Copper Tracks Research Articles

Photothermocapillary detection of conductive track ruptures on a printed circuit board coated with a protective film

The photothermocapillary (PTC) method has been proposed to detect ruptures of the copper tracks of a printed circuit board coated with a black protective film absorbing the pump laser radiation. The ruptures were simulated by obtaining parallel tracks of different lengths by etching in ferric chloride solution. The method consisted of the scanning with the pump laser of the tracks along a line perpendicular to them and passing through their midpoints, and plotting a scan-profile of the diameter of PTC signal as a function of the scan coordinate. The scan-profile was a sequence of maxima and minima the diameters of the PTC signal corresponded to the beam position in the middle between adjacent tracks and in the midpoint of the track, respectively. It was found that with an increase in the track length above a critical value, dependent on the laser beam power, the diameter of PTC signal reaches saturation. With increasing power by 1.85 times, the sensitivity of the PTC method increases by 2.57 times. The spatial resolution of the PTC method reaches tens of micrometers. Experimental results have shown that the proposed PTC method is simple and efficient for detecting of hidden defects of the copper tracks on the PCB.

Electrochemical characterization of plasma coatings on printed circuit boards

Printed Circuit Boards (PCB) are the backbone of electronic devices and communication technology. The corrosion of copper tracks in PCBs is the main reliability issue in case of exposure to humidity. To overcome this, several surface finishing methods have been introduced in the industry such as plasma coatings. In this study, several electrochemical characterisation methods are explored on blank and plasma-coated PCBs to identify reliable measurement techniques and to get insight in the protective properties of the coatings on an overall macroscopic visual scale, a dedicated surface-average scale, as well as on a localised microscopic scale. The macroscopic visual corrosion behaviour was evaluated by standard salt-spray exposure tests. Odd Random Phase multisine Electrochemical Impedance Spectroscopy (ORP-EIS) provided insight into the average barrier properties of the coatings. Scanning Vibrating Electrode Technique (SVET) and Scanning Kelvin Probe Force Microscopy (SKPFM) were used to evaluate the samples’ reactivity on a local scale. Scanning Electron Microscopy-Energy Dispersive X-ray (SEM-EDX) analysis was used as a complementary surface analysis method to characterise the coatings. Blank PCBs were studied as reference substrates, and their behaviour was compared to three plasma-coated PCB variants, based on fluorinated organic precursor chemistry. The salt-spray tests illustrated the protective behaviour of the coatings but did not allow to differentiate between the different coatings. With ORP-EIS, it was observed that the coatings act as a barrier against the electrolyte. This is confirmed on the local scale, where no activities were seen on the surface of the coated samples using SVET, except after 10 days of immersion when single layer plasma coatings showed higher activities. SKPFM revealed much higher surface potentials for the coated PCBs compared to the blank PCB allowing to differentiate between the various coated samples.

Scalability of Copper-Interconnects down to 3μm on Printed Boards by Laser-assisted-subtractive process

Abstract As per the latest roadmap of iNEMI, the global electronics market is emphasizing to identify disruptive technologies that can contribute towards denser, robust and tighter integration on the board level. Therefore, reduction in packaging factor of printed board can accommodate greater number of ICs to support miniaturization. This paper has shown an experimental method to pattern the metallic layer on a Printed circuit Board (PCB) to the smallest feature size. To investigate this, a commercially available FR-4 PCB with photosensitive material coat and a Copper (Cu) layer on it, is used. A reverse-mode Laser assisted writing is implemented to pattern the desired copper tracks. Soon after, a well-controlled development and chemical etching of the Laser-activated regions are done using Sodium Hydroxide solution followed by an aqueous solution of Sodium Persulfate. Current PCB interconnects used by the industries are of the order (~20 μm). Whereas the present work is a contribution towards achieving Copper interconnects with feature size 3.0μm. This miniaturization corresponds to 70% reduction in the feature size from 20 μm to 3 μm. The natural adhesion of the Cu layer has remained intact even after the etching, shows the efficiency of the method adopted. Also, variation in the parameters such as etching time, etchant solution concentrations, temaperature, gain and exposure time of Laser beam and their corresponding effects are discussed. Other highlights of this subtractive method includes its cost-efficiency, lesser production time and repeatability.

