Any time you plan to sell your electronic product in the US, the Federal Communications Commission (FCC) requires your product to pass standards for EMI (electromagnetic interference). Just because your designers know this fact doesn't mean they always take the FCC requirements into account during the design phase of the project. Too often, problems are not detected until late in the product development cycle - when you're getting ready to ship your product. The old adage holds true: It costs a penny to make a change in engineering, a dime in production, and a dollar after a product is in the field.

Because the FCC and equivalent organizations around the world set the emissions standards that all designs must meet, controlling unwanted electromagnetic radiation is an important concern for every electronic device designer. Understanding the most common reasons that products fail FCC testing enables you to take control by designing and building your product to meet these standards so you can pass FCC testing the first time.

Here are the 10 most common reasons products fail FCC testing:

1. Ignoring or downplaying FCC requirements for your product during the initial design phase.

Designers should determine what FCC and other global compliance regulations apply to their product, and what the radiated and conducted limits before starting the design phase. Thus proper EMC (electromagnetic compatibility) design techniques can be applied for PCB's, clocks, cables, connectors, enclosures and other components that strongly affect the overall EMC performance of your product.

Working with an experienced compliance engineer to review your design for proper EMC practices and conducting a pre-scan in the early stages of the design process can increase odds of first time success of FCC testing. This can save significant amounts of time and money, enabling you to meet your budget and timeline goals. Correcting an EMC problem early on may be as simple as moving components and traces around on a pc board - a relatively simple and inexpensive process during the design phase.

2. Selecting the fastest components and highest clock rate

Components with fast rise times are key contributors to radiated interference, so it's critical to control rise times by using the right components. The simplest and least expensive way to do this is to use a series resistor terminator to add resistance and help slow the rise time of the signal.

The main sources of radiation in digital circuits are the clock(s) and other fast rise time signals that are widely distributed in the system. In general, lowering the clock speeds of the system will reduce emissions. A good design approach for reducing EMI is to use the minimum clock speed possible for your design, with controlled rise times.

3. Using a single or two layer board in place of a multi-layer PC board

Use multi-layer PC boards rather than single-layer boards whenever possible. Top and bottom ground planes with controlled impedances can reduce radiation from multi-layer boards by up to 10 dB or more.

4. Not considering emissions in clock layout

There are several key considerations in clock layout. Separating the I/O lines from clocks on circuit boards can minimize unwanted coupling and the resulting higher emissions. Additionally, it's best to keep clock traces as short as possible to minimize lead inductance and loop area, which in turn minimizes radiation. It's also important to keep the return path impedance low, and to properly terminate clock lines to avoid excessive ringing.

5. Not using enough bypass capacitors

Bypass capacitors are used to reduce noise on printed circuit boards. When determining how many and what technology type of capacitors to be used, designers should consider the type, speed, purpose and quantity of components on the board. Murata and other cap manufacturers offer simple simulation programs that help you determine which capacitor will best meet your design needs.

6. Using unshielded cables

Cables within your design often become unintentional noise antennas that create huge EMI problems. Shielded cables can reduce the emissions by up to 20 dB as well as minimize the problem of crosstalk. If high-speed clocks or signals with high rise times travel across your cables, insure proper shielding and termination. Avoid using cables with excessive pigtails, as they are hard to terminate properly.

The maximum benefits of a well-shielded cable will only be realized if the shield is properly terminated. The requirements of a proper shield termination are:

• Very low impedance ground connection
• 360 degree contact with the shield

7. Using plastic connectors

Connector leakage is a major source of cable problems. Metal or conductive plastic connectors offer protection against EMI at the termination point on the connector shell. Generally, you should choose metal or conductive plastic connectors when using shielded cable.

8. Not using ferrites in cable design

Common mode noise is often present in cables due to the PCB signal connections and returns forming a common impedance. This type of noise may be reduced through the use of proper PCB design techniques by reducing the common mode impedance or by placing a ferrite bead around the cable. Ferrites absorb energy and can reduce emissions by up to 10-20 dB.

9. Not utilizing a power line filter

Powerline Conducted RFI (Radio Frequency Interference) can be brought to satisfactory levels by including a power line filter in the system. The filter suppresses conducted noise leaving the unit, reducing RFI to acceptable levels and lowering the susceptibility of the equipment to incoming power line noise that can affect its performance. A typical power line filter includes components to block both common mode and differential mode noise.

