Copper Clad FR4 Research Articles

Development and Improvement of a Piezoelectrically Driven Miniature Robot.

In this paper, we proposed a miniature quadrupedal piezoelectric robot with a mass of 1.8 g and a body length of 4.6 cm. The robot adopts a novel spatial parallel mechanism as its transmission. Each leg of the robot has two degrees of freedom (DOFs): swing and lift. The trajectory necessary for walking is achieved by the appropriate phasing of these two DOFs. A new manufacturing method for piezoelectric actuators was developed. During the stacking process, discrete patterned PZT pieces are used to avoid dielectric failure caused by laser cutting. Copper-clad FR-4 is used as the solder pad instead of copper foil, making the connection between the pad and the actuator more reliable. The lift powertrain of the robot was modeled and the link length of the powertrain was optimized based on the model. The maximum output force of each leg can reach 26 mN under optimized design parameters, which is 1.38 times the required force for successful walking. The frequency response of the powertrain was measured and fitted to the second-order system, which enabled increased leg amplitudes near the powertrain resonance of approximately 70 Hz with adjusted drive signals. The maximum speed of the robot without load reached 48.66 cm/s (10.58 body lengths per second) and the payload capacity can reach 5.5 g (3.05 times its mass) near the powertrain resonance.

Development of Miniaturized Interdigitated Electrode Sensors and Their Application in Taste Sensing

Interdigitated Electrodes (IDEs) or Interdigitated Arrays (IDAs) are frequently used in a variety of sensing mechanisms including electrochemical detection and have been subjected to extensive miniaturization in recent times. Multiple methods involving the fabrication of IDEs have been reported. However, these fabrication methods are often time consuming, multistep, skill intensive, expensive and require clean room conditions. This work reports on the fabrication and comparison of miniaturized IDEs fabricated using two inexpensive and clean room free approaches - inkjet-printing and direct laser writing (DLW) based photolithography. For inkjet-printing approach, a commercially available printed-circuit board (PCB) printer was used with a carbon ink to print the IDEs on a glass slide. For photolithography-based fabrication, a DLW system was used for the fabrication of IDEs on a copper-clad FR4 PCB board. Previously established, validated and reported models were employed for the design of IDEs. The design parameters were selected to optimize sensitivity while striking a balance with the overall size of the sensor. The application of the developed IDE sensors was demonstrated for its taste sensing capability. Sensing of five fundamental tastes, namely salty, sweet, sour, bitter, and umami, was established with electrochemical impedance spectroscopy (EIS). The chemicals which can simulate these fundamental tastes for experimental purposes were identified as sucrose (sweet), sodium chloride (salty), citric acid (sour), L-tryptophan (bitter) and guanosine monophosphate (GMP) (umami). EIS was performed on a benchtop electrochemical workstation with two electrode configurations and data was analysed in the frequency range of 1 Hz to 1 MHz. The obtained data was analyzed for different chemicals at varying concentrations and compared for changes in the response. DLW photolithography-based approach produces IDEs with excellent geometric dimensional repeatability. The IDEs produced on glass slides using Carbon ink-based printing were fabricated in under 2 minutes and cost less than US$ 0.3. Both approaches demonstrate the applications of IDEs with fairly reasonable and benchmarked taste sensing capabilities.Figure: a) Optimised Design b) Carbon ink-based printing c) IDE printed on glass slide d) Photlithography based DLW IDE fabrication e) IDE on a copper cladded FR4 PCR board. Figure 1

Modeling and development of radio frequency planar interdigital electrode sensors

The interdigital sensor has been implemented in various field of applications such as microwave device, chemical sensor and biological sensor. This work describes the design and fabrication of an interdigital sensor (IDS) design that has the potential of estimating blood glucose levels using capacitive measurements. The IDS was first designed using theoretical equations and later was optimized by using CST Microwave Studio®. The electrode widths of the sensor were varied from 0.5mm to 0.7mm and the S11 reflection characteristics were simulated.Upon completion of simulations, the sensor was fabricated using copper clad FR4 boards. The fabricated sensors were measured using a vector network analyzer (VNA) and produced resonance frequencies of 2.02, 2.11 and 2.14 GHz. The highest Q obtained was 11.72 from the 2.11 GHz sensor.

Solvent presence and its impact on the lap-shear strength of SDS-decorated graphene hybrid electrically conductive adhesives

The mechanical bonding strength of electrically conductive adhesives (ECAs), as well as the impact of residual solvent on the bonding strength was investigated between a copper clad FR-4 surface and conductive adhesives using Lap-shear testing. Both solvent-free and solvent-assisted formulations with various filler concentrations of silver (Ag) and sodium dodecyl sulfate (SDS)-decorated graphene (Gr(s)) in epoxy matrices were prepared and compared. It was found that the introduction of 0.75wt% Gr(s) in solvent-free formulations increased the Lap-shear strength (LSS), while the combination of ethanol solvent and SDS in solvent-assisted formulations significantly decreased the LSS. In addition, it was found that increasing the Ag content generally lowers the LSS for both the solvent-free and solvent-assisted formulations. By examining the structure and interface of both formulations using optical microscopy, surface profilometry and SEM, we found that the solvent-assisted formulations exhibit more voids at the surface of the paste and more bubble formation throughout the material compared to the solvent-free formulations. Therefore, the significant drops of LSS in solvent-assisted Gr(s)-filled formulations may be attributed to the formation of bubbles at the micron range during the curing process.

