PCB Edge Shielding Effectiveness Evaluation and Design Guidelines

Modeling and simulation for a drop-impact analysis of multi-layered printed circuit boards

The micro-hole is a key structure in multilayer printed circuit board (PCB), as it enables the effective transmission of electrical signals. At present, the most common way to machine PCB micro-holes is mechanical drilling using micro-bit. However, in the mechanical drilling of micro-holes, these holes are prone to burring at the hole mouth due to the micro-bit failing to cleanly cut through the first layer of copper foil on the PCB. Hole mouth burr can seriously affect the performance of the PCB, resulting in potential short circuiting or even ruining the PCB. To solve the above problems, this paper proposed to machine the first layer of copper foil on the PCB via micro electro-discharge machining (micro-EDM) to eliminate hole mouth burr. Compared with the mechanical drilling, micro-EDM is a form of non-contact machining, and the high temperature generated from the electric spark discharge can erode the first layer of copper foil, thus fully eliminating hole mouth burr. This paper performed a detailed study of the influence of spindle speed, machining voltage, pulse width, and pulse interval on hole mouth quality. After that, the technological parameters for eliminating hole mouth burr were obtained. Finally, under the effects of 20,000 rpm spindle speed, 26 V machining voltage, 4 μs pulse width, and 8 μs pulse interval, a micro-bit with a diameter of 200 μm was used to perform micro-EDM of the first layer of copper foil. From the machining results, it can be known that the PCB micro-hole was possessed of overall good quality, with good hole wall surface quality and almost no visible hole mouth burr.

This paper reports on the characterization of the Shielding Effectiveness (SE) of Board Level Shielding (BLS) components up to 44 GHz, using a dedicated stripline measuring setup. The setup is based on a similar measuring method for the characterization of shielding gaskets, as described in SAE ARP 6248. In this paper, it is shown that the SE of both BLS components and the mounting technique on a Printed circuit board (PCB) can be characterized using this stripline setup. The measurements show the effect on the SE values due to the fact that the ground (GND) layer is embedded in a multilayer PCB, forming a slit between this GND layer and the BLS component. Techniques, based on a waveguide beyond cut-off (WGBC) by an appropriate use of multiple vias, are evaluated using this dedicated stripline setup.

Recently, electric circuits may be become small, and also high-density electrical technologies have advanced. In order to place many elements on the small printed circuit board (PCB), a high-density multi-layered PCB may be used. Many vias are used in such multi-layered PCB to connect lines on each layer. If many vias are placed in narrow area, they make ground slots. If a ground slot exists near a transmission line, the distortion of the signal may be occurred. Then, existence of slots is issue for high-speed circuit designs. In this paper, we analyzed the transmission characteristic of a microstrip line above a ground slot on a PCB using multiconductor transmission-line (MTL) method. First, we measured it for various slot width. And also, we analyzed it using FDTD method. Comparing the results of measurement value and analysis value, a validity of the model of the FDTD method was confirmed. Next, we derived the characteristic impedance of the microstrip line using spectral domain approach (SDA). We calculated the transmission characteristics of the microstrip line above the slot by applying MTL method. And, the analysis values of MTL and FDTD are almost same in the case of small slot up to high frequency.

In recent years, electronic devices are strongly required to be smaller, lighter, and more powerful. As a result, mounted components have become smaller, more powerful, and denser, and the heat generation density on printed circuit boards (PCBs) has increased. Since rising component temperatures can lead to component failure, efficient heat removal from the generated heat has become an urgent issue. Since general PCBs have low thermal conductivity, when high heat dissipation is required, methods to increase the thermal conductivity of PCBs have been employed by increasing the copper (Cu) content in the PCB or by placing an aluminum (Al) alloy in the inner layer. However, while Cu and Al have high thermal conductivity, they also have high coefficients of thermal expansion (CTE) and young’s modulus, and the CTE of a PCB with increased thermal conductivity using these materials is high. If the thermal expansion difference between the PCB and mounted components is large, reliability against heat cycles cannot be obtained. Therefore, we have focused on copper-molybdenum (CuMo) composite materials with high thermal conductivity, high elastic modulus, and low thermal expansion. We have been utilizing Cu-Mo for the development of our PCBs and fabricated multilayered CuMo composite PCBs; therefore, this report will focus on the results regarding thermal characterization of prototype PCBs.

