Printed Circuit Board Materials Research Articles

A wearable tracking device inkjet-printed on textile

Despite the abundance of localization applications, the tracking devices have never been truly realized in E-textiles. Standard printed circuit board (PCB)-based devices are obtrusive and rigid and hence not suitable for textile based implementations. An attractive option would be direct printing of circuit layout on the textile itself, negating the use of rigid PCB materials. However, high surface roughness and porosity of textiles prevents efficient and reliable printing of electronics on textile. In this work, by printing an interface layer on the textile first, a complete localization circuit integrated with an antenna has been inkjet-printed on the textile for the first time. Printed conductive traces were optimized in terms of conductivity and resolution by controlling the number of over-printed layers. The tracking device determines the wearer's position using WiFi and this information can be displayed on any internet-enabled device, such as smart phone. The device is compact (55mm×45mm) and lightweight (22g with 500mAh battery) for people to comfortably wear it and can be easily concealed in case discretion is required. The device operates at 2.4GHz communicated up to a distance of 55m, with localization accuracy of up to 8m.

A highly sensitive and specific capacitive aptasensor for rapid and label-free trace analysis of Bisphenol A (BPA) in canned foods

A rapid, highly sensitive, specific and low-cost capacitive affinity biosensor is presented here for label-free and single step detection of Bisphenol A (BPA). The sensor design allows rapid prototyping at low-cost using printed circuit board material by benchtop equipment. High sensitivity detection is achieved through the use of a BPA-specific aptamer as probe molecule and large electrodes to enhance AC-electroelectrothermal effect for long-range transport of BPA molecules toward electrode surface. Capacitive sensing technique is used to determine the bounded BPA level by measuring the sample/electrode interfacial capacitance of the sensor. The developed biosensor can detect BPA level in 20s and exhibits a large linear range from 1 fM to 10 pM, with a limit of detection (LOD) of 152.93 aM. This biosensor was applied to test BPA in canned food samples and could successfully recover the levels of spiked BPA. This sensor technology is demonstrated to be highly promising and reliable for rapid, sensitive and on-site monitoring of BPA in food samples.

Liberation characteristics after cryogenic modification and air table separation of discarded printed circuit boards

Liberating useful materials from printed circuit boards (PCBs) is challenging because PCBs are flexible and complex in terms of materials and components. In this study, the crushing of PCBs at low-temperature was investigated. The results indicated that when the temperature was decreased to approximately −20°C, the strength of PCBs decreased and their brittleness increased, making them easier to crush. A double roll crusher was selected to crush the PCBs. The particle size distribution and power consumption were studied under different working conditions. The results showed that the particle size of most of the lumps was in the range 15×20–25×20mm, and that power consumption was minimal when the frequency of the crusher was 40–50Hz. A small shredder was used for cryogenic grinding, and it was found that its power consumption strongly depended on the cooling temperature. An orthogonal experiment was conducted, which revealed that a smaller cutter gap and higher rotational speed could achieve higher yield. Furthermore, the results indicated that the air table developed to liberate PCB materials could effectively separate 2.8–0.5mm grade materials. Overall, the results of this study provide an experimental foundation for more effectively recycling discarded PCBs.

Long-lasting FR-4 surface hydrophilisation towards commercial PCB passive microfluidics

Printed circuit boards (PCB) technologies are an attractive system for simple sensing and microfluidic systems. Controlling the surface properties of PCB material is an important part of this technology and to date there has been no study on long-term hydrophilisation stability of these materials. In this work, the effect of different oxygen plasma input power and treatment duration times on the wetting properties of FR-4 surfaces was investigated by sessile droplet contact angle measurements. Super and weakly hydrophilic behaviour was achieved and the retention time of these properties was studied, with the hydrophilic nature being retained for at least 26 days. To demonstrate the applicability of this treatment method, a commercially manufactured microfluidic structure made from a multilayer PCB (3-layer FR-4 stack) was exposed to oxygen plasma at the optimum conditions. The structures could be filled with deionised (DI) water under capillary flow unlike the virgin devices.

