Printed Circuit Board Fabrication Research Articles

A Build-Your-Own Three Axis CNC PCB Milling Machine

The need for fabricating a prototype circuit arises frequently in electronics, including education and research laboratories. In resource-poor countries in the developing world, this is hindered by the high cost of commercial Printed Circuit Board (PCB) prototyping machines and long turn-around commercial fabrication process. Practical, hands-on laboratory teaching and experimentation is necessary to improve learning in electronics. In this paper, a low-cost build-your-own (BYO) semi-automated three-axis PCB milling machine for double-sided PCB prototyping is developed using commercial components and open source hardware and free open source software, to provide students, teachers, and engineers an accessible and affordable resource for PCB prototyping. Also, the main problems encountered during fabrication of PCB have been mentioned and the techniques used to solve them are discussed in detail.

Interconnects on elastomers: optimizing for stretchability, speed and layout area

The design of interconnects on elastomers is of interest in flexible electronics. The geometric design of interconnects must take into account the electrical and mechanical aspects, along with layout area. This work discusses the impact of the geometry of stretchable interconnects on various user specifications, namely layout area, stretchability given by mechanical stiffness coefficient and speed given by electrical impedance. Analytical models have been derived and an optimization methodology is developed to help pick the best design for the given application. The analytical models are corroborated with simulations and experiments. Interconnect designs have been fabricated on a copper-viscoelastic adhesive-elastomer stack architecture, using laser toner-transfer process where the viscoelastic adhesive prevents delamination and in which the process flow is in line with conventional printed circuit board fabrication techniques.

Design and Performance of a High- $Q$ Narrow Bandwidth Bandpass Filter in Empty Substrate Integrated Coaxial Line at $K_{u}$ -Band

This letter presents the design and performance of a planar narrow bandwidth bandpass filter with high quality factor. The structure is composed of an empty substrate integrated coaxial line with the center conductor suspended in air. The component dimensions have been calculated by means of classical microwave filter design theory. The filter has been manufactured using standard printed circuit board fabrication processes. A measured insertion loss of 1.59 dB, 2.93% fractional bandwidth, and a $Q$ -factor of 1505 have been obtained at 15 GHz. A $Q$ -factor comparison with other substrate and empty substrate integrated technologies shows the advantages of the solution considered in this letter. The proposed filter proves to be suitable for the implementation of integrated microwave or millimeter-wave subsystems with severe restrictions, i.e., low in-band losses, very narrow bandpass responses, low frequency dispersion, high out-of-band rejection, and low manufacturing cost.

A Stretchable Multimodal Sensor for Soft Robotic Applications

This paper presents the design, fabrication, and characterization of a multimodal sensor with integrated stretchable meandered interconnects for uniaxial strain, pressure, and uniaxial shear stress measurements. It is designed based on a capacitive sensing principle for embedded deformable sensing applications. A photolithographic process is used along with laser machining and sheet metal forming technique to pattern sensor elements together with stretchable grid-based interconnects on a thin sheet of copper polyimide laminate as a base material in a single process. The structure is embedded in a soft stretchable Ecoflex and PDMS silicon rubber encapsulation. The strain, pressure, and shear stress sensors are characterized up to 9%, 25 kPa, and ±11 kPa of maximum loading, respectively. The strain sensor exhibits an almost linear response to stretching with an average sensitivity of -28.9 fF% <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> . The pressure sensor, however, shows a nonlinear and significant hysteresis characteristic due to nonlinear and viscoelastic property of the silicon rubber encapsulation. An average best-fit straight line sensitivity of 30.9 fFkPa <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> was recorded. The sensitivity of shear stress sensor is found to be 8.1 fFkPa <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> . The three sensing elements also demonstrate a good cross-sensitivity performance of 3.1% on average. This paper proves that a common flexible printed circuit board (PCB) base material could be transformed into stretchable circuits with integrated multimodal sensor using established PCB fabrication technique, laser machining, and sheet metal forming method.

