Application of the cavity model to lossy power-return plane structures in printed circuit boards

Power-return plane pairs in printed circuit boards are often modeled as resonant cavities. Cavity models can be used to calculate transfer impedance parameters used to predict levels of power bus noise. Techniques for applying the cavity model to lossy printed circuit board geometries rely on a low-loss assumption in their derivations. Boards that have been designed to damp power bus resonances (e.g., boards with embedded capacitance) generally violate this low-loss assumption. This paper investigates the validity of the cavity model when applied to printed circuit board structures where the board resonances are significantly damped. Cavity modeling results for sample lossy power-return plane structures are validated using a three-dimensional full wave numerical code. A simple method is also established to check the validity of the cavity model for a power-return plane structure with imperfect conductors and lossy dielectric substrates.     

Circuit models for power bus structures on printed circuit boards using a hybrid FEM-SPICE method

Power bus structures consisting of two parallel conducting planes are widely used on high-speed printed circuit boards. In this paper, a full-wave finite-element method (FEM) method is used to analyze power bus structures, and the resulting matrix equations are converted to equivalent circuits that can be analyzed using SPICE programs. Using this method of combining FEM and SPICE, power bus structures of arbitrary shape can be modeled efficiently both in the time-domain and frequency-domain, along with the circuit components connected to the bus. Dielectric loss and losses due to the finite resistance of the power planes can also be modeled. Practical examples are presented to validate this method.     

On the external inductive coupling of differential signalling on printed circuit boards

A study of the common-mode radiation behavior of differential signalling is presented, considering small current imbalances, which may originate from differential driver phase skew and circuit asymmetries. Two configurations are investigated, a solid ground plane and a ground plane with an open slit as an example of a ground-plane discontinuity. The external coupling voltage responsible for common-mode radiation is quantified through coupling inductances, for which closed-form expressions are derived and numerically validated. It is found that common-mode electromagnetic interference from differential signalling may become comparable to conventional single trace routing when traces are placed near the edge of the ground plane. For traces routed across a ground-plane discontinuity, differential signalling is only an effective means for reducing radiation when signal imbalance can be kept small.     

On resonance and shielding of printed traces on a circuit board

A rigorous formulation in the spectral domain is used to investigate the radiation from unterminated traces printed on a circuit board in the frequency range from 30 MHz to 1 GHz. The effect of coupling among adjacent traces on the resonant frequencies and the shielding effectiveness of metallic coating on the plastic cover are analyzed. It is found that the radiation around resonant frequencies is critical to comply with the Federal Communications Commission (FCC) specifications and that an appropriate coating can resolve the problem     

Gbit/s transmission via two-photon-absorption-inscribed optical waveguides on printed circuit boards

Optical waveguides were inscribed into a 300 mm-thick polymer layer applied onto standard printed circuit boards via two-photon-absorption. VCSELs and photodiodes embedded in this layer of ORMOCERw complemented optical interconnects for multi-Gbit/s data transmission at a wavelength of 850 nm.     

A simple and effective model for electromagnetic bandgap structures embedded in printed circuit boards

Using a transmission-line model and considering a simple lumped-element substitute for the patch-via structure, a first-order, but detailed, quantitative and qualitative analysis of the filtering properties of a metallo-dielectric electromagnetic bandgap structure embedded in a printed circuit board is presented. This model is able to describe the resonant properties of the structure as well as its pass-band and stop-band regions.     

Characterization and modeling of a new via structure in multilayered printed circuit boards

We demonstrate that structure engineering of the transmission line near the via can reduce the amount of reflection of the RF signal. We have fabricated two types of vias with different transmission line geometries and have measured the reflection. The measured results show that the shape of the transmission line near the via hole is important in determining the total reflection of the via structure. The amount of reflection obtained from full three-dimensional (3-D) electromagnetic simulations can reproduce the measured results with reasonable accuracy, which suggests that efficient design of the via structure could be possible without resorting to hardware fabrication and characterization.     

A numerical investigation of interior resonances in the hybrid FEM/MoM method

The interior resonance problem that can occur when using a hybrid finite-element method/method of moments (FEM/MoM) method to model electromagnetic scattering problems is investigated. Calculations of the bistatic radar cross section of a coated dielectric sphere are presented using different formulations, solution approaches, and solvers. The solutions using the electric-field integral equation have significant errors near an interior resonance frequency. When the combined-field integral equation is employed, satisfactory solutions can be obtained that do not depend on the particular solution approach or solver.     

