If you are unfamiliar with boats, you may be surprised at how specialized they can be. I didn’t understand this when I bought my boat many years ago, and I only chose it because it was large and powerful with an open square bow that held a lot of people. What I came to realize, however, was that due to its size and weight, my boat created a nice large wake that was very attractive to the wakeboarders. On the other hand, it wasn’t nearly as popular with the water skiers who prefer a smaller wake. Who knew?
Just as the design of a boat will determine its use for water sports, how electronics are designed will also determine if they can be used in medical applications. Specifically, there are standards for electromagnetic interference (EMI) that have to be tested for in order to meet the electromagnetic compatibility (EMC) requirements of the medical devices. It is very important that medical equipment not be disrupted from the operation of other electronics like cell phones, and these standards ensure that. Here’s some more information on EMI & EMC standards for medical devices, and how that will affect you in the design and manufacturing of your medical equipment printed circuit boards.
What are the EMI/EMC Standards for Medical Devices?
The main standard for EMI and EMC in electronic medical equipment and systems is IEC 60601-1-2. This is a series of general standards created to define the essential performance and safety expectations of medical electronic equipment in the presence of electromagnetic interference. As part of the U.S. Food & Drug Administration (FDA) submission requirements, you need to have your equipment tested according to the IEC 60601-1-2 requirements by an accredited laboratory.
It is also recommended that medical equipment manufacturers apply the EMI emission and immunity requirements for automobile and ambulance use in their designs. Depending on the application, the manufacturers should also give consideration to the EMI standards for general aviation and medical helicopter use, as well as railway environments. These requirements are found in the following standards:
Another standard that medical equipment manufacturers should take guidance from in their designs, is ANSI C63.27 for the coexistence of wireless systems equipment. This governs the correct operation of medical devices with RF transmitters that are near to each other such as cell phones, Wi-Fi, and biotelemetry.
The goal of working towards these standards is to design your medical equipment printed circuit boards to pass the IEC 60601-1-2 testing for FDA submission. To do this, you will want to make sure to incorporate good EMC practices in your design.
PCB Design Techniques to Prevent EMI
There are a number of different design techniques to control electromagnetic interference on your PCB design in order to make it compatible with medical equipment standards. Some of these include the following:
- Multilayer stackups: To best shield your high speed transmission lines, a stripline layer configuration in a multilayer board is preferred. By routing your sensitive traces between ground planes, you will be able to reduce the potential for broadside crosstalk to signals on other layers, and restrict emissions from radiating from the routing.
- Bypass caps: Place these capacitors close to every power pin on the active components of your circuit board. These caps buffer current for the ICs that are switching, which reduces their need to pull current in rapid spikes from across the board.
- Isolate different circuitry: It is important to maintain a separation between analog and digital circuitry to keep one from influencing the other. You will also want to make sure that each area of circuitry has its own dedicated ground plane. These grounds can be joined together all at one point, but you want to minimize any chance that digital return paths end up crossing through an analog ground plane.
- Minimize trace lengths: Long looping traces may inadvertently create antennas that could radiate noise. It is also important for signal integrity to keep your entire signal path as short as possible from the driver, through its components, and ending at its termination. You can’t avoid lengthening traces on signals that have to match their lengths, but keep all the other traces as short as possible.
- Ground planes: In addition to the benefits of a stripline configurations and separate planes for different areas of circuitry, ground planes can also help with shielding for sensitive circuitry. Using metal area fills around noisy components along with stitching vias can help control EMI. Keep one warning in mind, though: if you have to split an internal plane for different grounds or voltages, don’t ever cross the plane split with sensitive signals. The return path of the signal will create a lot of noise as it tries to find its way back to the source through the split plane.
These are some of the ways that you can design in EMI control into your PCB, and there are many others that may be helpful in your specific application.
How a PCB Contract Manufacturer Can Help
To understand EMI and how it may affect and/or how you can better control it in your PCB design, don’t be afraid to get more help. Here is where your PCB contract manufacturer will be a good source of information on different design techniques for EMI. CMs have years of experience building boards for many different PCB technologies, and will have a good understanding of what you will need.
At VSE we have been working with customers in the medical field for a long time. Our first step will be to spend time with you to understand your needs, and how much further evaluation and research will be required to conform your design to the IEC 60601 standard. From there we will develop the manufacturing plan for your project. Our goal is to make you successful, and we will leverage our expertise and experience to build your board according to your specifications.