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How to plan for CE and FCC certifications when designing PCBs

When you want to distribute your radio frequency products in some countries, you will have to perform different tests to obtain the conformity that your products will not affect to the performance of other products neither these other products will affect to the performance of your product

In order to demonstrate these facts, you will have to pass different tests defined by different directives and standards, depending on what your product offers and where is going to be sold.

If you want to sell your RF product in the European Union you will need to get the CE (Conformité Européene) mark and if you want to sell it in the United States you will need to go through an FCC (Federal Communication Commission) certification.

Both CE mark and FCC are very similar in the way if you are able to pass the tests in one of them you should also be able to pass the tests for the CE mark. The required tests are different for both certifications and if you want to sell your product in both United States and European Union you will have to pass the tests for both of them and pay for it.

 

Testing

These tests are not cheap and they take long time. For this reason, you need to be very sure your product is going to pass the tests if you do not want to waste your money and your time. To accomplish this, you need to design very carefully and, if possible, and if you have the knowledge and equipment, you can do some preliminary tests to check if you will be able to pass the tests, or at least be able to demonstrate you will not fail for sure the tests. You will also have to send the best documentation you can to the laboratory so they know how to perform the tests. Depending on the laboratory you can also (or even it will be mandatory depending on the difficulty for testing your product) witness the tests and help to manage your product.

 

Laboratories to pass CE mark and FCC certifications

There is a very wide number of facilities that can perform this kind of tests, then you will need to request different quotation and be sure about how they will charge you at the end. Because there are facilities that at the beginning may seem more expensive, but they include all the possible cases (states in which your product can be working), and if they find a fail in some of the tests they can do some additional tries for you or tell you how to solve the problem for free. On the other hand, there are facilities that will charge you independently for each working mode, they will not do troubleshooting for you and if they need more hours than expected to perform your tests they will charge you with additional expensive hours.

When you are new passing these tests, you do not have the information about what is the best facility to pass them, then you can ask to other companies that have been through these tests in the past to have some feedback or if you do not have this possibility you will find with your experience what of them to select.

If you are interested in your product to be distributed on both United States and European Union you should check for a facility that is able to pass the tests for both FCC and CE mark in order to save money and time.

 

Example of a laboratory for EMC (Electromagnetic compatibility) testing.
Example of a laboratory for EMC (Electromagnetic compatibility) testing.

 

Main directives and standards

To find the correct directive and the standards you need to fulfil, it can require and extensive search unless you have experience. There are many of them depending what your product is. Below some of most important directives associated to electronic products are shown, and some examples of main standards that can cover each directive are summarized. You have to think that each standard will have hundreds of pages.

  • EMC directives

This is one of the most important directives, since applies to all the electronic components, and maybe the most complicated to reach, to pass the tests and to find the required information you need. In this directive the radiated, conducted and induced emissions and immunity performance of the equipment is tested.

That means many tests have to be performed in which your equipment will not affect to other electronic equipment around of it and that will not be affected by other electronic hardware that could be emitting signals. One small difference between CE and FCC requirements is that FCC do not request to pass the immunity tests.

To pass this directive is typically very expensive since it requires special equipment to perform the test like signal generators, spectrum analysers, anechoic chambers, antennas and amplifiers. It also takes a huge time to perform the tests. An EMC test can cost you from €3000 (about $3500) if only covers a couple of tests up to more than €20000 (about $23400) if you need to pass most important ones. That could take more than one week of work for the laboratory.

Depending on whether you are going to sell your product in Europe or in United States the directives will be different. For FCC you will have to look information in the standard FCC part 15 while if you need to follow CE mark you will have to follow the European standards. There are also different directives is you want to distribute your product in Australia, Canada, Japan, Russia or China. You can also look information depending on your product. Main directives depending on your applications are shown below:

- For Medical Applications the main standard is:

EC 60601-1-2

 

- For Automotive many standards can be requested

SAE
ISO7637
IEC CISPR-25
Automotive Directive ("E-mark" for Europe).
ISO1145-1
ISO1145-2

 

- For Military applications there are also different standards

MIL-STD-461
DEF STAN 59/411
⚬ RTCA-DO-160
MIL-STD-704 (for aircraft)
MIL-STD-1275 (for land vehicles)
MIL-STD-1399 (for ships)

 

  • Safety directives

This directive applies to the equipment is safe for people and will not be dangerous due to possible discharges, especially when they are very power consuming devices.