Estimating the noise mitigation effect of local decoupling in printed circuit boards

Local decoupling, i.e., placing decoupling capacitors sufficiently close to device power/ground pins in order to decrease the impedance of power bus at frequencies higher than the series resonant frequency, has been studied using a modeling approach, a hybrid lumped/distributed circuit model established and an expression to quantify the benefits of power bits noise mitigation due to local decoupling developed. In this work, a test board with a local decoupling capacitor was studied and the noise mitigation effect due to the capacitor placed adjacent to an input test port was measured. Closed-form expressions for self and mutual inductances of vias are developed, so that the noise mitigation effect can then be estimated using the previously developed expression. The difference between the estimates and measurements is approximately 1 dB, which demonstrates the application of these closed-form expressions in the PCB power bus designs. Shared-via decoupling, capacitors sharing vias with device power/ground pins, is also modeled as an extreme case of local decoupling.     

Research on applying direct plating to additive process for printed circuit board

The feasibility of applying direct-metallization as an additive process for printed circuit board was explored. Pd/Sn catalyst was used in the activation step and the content of Pd adsorption was found to be the controlling factor. The Pd content was affected by the conditions of various steps including condition, activation, acceleration, and promotion. The sequence of applying photoresist and activation with Pd/Sn catalyst plus promotion with Na₂S solution was also studied. It was found that a well-defined pattern could be obtained by applying the Pd/Sn catalyst layer before applying the photo-resist film. If the photoresist was applied before the activation step, copper deposition tended to develop beyond the desired pattern region on the surface. We also found that the lateral growth rate of copper deposition was inversely affected by the concentration of copper sulfate. This can be explained by a deposition model in which the lateral growth of copper deposition is caused by the charge transfer of the sulfur atom as a bridging ligand.     

Model of the electromagnetic fields inside a cuboidal enclosurepopulated with conducting planes or printed circuit boards

We examine the extension of a simple and versatile model of the electromagnetic fields in an equipment enclosure with an aperture to include the effects of loading the enclosure with conducting planes or printed circuit board structures (PCB). Modeling results are compared with experimental measurements of the shielding effectiveness in a cuboidal enclosure loaded with both grounded and ungrounded conducting planes and/or PCBs with a range of grounded and ungrounded tracks. Measurement results are compared with full electromagnetic simulations and the simple model to demonstrate the accuracy and range of validity of the simple model     

Twisted differential line structure on high-speed printed circuit boards to reduce crosstalk and radiated emission

Differential signaling has become a popular choice for high-speed digital interconnection schemes on printed circuit boards (PCBs), offering superior immunity to crosstalk and external noise. However, conventional differential lines on PCBs still have unsolved problems, such as crosstalk and radiated emission. When more than two differential pairs run in parallel, a line is coupled to the line adjacent to it because all the lines are parallel in a fixed order. Accordingly, the two lines that constitute a differential pair are subject to the differential-mode crosstalk that cannot be canceled out by virtue of the differential signaling. To overcome this, we propose a twisted differential line (TDL) structure on a high-speed multilayer PCB by using a concept similar to a twisted pair in a cable interconnection. It has been successfully demonstrated by measurement and simulation that the TDL is subject to much lower crosstalk and achieves a 13-dB suppression of radiated emission, even when supporting a 3-Gb/s data rate.     

Analysis of noise coupling from a power distribution network to signal traces in high-speed multilayer printed circuit boards

As layout density increases in highly integrated multilayer printed circuit boards (PCBs), the noise that exists in the power distribution network (PDN) is increasingly coupled to the signal traces, and precise modeling to describe the coupling phenomenon becomes necessary. This paper presents a model to describe noise coupling between the power/ground planes and signal traces in multilayer systems. An analytical model for the coupling has been successfully derived, and the coupling mechanism was rigorously analyzed and clarified. Wave equations for a signal trace with power/ground noise were solved by imposing boundary conditions. Measurements in both the frequency and time domains have been conducted to confirm the validity of the proposed model.     

Numerical simulation of the electrical performance of printed circuit boards under cyclic thermal loads

Different Printed Circuit Board (PCB) designs were tested in an Interconnection Stress Test. In such a test, PCBs were subjected to temperature cycles alternating between two extremes (e.g. − 40 °C to 160 °C). The electrical resistance was measured on-line during these tests. If the resistance rose by more than 10% of the initial value at the highest temperature, the test was terminated. The PCB structures were modeled by means of the Finite Element Analysis (FEA) Software Abaqus using a viscoplastic material model extended by a mean backstress memorization for the domain representing the copper interconnections. The stress/strain states computed by Abaqus served as input to a pore growth model which eventually allowed working out an indicator for the electrical performance loss. Subsequently, electrical FEA were conducted to obtain a correlation between the pore volume fraction distributed over the structure and the electrical resistance increase. The results of the simulations were compared to experimental results to determine parameters for the pore growth model. A well calibrated pore fraction evolution law allowed reliably predicting the electrical performance of various PCB designs as well as drawing some conclusions on the initial pore volume fraction in the PCB prior to operation.     

