Printed Circuit Board Materials Research Articles

Millimeter-Wave Printed Circuit Board Characterization Using Substrate Integrated Waveguide Resonators

This paper proposes a substrate integrated waveguide (SIW) cavity-based method that is compliant with ground-signal-ground (GSG) probing technology for dielectric characterization of printed circuit board materials at millimeter wavelengths. This paper presents the theory necessary to retrieve dielectric parameters from the resonant characteristics of SIW cavities with particular attention placed on the coupling scheme and means for obtaining the unloaded resonant frequency. Different sets of samples are designed and measured to address the influence of the manufacturing process on the method. Material parameters are extracted at <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i> - and <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">W</i> -band from measured data with the effect of surface roughness of the circuit metallization taken into account.

Cutting Performances of Boron-Doped Diamond Coated Milling Tools in Machining PCB

Boron-doped diamond films are deposited on cobalt cemented tungsten carbide (WC-Co) printed circuit board (PCB) milling tools using hot filament chemical vapor deposition (HFCVD) method. Trimethyl borate is used as boron source. Scanning electron microscope (SEM) and Raman spectroscopy are used to characterize the as-deposited diamond films. To evaluate the cutting performances of as-fabricated boron-doped diamond (BDD) coated milling tools, milling tests are conducted using copper-clad laminate（CCL）as the workpiece material, compared with microcrystalline diamond (MCD) coated and uncoated milling tools. The experimental results show that the BDD films have strong adhesive strength to the substrate and can protect the cutting edge from rapid wearing out. The results suggest that depositing BDD coating on WC-Co milling tools is a viable way to improve their cutting performances in machining of PCB materials.

Embedded Chip Technology: Technologies, Applications and Future Developments

Technology approaches for the embedding of active and passive components using printed circuit board materials and processing gained an increasingly high interest over the last years. The use of such technologies for industrial fabrication has attracted increasingly interest by manufacturers and commercial products have been released. The realization of embedded modules is quite a robust process for different applications. Several approaches for a laminate based embedding of components were developed and implement into the manufacturing. An overview and status of the different methods and their advantages for specific applications will be given. The process flow, yield and challenges of such technologies for miniaturized packages and modules will be presented briefly. By nature of the process, extremely flat packages can be realized. The routing of electrical contacts from the embedded components to the top and bottom side of the package allows the fabrication of highly versatile package layouts. The flatness and freedom in design makes these packages ideal candidates for package on package stacking. The main focus of the presentation will be the discussion of different applications. Single and multi-component packages will be presented. Extensive reliability testing of single die packages was done in order to compare different material sets for embedding, but also to compare the reliability of such embedded die packages with conventional packages. In addition, new process developments targeting the embedding of ultra-fine pitch dies, with pad pitches below 100 μm, will be shown. Manifold applications targeting e.g. medical and power electronic modules will be presented and their way of manufacturing will be described. Recent developments focus on the use of such embedding technologies for the integration of high-power modules e.g. for automotive applications (Hybrid and eCars). Beside the integration of semiconductors, to achieve miniaturization and high robustness of such modules, also the use of organic substrates as an alternative to currently used direct copper bonded (DCB) boards is of high interest. The need to handle high current and to realize an excellent thermal management are the main challenges for these modules. The concepts and first results of these latest developments will be presented in detail. Rozalia/Ron ok move from 2.5/3D to Passive 1-3-12.

PCB Related Failures in Electronic Assemblies

The complexity of Printed Circuit Boards (PCBs) has increased dramatically over the last three decades with the development of surface mount technology (SMT). The typical manufacture of rigid multilayer PCB contains many process procedures, which makes manufacture and application much more challenges. This paper focuses on some typical PCB related failures. Recommendations are provided on optimizing PCB manufacture process and material application. Microvia crack, black pad, galvanic attack, pad design, conductive anodic filament and pad crater are presented in detail.