The advent of High Density Printed Circuit Board (HD PCB) into electronic assemblies has enabled the evolution of mobile computing devices like smartphones and tablets. System level failure analysis to understand quality and reliability issues of such products is challenging. The presence of blind and buried vias stacked in a multi-layer Printed Circuit Board (PCB) coupled with double sided assemblies without test or probe points for electrical continuity access adds to the complexity. This paper presents one such case study where a detailed failure analysis approach was adopted to identify the root cause of failures. Coupling software and complimentary electrical techniques the problem was isolated to the PCB part of the system assembly. Deep dive material analysis of the fault isolated signals revealed cracks in inner layers of the PCB. The study also highlighted the fact that marginal PCB manufacturing issues could worsen during the thermal exposures associated with motherboard assembly and product usage.

Shielding effectiveness (SE) is an important measure of how well an enclosure reduces the electromagnetic (EM) field incident upon it. Commonly, when the shielding effectiveness of an enclosure is stated it is for the case when the enclosure is empty. Including contents such as printed circuit boards (PCBs) in the enclosure will affect the shielding effectiveness as the PCB absorbs EM energy. One technique of determining how much energy a PCB absorbs is to measure its absorption cross section (ACS) using a reverberation chamber (RC). The measured ACS can be used to predict the shielding effectiveness of an enclosure when the PCB is inside it using power balance techniques. In this paper the ACS of a number of PCBs are measured both individually and in closely stacked groups. This information is then used to show how the ACS can be used to calculate shielding effectiveness and the results are compared to direct measurement of the SE of the enclosure containing a PCB. Knowledge of the ACS of typical or particular PCBs could be used by engineers to estimate the real shielding effectiveness of an enclosure with contents, when designing electronic systems.

The rapid development of information and communication technologies has driven the rapid growth of data traffic and the large requirement of high-speed optical transceiver modules. Usually, optical subassemblies through flexible printed circuit boards (PCBs) connect with the hard PCBs to compose as optical transceiver modules. Because of the impedance mismatch of connection between flexible PCB and hard PCB, the operation bandwidth of the module can be limited. In this paper, the design of connection between flexible PCB and hard PCB in optical subassembly modules will be investigated for increasing the operation speed of the module. First, the transmission bandwidth of flexible PCB is analyzed. High-frequency performances of three transmission line structures, micro-strip line, grounded coplanar waveguide, and top ground micro-strip line, are investigated in flexible PCB. High-frequency performances of flexible PCB with different bending types are also investigated. The flexible PCB has been verified to be suitable to use in 25 Gb/s applications. Next, the high-speed transmission performance is analyzed through the connection between flexible PCB and hard PCB, because the impedance mismatch usually occurs at the connection. The ground pads are added near the signal line of flexible PCB, and the ground pads are connected to the ground layer in PCB through ground vias. The anti-pad in hard PCB is added under the signal solder pad. The dip of S21 response can be eliminated by the optimized ground pad. The impedance mismatch can be reduced by the optimized anti-pad, the impedance increases from 40-Ω to 49-Ω at the connection between flexible PCB and hard PCB, and the transmission bandwidth can increase from 16.5 GHz to 23.5 GHz. TO-46 header is a common and low-cost packaging solution for DFB laser and photodiodes. The connection between flexible PCB and TO-46 header is also investigated. While the connection has a gap, the dip of frequency response will occur at lower frequency. While the connection is very close, the bandwidth can be larger than 25 GHz. The flexible PCB, hard PCB, and TO-46 header are combined together, and the 23 GHz transmission bandwidth can be obtained. The 25 Gb/s transmission eye diagram is also measured, and the eye height, rise time, fall time, and Q-factor are 268.14 mV, 13.78 ps, 13.56 ps, and 8.76, respectively. The combined flexible PCB, hard PCB, and TO-46 header are verified to be suitable to apply in 25 Gb/s optical subassembly modules, and will be able to be used in 100G Ethernet.