An investigation of the influence of thermal process on the electrical conductivity of LIFT printed Cu structures

The electrical properties of copper tracks printed by laser-induced-forward-transfer (LIFT) are typically inferior to the bulk values. Several limiting factors have been indicated such as oxidation, droplet boundaries and grain boundaries. However, the relative contribution of each of these factors has not been determined. To improve the electrical properties of LIFT printed structures, an analysis of various factors is essential. Here, we concentrate on the effect of post-printing thermal treatment on LIFT printed copper structures. A reduction in electrical resistivity by a factor of ~3 is obtained resulting in a value lower than 3 times the bulk copper value (1.68 µΩ · cm). Real time resistance measurements indicate that an efficient thermal annealing can be achieved at 200 °C–300 °C within a couple of minutes. The morphological changes associated with such thermal treatment were analyzed using HR-SEM and XRD and highlight the role of stress relief, grain growth and formation of new grains primarily at the inter-droplet interfaces.

Chemical Imaging of Buried Interfaces in Organic–Inorganic Devices Using Focused Ion Beam-Time-of-Flight-Secondary-Ion Mass Spectrometry

Organic-inorganic hybrid materials enable the design and fabrication of new materials with enhanced properties. The interface between the organic and inorganic materials is often critical to the device's performance; therefore, chemical characterization is of significant interest. Because the interfaces are often buried, milling by focused ion beams (FIBs) to expose the interface is becoming increasingly popular. Chemical imaging can subsequently be obtained using secondary-ion mass spectrometry (SIMS). However, the FIB milling process damages the organic material. In this study, we make an organic-inorganic test structure to develop a detailed understanding of the processes involved in FIB milling and SIMS imaging. We provide an analysis methodology that involves a "clean-up" process using sputtering with an argon gas cluster ion source to remove the FIB-induced damage. The methodology is evaluated for two additive manufactured devices, an encapsulated strain sensor containing silver tracks embedded in a polymeric material and a copper track on a flexible polymeric substrate created using a novel nanoparticle sintering technique.

Heat transfer in the flow with forced pulsations in a rib-roughened channel

Heat transfer in pulsating air flow in a rib-roughened channel has been studied experimentally. Heat transfer was estimated using the technique of simultaneous wall heating and wall temperature measurement by the same copper tracks. Distributions of heat transfer coefficient over the channel wall in steady and pulsating regimes of flow have been obtained. 30% augmentation of heat transfer compared with the steady flow values has been revealed in pulsating flow. The frequency range of (0–100) Hz and the relative amplitude of forced velocity pulsations of 0.3 have been studied.

Heat transfer in pulsating flow behind a rib in the channel inlet region

Heat transfer in pulsating air flow behind the rib in the channel entrance has been studied experimentally. An experimental facility and the technique to estimate heat transfer with simultaneous wall heating and wall temperature measurement by the same copper tracks have been developed. Distributions of heat transfer coefficient over the heated channel wall in steady and pulsating regimes of flow have been obtained. Enhancement of heat transfer in pulsating flow up to 25% in comparison with a steady flow has been revealed. The studies have been carried out within the frequency range of 0-15 Hz and the relative amplitudes of forced velocity pulsations of 0.8.

Industrial technology for mass production of SnO2 nanoparticles and PbO2 microcube/microcross structures from electronic waste

Waste Printed Circuit Boards (WPCBs) are one of the major recycling challenges in this century with Through-Hole Solder Joint (THSJ) components representing more than 40 wt% of their metallic fraction. THSJs are composed mainly of three metals - Cu, Sn, and Pb; in addition, THSJs can contain a very small amount of Pd and other additives such as Ni, Fe, Al, etc. Recently, dissolution treatment has successfully been used to liberate THSJs as received as well as copper foils, contacts, and tracks. In order to close the lifecycle loop of WPCB metallic fraction, this research has an aim to recover Sn and Pb from the liberated THSJs in the form of SnO2 nanoparticles and PbO2 micro cross/cubic structures as high added-value products using sustainable leaching technique. Nitric Acid was employed to prepare leaching solution, whereas ultrasound treatment was used to precipitate SnO2 and PbO2 precursor from the solution. With time, particles of other metals (Pd, Ni, Fe, Al, etc.) started to precipitate, acting as catalysts (or doping agents) and increasing the precipitation of SnO2 and PbO2. Under the effect of sound waves, temperature, and catalysts, SnO2 and PbO2 precursors transformed into nanoparticles and micro cross/cubic structures; formation and refining degree of these structures was controlled by changing the treatment time. Micro-filtration process was used to separate SnO2 nanoparticles from PbO2 microstructures. Also, copper was recovered from the remaining acidic solution as a Cu(OH)2 by neutralization with NaOH at pH 8. SEM-EDS, TEM, FTIR, XRD, and ICP were used to examine the extracted THSJs, produced nano/micro products and recovered metals. The results showed that the SnO2 and PbO2 had average sizes of 7 nm and 1 μm respectively, while the preparation costs were 6 times lower in comparison to the commercial counterparts. Finally, the authors suggested a layout for applying the developed approach on an industrial scale while referring to the concepts of Circular Economy and Sustainable Development.

