Arrangements of printed circuit boards parallel to a metallic cover plane are used in various applications. Some examples are automotive control devices, mobile devices, parallel stacked PCBs in rack applications, PCBs parallel to a cooling device, computer motherboards mounted parallel to an enclosure plane, CD/DVD and hard disk drives. Figure 1.1 and Figure 1.2 illustrate the arrangements of PCBs parallel to a metallic enclosure or parallel to a PCB ground plane for some example applications.
|(a) Motor control device.||(b) Car audio device.|
|(a) Cell phone.||(b) Rack mounted parallel PCB stack.|
The following list of technical facts from a typical automotive control device, of the BOSCH MED17 generation, gives a perception of the complexity.
In addition to this complex device internal structure, a quantitative electromagnetic
emission simulation has to consider external appliances which are connected to the
control device by a cable harness. Although mobile devices are smaller, the integration
density in the package is much higher. Usually industrial and computer PCBs are also very
dense, sizeable, and are operated at even higher clock rates. Therefore, the complexity
is a challenge for the EMC simulation in nearly every application. The complexity will
further increase, because the strong demand of rising functionality leads to more density
and higher clock rates in the future. Figure 1.3 from 
depicts a forecast on microprocessor and microcontroller clock rates and emission
requirements until 2020. The content of Figure 1.3(a) is based on
data from ITRS , which sets industry and technology milestones for the next 15
years. By 2020 processors are imaginable to run at about 25GHz. By 2016 the ITRS road map
projects the minimum physical gate length of transistors to be close to 9nm, which is
considered by most researchers to be kind of the physical limit of silicon. The
saturation scenario considers several limiting factors for frequency increase, such as,
for example, MOS mobility degradation and interconnect delay. In fact, there is a five
year gap between microprocessor development and microcontroller development regarding
density and clock rates. This enables a further MOS technology based performance
enhancement of microcontrollers beyond 2020. According to , functional
diversification by integration of analog, RF, power, and passive functions provides
additional opportunities beyond scaling in order to increase device performance.
The described complexity increase of microcontrollers provides an impression of the future complexity increase of electronic devices, because nearly every electronic device will be based on a processor or controller. The increased controller performance and functionality will lead to enhanced peripherals and busses, more connector pins, more device interfaces, and denser enclosure designs.
Figure 1.3(b) depicts the evolution of the RF emissions from ICs
. There is a strong IC customer pressure for achieving low emissions.
IC designs without EMC optimization suffer from high RF emissions and require expensive
on board decoupling and filtering. Therefore, EMC concerns have increased in importance.
Within the last 10 years low emission and high immunity to interference have emerged as
the key differentiators of overall IC performances. A 20dB emission reduction could be
achieved by design guidelines and new EMC knowledge in 2000. EMC optimization will lead
to a further emission reduction of about 40dB in 2020. Examples have already been
presented . However, the technology trend towards more density and
higher clock rates leads to higher emissions. Thus, a gap is expected to remain between
the customer demand and the emission level of the devices. To meet the customer
requirements, low emission design guidelines and simulation based design techniques for
SoC and SiP have to be enhanced and generalized.
|(a) Core frequency increase until 2020.||(b) Maximum emission level.|
In the definition, specification, and predesign phase of the product life cycle,
adaptability is at a maximum, when costs of change are at their lowest. The uncertainties
of the functional device definition, which is not finalized in the very early stage,
inhibit accurate quantitative simulations of the final device. However, with progressing
product definition, the quality assurance investment must increase to benefit from high
adaptability at low costs. Most predesign definitions can scarcely be changed in the
later design process and have a significant influence on the attainable quality
performance. Conceptual simulations in the predesign phase powerfully support design
decisions in the functional product definition process.
The required quality performance of a product must be reached in the design phase to achieve 100% first pass yield. The 100% yield is necessary to enable the supplier of a product to omit rework phases in the project road map, without any failure risk on agreed customer deadlines. Only simulation provides the opportunity to make performance predictions and optimizations as long as no prototype is available. There must not remain any open quality issues, when a product has been finalized and series fabrication has started.
The main motivation of electromagnetic emission simulation is to ensure the EMC compliance in the design phase of a new device, in order to avoid redesign costs and time delays. However, the simulation methods must be very efficient to enable simulation based CAD of EMC properties within short, time optimized product development cycles. The objective of this work is to develop efficient methods by using analytical and semi-analytical methods, domain decomposition, and methods with an explicit assignment to source and coupling path. This enables fast conceptual simulations in the predesign phase and swift product quality performance optimization in the design phase.
C. Poschalko: The Simulation of Emission from Printed Circuit Boards under a Metallic Cover