Conductive filament formation in printed circuit boards: effects of reflow conditions and flame retardants

Conductive filament formation, a major cause of failures in printed circuit boards, is an electrochemical process that involves the transport of a metal through or across a nonmetallic medium under the influence of an applied electric field. With an increasing potential to market “green” electronics, environmental and health legislations, and the advent of lead-free and halogen-free initiatives, newer types of printed circuit board materials are being exposed to ever higher temperatures during solder assembly. The higher temperatures can weaken the glass-fiber bonding, thus enhancing conductive filament formation. The effects of the inclusion of halogen-free flame retardants on conductive filament formation in printed circuit boards are not completely understood. Previous studies, along with analysis and examinations conducted on printed circuit boards with failure sites that were due to conductive filament formation, have shown that the conductive path is typically formed along the delaminated fiber glass and epoxy resin interfaces. This paper is a result of a year-long study on the effects of reflow temperatures, halogen-free flame retardants, glass reinforcement weave style, and conductor spacing on times to failure due to conductive filament formation.

Analytical Solutions for the Radiated Emission of Parallel Microstrip Traces

A closed-form expression of the unintentional electromagnetic radiation of parallel microstrip traces is proposed. Based on transmission line theory, far-field Green's function, and concept of array factor in antenna theory, analytical solutions for the electric field radiated from a pair of parallel microstrip lines are developed. Depending on the printed circuit board material, dimension parameters, and termination impedances, the frequency and angular responses of far-field radiated emission on the upper half-plane can be analyzed by the presented method. The differential- and common-mode radiated emission solutions are validated by a full-wave simulator and test board measurements in a full-anechoic chamber.

Pressure leaching of metals from waste printed circuit boards using sulfuric acid

Printed circuit boards (PCBs) are essential components of electronic equipments which contain various metallic values. This paper reports a hydrometallurgical recycling process for waste PCBs, which consists of the novel pretreatment consisting of organic swelling of PCBs followed by sulfuric acid leaching of metals from waste PCBs. To recycle the waste PCBs, experiments were carried out for the recovery of copper from the crushed and organic swelled materials of waste PCBs using sulfuric acid leaching in presence of hydrogen peroxide under atmospheric and pressure condition. The leaching of PCBs at 90°C, pulp density 100 g/L under atmospheric condition, using 6M sulfuric acid resulted in the dissolution of a minor amount of copper due to the presence of plastic coating on the surface of metallic layers. On the other hand, when the liberated metal sheets from organic swelled PCBs were treated with dilute sulfuric acid of concentration 2M along with hydrogen peroxide in an autoclave under oxygen atmosphere, the percentage recovery of copper was found to increase from 59.63% to 97.01% with an increase in hydrogen peroxide concentration from 5 to 15% (v/v) keeping constant pulp density 30 g/L.

Design Synthesis of Electromagnetic Vibration-Driven Energy Generators Using a Variational Formulation

This paper reports upon the design of electromagnetic vibration-driven energy generators using a variational formulation to derive the equation of motion of such generators, thereby gaining insight into the device physics. Using this approach, the characteristics of the generator are analytically studied, a newly developed optimization theory of the generator is derived, and a guide for the sizing process is described. A fabricated prototype of an electromagnetic vibration harvester is presented. For the fabrication of the prototype, printed circuit board materials and PMMA have been used to lower the cost and to achieve lightweight device. Analytical and experimental results are presented and compared. The fabricated harvester weighs 7 g, delivers 315 μW at optimum excitation parameters at room temperature, and has a mechanical damping ratio of 0.0186. Experimental and analytical results show good agreement with the newly developed optimization theory. An analytical expression of the optimum load resistance is also developed and validated with experimental results, which show the frequency dependence of the optimum load resistance. It is also demonstrated that the optimization process needs two iterations if the mechanical damping ratio is unknown at the start of development and that the coil parameters represent the degree of freedom of the designer.

Failure Mechanism and Testing of PCB Pad Cratering

Pad cratering of printed circuit board (PCB) is becoming a prevailing issue encountered in the PCB assemblies which is accelerated when switching to leadfree process. These units with pad cratering may not fail during functional test as and raise potential failure in the field. This paper uses both experimental and finite element analysis (FEA) approaches to understand the pad strength and pad stresses. An extensive mechanical test by pin pull tests are performed on PCB materials. Cohesive elements are employed to simulate the bonding at the interfaces of pad, laminate and fibers. The results from FEA show that the laminate cracking can be successfully simulated. The design variables such as traces and solder fillet impact are also critical for pad cratering.