An efficient path-based equivalent circuit model for design, synthesis, and optimization of power distribution networks in multilayer printed circuit boards

In high-speed printed circuit boards, the decoupling capacitors are commonly used to mitigate the power-bus noise that causes many signal integrity problems. It is very important to determine their proper locations and values so that the power distribution network should have low impedance over a wide range of frequencies, which demands a precise power-bus model considering the decoupling capacitors. However, conventional power-bus models suffer from various problems, i.e., the numerical analyzes require huge computation while the lumped circuit models show poor accuracy. In this paper, a novel power-bus model has been proposed, which simplifies the n-port Z-parameters of a power-bus plane to a lumped T-network circuit model. It exploits the path-based equivalent circuit model to consider the interference of the current paths between the decoupling capacitors, while the conventional lumped models assume that all decoupling capacitors are connected in parallel, independently with each other. It also models the equivalent electrical parameters of the board parasitic precisely, while the conventional lumped models employ only the inter-plane capacitance of the power-ground planes. Although it is a lumped model for fast and easy calculation, experimental results show that the proposed model is almost as precise as the numerical analysis. Consequently, the proposed model enables a quick and accurate optimization of power distribution networks in the frequency domain by determining the locations and values of the decoupling capacitors.     

A new twisted differential line structure on high-speed printed circuit boards to enhance immunity to crosstalk and external noise

Differential signaling has become a popular choice for high-speed interconnection schemes on Printed Circuit Boards (PCBs), offering superior immunity to external noise. However, conventional differential transmission lines on PCBs have problems, such as crosstalk and radiated emission. To overcome these, we propose a Twisted Differential Line (TDL) structure on a multilayer PCB. Its improved immunity to crosstalk noise and the reduced radiated emission has been successfully demonstrated by measurement. The proposed structure is proven to transmit 3 Gbps digital signals with a clear eye-pattern. Furthermore, it is subject to much less crosstalk noise and achieves a 13 dB suppression of radiated emission.     

On the modeling of a gapped power-bus structure using a hybrid FEM/MoM approach

A hybrid finite-element-method/method-of-moments (FEM/MoM) approach is applied to the analysis of a gapped power-bus structure on a printed circuit board. FEM is used to model the details of the structure. MoM is used to provide a radiation boundary condition to terminate the FEM mesh. Numerical results exhibit significant errors when the FEM/MoM boundary is chosen to coincide with the physical boundary of the board. These errors are due to the inability of hybrid elements on the boundary to enforce the correct boundary condition at a gap edge in a strong sense. A much better alternative is to extend the MoM boundary above the surface of the board.     

Processing quality results for electroless/electroplating of high-aspect ratio plated through holes in industrially produced printed circuit boards

The plating quality results of high-aspect ratio through holes in industrially produced and sized printed circuit boards are reported in this paper. Test panels with 32,000 PTHs were processed on an existing industrial production line in order to test the possibilities of modifying the line for panels with higher aspect-ratio plated through holes. Depending on the process parameters different types of faults in the plating of these plated through holes were detected, varying from gas bubbles stuck inside the plated through hole, rough and non-plated glass fibers caused by the drilling of the holes, to parts of resist stuck inside the through holes. The type of error occurring is dependent on the processing used. Because each individual processing step can influence the following processing steps, an integrated quality approach has to be considered. Most of these problems could be solved by small changes in process parameters. Making a quantitative analysis of the type of errors resulted in a drastic reduction in the number of unplated through holes on industrial panels. This was done by identifying and classifying the type of error occurring. Aspect ratio’s of 10.7 could be plated with a high yield on an existing vertical electroless plating line.     

Optimization of the printed circuit boards placement at thermal design of the units with natural air cooling

It is considered an influence of printed circuit boards placement on temperature distribution in electronic equipment units with natural air cooling. Modeling of the temperature distribution in the unit and research of mass-dimension characteristics were carried out by means of CADs and engineering analysis. There are developed simplified geometric and thermal models of the unit. Here we analyze specificities of heat exchange in the units of radio electronic equipment with natural air cooling. It is developed an algorithm for optimization of printed circuit boards placement in radio electronic equipment with natural air cooling taking into account non-uniform power distribution between printed circuit boards. Proposed algorithm can be used as one of the stage of optimization of size, carrying or mass-dimension factors of the unit in case where unit powers are distributed non-uniformly.