3D Metamorphic Stretchable Microphone Arrays

AbstractThis article describes the realization of a metamorphic microphone array. The array morphs from a concave to a planar and then to a convex shape. The morphing array enables a better (12×) sound source localization when compared to existing static and planar arrangements. To enable the realization, a novel stretchable (elongated up to 320% of the original length) printed circuit board fabrication process is reported. The fabrication process enables high‐temperature processing, alignment, and registration. Moreover, conventional and otherwise rigid surface mount devices (SMDs) can be used. The process allows the researcher to increase the number of devices (30 SMDs) and interconnects (60 in total) to the required level. As electrical connections, a polyimide‐cladded metal track design is reported; the design sustained 11 050 stretch and release cycles. Moreover, 3D reinforcement frames are reported as an effective measure to shield the SMD components from high levels of stress. The resulting products are millimeter‐thin stretchable rubber‐embedded and electrically interconnected electronic structures with mechanical rubber‐membrane‐like properties. Morphology changes involve deflation and inflation of the membrane to bulge inward or outward. Finally, the use of 3D‐shaped chaperon is discussed to provide additional shape control.

PCB Fault Detection Using Image Processing

The importance of the Printed Circuit Board inspection process has been magnified by requirements of the modern manufacturing environment where delivery of 100% defect free PCBs is the expectation. To meet such expectations, identifying various defects and their types becomes the first step. In this PCB inspection system the inspection algorithm mainly focuses on the defect detection using the natural images. Many practical issues like tilt of the images, bad light conditions, height at which images are taken etc. are to be considered to ensure good quality of the image which can then be used for defect detection. Printed circuit board (PCB) fabrication is a multidisciplinary process, and etching is the most critical part in the PCB manufacturing process. The main objective of Etching process is to remove the exposed unwanted copper other than the required circuit pattern. In order to minimize scrap caused by the wrongly etched PCB panel, inspection has to be done in early stage. However, all of the inspections are done after the etching process where any defective PCB found is no longer useful and is simply thrown away. Since etching process costs 0% of the entire PCB fabrication, it is uneconomical to simply discard the defective PCBs. In this paper a method to identify the defects in natural PCB images and associated practical issues are addressed using Software tools and some of the major types of single layer PCB defects are Pattern Cut, Pin hole, Pattern Short, Nick etc., Therefore the defects should be identified before the etching process so that the PCB would be reprocessed. In the present approach expected to improve the efficiency of the system in detecting the defects even in low quality images

Ultra‐wideband phased array for small satellite communications

There is a continuing need for reducing size and weight of satellite systems, particularly in light of recent efforts to increase the functional role of small- and nano-satellites (for instance SmallSats and CubeSats). To this end, a family of arrays is presented, demonstrating ultra-wideband operation across the numerous satellite communications frequencies up to the Ku-, Ka-, and millimetre-wave bands. The first design is demonstrated to operate from 3.5–18.5 GHz with VSWR < 2 at broadside, and validated through fabrication of an 8 × 8 prototype. Additional designs operating from 7–37 and 9–49 GHz, both with VSWR < 2.1 at broadside, are verified via simulations only. These designs are optimised for low cost, using printed circuit board fabrication and appropriate materials selection for space application. E- and H-plane scanning patterns are provided. Finally, multi-physics simulations of the array in high-power transmit are conducted. Temperature trends and distribution are given, with the array showing favourable distribution of thermal energy at up to 2 W of RF input power per element, and a peak temperature only 40°C above ambient.

Scalable 2.45 GHz electrically small antenna design for metaresonator array

In many planar antenna array designs, impedance transformers are required to interconnect the elements to ensure that their impedances are matched. However, impedance transformers take up space and reduce area utilisation. If each element is electrically small and able to function individually as an electrically small antenna (ESA), they can be combined into an array without using impedance transformers. In this study, a stubbed hexagonal shaped folded dipole ESA of one tenth of the wavelength is proposed and developed. This metamaterial inspired design of loading the folded dipole with split ring resonator overcomes the problem of fabricating ESA of one tenth of the wavelength using typical printed circuit board fabrication technologies for the 2.45 GHz band. To show the potential of using this ESA as a unit element for antenna array without using impedance transformers, a seven-element array is designed and fabricated. By optimising the element separation distance, and stub lengths, the ESA array shows good S 11 of less than −25 dB, and gain improvement of up to 12 dB compared with a single unit ESA.

A Wideband Differentially Fed Dual-Polarized Antenna with Stable Radiation Pattern for Base Stations

A new wideband differentially fed dual-polarized antenna with stable radiation pattern for base stations is proposed and studied. A cross-shaped feeding structure is specially designed to fit the differentially fed scheme and four parasitic loop elements are employed to achieve a wide impedance bandwidth. A stable antenna gain and a stable radiation pattern are realized by using a rectangular cavity-shaped reflector instead of a planar one. A detailed parametric study was performed to optimize the antenna’s performances. After that, a prototype was fabricated and tested. Measured results show that the antenna achieves a wide impedance bandwidth of 52% with differential standing-wave ratio $\approx 8$ dBi) and a stable radiation pattern with 3-dB beamwidth of 65° ±5° were also found over the operating frequencies. Moreover, the proposed antenna can be easily built by using printed circuit board fabrication technique due to its compact and planar structure.