Two-step bioleaching of copper and gold from discarded printed circuit boards (PCB)

An effective strategy for environmentally sound biological recovery of copper and gold from discarded printed circuit boards (PCB) in a two-step bioleaching process was experimented. In the first step, chemolithotrophic acidophilic Acidithiobacillus ferrivorans and Acidithiobacillus thiooxidans were used. In the second step, cyanide-producing heterotrophic Pseudomonas fluorescens and Pseudomonas putida were used. Results showed that at a 1% pulp density (10g/L PCB concentration), 98.4% of the copper was bioleached by a mixture of A. ferrivorans and A. thiooxidans at pH 1.0–1.6 and ambient temperature (23±2°C) in 7days. A pure culture of P. putida (strain WCS361) produced 21.5 (±1.5)mg/L cyanide with 10g/L glycine as the substrate. This gold complexing agent was used in the subsequent bioleaching step using the Cu-leached (by A. ferrivorans and A. thiooxidans) PCB material, 44.0% of the gold was mobilized in alkaline conditions at pH 7.3–8.6, and 30°C in 2days. This study provided a proof-of-concept of a two-step approach in metal bioleaching from PCB, by bacterially produced lixiviants.

High-Temperature Storage Testing of ACF Attached Sensor Structures.

Several electronic applications must withstand elevated temperatures during their lifetime. Materials and packages for use in high temperatures have been designed, but they are often very expensive, have limited compatibility with materials, structures, and processing techniques, and are less readily available than traditional materials. Thus, there is an increasing interest in using low-cost polymer materials in high temperature applications. This paper studies the performance and reliability of sensor structures attached with anisotropically conductive adhesive film (ACF) on two different organic printed circuit board (PCB) materials: FR-4 and Rogers. The test samples were aged at 200 °C and 240 °C and monitored electrically during the test. Material characterization techniques were also used to analyze the behavior of the materials. Rogers PCB was observed to be more stable at high temperatures in spite of degradation observed, especially during the first 120 h of aging. The electrical reliability was very good with Rogers. At 200 °C, the failures occurred after 2000 h of testing, and even at 240 °C the interconnections were functional for 400 h. The study indicates that, even though these ACFs were not designed for use in high temperatures, with stable PCB material they are promising interconnection materials at elevated temperatures, especially at 200 °C. However, the fragility of the structure due to material degradation may cause reliability problems in long-term high temperature exposure.

Could application of column-grid-array (CGA) technology result in inelastic-strain-free state-of-stress in solder material?

Physically meaningful and easy-to-use analytical stress model is developed for a short cylinder (beam) clamped at the ends and subjected to bending caused by the ends offset. The offset is due, in its turn, to an external lateral force that has to be determined from the known offset. It is envisioned that such a beam can adequately represent the state of stress in a column-grid-array (CGA) solder joint interconnection experiencing thermal loading due to the thermal expansion/contraction mismatch of the IC package and the printed circuit board (PCB). The CGA designs are characterized by considerably higher stand-off heights than ball-grid-array (BGA) systems. The offset Δ = lΔαΔt for a CGA solder joint located at the distance l from the mid-cross-section of the package/PCB assembly (the neutral point (DNP)), can be determined, in an approximate analysis, as a product of this distance and the “external” thermal mismatch strain ΔαΔt between the IC package and the printed circuit board (PCB). Here Δα is the difference in the effective coefficients of thermal expansion (CTE) of the PCB and package materials, and Δt is the change in temperature. The objective of the analysis is to demonstrate that the application of a CGA design, in which the solder joints are configured as short clamped–clamped beams, enables one not only to significantly relieve the thermally induced stresses, compared to the BGA system, but possibly to do that to an extent that the stresses in the solder material would remain within the elastic range. If this is achieved, the low-cycle-fatigue condition for the solder material will be replaced by the elastic-fatigue condition, thereby leading to a significantly longer fatigue lifetime of the joint. The elastic fatigue lifetime can be assessed, as is known, based on the Palmgren–Miner rule of linear accumulation of damages. Our analysis is limited therefore to elastic deformations.

Design and Fabrication of Riot Shield from E-Waste Printed Circuit Board

Recycling of Printed Circuit Boards (PCB) has been carried out by powdering it into granular size of less than 10 microns. The properties of PCB reveal that it possesses density of 1.3 g/cm3 and Tensile Strength of 310 MPa which is comparatively high when compared to the Polycarbonate material which is normally used in the fabrication of Riot shield. The PCB material was subjected to SEM and EDAX analysis for determining their structure, porosity and material composition. Riot shield fabricated from PCB reduces the environmental effects of E-waste PCBs by the recycling technique, improves the material strength and reduces the weight and cost to a larger extent.

