choke coil is in the inner ring. We designed this component to reduce the loss and the height, especially focusing on the relationship of winding resistance to the thickness of copper foil. This integrated magnetic component was utilized in switching power supplies to evaluate the properties. The experimental results show that the component offers better efficiency and lower electromagnetic noise than conventional components.

Changes in the tensile strength and fracture mode with thickness of electrodeposited copper foil

The tensile strength and fracture mode changed with thickness of copper foil obtained from an acid copper sulfate bath under a same electrodeposition condition. The tensile strength decreased with increasing foil thickness due to an increase in average grain size of the foil. The tensile fracture mode changed from fractures normal to tensile axis to inclined fractures with increasing film thickness. The phenomena have been discussed based on a hardness distribution along the thickness and the local necking and fracture strains.

Transient liquid-phase bonding of alumina and metal matrix composite base materials

Transient liquid-phase (TLP) bonding of aluminium-based metal matrix composite (MMC) and Al2O3 ceramic materials has been investigated, particularly the relationship between particle segregation, copper interlayer thickness, holding time and joint shear strength properties. The long completion time and the slow rate of movement of the solid–liquid interface during MMC/Al2O3 bonding markedly increased the likelihood of forming a particle-segregated layer at the dissimilar joint interface. Preferential failure occurred through the particle-segregated layer in dissimilar joints produced using 20 and 30 μm thick copper foils and long holding times (≥20 min). When the particle-segregated layer was very thin (<10 μm), joint failure was determined by the residual stress distribution in the Al2O3/MMC joints, not by preferential fracture through the particle-segregated layer located at the bondline. Satisfactory shear strength properties were obtained when a thin (5 μm thick) copper foil was used during TLP bonding at 853 K.

Counteraction of particulate segregation during transient liquid-phase bonding of aluminium-based MMC material

Particle segregation during transient liquid-phase bonding of aluminium-based metal matrix composite material using copper filler metal was investigated. Segregation was promoted by the slow movement of the solid-liquid interface during isothermal solidification and alumina particles with diameters less than 30 Μm were segregated when the copper foil thickness exceeded 5 and 15 Μm for the base metals examined. When bonding at 853 K, the liquid widths produced using these copper foil thiciknesses were almost identical to the median inter-particle spacing in the base metals investigated. When the amount of liquid formed at the bonding temperature decreased below a critical level, the test specimens broke apart immediately following the joining operation. The minimum film thickness of copper for satisfactory joint strength increased from 0.6 Μm to 2.4 Μm, when the heating rate to the bonding temperature decreased from 1 Ks−1 to 0.01 Ks−1.

Anisotropic Chemical Etching of Copper Foil: I . Electrochemical Studies in Acidic Solutions

Etching of thick copper foil masked except for a single rectangular opening having an aspect ratio (width:depth) of 5:1 or 1:1 was investigated in the presence of controlled laminar flow across the width of the pattern opening. In a solution of, copper was found to form a surface film spontaneously at the “corrosion potential,” to dissolve at a rate that depended upon convective mass‐transfer conditions, and also to exhibit anisotropic wet chemical etching. Based on thermodynamic calculations, it was estimated that the dominant cupric species were Cu+2, , , and , and that the dominant cuprous species was . Based on rotating disk measurements it was concluded that anisotropic chemical etching was related to the presence of a sparingly soluble surface film of . Under operating conditions for which anisotropic etching was observed, current transients were found to exhibit a characteristic “overshoot” response that may represent a useful diagnostic signal for process control.

Particulates in laser-deposited copper oxide films

We have studied the particulates formed on single-phase copper oxide thin films obtained by laser deposition in a variable oxygen atmosphere. Two different targets have been used: a thick copper foil and a sintered copper powder. We conclude that there are two very different kinds of particulates. The first have very irregular morphology and very similar average size. They are due to solid debris coming from the surface target. The second kind of particulate observed has a round perimeter and is formed in the liquid phase. The morphology of the latter round particulates, which varies considerably, is dependent on the substrate and the oxygen content. Thus, we have been able to determine the conditions for growing particulate-free single-phase copper oxides.

Double-label image analysis using storage phosphor technology

We describe a method for quantitatively discriminating between two isotopes in a single sample using storage phosphor technology. A double-labeled sample is exposed to a storage phosphor screen first directly and then with a filter between the sample and the screen. The filter is chosen to differentially attenuate the emissions from the two isotopes. We used 0.0014-in.-thick copper foil, which reduces 35 S by 750-fold and 32 P by only 30%. The images resulting from the two exposures can be precisely aligned, thereby allowing accurate spatial comparison of both labels. By using detection efficiencies determined from standards for each isotope, we can calculate the amount of 35 S and 32 P contributing to the total activity of any spot or band. The predominant isotope in any double-labeled sample is always calculated accurately. The amounts of both isotopes in our sample were determined within 20% of known values for isotope ratios ranging over four orders of magnitude. Double-label image analysis is ideally suited to the identification of phosphoproteins on two-dimensional gels. The method should also be valuable in many other applications with other pairs of isotopes as well.

A study on the lifetime of flexible printed circuits under bending based on the conventional works of fatigue.

The mechanical reliability of flexible printed circuits, FPC was studied upon the basis of the conventional works on fatigue of structural materials. The lifetime of FPC, Nf was related to the maximum strain of copper Δεcu as the straight relation of Δεcu∝Nf-0.36 in the log-log diagram. It was found by experiment that the lifetime of FPC could be varied by controlling the tensile properties of adhesives and the thickness of copper foil, Kapton of the base material and adhesives. The lifetime, Nf could be improved by thinning the copper foil and adhesive and inversely by thickening Kapton of the base material. Also, there was an optimum rigidity-coefficient of the adhesive for the lifetime, Nf of FPC. During the lifetime of FPC, the fatigue process observed on copper foil could be divided into three stages as follows : the crack intiation, the crack density increase, the crack opening. The NG life of FPC, that is the electric resistance rising up to 10 % of the original value, was corresponded to stage of, the crack initation.