Evaluation of anisotropic tangential conduction in printed-circuit-board heated-thin-foil heat flux sensors

The effect of the tangential conduction contribution in a thermally anisotropic heated-thin-foil heat flux sensor is examined. A parameter to assess the degree of importance of tangential conduction in the sensor is defined and evaluated in order to justify the need of tangential conduction corrections. Printed circuit boards (PCBs) are typical examples of sensors with anisotropic thermal conduction properties, due to the different conductance values in the directions either parallel or orthogonal to the copper tracks which are placed onto a fiberglass substrate. A parametric study on PCBs with different tracks coverage fraction and copper-to-fiberglass heat conductance ratio is carried out. A revised heated-thin-foil formulation, including a correction for anisotropic thermal properties of the PCB, is experimentally tested. The selected thermo-fluid-dynamic test case is the convective heat transfer of a normally impinging round jet for which axisymmetric maps of the Nusselt number are expected. The anisotropic tangential conduction results in non-axisymmetric temperature distributions. Consequently, if anisotropy is not properly accounted for, non-axisymmetric Nusselt number maps are obtained. The anisotropic conduction effects are shown to be weakly sensitive to the copper tracks coverage fraction while strongly dependent on a parameter called degree of anisotropy, which accounts for the copper-to-fiberglass heat-conductance ratio. Anisotropic conduction effects are found to be almost negligible in PCBs with low values of the degree of anisotropy and/or low values of the tangential conduction degree of importance. Accounting for the anisotropic tangential conduction in the heated-thin-foil formulation allows minimizing the differences between the Nusselt number profiles measured in the directions parallel and orthogonal to the copper tracks. For all the considered PCBs, differences after correction are found to be below the measurement uncertainty expected for an equivalent thermally-isotropic sensor. The proposed approach also allows reducing below the measurement uncertainty the spread between the Nusselt number values measured with all the considered printed circuit boards, providing measurements practically independent of the sensor characteristics.

PCB Embedded Bondwire Inductors With Discrete Thin-Film Magnetic Core for Power Supply in Package

This paper details the design, assembly, and detailed characterization of printed circuit board (PCB) embedded thin magnetic film inductors for Power Supply in Package applications. Solenoidal inductors were assembled on copper tracks printed on PCB with wire bonds to complete the copper loop. Furthermore, the solenoid inductors have laminated amorphous soft magnetic thin films embedded between the two conductor layers. The devices have chemically thinned Vitrovac films laminated as core material. Three different designs of solenoid inductors with different numbers of turns are assembled and characterized. The assembled PCB inductor measured a highest quality factor of 8.5 for a three-turn device at 10 MHz.

Organic Hybrids for Circuit Assemblies – Initial environmental testing of a low cost alternative to ceramic substrate based assemblies

Abstract There are an increasing number of electronics applications in aerospace, automotive, shale/gas and power management, which are required to operate at or above 200 °C. Organic matrix reinforced substrates such as polyimide, have maximum operating temperatures in the region of 175 °C. Reliable operation of electronics at temperatures higher than this requires a combination of performance improvements in components, interconnects and substrates. Ceramic based substrate options are based on alumina substrates with printed inks fired at ~ 600 °C and can be costly, heavy and prone to mechanical damage. Printed circuit board (PCB) options are restricted to lower working temperatures of the organic resins and degradation of their conductive copper tracks through oxidation. This paper highlights earlier work undertaken by the authors and partners to understand the deficiencies of copper-clad PCB technology and details work to develop a low cost alternative to ceramic substrate based assemblies. The authors have investigated replacing the alumina substrates with high temperature engineering thermoplastics such as PEEK. The high temperature fired inks conventionally used in hybrid circuit manufacture have been replaced with screen-printable silicone based ink systems curing at 250 °C. The specially developed electrically conductive and dielectric inks were utilised to produce a multilayer system demonstrator with high temperature compatible components attached using a high temperature conductive adhesive. Such an assembly system has the potential to benefit from reductions in substrate cost and assembly weight. Energy cost associated with manufacture are significantly reduced. In addition the organic substrate is easier to machine and form into complex shapes and offers the possibility of integrating thermal management solutions. Environmental testing has been undertaken to determine the suitability of the system to operate for extended periods at 250 °C and the results of the electrical and mechanical performance for continuous ageing of test assemblies at 250 °C will be given.