Adhesion energy of printed circuit board materials using four-point-bending validated with finite element simulations

Modern printed circuit boards (PCB) are high performance products consisting of metal and dielectric materials in a multi-layered structure. Due to this build-up different failures, such as cracking or delamination, may occur during manufacturing and use leading to failure of the entire electronic device. The mismatch in the thermal expansion coefficients leads to stresses in the structure during temperature change, e.g., during the reflow process. To improve device reliability, it is critical to understand the delamination between different layers and to know the adhesion energy of the interfaces in a PCB. The adhesion energy in test PCBs was determined using four point bending (4PB) experiments before and after 15 reflow cycles. The investigations show that 4PB is applicable for determining the adhesion energy in samples made of halogen free pre-pregs and copper sheets with standard manufacturing processes. Furthermore, the applicability of the analytical adhesion energy calculation in the presence of non-linearities was examined by finite element simulations. It was found that friction between the sample and the pins of the loading device has an influence on the reaction force used for the calculation of the critical energy release rate. Plastic deformation of the 4PB sample, especially in the ductile copper layers, also will affect the analytically determined critical energy release rate. The role of both factors on the analytical approach to measure adhesion energies of PCB interfaces with 4PB will be shown and discussed.

Investigating and compensating printed circuit board shrinkage induced failures during reflow soldering

Purpose – This paper aims to reveal the causes and find an efficient method to compensate the shrinkage to reduce failure costs. Reflow-induced printed circuit board (PCB) shrinkage is inspected in automotive electronics production environment. The shrinkage of two-sided, large PCBs results in printing offset errors and consequently soldering failures on smaller components during the reflow soldering of the second PCB side. Design/methodology/approach – During the research, the investigations had to adapt to actual production in an electronics manufacturing plant. A measurement method was developed to approximate the overall shrinkage of the given product. With the shrinkage data, it is possible to perform an efficient compensation on the given stencil design in computer-aided manufacturing environment. Findings – It was found that even with the investigated lower-quality PCB materials, the compensation on the stencil significantly reduces the quantity of failures, offering an efficient method to improve the yield of the production. Research limitations/implications – Research was oriented by the confines of production (fixed PCB sources, given PCB materials, reflow process and production line), where an immediate solution is needed. Future investigations should be focussed on the PCB parameters (different epoxy types, glass-fibre reinforcements, etc.). Practical implications – The optimised production reduces overall failure costs. The stencil re-design and application is a fast and efficient way to immediately act against the shrinkage-induced failures. The method was successfully applied in automotive electronics production. Originality/value – The paper presents a novel approach on solving an emerging problem during reflow.

Embedded Power Modules – A new approach using Power Core and High Power PCB

Power electronics packaging applications has strong demands regarding reliability and cost. The fields of developments reach from low power converter modules, over single or multichip MOSFET or IGBT packages, up to high power applications, like needed e.g. for solar inverters and automotive applications. This paper will give an overview about these applications and a description of each ones demand. The spectrum of conventional power electronics packaging reaches from SMD packages for power chips to large power modules. In most of these packages the power semiconductors are connected by bond wires, resulting in large resistances and parasitic inductance. Additionally bond wires result in a high stray inductance which limits the switching frequency. The embedding of chips using Printed Circuit Board (PCB) technology offers a solution for many of the problems in power packaging. This paper will show today's available power packages and power modules, realized in industrial production as well as in European research projects. All technologies which are used are based on PCB materials and processes. Chips are mounted to Cu foils, lead frames, high power PCBs or even ceramic substrates, embedded by vacuum lamination of laminate sheets and electrically connected by laser drilling and Cu plating. A new approach for embedded power modules will be presented in detail. In this project, different application fields are covered, ranging from 50 W over 500 W to 50kW power modules for different applications like single chip packages, over power control units for pedelec (Pedal Electric Cycle), to inverter modules for automotive applications. This approach will focus on a power core base structure for the embedded semiconductor, which is then connected to a high power PCB. The connection to the embedded die is realized by direct copper connection only. The technology principle will be described in detail. Frist manufactured demonstrators will be presented. The presented new approach for the realization of a power core structure offers new possibilities for the module manufacturing, avoiding soldering or Ag sintering of the power semiconductors and the handling of thick copper substrates during the embedding process.

