Printed Circuit Design & Fab - December 2008 - (Page 16)

Buyers Beware: There’s No Free lunch Knowing the ins and outs of EMC software tools can save time and money. IF yOU are INVOlVeD in Printed Circuit Automated EMC Design Rule Checking The EMC performance of a printed circuit board is primarily based on the location of the various components and critical high speed and I/O nets/traces. Manually checking the various layers of today’s high speed circuit boards is too time consuming and prone to human error. Automated Rule checking software relieves the tedium and removes the human error by reading the CAD design file, taking each critical net/trace in turn, and checking that it does not violate any of the most important EMC design rules. The usefulness of this kind of tool is largely based on the EMC design rules and whatever limits are used for each of the various design rules. Naturally, for different types of industries, some of the design rules will vary. So it is important that the automated design rule checking software allows for the creation of customer or industry specific rules. There are many EMC design rules available from numerous sources, but most of these are in conflict with one another. So a user might reasonably ask, “Which rule is right for my products?” Some of the automated EMC design rule checking software implement rules that are based on more detailed laboratory testing and/or fullwave simulations. Each rule should be based on solid electromagnetic physics and not on faith. Users should be very cautious before accepting EMC design rules; these rules should not only have detailed justifications but make sense with the basic fundaments of physics. Just because a rule might be commonly accepted does not mean it is right for every product or industry. Remember, it was not very long ago when it was commonly accepted that the earth was flat. Board (PCB) design, you are likely to be inundated by the many different tools now available for EMC engineers to help predict EMC performance of products before they are built. Many of these tools are excellent, but the buyer must understand what the tools can really dr. BruCE do– and what they cannot do! ArCHAmBEAult Tight schedules, tighter budgets and the rapid growth of high speed devices have made EMC software tools more attractive than ever before. Radiated emissions are always a challenge, and the lower voltage levels of very high-speed devices mean that immunity (ESD, radiated, conducted) has become even more important than in the past. Certainly, there will be no shortage of work for EMC engineers in the near future. However, there is actually a shortage of trained/experienced EMC engineers. Many companies do not have a full time EMC engineer (if they have any at all), or if there is an EMC engineer, he/she might be relatively inexperienced. This means that product designers are looking for help to replace the shortage of experienced EMC engineers, and software tools seem to hold great promise. In recent years, many vendors have created software tools to help with EMC design. Vendors will often claim that their tools can do PCB-level analysis through system-level analysis, and they will have very impressive color 3D plots to prove it. However, the phrase “there is no such thing as a free lunch” has new meaning in this context. The tools can do some things very well, but they do not replace the need for experienced EMC engineers, basic knowledge of electromagnetics and knowledge of the various simulation techniques’ strengths and weaknesses. Actually, “free lunch” might not be the best phrase as these tools can cost $20,000 and more. Wide ranges of automated EMI/EMC tools are available to the engineer. Automated tools include design rule checkers that check PCB layout against a set of predetermined design rules; quasi-static simulators, which are useful for inductance/capacitance/resistance parameter extraction when the component is much smaller than a wavelength; quick calculators using closed-form equations calculated by computer for simple applications; full-wave numerical simulation techniques which will give a very accurate simulation for a limited size problem and expert-system tools, which provide design advice based on a limited and predetermined set of conditions. It is clear that these different automated tools are applied to different EMI problems and at different times in the design process. 16 Fullwave Electromagnetic Simulation Software Today’s full wave EM simulation software tools cannot do everything. They cannot take the complete mechanical and electrical CAD files, compute for some limited time or provide the engineer with a green/red light for pass/fail for the regulatory standard desired. An EMI and/or design engineer is needed to reduce the overall product into a set of problems that can be realistically modeled. The engineer must decide where the risks are in the product design and analyze those areas. Vendor claims must be carefully examined. Vendors might claim to allow an engineer to include detailed PCB CAD designs along with metal shielding enclosures to predict the overall EMI performance. However, these tools are not really capable of such analysis. There are too many things that will influence the final product to make such DECEMBER 2008 printEd CirCuit dESign & fAB

Table of Contents Feed for the Digital Edition of Printed Circuit Design & Fab - December 2008

Printed Circuit Design & Fab - December 2008 Contents Our Line Market Watch Around the World Happenings ROI Global Sourcing EMC for the Real World Interconnect Strategies On the Forefront Final Finish Forum Test and Inspection Electronic System Design Data Management 101 Designers Take on Technology Challenges in 2008 PCB Signal Integrity, Power Integrity and EMC Challenges What’s in a Name? Ad Index PCB Dielectric Materials for High-Speed Applications Off the Shelf Marketplace BGA Bulletin

Printed Circuit Design & Fab - December 2008

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