With every day that passes, it feels as though the world is getting smaller. Well, not actually smaller, dimensionally, but more accessible. We owe this progression to many technological advances. For example, air travel, radio, TV, and of course, the Internet serve as conduits for the exchange of information throughout the world. The best use of this interconnectivity is still in its infancy. That is the current expansion of the IoT, where people connected via the devices that we utilize. And one of the most promising embodiments of IoT is in connecting medical devices that may be located at remote locations.
Connectivity through IoT
The interconnectivity possibilities with IoT for medical care include everything from simple analysis of testing results by a physician at a different facility to robotic telesurgery, where a medical procedure is performed by a local robot controlled by a remote surgeon. Regardless of the actual procedure, the increased usage of IoT to provide health care requires the ability to accurately gather, process, transmit, and receive data reliably; principally RF. And the responsibility for this functionality rests with the PCBAs that comprise the medical devices in use. Therefore, PCB layout with partitioning for RF design must be a major design objective. Let’s see why this is true and then take a look at how to best design boards for RF processing for medical devices.
Why Is Partitioning for RF Design Important?
There was a time when circuit boards were fairly large and typically performed only a small number of functions. Usually, this was for a single signal type. Well, those days have all but disappeared. Today, PCB industry trends are HDI, which provides for the processing of larger numbers of signals in a smaller space, and more advanced utilization of IoT. This is certainly true in the health industry as small size, vast complexity, and high functionality are the requirements of PCBAS for innovative medical devices.
Complexity on circuit boards goes hand-in-hand with a large number of traces and/or vias and the need to best manage the propagation of multiple signal types, including:
DC is the source of power for the board and biasing for amplifiers, which may be distributed from an external supply, an on-board converter or a battery.
Digital signals are used by processors and other logic devices for processing and control as they are fixed width and easily readable.
Analog signals; such as naturally occurring EEG inputs, are continuous-time signals that can be readily converted to and from digital signals.
For medical applications, these are typically high frequency signals for communications to and from other boards or devices.
It is not atypical for medical device PCBAs to have all of the above signals being propagated within a small board form-factor. For these designs, the probability of board signal integrity degradation due to noise or EMI can be significant, if actions are not taken to mitigate it.
Design of Medical Devices PCBA Layout for RF Design
Perhaps more so than any other industry, the design and manufacturing of medical devices are heavily regulated. This scrutiny has not stopped the industry from being a leader in embracing and applying new technologies; such as HDI and IoT. Although the improvements to the quality of healthcare and services that can be provided to patients are quite substantial, including the proliferation of medical expertise and capability to remote locations, the boards that drive the medical devices require special development considerations. Not least among these is layout construction that targets the partitioning of RF design away from the layout for other signal types to reduce issues, such as crosstalk, noise, and stray capacitance. These can be done by following essential guidelines, as listed below.
Partitioning for RF Design Essentials for Medical Device Boards
- Mount RF components together and away from other component types
- Make use of HDI and microvias to minimize space and aid in isolation of components
- Isolate RF transmission lines on ground separated layers, if possible to improve small signal fidelity and reduce EMI
- Use EMI shielding for Class 3 devices to prevent and/or reduce EMI radiation to patient
- Use via fences to help isolate a coplanar waveguide and prevent board edge EMI radiation
The preciseness and complexity of medical devices PCBAs mandate that the above guidelines are followed. Although, it is not a bad idea to apply these to all of your RF or multi-signal board designs, along with other layout guidelines.
It is always desirable to have the best signal integrity for your board; however, for medical devices PCBAs, this is more than a goal. Due to the potential negative outcomes that may occur for imprecise data processing, optimal accuracy is a mandate.
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And to help you get started on the best path, we furnish information for your DFM checks and enable you to easily view and download DRC files. If you’re an Altium Designer or Cadence Allegro user, you can simply add these files to your PCB design software. For Mentor Pads or other design packages, we furnish DRC information in other CAD formats and Excel.