Effect of heat convection on the thermal and structure stress of high-power InGaN light-emitting diode

In this study, two models are investigated: (1) the convection cooling of high-power indium–gallium–nitride light-emitting diodes (LEDs) and (2) the effects of thermal stress distribution. The first model chip (model A) has power of 1 and 3 W and dimensions of 1 mm × 1 mm × 0.005 mm, whereas the second model chip (model B) has power of 6 and 10 W and dimensions of 1.8 mm × 1.8 mm × 0.005 mm. The results of an analysis of natural convection, forced cooling, and thermal stress are compared with 1, 3, 6, and 10 W thermal specification data. High heat conductivity Al2O3 material used as a printed circuit board (PCB) facilitates the heat conduction and thermal cooling of high-power LEDs and thus increases the strength of the structure. This LED structure model is used in full-scale packaging structures. The wire bonding convection cooling and effect of thermal stress distribution of this packaging design are investigated. We simulate thermal performance and effect of thermal stress distribution of the LEDs using a finite element method with ANSYS software. Heat transfer is coupled with heat conduction, heat convection, and thermal radiation, with the distribution of thermal stress equivalent to that of the von Mises criterion stress. LED is attached to a silicon substrate by wire bonding; the die bond material used is epoxy. LED packaging material is important. If the LED lighting power is fixed, it can increase the convection cooling coefficient, decreases the T j temperature, and the distribution of structural stress. The T j temperature is stable when the heat transfer coefficient had a critical or optimal value. Thermal cooling performance and overall structural strength can be improved when the LED is mounted on the Al2O3 PCB material and heat sink. The models are employed accurately to determine the heat transfer effect, structural strength, life span, performance enhancement, and efficiency.

Experimental study on micro-drills wear during high speed of drilling IC substrate

Purpose – Compared with the traditional printed circuit board (PCB) drilling process, the technology of drilling IC substrate is facing more problems, such as much smaller hole diameter, more intensive hole space, thinner sheet and more complicated materials are drilled in process. Moreover, the base material of IC substrate is different from traditional PCB, more kinds of fillers added in IC substrate which make the drill worn seriously during drilling process. Micro-drills wear and micro holes quality are the most important questions when drilling IC substrate so far. Wear morphology of micro-drill, holes wall roughness and hole location accuracy are researched in this paper. The influence factors of micro-drills wear and micro holes quality are also studied in this drilling process. The paper aims to discuss these issues. Design/methodology/approach – Two drills with same structure and different diameter are used to drill different stacks of IC substrate and drill different holes in this paper. There are four experiments made and the drilling parameters including spindle speed (n), feed rate (vf) and retraction speed (vr) are recommended by drill manufacturing company. Wear morphologies of drill are observed, holes wall roughness (Rmax) and holes location accuracy (Cpk) are measured in this paper. Analyzing the main factors influence on drill wear, holes wall roughness and holes location accuracy through these experiments. Findings – The micro-drills of IC substrate wear more severely compared with other material of PCB through the experimental results in this paper. Drill diameter has influence on micro-drill wear when drilling IC substrate, the smaller of drill is, the more severely of micro-drill wears. Drill diameter affect the holes wall roughness too, the holes wall roughness of larger holes is better than smaller one in a certain range. The drilled holes number also has influence on micro-drills wear, holes wall roughness and holes location accuracy. The more drilled holes, the seriously of micro-drills wear, and the worn drill would destroy the hole quality. Therefore, the more drilled holes lead the bad holes wall roughness and holes location accuracy in this paper. In addition, stacks of IC substrate affect much on the holes location accuracy, the more stacks, the worse holes location accuracy. Originality/value – Chinese Mainland is obviously lagging behind in technology and manufacturer of IC substrate which is incompatible with the nation circumstances. There is few research of drilling IC substrate in China and research data are lacking so far. It is most necessary to improve the technology level of drilling IC substrate in China. In order to reduce the wear of micro-drills and improve the quality of micro-holes, many experimental tests about drilling IC substrate are researched in this paper.