Comparison between Modelled and Measured Magnetic Field Scans of Different Planar Coil Topologies for Stress Sensor Applications.

The investigation of planar coils of differing topologies, when combined with a magnetostrictive amorphous ribbon to form a stress-sensitive self-inductor, is an active research area for applications as stress or pressure sensors. Four topologies of planar coil (Circular, Mesh, Meander, and Square) have been constructed using copper track on 30 mm wide PCB substrate. The coils are energized to draw 0.4 A and the resulting magnetic field distribution is observed with a newly developed three-dimensional magnetic field scanner. The system is based on a variably angled Micromagnetics® STJ-020 tunneling magneto-resistance sensor with a spatial resolution of 5–10 µm and sensitivity to fields of less than 10 A/m. These experimental results are compared with the fields computed by ANSYS Maxwell® finite element modelling of the same topologies. Measured field shape and strength correspond well with the results of modelling, including direct observation of corner and edge effects. Three-dimensional analysis of the field shape produced by the square coil, isolating the components H(x) and H(z), is compared with the three-dimensional field solutions from modelling. The finite element modelling is validated and the accuracy and utility of the new system for three-dimensional scanning of general stray fields is confirmed.

Plasma-Induced Decomposition of Copper Complex Ink for the Formation of Highly Conductive Copper Tracks on Heat-Sensitive Substrates.

The use of Cu-formate-2-amino-2-methyl-1-propanol ink and low-pressure plasma for the formation of highly conductive patterns on heat sensitive plastic substrates was studied. It was found that plasma results in decomposition of copper complex to form metallic copper without heating at high temperatures. Ink composition and plasma parameters (predrying conditions, plasma treatment duration, gas type, and flow rate) were optimized to obtain uniform conductive metallic films. The morphology and electrical characteristics of these films were evaluated. Exposing the printed copper metallo-organic decomposition (MOD) ink to 160 W plasma for 8 min yielded resistivity as low as 7.3 ± 0.2 μΩ cm, which corresponds to 23% bulk copper conductivity. These results demonstrate the applicability of MOD inks and plasma treatment to obtain highly conductive printed patterns on low-cost plastic substrates and 3D printed polymers.

Characterization of waste printed circuit boards recycled using a dissolution approach and ultrasonic treatment at low temperatures

All the WPCB samples had similar structure, which comprises six layers of fiberglass (representing WPCB substrate), two copper foil layers (upper and lower layers), copper tracks, through-hole pads and two soldermask layers (upper and lower layers).

New experimental results on local heat transfer inside a rectangular channel with rib-roughened surfaces

In this paper we present new experimental results on local heat transfer characteristics of a forced air-flow through a 12-mm-height, rectangular channel of 1:10 aspect ratio, with square-cross-section ribs mounted onto the lower surface. Data are collected on a completely redesigned test section. Specifically, the electric heater is made of very thin copper tracks, in direct contact with the air flow and covering at 97.5% the channel lower surface to guarantee a very uniform heat flux. The copper tracks are laminated onto a 2-mm thick board of FR-4 glass epoxy to provide negligible heat conduction inside the plate and heat losses from its sides. Finally, the channel walls are in XPS and, into the upper one, a double glazing consisting of two 120 mm x 120 mm Germanium windows is mounted to allow optical access to the IR camera and to reduce local heat dispersions. Data here presented refer to convection over 4 mm x 2 mm ribs in transverse configuration for Reynolds numbers, based on the duct hydraulic diameter, ranging between 700 and 8000. Preliminary tests show how the new apparatus has significantly improved the quality, the ease and the quickness of the measurements.

