The steep evolution in the medical field has sharpened the diagnostic powers of the medical fraternity. Rather than diagnose based on visible symptoms that is often subjective and misleading, the application of proper test equipment helps to produce more accurate diagnoses.
At the heart of each such test equipment is a medical Printed Circuit Board or PCB. In fact, this medical PCB is the major element imparting to the test equipment its safety, precision, reliability, accuracy, and repeatability.
Medical PCBs almost always relate to a human life at some point or the other. Therefore, safety is the most significant point. The medical instrument needs to be precise, and for this, medical PCBs need signal integrity, high number of interconnections, and lead-free joints. Reliability, accuracy, and repeatability are equally important over the lifetime of the device—requiring use of high-quality components and materials in the medical PCB.
Healthcare involves a vast range of devices covering small wearables to large full-body imaging systems. While wearables promote wellness, larger systems can analyze the health of internal organs. Whatever the size of the device, it depends on a medical PCB for its functionality. In fact, one can find a medical PCB in heart monitors, MRIs, CT scanners, pacemakers, defibrillators, temperature monitors, electrical muscle stimulators, blood glucose monitors, and many more.
With so much electronics in use in monitoring health conditions, it is imperative that medical electronics conform to several safety and quality standards. Several agencies such as Federal Communications Commission or FCC, US Food and Drug Administration or FDA, International Standards Organization or ISO, International Electrotechnical Commission or IEC, and others publish regulations and standards to which medical devices must conform and comply.
Geopolitics controls these standards to a large extent, as each country has its own standards and governing bodies. Although abiding by standards such as ISO and IEC cover almost all countries, there are specific regulations for special medical devices. This is necessary as medical devices vary widely to be suitable for use in different areas of application. This makes it nearly impossible to compile a complete listing of regulations. Moreover, publishing such listings makes them immediately outdated due to the accelerating innovations in medical technologies.
Categories of Medical Devices
Medical devices may range from standard equipment to very complex systems. It is usual to group them into three different categories:
General Medical Equipment—Class 1: While the healthcare industry uses these products for medical purposes, they are low risk as they are unlikely to cause personal injuries. Products belonging to this category include dental mirrors, gauges, gloves, and scales for measuring weight.
Instruments with some Risk—Class 2: Although these products are a higher risk than those in Class 1, the risk is only in the maintenance and operational areas and not life-threatening. Products belonging to this category include monitoring instruments, and electric wheelchairs.
Life-Sustaining Devices—Class 3: These are life-critical products. Production of these equipment must conform to the highest standards to ensure reliability. Heart valves and pacemakers are examples of products belonging to this category.
Regulations for Medical Devices and Equipment
All medical devices and equipment must conform to a few key regulations:
Quality Management Systems ISO 9001, ISO 13485: These define the specific requirements for managing the overall quality in the organization supplying the medical devices. While ISO 9001 is generic for almost any industry, ISO 13485 specifically deals with managing the quality in organizations involved in the design, production, installation, and service or medical devices. Apart from helping with internal auditing processes, external parties use these standards during certification audits.
Organizations with the above QMS certifications can design and develop, produce, store, distribute, install, or service medical devices and provide technical support.
Risk Analysis System ISO 14971: This is applicable to medical devices used as implants or as in-vitro diagnostic devices. The standard helps in identifying the menace associated with using the medical device, estimating, and evaluating the risks related to its use, control of the risks, and monitoring the effectiveness of controls. The standard is applicable throughout all stages of the life-cycle of a medical device.
Medical Electrical Equipment Standards IEC 60601: This is a group of 70 separate standards covering the essential performance, safety, and electromagnetic compatibility of medical electrical systems and equipment.
General Medical and Dental Equipment Safety Standards IEC 60601-1:This part of the standard covers the basic safety and essential performance of the equipment.
Programmable Instrumentation Standards IEC 60601-1-4:This part of the standard covers software confirmation in programmable instrumentation.
Electromagnetic Interference Standards IEC 60601-1-2, FCC Title 47:These standards certify any electronic equipment containing an RF device in the range 9 kHz to 3000 GHz. They cover requirements for specific product groups and specific measures built into the products.
In-Vitro Diagnostic Medical Devices Safety Standards IEC 61010: This standard covers in-vitro diagnostic medical devices, disinfection equipment, and cleaners.
Biocompatibility Standard ISO 10993-1: This guidance document from the FDA assists the medical industry in determining the potential of a medical device that touches the body generating an unacceptable adverse biological response.
Elements of Medical PCB Related to Safety
To conform to the above standards, design and manufacture of medical PCBs must consider several aspects that direct influence the acceptance of the PCB and the reliability of the product in the field. These aspects are crucial to the safety of the device:
- Selection of suitable materials—use of higher-grade materials
- Prepreg and Core thickness greater than 0.1 mm / 4 mils
- Copper thickness greater than 1 oz.
- Interfacing between different circuits
- Using slots for creepage and isolation guarantee
- Maintaining proper safety clearance between low and high voltages
- Track width greater than 0.127 mm / 5 mils
- Via hole diameter greater than 0.3 mm / 12 mils
- Crosstalk between traces on same and adjacent layers
- Signal integrity for high frequency and high-speed signals
- Control impedance tolerance typical ±10%
- No annular ring breakout
- IPC Class 3 requirements for conductor width, spacing between traces, hole wall copper thickness, surface copper thickness
In addition to the above, medical PCBs often must comply with requirements such as:
- Cleanliness beyond IPC Standards
- Base materials meeting international standards
- Solder mask of specified thickness both on board surface and on conductors
- Specified repair and cosmetic requirements
- Specified depth of via fill for certain solder masks
Although medical applications require PCB design with specific elements covering power, crosstalk, grounding, and signal integrity, the most important aspects are safety and reliability. It is imperative to uphold safety in all areas, including mechanical, thermal, and radiation aspects. IPC Class 3 standards must drive all the above.