Cost-Effective, Microstrip Antenna Driven Ring Resonator Microwave Biosensor for Biospecific Detection of Glucose

We present a biosensor based on electromagnetic ring resonator for label-free detection of glucose. The sensing mechanism is based on the principle that the resonant frequencies of such structures depend on the structure geometry and the physical properties of the medium they are in, such as electrical permittivity. The sensor in this paper uses a split-ring resonator fabricated on a flame retardant four substrate via simple printed circuit board fabrication techniques. Glucose oxidase enzyme was incorporated in order to provide biospecificity for glucose. Conductive polymer poly(3,4-ethylenedioxythiophene)poly(styrenesulfonate) , also known as PEDOT:PSS, was used for the immobilization of the enzyme on sensor surface. The redshift of the resonant frequency of the sensor in response to DI water, glucose, and NaCl solutions are shown to be in agreement with simulation results and theoretical expectations. In the presence of the enzyme, the sensor loaded with a glucose solution was observed to experience a resonant frequency shift of 17.5 MHz in 15 min, whereas other reagents such as fructose, sucrose, and NaCl did not respond significantly, confirming the biospecificity. The sensor was measured to have a sensitivity of 0.107 MHz/mgml $^{-1}$ .

Design of a 75-140 GHz high-pass printed circuit board dichroic filter.

A new high-performing PCB (Printed Circuit Board) dichroic filter, which can be used for the KSTAR (Korea Superconducting Tokamak Advanced Research) electron cyclotron emission imaging system, is proposed. The current dichroic filter consists of a triangular lattice array of circular holes on the 6-mm thick metal plate, while circular hole spacing limitation caused relatively narrow passband (∼20 GHz). On the other hand, the proposed PCB dichroic filter utilizes the inexpensive commercial PCB fabrication process with a flexible adjustment of circular hole spacing. Therefore, the proposed PCB dichroic filter provides significantly wider passband (∼60 GHz with 0.84 dB insertion loss) with much reduced weight and expense. Also, it is shown that a steep skirt property can be obtained with the thick PCB filter substrate. The design process, fabrication, and measurement results of the new PCB dichroic filter are described.

Testing and Analysis of Boron-Doped Aluminum Nitride Thin-Film-Coated Al as Thermal Substrates in PCB Fabrication for LED Application

Chemical vapor deposition was used to coat boron-doped AlN thin film on Al substrates and used as thermal substrates in the fabrication of printed circuit boards (PCBs). Conventional screen printing method was used to deposit dielectric, conductor, and protective coating on thin-film-coated Al substrate for the printed metal PCBs (MPCBs). Commercial light emitting diode (LED) was fixed on MPCB and tested for thermal and optical properties under various driving currents. The observed results are compared with those of commercial metal-core printed circuit board (MCPCB). The measured total thermal resistance ( $R_{\mathrm {th-tot}})$ of the LED was low for MPCB and recorded good difference in $R_{\mathrm {th-tot}}$ ( $\Delta R_{\mathrm {th-tot}}= 7.55$ K/W) when compared with MCPCB. An impressive difference on rise in junction temperature ( $T_{\mathrm {J}})$ was noticed ( $\Delta T_{\mathrm {J}}= 13.72$ ) with MPCB at 700 mA as compared with MCPCB. As a result of reduced $T_{J}$ , an improved light output was recorded for MPCB in all driving currents and a higher value also with MPCB. Hence, B-AlN thin-film-coated Al substrate could be used as thermal substrates in PCB fabrication for efficient electronic packaging in LED industries.