Effect of Moisture on Thermal Properties of Halogen-Free and Halogenated Printed-Circuit-Board Laminates

Moisture plays an important role in the integrity and reliability of printed circuit boards (PCBs). The presence of moisture in a PCB alters its thermal performance and thermomechanical properties, thereby affecting overall performance. Due to the shift in market trends toward halogen-free products, halogen-free PCB materials have recently gained popularity. There are many studies on the behavior of halogenated PCBs exposed to moisture, but there are less data available on the use of halogen-free flame retardants in PCBs. Therefore, it is necessary to understand the moisture behavior of halogen-free PCB materials and the effect of moisture on material thermal properties when compared with halogenated PCBs materials. In the past, the Center for Advanced Life Cycle Engineering has conducted thermal-property measurements on halogen-free PCB materials. Measurements were conducted per industry-adopted test methods, including preconditioning of test samples. Some measurement results did not match manufacturers' datasheets. This paper examines the dependence of out-of-plane coefficient of thermal expansion, glass-transition temperature, time to delamination, and decomposition temperature on the moisture content in halogenated and halogen-free PCB materials. Four types of PCB materials from two manufacturers, including two halogen-free and two halogenated, were tested in this paper. Furthermore, this paper investigates the suitability of IPC-TM-650 preconditioning steps for thermal-property measurements.

Evaluation of Internal Charging of PC Board Materials Used for Spacecrafts

This paper deals with charge-up characteristics of printed circuit (PC) board materials due to electrons penetrating inside a spacecraft body. Glass-fiber-reinforced plastic (GFRP) plates, typical PC board material, were irradiated by electron beam with the energy lower than 20keV simulating decelerated high-energy electrons penetrating through the satellite skin. The charge-up characteristics were obtained as parameters of irradiation time, the energy and the current density of the electron beam. The volume resistivities of the GFRP plates were also evaluated by the decay time constants of the surface potential after electron irradiation. The influence of a protective coating on the charging of the GFRP plates was also tested.

Large-Scale Silicone-Rubber-Based Optical Interconnect Packaged With FR4

Polydimethylsiloxane (PDMS)-based large-scale electrical-optical circuit boards (EOCBs) have been developed based on a combination of a large-scale PDMS waveguide fabrication technique and a process for efficient interfacial bonding between PDMS optical layers and standard FR4 (fiberglass-reinforced epoxy and grade 4 on flame retardance) printed circuit board materials using a specially developed surface adhesion promoter (SAP). The main mechanism of forming a good bonding between PDMS and FR4 has been identified. The optical properties of the PDMS waveguide layer remained unchanged by the addition of the SAP. According to the defined test procedures from the Institute of Printed Circuits, the International Electro Technical Commission, and Telcordia, the environmental stability of packaged EOCBs has been tested with the result that they exhibited excellent mechanical, optical, and thermal stabilities. The mechanical stability limit of the tested EOCBs is determined only by the intrinsic mechanical stability of the used PDMS materials. The optical waveguide propagation loss at 850 nm is less than 0.1 dB/cm after surviving from the defined environmental test procedures.

RF‐MEMS switches on a printed circuit board platform

PurposeThe purpose of this paper is to present a new class of printed circuit board (PCB)‐based, radio frequency micro‐electro‐mechanical systems (RF‐MEMS) switches and to describe the packaging method and evaluate performance.Design/methodology/approachTraditional PCB materials and processes were combined with photolithographic high‐density interconnect (HDI) and MEMS to form 3D high‐performance RF switches.FindingsA new type of MEMS RF switch has been developed on a PCB platform. Using processes analogous to those used for silicon MEMS, PCB, and HDI technologies were utilized to fabricate these 3D structures. The PCB‐based microstructures are “mil‐scale” rather than the “micro‐scale” of silicon MEMs. A co‐fabrication packaging method for the MEMS RF switch was also developed. The PCB‐based MEMS switches have demonstrated excellent RF performance and “hot‐switching” RF power‐handling capability. PCB‐based MEMS RF switches have the advantages of low cost and amenability to scale‐up for a high degree of integration.Research limitations/implicationsFurther development on photo imageable dielectric materials will enable this technology to improve yield and processability.Originality/valueThe paper describes the development of PCB‐based MEMS RF switches. These elements will enable new applications and enhance the functionality of PCBs. They are also more amenable to system integration compared with silicon MEMS.