Monitoring extent of curing and thermal–mechanical property study of printed circuit board substrates

Precise control of curing conversion for epoxy-based printed circuit board (PCB) substrates and clarification of curing–property relationship are critical for the performance and reliability assessment, and for the design optimization of electronic systems. In this article, various epoxy composites for PCB substrates were analyzed by infrared spectroscopy (IR), differential scanning calorimetry (DSC), rheometry, dynamic mechanical analysis (DMA), and scanning electron microscope (SEM). Compared with mid-IR and DSC, near-IR (NIR) is found to be a reliable method for the characterization of curing conversion process by detecting the consumption of epoxy groups. And DMA is a powerful method for measuring the conversion of PCB materials by testing glass transition temperatures (Tg) and viscoelastic properties. The curing behaviors of a variety of epoxy composites show distinct differences in both curing rate and activation energy, and the growth tendency of Tg with curing conversion also changed depending on the material compositions. Correlation of curing conversion versus thermal properties shows that the activation energy of curing at different stage by DSC resembles the tendency of Tg transitions tested by DMA. Mechanical properties of the composites show close relationship with the curing conversions. Peel strength, the indicator of adhesion strength between copper foil and epoxy composites, was tested on all the specimens of different curing conversions, and the results showed a maximum value at curing conversion between ca. 90 and 95%.

Failure mechanism of solder bubbles in PCB vias during high‐temperature assembly

PurposePb‐free soldering challenged printed circuit board (PCB) assembly with high temperature. The purpose of this paper is to explain the failure mechanism of printed circuit board (PCB) assembly with solder bubbles of vias to avoid the problems of via‐drilling defects and solder joint failure.Design/methodology/approachThe failure of PCB vias with solder bubbles was investigated through cross sections and SEM microstructure inspection, TMA measurement, moisture absorption analysis and DSC measurement. The moisture absorption and CTE of FR4 laminate matched with manufacturing requirement to avoid the effects of solder bubbles. The effects of via drilling with a dull drill bit were compared to that with a new drill bit.FindingsThe moisture absorbed inside holes of via plating layers could be exposed to induce solder bubbles during Pb‐free soldering assembly and dull drill bits should be prevented during the drilling process to avoid the no‐bearing drilling effects.Originality/valueThe failure of PCB vias is not only involved in the voiding in solder joints but manufacturing processes of PCB. The paper designs an approach to analyse the properties of PCB materials and the drilling effects of vias to find out the mechanism resulting in solder bubbles of vias. The problem of drill bits should be considered to prevent the moisture absorbed in drilling vias with defects.

Effect of High-Humidity Testing on Material Parameters of Flexible Printed Circuit Board Materials

The tendency of polymers to absorb moisture impairs especially their electrical and mechanical properties. These are important characteristics for printed circuit board (PCB) materials, which should provide mechanical support as well as electrical insulation in many different environments in order to guarantee safe operation for electrical devices. Moreover, the effects of moisture are accelerated at increased temperatures. In this study, three flexible PCB dielectric materials, namely polyimide (PI), fluorinated ethylene-propylene (FEP), and polyethylene terephthalate (PET), were aged over different periods of time in a high-humidity test, in which the temperature was 85°C and relative humidity 85%. After aging, the changes in the structure of the polymers were studied by determining different material parameters such as modulus of elasticity, glass-transition temperature, melting point, coefficient of thermal expansion, water absorption, and crystallinity, and changes in the chemical structure with several techniques including thermomechanical analysis, differential scanning calorimetry, Fourier-transform infrared spectroscopy, moisture analysis, and a precision scale. The results showed that PI was extremely stable under the aging conditions and therefore an excellent choice for electrical applications under harsh conditions. Similarly, FEP proved to be relatively stable under the applied aging conditions. However, its crystallinity increased markedly during aging, and after 6000 h of aging the results indicated oxidation. PET suffered from hydrolysis during the test, leading to its embrittlement after 2000 h of aging.