10. Not shielding the chassis properly

A properly grounded and enclosed chassis design is key to controlling EMI. Designers should keep openings to a minimum, using the 1/20 wavelength rule. Avoid using a chassis with oxidized or painted steel pieces, and make sure that the various chassis pieces make good electrical contact.

While your engineering staff may have the top design experience for your product's intended market, a review by a competent compliance engineer and prototype pre-scans in the design phase can help you avoid costly fixes later on. Percept has a staff of experienced compliance engineers and lab facilities to help you meet your compliance regulations with margin to spare.

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by Kenneth A. Crow, DRM Associates

For many durable goods, there are a variety of other design considerations related to the total product life cycle. For consumable products, some of these life cycle factors may be of lesser importance. Life cycle factors that may need to be addressed during product design include:

• Testability/Inspectability
• Reliability/Availability
• Maintainability/Serviceability
• Design for the Environment
• Upgradeability
• Installability
• Safety and Product Liability
• Human Factors

The relative importance of these factors and their orientation will vary from industry to industry and product to product. However, there are general design principles for these life cycle requirements that will be generally applicable to many items. A basic integrated product development concept is the parallel design of support processes with the design of the product. This parallel design requires early involvement and early consideration of life cycle factors (as appropriate) in the design process. However, in many organizations, consideration or design of the support processes is an after-thought and many of these developmental activities are started after the design of the product is well under way if not essentially complete.

DESIGN FOR TESTABILITY / INSPECTABILITY

Test and inspection processes can consume a significant amount of effort and the development or acquisition of test equipment can require considerable time and expense with some products. Early involvement of the test engineering or quality assurance functions can lead to design choices that can minimize the cost of developing or acquiring necessary equipment and the effort to test or inspect the product at the various stages of production. A starting point is to establish a common understanding between Engineering, their customers, and other functional departments regarding the requirements for product qualification, product acceptance after manufacture, and product diagnosis in the field. With this understanding, a design team can begin to effectively design products and test and inspection processes in parallel.
Increasingly complex and sophisticated products require capabilities and features to facilitate test and acceptance of products and diagnosis products if a defect is identified. Specific principles which need to be understood and applied in the design of products are:

• Use of Geometric Dimensioning and Tolerancing (GD&T) to provide unambiguous representation of design intent
• Specification of product parameters and tolerances that are within the natural capabilities of the manufacturing process (process capability index Cp and Cpk)
• Provision of test points, access to test points and connections, and sufficient real estate to support test points, connections, and built-in test capabilities
• Standard connections and interfaces to facilitate use of standard test equipment and connectors and to reduce effort to setup and connect the product during testing
• Automated test equipment compatibility
• Built-in test and diagnosis capability to provide self test and self-diagnosis in the factory and in the field
• Physical and electrical partitioning to facilitate test and isolation of faults

In addition, test engineering should be involved at an early stage to define test requirements and design the test approach. This will lead to the design or specification of test equipment that better optimizes test requirements, production volumes, equipment cost, equipment utilization, and testing effort/cost. Higher production volumes and standardized test approaches can justify development, acquisition, or use of automated test equipment. The design and acquisition of test equipment and procedures can be done in parallel with the design of the product which will reduce lead-time. Design of products to use standardized equipment can further reduce the costs of test equipment and reduce the lead-time to acquire, fabricate, and setup test equipment for both qualification testing and product acceptance testing.

DESIGN FOR RELIABILITY

Reliability consideration has tended to be more of an after-thought in the development of many new products. Many companies' reliability activities have been performed primarily to satisfy internal procedures or customer requirements. Where reliability is actively considered in product design, it tends to be done relatively late in the development process. Some companies focus their efforts on developing reliability predictions when this effort instead could be better utilized understanding and mitigating failure modes, thereby developing improved product reliability. Organizations will go through repeated (and planned) design/build/test iterations to develop higher reliability products. Overall, this focus is reactive in nature, and the time pressures to bring a product to market limit the reliability improvements that might be made.