Effects of Moisture Content on Dielectric Constant and Dissipation Factor of Printed Circuit Board Materials

In the past we conducted experiments to measure the dielectric properties of PCB materials as per industry adopted methods, including preconditioning of test samples. It was observed that some measurement results were not in accordance with manufacturer datasheets. This paper presents follow-up experimental studies on the dependence of dielectric constant and dissipation factor on the moisture content of laminates. Four types of PCB materials from two manufacturers, including two halogen-free and two halogenated, were tested in this study. The paper further establishes whether preconditioning steps outlined in the IPC-TM-650 2.5.5.9 test method account for varying moisture contents in laminate samples.

Electrical properties of chicken feather fiber reinforced epoxy composites

We have fabricated composites with epoxy, chicken feather fiber (CFF), and E-glass fibers and investigated their properties for potential applications as printed circuit boards (PCBs). The electrical resistivity of the CFF composites was two to four orders of magnitude higher than that of E-glass fiber composites. The dielectric constant of the composites decreased with fiber contents. Composite with hybrid fiber had a low dielectric constant of 3.6–4.2 and a loss tangent of 0.027, which is similar to those of commercial PCB materials. The CFF composite can be potentially used for PCBs industry and the hybrid fiber composite has a good balance of properties and costs, while being more sustainable.

Biobased composite resins design for electronic materials

AbstractBiobased materials developed from triglycerides contain a large variety of structures, which makes it difficult to predict their properties. In this study, we used a structure–property relation to design biobased materials, both theoretically and experimentally. A general equation to predict the crosslink density in terms of the level of chemical functionalities of the triglycerides was derived and used as a design rule for high‐crosslinked polymer materials. The twinkling fractal theory and the Clausius–Mossotti equation were used to guide two approaches of synthesis to improve the properties of the biobased thermosets: the biobased resin acrylated epoxidized soybean oil (AESO) was either crosslinked with divinylbenzene (DVB) or chemically modified by phthalic anhydride. The DVB‐crosslinked resins had a 14–24°C increase in their glass‐transition temperatures (Tg′s), which was dependent on the crosslink densities. Tg increased linearly as the crosslink density increased. Phthalated acrylated epoxidized soybean oil (PAESO) had an 18–30% improvement in the modulus. The dielectric constants and loss tangents of both DVB‐crosslinked AESO and PAESO were lower than conventional dielectrics used for printed circuit boards (PCBs). These results suggest that the new biobased resins with lower carbon dioxide footprint are potential replacements for commercial petroleum‐based dielectric materials for PCBs. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

TH‐C‐BRB‐09: Design and Initial Performance of a Large Cross‐Section Multi‐Element Ionization Chamber System for Water Equivalent Range Measurements of Pristine Proton Fields

Purpose: To describe the design and initial testing of a large diameter multilayer ionization chamber (MLIC) system for water equivalent range measurements of pristine proton fields. Method and Materials: The MLIC uses a large 120 mm physical diameter collecting cross‐section in a stacked vented parallel plate geometry of 180 layers spaced 0.8 mm apart. The plates are fabricated from printed circuit board material where copper traces have been etched to form the conductive elements for the ionization chambers. In addition a dedicated software package was developed to assist with device calibration data acquisition and analysis.Computer modeling of the MLIC was performed with the Monte Carlo (MC) code FLUKA. Radiological testing was performed in a dedicated proton pencil beam scanning (PBS) therapeutic delivery system. The energies tested varied from 100–230 MeV. A series of 10 pristine depth profiles were first acquired for reference within this energy range by longitudinally scanning a discrete parallel plate ionization chamber of 84 mm diameter in a water phantom. After a calibration routine was applied to the MLIC the same energies were tested with the MLIC and the results compared. Additional tests were performed at different fluence rates to evaluate changes in response to detector bias and charge quantum (QC) settings. Results: The analyzed data from the MC simulation and MLIC physical data compared within one mm to the water phantom reference data under the conditions tested. The MLIC results were not sensitive to bias setting but depended with fluence rate on the QC setting. Conclusion: The initial test of the new MLIC prototype provided satisfactory results with regard to water equivalent range accuracy in comparison to reference measurements from the PBS system. Some flexibility is provided with different fluence rates by adjusting the QC. The detailed results will be presented and discussed.