Electromagnetic interference is a significant problem in high-speed circuits. To minimize its effect and improve the electrical characteristics of circuits such as signal integrity and electromagnetic compatibility, the application of an electromagnetic isolation structure with electromagnetic bandgap (EBG) is considered. In this paper, a novel wideband EBG structure is proposed for EMI reduction in multilayer printed circuit boards (PCB), in which a kind of improved L-bridge is used as additional series inductance, and the equivalent inductance can be increased significantly. Compared to the traditional mushroom-liked EBG structure with the same parameters, the L-bridge structure can broaden the relative bandwidth to nearly 250%, with a significant decline of the center frequency. The effectiveness and accuracy of this structure are verified by both simulations and measurements. © 2011 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2011. © 2011 Wiley Periodicals, Inc.

A compact common-mode suppression filter is proposed by employing the modified ground structure (MGS) for high speed digital interconnects using differential signals on the multi-layered printed circuit board (PCB). It consists of two folded U-shaped slot resonators and arranged via-holes. It has compact size of 0.073λ <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g</inf> × 0.225λ <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g</inf> when the center frequency is 5.2 GHz. A test board is fabricated on four-layered PCB through an optimizing process for verifying effects of the proposed MSG structure. The proposed MGS can suppress the common-mode noise over 10 dB from 4.34 to 6.07 GHz in the frequency domain and over 52% of amplitude in the time domain. Furthermore, the proposed filter still keeps good signal integrity characteristics with regard to the insertion loss of differential-mode signals. It is clear that the proposed filter structure can apply to the multi-layered PCB of commercial mobile devices due to its compact size and have some advantages such as wide bandwidth, gigahertz frequency range, low cost, and PCB embedded design‥

We have analyzed the effect of via in multilayer printed circuit boards (PCBs) on signal integrity and signal delay time of high-speed digital systems. First, the techniques of the circuit modeling of via are discussed. Electrical behaviors of via in interconnects according to its circuit model are characterized through HSPICE simulation. Based on these results, we show that via can behave as being capacitive or inductive according to the characteristic impedance of signal lines, which is different from the fact that via is generally regarded as being only capacitive. The proposed electrical characteristic of via is verified by results of TDR/TDT measurement of through-hole type via in 8-layer PCBs. Second, the methodology of measurement of delay caused by via is proposed. Because it is so difficult to measure the electrical delay of signal passing through one via, we extract the delay caused by single via from measuring the delay when the signal passes through several vias. For an example, we obtained the signal delay time of 12 psec caused by a throughhole type via in 8-layer PCBs. For just two vias, the delay time is about 24 psec and it is about 8% of flight time of 5 cm signal line.

Plated though-hole (PTH) vias are extensively adopted in multilayer printed circuit boards (PCBs). Unused portions of PTH vias become open stubs, which excite the resonance mode and degrade signal integrity (SI). This work investigates how open via stubs in multilayer PCBs affect the time-domain transmission (TDT) waveform and eye diagram. Exactly how time-domain reflection affects the open via stubs on TDT waveform is also studied using the lattice diagram. Additionally, the R and RL terminations of open via stubs are developed to improve SI in previous studies. Moreover, the RC termination of open via stubs is proposed to improve the performance of SI, which is the same as that of the R termination in this work. RC termination is also characterized by its nearly zero DC power consumption. Furthermore, different terminations are compared with respect to how they improve the TDT waveforms and eye diagrams.