In a integrated product development environment, the orientation toward reliability must be changed and a more proactive approach utilized. Reliability engineers need to be involved in product design at an early point to identify reliability issues and concerns and begin assessing reliability implications as the design concept emerges.
Use of computer-aided engineering (CAE) analysis and simulation tools at an early stage in the design can improve product reliability more inexpensively and in a shorter time than building and testing physical prototypes. Tools such as finite element analysis, fluid flow, thermal analysis, integrated reliability prediction models, etc., are becoming more widely used, more user friendly and less expensive.

Design of Experiments techniques can provide a structured, proactive approach to improving reliability and robustness as compared to unstructured, reactive design/build/test approaches. Further, these techniques consider the effect of both product and process parameters on the reliability of the product and address the effect of interactions between parameters. Finally, the company should begin establishing a mechanism to accumulate and apply "lessons learned" from the past related to reliability problems as well as other producibility and maintainability issues. These lessons learned can be very useful in avoiding making the same mistakes twice.
Specific Design for Reliability guidelines include the following:

• Design based on the expected range of the operating environment.
• Design to minimize or balance stresses and thermal loads and/or reduce sensitivity to these stresses or loads.
• De-rate components for added margin.
• Provide subsystem redundancy.
• Use proven component parts & materials with well-characterized reliability.
• Reduce parts count & interconnections (and their failure opportunities).
• Improve process capabilities to deliver more reliable components and assemblies.

DESIGN FOR MAINTAINABILITY / SERVICEABILITY

Consideration of product maintainability/serviceability tends to be an after-thought in the design of many products. Personnel responsible for maintenance and service need to be involved early to share their concerns and requirements. The design of the support processes needs to be developed in parallel with the design of the product. This can lead to lower overall life cycle costs and a product design that is optimized to its support processes.
When designing for maintainability/serviceability, there needs to be consideration of the tradeoffs involved. In high reliability and low cost products or with consumable products, designing for maintainability/serviceability is not important. In the case of a durable good with a long life cycle or a product with parts subject to wear, maintainability/serviceability may be more important than initial product acquisition cost, and the product must be designed for easy maintenance. In these situations, basic design rules need to be considered such as:

• Identify modules subject to wear or greater probability of replacement. Design these modules, assemblies or parts so that they can be easily accessed, removed and replaced.
• Use quick fastening and unfastening mechanisms for service items.
• Use common handtools and a minimum number of handtools for disassembly and re-assembly.
• Minimize serviceable items by placing the most likely items to fail, wear-out or need replacement in a small number of modules or assemblies. Design so that they require simple procedures to replace.
• Use built-in self-test and indicators to quickly isolate faults and problems.
• Eliminate or reduce the need for adjustment.
• Use common, standard replacement parts.
• Mistake-proof fasteners so that only the correct fastener can be used in re-assembly. Mistake-proof electrical connectors by using unique connectors to avoid connectors being mis-connected.

Design for Maintainability guidelines have much in common with Design for Manufacturability guidelines.
In addition, service and support policies and procedures need to be developed, service training developed and conducted, maintenance manuals written, and spare parts levels established. As these tasks are done in parallel with the design of the product, it reduces the time to market and will result in a more satisfied customer when inevitable problems arise with the first delivery of a new product.

ABOUT THE AUTHOR
Kenneth A. Crow is President of DRM Associates, a management consulting and education firm focusing on integrated product development practices. He can be reached at kcrow@aol.com.

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Percept Announces New Testing Services

Percept's Testing Experts Now Deliver Specialized Power Supply, Temperature Probing & Airflow, and Usability testing.

Building on its product test and compliance expertise, Percept Technology Labs has increased the breadth of its service offerings to include Usability, Power Supply, and specialized Temperature, Airflow and Humidity Testing.

As technology firms face increasing competitive and regulatory pressures, reliable, comprehensive product testing - throughout the product development cycle - is increasingly important.

Power Supply Testing & Qualification is another important consideration for any type of electronic product. Percept's thorough testing shows you if your power supply will meet your reliability goals and global safety requirements. In-depth expertise enables the Percept team to test virtually any power supply used in the telecommunications, networking, computing, office systems, medical, process control, test and instrumentation products.

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Through Usability Testing, Percept's experts help you determine exactly how your customers will react to and use your product in a true user environment. This valuable information helps you identify and solve any potential problems before your product reaches your customers.

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