Industry Compatible Embossing Process for the Fabrication of Waveguide-Embedded Optical Printed Circuit Boards

We demonstrate a cost-effective embossing process for the fabrication of waveguide-embedded optical printed circuit boards (OPCBs). The process involves the application of a polydimethylsiloxane mold for the production of polymer waveguides on a copper-clad FR4 substrate followed by the conventional lamination process. The embossing process is carefully tailored for the commercial polymer materials that are developed specifically to withstand the high temperature and high pressure environment during lamination. With this process, we are able to produce high-quality waveguide-embedded OPCBs with good repeatability. Our typical OPCB samples, each of which consists of 12 130-mm long fully embedded channel waveguides with a core size of approximately 50 × 50 μm and a pitch of 250 μm, show an average optical loss in the range 0.16-0.22 dB/cm at the wavelength 850 nm. The OPCBs survive the reflow process at 245 °C with a small change in the optical loss. The embossing process can be readily integrated with the existing PCB manufacturing process and thus offers a practical solution to mass production of OPCBs.

Polydimethylsiloxane (PDMS) based optical interconnect with copper-clad FR4 substrates

PDMS based optical interconnect has been developed based on a combination of PDMS waveguide fabrication technique and a process for efficient interfacial bonding between PDMS optical layers and standard copper-clad FR4 printed circuit boards (PCB) materials, in order to avoid outgas influences from epoxy based FR4 on waveguide loss of optical interconnect at 850 nm. The optimal bonding conditions between PDMS and copper-clad FR4 have been identified by applying a specifically developed surface adhesion promoter and surface treatment on copper-clad FR4. The optical and mechanical properties of the PDMS waveguide layer remained unchanged by the addition of the SAP and surface treatment on copper-clad FR4 as well as the environmental stability of realized optical interconnect.

Through hole plating of printed circuit boards using ultrasonically dispersed copper nanoparticles

PurposeThe purpose of this paper is to investigate if copper nanoparticles could be utilized for two types of through hole plating in printed circuit boards, namely: as a catalytic material to initiate the electroless copper deposition process; and as a “conductive” layer which is coherent and conductive enough to allow “direct” electroplating of the through hole. The employment of nanoparticles means that an effective method of dispersion is required and this paper studies the use of mechanical agitation and ultrasound for this purpose.Design/methodology/approachThe paper utilized drilled, copper clad FR4 laminate. The through holes were functionalized using a commercially available “conditioner” before being immersed in a solution of copper nanoparticles which were dispersed using either a magnetic stirrer or ultrasound (40 kHz). When the copper nanoparticles were utilized as a catalytic material for electroless copper plating, the efficacy of the technique was assessed using a standard “backlight” test which allowed the plating coverage of the through holes to be determined. As a control, a standard palladium catalysed electroless copper process was employed. The morphology of the electroless copper deposits was also analysed using scanning electron microscopy. In the “direct plate” approach, after immersion in the copper nanoparticle dispersion, the through holes were electroplated at 3 Adm−2 for 15 min, sectioned and examined using an optical microscope. The distance that the copper electroplate had penetrated down the through hole was then determined.FindingsThe paper has shown that copper nanoparticles can be used as a catalytic material for electroless copper plating. The coverage of the electroless copper in the through hole improves as the copper nanoparticle concentration increases and, at the highest copper nanoparticle concentrations employed, good, but not complete, electroless copper coverage is obtained. Dispersion of the copper nanoparticles using ultrasound is critical to the process. Ultrasonically dispersed copper nanoparticles achieve some limited success as a conductive layer for “direct” electroplating with some penetration of the electroplated deposit into the through hole. However, if mechanical agitation is employed to mix the nanoparticles, no through hole plating obtaines.Originality/valueThe paper has demonstrated the “proof of concept” that copper nanoparticles can be utilized to catalyse the electroless copper process, as well as their potential to replace costly palladium‐based activators. The paper also illustrates the potential for copper nanoparticles to be used as a “direct plate process” and the necessity for using ultrasound for their dispersion in either process.

Angle-independent microwave absorption by ultrathin microcavity arrays

The resonant absorption of microwave radiation by thin, two-dimensional microcavity arrays has been studied. Resonant modes associated with these structures, formed from copper-clad FR4 laminates, exhibit both an azimuthal and polar angle independent electromagnetic response. The experimental data agree well with the predictions of a finite element method computer model, which has been utilized to explore the electromagnetic character of the resonant modes supported.