Spectral imaging method for material classification and inspection of printed circuit boards

We propose a spectral imaging method for material classification and inspection of raw printed circuit boards (PCBs). The method is composed of two steps (1) estimation the PCB surface-spectral reflectances and (2) unsupervised classification of the reflectance data to make the inspection of PCB easy and efficient. First, we develop a spectral imaging system that captures high dynamic range images of a raw PCB with spatially and spectrally high resolutions in the region of visible wavelength. The surface-spectral reflectance is then estimated at every pixel point from multiple spectral images, based on the reflection characteristics of different materials. Second, the surface-spectral reflectance data are classified into several groups, according to the number of PCB materials. We develop an unsupervised classification algorithm incorporating both spectral information and spatial information, based on the Nystrom approximation of the normalized cut method. The initial seeds for the Nystrom procedure are effectively chosen using a guidance module based on the K-means algorithm. Low-dimensional spectral features are efficiently extracted from the original high-dimensional spectral reflectance data. The feasibility of the proposed method is examined in experiments using real PCBs in detail.

Novel Thin Copper Transfer Films for Fine Line Formation on PCB Substrates

Printed circuit boards (PCB) using Ajinomoto build-up films (ABF) as insulating layers are widely used as package substrates. Along with the increasing demand for downsizing electronic devices with advanced functions, package substrates are strongly required to be miniaturized with high-density circuit wirings.The manufacturing method for multilayer PCBs using ABF is a semi-additive process including the lamination and curing steps of ABF resin composition, laser via formation and then desmear process accompanied with roughening the ABF surface prior to electroless copper plating as a seed layer to electroplate a thicker copper layer. The high adhesion between the plated copper and ABF insulating layer depends mainly on an anchor effect; however a smooth surface is desired for fine line formation, for example, of less than L/S = 15/15 microns.Recently, we've developed very thin copper transfer films consisting of a supporter film, an alkaline-soluble resin layer, and a thin copper layer (150–1500 nm thick) deposited by vacuum evaporation or sputtering. In this paper, we report on the applications of very thin copper transfer films for both build-up PCB and core materials. With regard to build-up applications, the combination of a new ABF that has a low coefficient of thermal expansion and a high Young's modulus is demonstrated as a high-tech resin coated copper (RCC) film for fine line formation. Furthermore, the combination of very thin copper transfer film and ABF-prepregs, which are glass-cloth materials impregnated with ABF resin compositions, are proposed for use as core materials, especially for CSP substrates.These new applications can achieve the high adhesion between the copper and insulating layers without anchor effects and that mechanism is presumed from the analysis of its interface using XPS. In addition, reliability tests were performed under the stress conditions of reflow tests and HAST.

Impact of plasma etching on fabrication technology of liquid crystal polymer printed circuit board

Liquid crystal polymer (LCP) has attracted great attention as a potential candidate for high performance micro-wave substrate material in high frequency printed circuit boards (PCB). This is attributed to its low loss behaviour, excellent thermal stability, and outstanding chemical resistance. The use of LCP in PCB, however, is hindered by its extreme chemical inertness, causing fabrication challenges in desmearing and metallization processes. To overcome the challenges, plasma etching is suggested for its capability of smear removal, adhesion improvement and surface activation of PCB material. However, previous experimental and theoretical studies of the effects of plasma etching on LCP PCB at different treatment conditions are lacking. This paper thus evaluates recent developments on plasma etching technologies, involving the plasma etching investigation under different process conditions for manufacturing LCP PCB. Distinct process approaches are developed and proposed based on the illustrations of the experimental outcomes. Finally, examples are shown to demonstrate the effectiveness of the proposed plasma etching approach for controlling the fabrication of LCP PCB.