Possibilities of improvement in detection and characterisation accuracy concerning internal defects in multi-layered printed circuit boards (PCB) and electronic components by applying the ultrasonic immersion technique have been investigated. The experiments have been carried out on a real PCB with a mounted defective microchip. Defect-free and defective high-voltage semiconductor components have also been investigated. The investigations have been performed using the acoustic microscope produced by Ultrasonic Science Ltd and ultrasonic measurement system developed at the Ultrasound Institute of Kaunas University of Technology. The novel signal processing method based on the adaptive numerical model of ultrasonic wave propagation through a multi-layered electronic component and respective selection of signal components in time and frequency domains have been proposed. Two different signal processing techniques have been used to increase the contrast of defective regions and so improve reliability of ultrasonic inspection.

Gearless and compact motors rotating at speeds above 10,000 rpm are finding many applications nowadays. This study presents the multiphysics modelling and analysis of a multilayer printed circuit board (PCB) stator for high‐speed, low‐power axial flux permanent magnet motor. The possibility of circulating current in the multilayer PCB is studied. The two major effects of eddy currents at high frequencies: skin effect and proximity effect are investigated for the PCB winding. The losses in the PCB stator are estimated, and thermal analysis is performed to ensure reliable operation of the motor. MagNet 3‐D and COMSOL Multiphysics are used, respectively for the finite element analysis and optimisation of the motor; and the simulation results are presented. A prototype of the motor is fabricated and tested to validate the simulation results.

The behavior of reradiated fields from PCBs, with the radar cross section being the main parameter of interest is investigated in this work. A rigorous approach to predict radiation from PCBs in a GTEM cell is presented. The analysis is based upon the use of the reciprocity theorem in combination with the method of moment applied to the scattered field. Thus, yielding a generalized impedance matrix, whose determinant represents the characteristic polynomial of the scattering system. The effectiveness of the method is demonstrated by investigating some canonical circuit configurations and structures illustrating sources of fundamental EMI mechanism. The validity and the accuracy of the analysis becomes obvious in view of the one-to- one correlation with measurements. I. INTRODUCTION Printed-Circuits Boards (PCB) are of overriding importance in modern microelectronics where they undergo a continu- ous package complexity. Multilayer structures, split reference planes, various interconnects like bends, vias, etc. and trace circuit configurations in form of rectangular/circular loop, bent wire, linear dipoles, etc., are commonly mounted and present on hihgly integrated PCBs. These structures have led to an upsurge of interest in the analysis of the possible elec- tromagnetic interference (EMI) since they are often sources of unintentional radiated emission which can alter the EMC performance of real PCBs. Especially, in presence of an RLC- circuit, high-speed signals routed on the board may carry over resonances. These resonances tend, on their own, to carry interferences over much longer distances, which can not be predicted by field or gavanic coupling. The behavior of the reradiated field, with the PCB radar cross section (RCS) being the main parameter of interest, is therefore a good figure of merit in diagnosing radiation problems on the board. This paper addresses these particular points. Especially, it provides a rigorous approach to predict radiation from PCBs in a Giagahertz transverse electromagnetic (GTEM) cell. The analysis is based upon the use of the reciprocity theorem in combination with the application of the method of moment (MoM) to the scattered field yielding a generalized impedance matrix, whose determinant represents the characteristic poly- nomial of the scattering systems. After deriving an expression for the RCS in the next section, the generalized impedance matrix is evaluated for arbitrar- ily shaped wire radiating elements with a conducting plane reflector (section III). The real-axis method characterized by Sommerfeld-type integrals and moment-method solutions (1)- (3) is used to calculate elements of the impedance matrices. The effectiveness of the method is demonstrated by inves- tigating some canonical circuit configurations and structures illustrating sources of fundamental EMI mechanism (section IV). The validity and the accuracy of the analysis become ob- vious in view of the one to one correlation with measurements (section V).