Forced Convective Cooling of Electro-Optical Components Maintained at Different Temperatures on a Vertically Oriented Printed Circuit Board

Forced convective heat rejection from electro-optical components maintained at different maximum operating temperatures, 60/spl deg/C and 100/spl deg/C above ambient (25/spl deg/C), on the same vertically orientated single circuit board (either FR4 or copper clad FR4) was experimentally studied. Reynolds numbers ranged from 0-20 000 in which forced ambient air was passed in the horizontal direction parallel to the plane of the board in a wind tunnel. The effect of component proximity and orientation on maximum power dissipation was explored. Observed thermal behavior patterns included an increase in power dissipation with Reynolds number, an increase in power dissipation with component spacing, and in increase in power dissipation with circuit board thermal conductivity. A significant influence of component arrangement (on the same horizontal plane versus on the same vertical plane) and relative location of the hotter component on the power dissipated was also observed and was influenced by board conduction, thermal wake interactions and/or wake shedding. Results provide placement criteria needed for designers to optimally place optical and electrical components in close proximity to each other while still achieving maximum power dissipation within given thermal management constraints.

Natural Convection and Passive Heat Rejection from Two Heat Sources Maintained at Different Temperatures on a Printed Circuit Board

Natural convection and passive heat rejection from two independent heat sources maintained at different temperatures (60°C and 100°C above ambient) on single circuit boards (FR4 and copper clad FR4) are experimentally studied. The effect of heat source location on maximum power dissipation is presented for both horizontal and vertical orientations. Heat losses due to radiation, natural convection and board conduction are quantified. As long as the heat sources are more than 2 cm apart, they do not influence each other on the FR4 board. Vertical orientation increases the power dissipation in the components by up to 30% for the FR4 board and 15% for the copper clad board. Two ounces of copper cladding increases the overall power dissipation by 150–190%.

Metallization of microvias by sputter-deposition

In high-density interconnection technologies the size of via holes significantly effects the space available for component assembly. Commonly used CO2 lasers do not produce microvias small enough for future demands. In this paper we investigate metallization of UV-laser drilled microvias by magnetron sputtering.The core material of the test boards was a copper-clad FR-4 laminate. The boards were coated with two types of nonphotoimageable liquid dielectrics. A thin chrome layer (∼0.1 μm) with a subsequent copper layer (∼3 μm) or copper layer without any intermediate chrome layer was sputtered onto the surfaces and within the microvias. Copper was electrolytically grown onto the sputtered metal layers. In fine lines the adhesion of the metallic layer to the core material is essential. Our earlier studies have shown that chrome has good adhesion to epoxy and it is used as a seeding layer between epoxy and sputtered copper.The purpose of our research is to assess the usefulness of sputtering techniques for metallizing small vias and to find a combination of dielectric material, technologies for microvia formation and plating for achieving reliable microvia connections. Microvias were analyzed after every process stage by means of a microscope and a scanning electronic microscope.

Substrate studies of cesium-iodide photocathodes

Abstract We report on the quantum efficiency (QE) of cesium-iodide (CsI) photocathodes vacuum deposited on various substrates. The substrates, Ni, Au, solder, and Al were vacuum deposited on copper-clad FR4 and ceramic printed circuit boards. The results were obtained in a low-pressure, parallel-plate, pad-chamber with a solid CsI photocathode operated with ethane and isobutane gas. We present QE measurements for each of the different substrates used, the effect of substrate heating, the importance of surface quality, and our experience with ceramic printed circuit boards. Scanning electron microscope images of the photocathode surface are also shown for Cu and Al substrates.

CHARACTERISATION AND RELIABILITY STUDY OF ANISOTROPIC CONDUCTIVE ADHESIVES FOR FINE PITCH PACKAGE ASSEMBLY

The application of Anisotropic Conductive Adhesive (ACA) for the interconnection of fine pitch Surface Mount Devices (SMDs) to electroless nickel/gold plated copper clad FR4 board was investigated. One ACA tape, one ACA paste, and one isotropic conductive adhesive paste were used in a Taguchi (L9) experimental design.1 The experiment was carried out with three different gull-wing leaded, Ceramic Quad Flat Pack (CQFP) packages. The packages were mounted onto FR4 boards using a hot bar (thermode) system with adjustable temperature and pressure setting. Quality and reliability assessment was carried out by visual inspection, mechanical strength testing and electrical resistance measurements of individual leads before and after humidity testing and temperature cycling.The processing issues of conductive paste and tape adhesive assembly compared to solder assembly were examined and valuable information was also obtained from reliability testing. Although mechanical strengths and electrical resistances were obtained similar to those expected for solder assembly; reliability, humidity testing in particular, needs to be addressed in greater detail in order to make the application of ACAs a viable alternative to solder.