Medical electronics are getting more advanced by the day. With this rapid development of devices and equipment, the PCBs supporting these electronics play a vital role in reliability and, more importantly, safety. Like military and aerospace grade electronics, medical devices are subjected to stringent regulations and protocols since failure of these devices in use might cause a catastrophe. To host such electronics, a new grade of PCBs, popularly known as medical PCBs, is used. This article gives you a brief idea of the aspects of designing, manufacturing and regulations of medical circuit boards.
What is Medical PCB?
Medical PCBs are high-reliability PCBs that are designed to be a part of a medical device. With the increase in demand for medical devices like wearable trackers and health monitors, diagnostic devices, imaging devices, etc., the scope of medical devices has been wider than ever. Medical devices are required to pass quite stringent standards for performance, reliability and, most importantly, for safety. Some devices are required to maintain biocompatibility since they are expected to go inside the body.
Compliances for Medical PCBs
Before designing and sending medical PCBs for fabrication, it is important to know that Medical circuit boards are required to adhere to many standards to be even considered for testing, some of which are –
- IPC 6012 – IPC 6012 is a standard for governing the quality of rigid PCBs. It is a common standard that is classified into 3 classes, namely Class 1, Class 2 and Class 3, and the higher the class, the higher the grade of reliability. Class 3 PCBs demand the highest reliability, long-term performance and most importantly, absolutely zero tolerance for failure. In 2020, IPC released “IPC-6012EM, Medical Applications Addendum to IPC-6012E”, a guideline for medical electronics and recognised demands of implantable and lifesustaining devices. Devices categorised as “medical applications where failure can directly endanger life” are generally required to follow iPC 6012EM. Most of the medical devices are required to adhere to Class 3 guidelines, with some exceptions that may suffice with Class 2 PCBs.
- ISO 13485 – ISO 13485 is a certification that is required to manufacture, design or even distribute medical devices. If the PCB is to be used in a medical device, then there must be a clear record and documentation for control, inspection and traceability. Both the designer and PCB manufacturer are required to be ISO 1385 certified by appropriate third-party vendors and should be able to produce their certification when and if asked.
- IEC 60601-1 – IEC 60601-1 is the safety standard for medical devices that are expected to touch the patient, monitor vitals or provide imaging. However, these guidelines are required to be followed by the hardware designer, PCB designer and the product designer rather than the fabricator, since these guidelines are regarding the functional safety of the device. The guidelines mention the threshold limits for parameters like creepage, clearance of traces, leakage current, etc., along with the ratings of materials allowed and mandatory markings. The main objective of the guideline is to ensure that the device does not produce heat or cause a shock to anyone while in use.
Additionally, IEC 60601-1-2 (a collateral standard to IEC 60601-1) specifically mentions EMC and EMI compliances. In short, IEC 60601-1-2 tells the device should neither emit EM radiation such that it affects other devices nor should it be affected by other devices’ operation or noise.
Design Considerations for Medical PCBs
As seen above, medical design requirements are one of the most demanding in the industry. The following are some design considerations for medical PCBs –
- Grounding: To comply with EMI and EMC regulations, standard techniques like ground shielding and separation of analog ground can be used. However, the use of chassis ground can be objectionable and a bit tricky to use in medical PCBs. While chassis ground provides shielding from EMI, it also increases the risk of leakage current. The IEC 60601-1 divides the chassis ground into Functional Earth and Protective Earth. While the use of chassis ground is possible but for simplicity, try to avoid chassis ground for contact medical devices.
- Material Selection: Modern Medical devices are being miniaturised more than ever, and to cater to such applications. To cater to such applications, HDI and flexible PCBs can be used in manufacturing medical PCBs, however, it is worth noting that the material of flexible PCB or HDI PCB should be compliant with all the regulations.
- Heat Dissipation: Many medical PCBs are required to severely restrict their heat generation; therefore, it is highly recommended to use a higher copper weight per layer, for spreading heat evenly along the PCB and for avoiding the traces from being heated in case of high current.
- Design Specification: IEC 60601-1 defines the acceptable threshold values of creepage, trace clearance, etc. It is always recommended to add these restrictions to the CAD tool’s DRC. Modern tools like Altium Designer and Cadence Allegro can show violations while routing these nets, hence saving time and effort.
Common Materials Used in Medical PCBs
Although there are several restrictions on PCB materials that can be used in medical devices, leaving a few very commonly used in medical devices. Under IEC 60601-1, medical devices must meet strict creepage and clearance distances between conductive parts. Based on and for lower CTI (Comparative Tracking Index) value materials, the required creepage distance increases, thereby making lower CTI materials unfeasible for many designs. However, the following materials can be considered that have a low CTI and comply with their other norms –
- FR-4 – Many FR-4 variants have low CTI, which makes it unfeasible for many applications. However, variants of FR-4 like Isola 370hr and FR408HR that have 400+ CTI are ideal for most of the medical PCB applications.
- Polyimide – Polyimide is a common flexible PCB material that has impressive flexural and electrical properties. It even has a CTI of around 600, making it a very good option for Medical devices requiring flexible PCB.
Although more medical PCB materials are available for more niche applications but they are not used as extensively as the above-mentioned materials.
Application of Medical PCBs
There is a wide pool of applications for medical PCBs that are fueled by constant innovation in the industry. Some of the major applications of medical circuit boards are –
- Surgical Equipment – Many surgical systems rely on high-performance medical PCBs that host electronics processing high-speed, real-time data with high reliability.
- Imaging Devices – These types of equipment demand high-performance PCBs that can handle radio waves and microwaves for imaging with maximum precision.
- Monitoring Devices – Monitoring devices like ECG and other wearables use PCBs to host electronics to monitor various parameters.
- Therapeutic Devices – These devices generally use miniaturised, high-reliability medical PCBs with long operational life.
Conclusion
Medical PCBs used in the pharmaceutical industry are generally relatively precise PCBs. Therefore, this type of PCB needs to comply with many strict standards. Both in the design and manufacturing stages, as designers and manufacturers, it is necessary to have a certain understanding of PCBs in this application field. Otherwise, it is difficult to manufacture precision instruments that meet the requirements. The precision instruments used in the pharmaceutical industry are becoming increasingly high-end, and the PCBs used for these instruments will also become increasingly complex and require higher manufacturing requirements.
