EMC-compliant layout: test plan, lab support, corrective measures

Drawing up the EMC test plan: standards, test severity levels, set-up, operating states

The test plan comes before the lab appointment. It defines which standards apply, at which test severity level measurements are taken, what the test set-up looks like and in which operating states the device runs during the test. The laboratory receives a document it can work by. You know before the measurement what is being tested and why.

Which standards apply is settled by the project's regulatory requirements, such as IEC 60601 in medical technology or IEC 62368, each with its associated EMC limits. From this comes the list of applicable standards with their design consequences; the EMC test plan follows on from it. It can be commissioned on its own, including to prepare the EMC test for a layout designed in-house.

• Standards: which standards and EMC limits apply to your product
• Test severity level: how severely immunity and emissions are tested
• Set-up and operating states: the test set-up and the operating states in which measurements are taken

EMC-compliant layout from the first trace

Whether a device stays within its limits is decided at placement, routing and power supply. Noise sources and sensitive areas are placed apart, return current paths under fast signals stay closed, decoupling capacitors sit according to function, current loops at filters and power supply stages stay small. These decisions are made in Step 03 of the MHD process, the PCB layout.

The basis for this is certified training: the seminar on EMC assembly design from ZED IV (Zertifizierter Elektronik-Designer, the FED's certified electronics designer programme) and the EMC Designer training at the VDI (Association of German Engineers). Added to that is experience from measurement electronics and scientific instrumentation with low-noise analogue stages.

• Grounding scheme and return current paths: continuous reference planes under fast signals so that every return current path stays closed
• Power supply: small current loops at filters and power supply stages, decoupling capacitors placed according to function
• Placement and routing: noise sources and sensitive areas kept apart, crossing traces avoided, via fencing where needed

Lab support and corrective measures

On the test day, MHD supports the measurement. Emissions and immunity are run to the test plan, for immunity ESD, surge and burst among others. If a limit is exceeded, the cause is narrowed down and the corrective measure defined. You receive the test report with the measured values and, where necessary, the changes implemented.

If a retest becomes necessary, MHD knows the set-up, operating states and measurement data from the first run and supports the retest as well.

• Emissions: radiated emissions measured against the limits from the test plan
• Immunity: ESD, surge and burst in the defined operating states
• Corrective measure: cause narrowed down, change implemented in the design, documented in the design file

EMC consultancy for electronics designed in-house

EMC consultancy also applies to a design from your own house: as a check of layer stack-up, grounding scheme and placement before the first lab appointment, or as a review after a failed test. You receive findings and recommended corrective measures documented to a depth that satisfies purchasing, quality assurance and audit. The entry point for this is the independent design review.

The EMC-relevant design decisions are taken by Dr Häuser. For volume and peak load we work with the partner network, under the same specifications, reviews and releases.

The outcome

The outcome is a set of documents that the laboratory, quality assurance and approval can work with. They live in the design file, so months later, the reasoning behind every decision is still on record.