However, they are an important part of the design cycle. Thorough design reviews can catch functional problems before a product goes into prototyping, identify out-of-stock parts, determine circuits that require changes, and identify DFM/DFA problems that delay production. Spending a few hours looking through a design can eliminate a huge amount of development expense.
Everyone tends to focus on functional design reviews, but what about reviewing a product for EMC compliance? Every electronic product must comply with EMC standards and radiated and conducted emissions regulations, as well as industry standards on EMC pertaining to reliability and safety. A structured review process helps identify risks early in the design cycle, before a prototype is sent in for EMI testing. An EMC review should be based on two areas of the product specification:
The sections below show how to review each area, along with examples of what belongs in an EMC review checklist.
The product architecture shows how functional blocks interact, how power is distributed, and how signals connect to external interfaces. EMC is a system-level requirement, and the product architecture often hides EMI risks that are not clear by looking at individual functional blocks. Evaluating this early reveals design risks that won’t be obvious from schematics alone.
The product architecture is most commonly shown as a block diagram. A well-documented product architecture is shown below. Some of the areas where EMI can arise are summarized in the table below, and the important points to review and understand in an EMC design review are indicated in the table.
|
Category |
Items to Verify |
|
Power Distribution |
Input/output power rails, regulator voltage/current settings |
|
Interconnects |
Interface standard, filtering needs identified on buses, board-to-board or board-to-wire connectors identified |
|
Isolation |
If present, galvanic isolation requirement (RMS or peak) and applicable standard |
|
Grounding |
Ground domains identified with clear functional block segmentation |
|
Multi-PCB Systems |
Multiple PCBs identified in the product architecture with interconnects clearly identified |
The product architecture does not stand alone, each of the blocks in a product architecture is related to a requirement in the product specification. There is much more to be found in a product specification which will guide design and help prepare for lab testing.
All products should have a product specification document, which acts as the master source of information needed to engineer, design, manufacture, and test the product. In addition to the basic electrical requirements and product functionality, the product specification should include compliance standards that form the baseline for any EMC review. Product architects are responsible for determining the EMC regulations and industry standards that apply to the product as these will influence how the product is designed and what will be the test requirements.
During a review, engineers should confirm that each standard referenced in the specification has a clear implementation path in the design. For example, if IEC surge immunity testing applies, the design should show surge suppressors or isolation components. Important review points include:
A review of the product specification ensures these important compliance questions have been addressed before starting the design, ensuring the appropriate design actions are taken before a device is sent for testing.
An EMC review not only identifies risks in the design, it also influences how a product will perform in the laboratory. Testing is usually divided into pre-compliance testing and formal qualification testing, with emissions typically addressed before immunity. Reviews ensure that issues such as grounding, filtering, and shielding are considered while there is still freedom to make changes in the design.
The earlier EMC work is completed, the easier it is to adapt the design. Layout modifications, isolation practices, and component choices can be adjusted during development, but these changes become far more expensive once prototypes are built or production has started. A good rule of thumb is that about 80% of EMC-related design work should be complete by the midpoint of a project’s schedule; otherwise, qualification testing is likely to uncover problems that are difficult to fix.
In practice, lab testing does not always mirror real-world propagation. For example, conducted emissions below 30 MHz are measured to protect radio services, even if the actual disturbance couples radiatively in use.
An EMC review is only effective if the review findings are communicated clearly. Once the review is completed, the reviewers should compile a report outlining which parts of the product specification are at risk and any required design changes. It is also helpful to group issues by category (power, interconnects, architecture, and standards/regulatory compliance) with the corresponding errors and required design changes.
Typical findings include:
Such a structured report makes it easier for design teams to address issues in the next revision, ensuring that compliance is designed in rather than left to chance during testing.
If your team has never prepared a findings report for an EMC design review, you can access an expert-prepared report from DENPAFLUX that includes a checklist of items for an EMC review. The guide also includes example recommendations for changes to the PCB layout, product architecture, and product specifications. When you’re ready to quickly evaluate your PCB layout for potential EMI problems, look to the advanced analysis capabilities in DENPAFLUX.
To see how DENPAFLUX can help, schedule an appointment or contact Denpaflux to get started.