A Comparison of Immersion Gold and Tin Surface Finishes on Sensing Electrodes for PCB Environmental Saltwater Concentration Sensors

Abstract Printed circuit board (PCB) sensors using low-cost commercial printed circuit board fabrication processes have been demonstrated for environmental sensing applications. One configuration of these sensors uses exposed electrodes to measure saltwater concentration in freshwater/seawater mixtures, through monitoring the resistance between the electrodes when they are immersed in the saltwater/freshwater solution. The lowest cost commercial PCB processes use an immersion Sn HASL surface finish on exposed copper cladding, including the sensing electrodes. This commercial PCB process has been demonstrated to make an effective, low-cost, short-lifetime sensor for saltwater concentration testing. The Sn finish, however, may not be optimal for this application. Sn oxidizes, which can interfere with sensor performance. Additionally, Sn and Sn oxides are potentially reactive with chemical constituents in seawater and seawater/freshwater solutions. An immersion Au (ENIG) surface finish is certainly less reactive with the atmosphere and chemicals likely present in the testing environment. However, an immersion Au finish increases the cost of the sensors by 30% to 40%. To investigate if the possible benefits of the more expensive Au surface finish are worth the extra expense, a study was performed where identical PCB sensors were procured from a commercial vendor with their standard low-cost Sn HASL finish and with their standard ENIG surface finish. Both sets of sensors were then evaluated in concentrations of seawater and freshwater, from 0% to 100% seawater concentration, using freshwater samples from a natural freshwater source near the coast where the seawater was obtained. Testing demonstrated an insignificant difference in sensor performance between the Sn HASL and the ENIG coated sensing electrodes. The results of this investigation indicated that for applications where the sensors will not be used for long periods of time, the added expense of an immersion Au surface finish is not worth the added cost.

Arbitrary Power-Conserving Field Transformations With Passive Lossless Omega-Type Bianisotropic Metasurfaces

We present a general theory for designing realistic omega-type bianisotropic metasurfaces (O-BMSs), unlocking their full potential for molding electromagnetic fields. These metasurfaces, characterized by electric surface impedance, magnetic surface admittance, and magnetoelectric coupling coefficient, were previously considered for wavefront manipulation. However, previous reports mainly considered plane-wave excitations, and implementations included cumbersome metallic features. In this work, we prove that any field transformation which locally conserves real power can be implemented via passive and lossless meta-atoms characterized by closed-form expressions; this allows rigorous incorporation of arbitrary source and scattering configurations. Subsequently, we show that O-BMS meta-atoms can be implemented using an asymmetric stack of three impedance sheets, an appealing structure for printed circuit board fabrication. Our formulation reveals that, as opposed to Huygens' metasurfaces (HMSs), which exhibit negligible magnetoelectric coupling, O-BMSs are not limited to controlling the phase of transmitted fields, but can rather achieve high level of control over the amplitude and phase of reflected fields. This is demonstrated by designing O-BMSs for reflectionless wide-angle refraction, independent surface-wave guiding, and a highly-directive low-profile antenna, verified with full-wave simulations. This straightforward methodology facilitates development of O-BMS-based devices for controlling the near and far fields of arbitrary sources in complex scattering configurations.

A Study on the Deposit Uniformity and Profile of Cu Electroplated in Miniaturized, Laboratory-Scale Through Mask Plating Cell for Printed Circuit Board (PCBs) Fabrication

A miniaturized lab-scale Cu plating cell for the metallization of electronic devices was fabricated and its deposit uniformity and profile were investigated. The plating cell was composed of a polypropylene bath, an electrolyte ejection nozzle which is connected to a circulation pump. In deposit uniformity evaluation, thicker deposit was found on the bottom and sides of substrate, indicating the spatial variation of deposit thickness was governed by the tertiary current distribution which is related to <TEX>$Cu^{2+}$</TEX> transport. The surface morphology of Cu deposit inside photo-resist pattern was controlled by organic additives in the electrolyte as it led to the flatter top surface compared to convex surface which was observed in the deposit grown without organic additives.

Direct-writing lithography using laser diode beam focused with single elliptical microlens

A lithography method is proposed for arbitrary patterning using an elliptically diverging laser diode beam focused with a single planoconvex elliptical microlens. Simulations are performed to model the propagation properties of the laser beam and to design the elliptical microlens, which has two different profiles in the x- and y-axis directions. The microlens is fabricated using an excimer laser dragging method and is then attached to the laser diode using double-sided optically cleared adhesive (OCA) tape. Notably, the use of OCA tape removes the need for a complicated alignment procedure and thus significantly reduces the assembly cost. The minimum focused spot of the laser diode beam is investigated by performing single-shot exposure tests on a photoresist (PR) layer. Finally, the practical feasibility of this lithography technique to generate an arbitrary pattern is demonstrated by dotted and continuous features through thin chromium layer deposition on PR and a metal lift-off process. The results show that the minimum feature size for the dotted patterns is around 6.23 μm, while the minimum linewidths for continuous patterns is 6.44 μm. In other words, the proposed focusing technique has significant potential for writing any arbitrary high-resolution pattern for applications like printed circuit board fabrication.