 

  • RoHS/Reach directives

These directives define that hazardous components should not be present in your electronic devices so they cannot affect to the health of the people that use the devices or are around the places the devices are set up. Some of the main components that has to be avoided are lead, (so the soldering has to be done with tin without lead), cadmium, mercury, hexavalent chrome, and other hazardous chemical or contaminant products.

 

Declaration of Conformity

Once you have passed all the required tests, the laboratory will give you an extensive report, that can take weeks or even months, depending on the laboratory, since you finish the tests. They will also give you a signed Declaration of Conformity document, in which it is declared that the products meet all the requirements requested by the applicable directives and give all the information of the product under tests and also the information of the manufacturer and the date in which the tests have been passed. It must be issued by the manufacturer since it is the maximum responsible since the laboratories are only following the directives, standards and tests the manufacturer request them.

 

Advices to design according the standards for FCC and CE mark

One of the first step in the design of your electronic devices is the design of the printed circuit boards. An incorrect design in your PCB can complicate or even prevent your electronic device is able to fulfil the EMC directives. Below some tips are given to try to improve your PCB design to be compliant with the EMC tests and other directives for the compliance with the CE and FCC regulations.

  • Use good grounding practices in your printed circuit boards. This is a very extended topic in which there are even books with hundred of pages dedicated only to this subject. Grounding loops can produce undesired signals, even oscillations that can interfere in your product and other products being not compliance with EMC directives. The grounding practices are even more important when you work with both analog and digital signals. In these cases, it is recommended that at some points of your circuit the digital and analog grounds are separated so the digital and analog signals do not interfere one in another. Also ground planes should be placed between analog and digital traces to avoid coupling of signals. A good grounding can also help you to have the signals concentrated in the traces of your circuit and not going outside the electronic device.
  • When you work with multilayer PCBs try to have fully ground planes between layers that contain signals in order to avoid the signals can couple from one layer to another.
  • Some components like oscillators, clocks, FPGAs, ADC, can produce signals that can interfere with other devices. For this reason, they need to be isolated from the outside. If the envelope of your device is plastic, these components should be shielded with a metallic cover that work like a Faraday cage avoiding the signal can go to the outside and that other signals can go in the module and mixing products can occur in the component. For this purpose, it is recommended to put ground planes around these components in which the metallic cover can close the component. If your device is enclosed in a metallic box then this part is not so important but, in any way, it will help to not mix different signals.
  • Other components that can produce signals that can avoid your equipment pass the certifications are the DC/DC components used to convert a voltage value to any other value. These components have inside switches that are continuously changing at a certain frequency which produce signals at a frequency equal to 1/switching time. Typically, hundred of Khz or a few MHz. These frequencies have to be filtered by putting different bypass capacitors close to the DC/DC component. Then, you have to take in mind to leave enough space in your PCB to put these capacitors.
  • Put filters at the input of your DC pins. There are many possible filters than can be placed in the DC connectors to avoid that external RF signals can go inside your module through these connectors, generating spurious that are mixed with your RF signals, and also avoiding that your RF signal is going to the outside through these connectors. Depending on your RF device, you can place connectors including these filters, but if not, you will need to design your PCB with the corresponding footprint for a EMI filter. In many of the datasheets of these filter you can look they are compliant with EMI/EMC tests.
  • You need to isolate your input/output connectors to avoid crosstalk and feedback between them following good PCB/mechanic design practices.
  • Try to minimize the length of the tracks of the connection of your components to reduce the possibility that interfere signals can be absorbed. This is much important when these traces are for digital signals because the longer the trace, the higher the probability other signal is coupled.
  • Avoid 90º angles in your design since they generate radiation, impedances change and reflections than can cause EMI interferences. It is better to use if possible 45º angles.
  • One of the directives that in last years are required to be fulfilled in the CE mark and FCC regulations is RoHS. For this reason, you need to have in mind your products have to be soldered with lead free solder and select lead free RF components.

There are PCB design software that can help you not only in your design but also to detect if your design can show any problem in terms of EMC compliant like Altium Designer. In this software you can also provide what components are you planning to use and it will give you valuable information about whether these components are good since they have been used in previous EMC compliant products.
 

Do you know any other tips to keep in mind to plan for CE and FCC certifications when designing PCBs?

 Roberto
 2018-09-15 11:05
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