Preparation and Characterization of Composites Obtained of Polymeric Waste Coming from Boards Electronic Equipment

The objective of this work is to recycle the printed circuit boards of electronic equipment discarded and mix them with polypropylene (PP) to produce a new composite. Six types of mix of discarded printed circuit boards were analyzed: new boards with and without copper, used boards without components and with and without copper, used boards without components and without copper, used boards with copper track, used boards with copper track and burned and used boards with components. Boards were disintegrated and employed as reinforcement with polypropylene matrix (5% m/m). Specimens were produced for flexural and impact tests. Results showed that specimen’s properties depend on the mix composition. In all of the cases, pure PP properties were enhanced when it was replaced by 5% of waste materials discard.

Material design and process development of electrostatically patterning silver capsuled composite particle for preparing conductive tracks on flexible substrate

Abstract In this work, a silver-capsuled composite particle at micro-size has been facilely developed for electrostatic patterning of copper layers on flexible substrates, with high performance across manufacturing scalability, printing resolution and speed, and production affordability to end users. Herein, we launched a capping method for designing the particle as decorated with PVP capped silver ion as catalytic precursor all in one wet environment, in which the catalytic ion is successfully reduced and uniformly distributed when mixed with the primary particle. In further combination with an air plasma treatment on the surface of a flexible polyimide film, the toner particle can be successfully electrostatically developed and fused onto the substrates with retained lateral printing quality. We disclose a process of passing the patterned substrates through a gentle exposure to a sulfur acid solution for promoting electroless deposition of copper layer. The obtained copper tracks have electrical conductivity of ∼10 − Ω cm with controllable thickness up to about 40 μm, which is feasible for applications in wearable electronics, embedded systems, and implanted biomedical devices.

Arbitrarily Shaped Rigid and Smart Objects Using Stretchable Interconnections

In this paper, we present the developments of a new technology to realize 2.5-/3-D electronic circuits. The starting point is an electronic circuit embedded in a hard thermoplastic material, which is transformed into a 2.5-/3-D shape using a thermoforming process. The electronic circuit consists of stretchable copper interconnections in combination with electronic components. The circuit is produced using conventional printed circuit board process steps: a copper sheet is laminated on a thermoplastic material, such as Polycarbonate (PC) or Polyethylene Terephthalate Glycol (PET-G). The copper is structured using lithography and wet etching, and the electronic components are assembled using conductive adhesives. We investigated the use of different designs for stretchable interconnects to overcome the stretching of the electronic circuit by thermoforming it. A semispherical-shaped mold was used for this purpose where the local strain of the substrate can reach 100% with a sharp bending. It was shown that meander-shaped interconnects could accommodate the gradual deformation during the forming of the substrate either for PC and PET-G. However, at the mold’s edge, the copper-meandered tracks showed a delamination of the copper from the substrate. In the meanwhile, the electrical conductivity of the copper tracks did not show any significant variation. Another meander design based on an elliptical shape (in order to increase the length of the track) is proposed and compared with the first design.

A load-lock compatible system for in situ electrical resistivity measurements during thin film growth.

An experimental setup designed for in situ electrical resistance measurement during thin film growth is described. The custom-built sample holder with a four-point probe arrangement can be loaded into a high-vacuum magnetron sputter-deposition chamber through a load-lock transfer system, allowing measurements on series of samples without venting the main chamber. Electrical contact is ensured with circular copper tracks inserted in a Teflon plate on a mounting holder station inside the deposition chamber. This configuration creates the possibility to measure thickness-dependent electrical resistance changes with sub-monolayer resolution and is compatible with use of sample rotation during growth. Examples are presented for metallic films with high adatom mobility growing in a Volmer-Weber mode (Ag and Pd) as well as for refractory metal (Mo) with low adatom mobility. Evidence for an amorphous-to-crystalline phase transition at a film thickness of 2.6 nm is reported during growth of Mo on an amorphous Si underlayer, supporting previous findings based on in situ wafer curvature measurements.

Mixed-dimensional elements in transient thermal analysis of gradient coils

ABSTRACTThis article proposes a numerical formulation for handling mixed-dimensional elements embedded in a standard three-dimensional (3d) mesh, avoiding thus the volume meshing of filaments and strips. The method is then applied to predict the temperature heating and cooling profile of gradient coils in magnetic resonance imaging. These coils are typically constructed from copper wires or tracks and embedded in an epoxy layer. It was found that the new method significantly reduces the computational time of steady-state and transient simulations, with speedups in the range of 3.5-5. The method proved to be accurate, with relative errors below 0.5% for steady-state simulations and 1.5% with respect to a complete 3d simulation.