Analysis and Design of Three-Layer Perfect Metamaterial-Inspired Absorber Based on Double Split-Serration-Rings Structure

We systematically analyzed, designed, fabricated, and measured a three-layer perfect metamaterial-inspired absorber based on the double split-serration-rings (DSSRs) structure in this communication. The equivalent circuit model was presented to demonstrate the absorbing mechanism. The characters of polarized-insensitivity, wideband, and multiband absorption for the absorber were illuminated by the angular absorptions and surface current distributions. Transformation from wideband absorption with a relative bandwidth of 93.5% from 5.34 to 14.72 GHz, of which the absorptivity was larger than 90%, to multiband absorption was obtained by rotating DSSR-II of 90°. Two absorber prototypes with a thickness of 3.6 mm had been easily implemented using the common printed circuit board fabrication techniques and measured in a microwave anechoic chamber. Simulated and experimental results indicated that the perfect metamaterial-inspired absorber performed wideband and multiband absorption when DSSRs were perpendicular and parallel to each other, respectively.

A Simple, Low-Cost Platform for Real-Time Isothermal Nucleic Acid Amplification.

Advances in microfluidics and the introduction of isothermal nucleic acid amplification assays have resulted in a range of solutions for nucleic acid amplification tests suited for point of care and field use. However, miniaturisation of instrumentation for such assays has not seen such rapid advances and fluorescence based assays still depend on complex, bulky and expensive optics such as fluorescence microscopes, photomultiplier tubes and sensitive lens assemblies. In this work we demonstrate a robust, low cost platform for isothermal nucleic acid amplification on a microfluidic device. Using easily obtainable materials and commercial off-the-shelf components, we show real time fluorescence detection using a low cost photodiode and operational amplifier without need for lenses. Temperature regulation on the device is achieved using a heater fabricated with standard printed circuit board fabrication methods. These facile construction methods allow fabrications at a cost compatible with widespread deployment to resource poor settings.

DEVELOPMENT OF A POWER MANAGEMENT CIRCUIT FOR MICROENERGY HARVESTERS

This work reports on the development a power management circuit (PMC) for micro energy harvesters. The circuit is design to regulate the power between three different power sources for the operation of a wireless sensor nodes (WSNs). The main components of the circuit are resistors (carbon film), capacitors (electrolytic), inductors (ferric bead, axial leaded), and a DC voltage regulators (TPS62100DRC-BRR). The layout of the circuit is patterned on a printed circuit board (PCB) using PCB fabrication technology. To the circuit three different types of sources (DC power source, rectified AC voltage and a solar energy harvester) are connected and the output regulated voltage provided by the PMC is measured and analyzed. At different input voltage levels (0.5 to 5.5 V) the circuit successfully regulated to almost a uniform output voltage (2.75 to 2.96 V). With the circuit using a DC power source and a solar (solar cell) energy harvester a super capacitor is charged to a voltage of 2.75 and 2.05 V in 180 s and 840 s respectively. Beyond 100 Ω load resistance the PMC regulated a constant output current of 180 mA. Moreover, beyond 100 Ω load resistance the power consumption of the circuit is almost steady for different input voltage levels. The average consumption of the developed PMC is about 70 mW.

Hybrid metamaterial device with wideband absorption and multiband transmission based on spoof surface plasmon polaritons and perfect absorber

We reported on the design, realization, and numerical characterization of a hybrid metamaterial (HM) with the absorption and transmission at different frequencies based on the spoof surface plasmon polaritons and perfect absorber. A unit cell is composed of a three-layer metamaterial with double orthogonal split ring resonators and a ground plate loaded with two-sided metallic grooves. It is shown that the hybrid metamaterial primarily exhibits a broadband polarization-sensitive absorption from 6.57 to 28.16 GHz with a full-width at half-maximum in one direction and a multiband transmission in the opposite one. When the incidence is parallel to HM, the ground plate loaded with two-sided metallic grooves can support a structural vibration of spoof surface plasmon polaritons. To demonstrate design, a HM device easily implemented using common printed circuit board fabrication method is fabricated and measured and the experimental results agree well with the simulated results.