Micropump Pattern Replication Using Printed Circuit Board (PCB) Technology

This article shows a low-cost rapid hot embossing poly (methylmeth acrylate) (PMMA)–based micropump replication with printed circuit board (PCB) mold. PCB material offers advantages of low cost, rigid, and rapid thermal response characteristic. Unlike conventional hot embossing setup, the presented process involved the usage of simple machinery tools: laboratory oven (heat transfer), G-clamp (force deliver), and two aluminium plates (isothermal heat plates). Diffuser and pump chamber were successfully imprinted with the depth of 450 µm and verified pump performance with other reported literatures. To avoid complex bonding process between actuator and membrane, electromagnetic pinch actuation is introduced. The micropump poses flow rate characteristic of 6.66 ml/min and a back pressure of 1.6 kPa under optimum pinch frequency.

Effects of Board Design Variations on the Reliability of Lead-Free Solder Joints

Sn-Ag-Cu (SAC) solder alloys, such as Sn-3.0Ag-0.5 Cu (SAC305) are the popular choices of lead-free solders replacing SnPb solders. However, SAC solders are more brittle in nature due to stiffness and excessive intermetallic compounds growth at the solder joint to pad interface. This leads to higher risk of solder joints failures. Memory module-type smaller lead-free ball grid array (BGA) packages are constantly under dynamic stresses during handling and thermal stresses during operations. It is important to understand the dynamic performance and long-term reliability of memory module lead-free BGAs. It is believed that the printed circuit board (PCB) design variations cause dynamic and long-term failure discrepancies in the fields. In this paper, different pad and trace designs are introduced to evaluate the effects of PCB design variations on the bend and accelerated thermal cycling (ATC) performance of lead-free solder joints. Pad designs with nonsolder mask defined, solder mask defined (SMD), and a unique web design are assembled and tested. Different solder alloys, including SAC305, Sn-1.0Ag-0.5Cu (SAC105) SAC105, and SnPb solders, have been evaluated in this paper. Different PCB materials have also been evaluated in the test. Four-point monotonic bend tests are performed to characterize the bending performance variations with different PCB designs and compared with conventional Sn-Pb solder. The SMD pad is shown to have the best bend performance among all other types of designs in this paper. In addition, this design also shows improvement in mitigation of PCB pad cratering with lead-free solders. Wide trace width seems to degrade the strength and is not preferred. Just as it shows superior shock resistance when compared with SAC305, the SAC105 solder alloy also shows better bend performance. There is no significant improvement in bend performance with web design. After aging treatment, bend performance of both SAC305 and SAC105 degraded by up to 34% and 29%, respectively. However, the bend performance of eutectic SnPb is actually improved after aging. ATC tests are performed to investigate the effects of design variations on the long-term reliability of lead-free solder joints; SMD design shows less reliability life than others. The implications of these results for the reliability of lead-free solder joints are discussed in this paper.

Analytical Performance of Printed Circuit Board Ion Trap Array Mass Analyzer with Electrospray Ionization

Abstract The analytical performance of rectilinear ion trap array made up of printed circuit board material has been investigated. The experimental results indicated the intensity of ions determined were dramatically affected by ion kinetic energy, as in 18 eV, the arginine (Arg) ion (m/z 175.2) dominated in the mass spectrum. The ion trap array can perform multiple sample ion storage, mass-selected ion isolation, ion ejection, collision induce dissociation. The ions of m/z 175.2, 117.3 and 71.8 were isolated by SWIFT notch 50-60 kHz, 75-85 kHz and 130-145 kHz, respectively. The ions of m/z 175.2, 117.3 and 71.8 were selectively ejected using 55, 80 and 135 kHz sine wave. In helium gas, the fragment ions of m/z 157.2, 130.3 and 117.3 were obtained by the fragmentation reaction of Arg precursor ion (m/z 175.2) using 102 kHz sine wave. The ion detection efficiency was investigated by electric current integration method, which indicated that the ion detection efficiency was estimated to be 46.3% in 256 kHz AC resonant ejection and was about 9.7% in boundary ejection.

Frequency Dependence Examination of PCB Material FR4 Relative Permittivity

At the microwave frequencies high requirements are put on the materials for construction of final devices. A number of dielectric substrates are available for microstrip technologies but the prices of these materials are directly proportional to their good dielectric features. Application of low cost materials can cause serious inaccuracies if the design of device assumed better quality of materials. This paper deals with examination of relative permittivity (dielectric constant) of widely used FR4 material for construction of PCB (Printed Circuit Boards). The examination is based on calculations and measurements of functional sample which was manufactured for this purpose.