Medical Device PCB Design

With the advancement of medical technology, the integration of computerization has significantly influenced diagnostic and treatment practices. One crucial component driving this transformation is the development of medical device PCBs. Specifically, medical device PCB design utilizes a variety of techniques to ensure the reliability and safety of medical devices. Incorporating standards, good design practices, and other technical features ensures that medical products are both reliable and accurate. As the trend in medical devices shifts towards creating smaller products with even greater component density, it is important to know what considerations, design tips, challenges, and manufacturing standards have the most impact on your medical device PCB design.

Medical Device PCB design is a nuanced topic with many contributing factors.

Medical Device Board Material Choices

BOARD MATERIAL CONSIDERATIONS FOR MEDICAL DEVICE PCBS
Board Material	Description
FR-4	Common choice due to cost-effectiveness and straightforward manufacturing. Suitable for many medical devices.
Polyimide	Offers excellent tensile strength, flexibility, thermal stability, and chemical resistance. Suitable for prosthetics and implants.
Teflon, PTFE	Low dielectric constant, reducing signal loss and suitable for high-frequency applications.
Ceramic	Suitable for devices requiring low thermal expansion, high thermal conductivity, and high-frequency performance.
Flexible PCBs	Ideal for medical devices with non-traditional shapes, offering space optimization and mechanical advantages.
Rigid-flex PCBs	Combine durability and design versatility, commonly used in various medical applications.

Especially critical in medical device PCB design is the choice of board material. Carefully consider where and how you expect your device to be used, and based off the requirements select the best board material for your application. Board materials can range from typical FR-4 to a variety of other available solutions.

Choosing the Right Laminate

For medical PCBs, choosing the most appropriate laminate is crucial to device success. FR-4 is the most common choice due to its cost-effectiveness and straightforward manufacturing. However, some medical devices demand expertise in other materials like polyimide, Teflon, ceramic, and more, based on their specific requirements. In cases where more advanced equipment or devices of higher risk classes are involved, consider using special laminates such as polyamide, Teflon, PTFE, or ceramics. These materials are especially suitable for high-frequency electronic applications. For instance, the dielectric constant of FR-4 material is around 4.5, leading to significant signal losses during transmission through the printed circuit board. However, materials like Teflon offer a lower dielectric constant, 3.5 or less, reducing signal loss. Additionally, these materials boast exceptional thermal characteristics, with some reaching Tg values up to 280°C.

Board Material Considerations

Printed circuit boards made with flex or semi-flexible materials are widely used in medical devices. Particularly in wearable applications, material choice may vary in medical boards that require non-traditional shapes, as they optimize space, reduce weight, and offer mechanical advantages over rigid PCBs. See below for tips on medical device board materials.

Standard “Flexible PCBs” are a popular choice for medical devices due to their malleable nature, making them suitable for devices that require folding and wrapping.
Flexible aluminum PCBs are ideal for high-power medical devices, offering heat transfer qualities, making them suitable for scanning and surgical lighting applications.
PCB microcircuits provide malleability and enhanced performance, making them suitable for small medical devices like industrial sensors, wearable technology, and hearing aids.

Polyimide PCB materials are a favorable choice for medical devices like prosthetics and implants due to their excellent tensile strength, flexibility, thermal stability, and chemical resistance.
Ceramic PCBs are suitable for medical devices requiring low thermal expansion and high thermal conductivity, as they can operate in high temperatures and offer excellent high-frequency performance and chemical erosion resistance.
Rigid-flex PCBs combine the benefits of flexible circuits and rigid PCBs, providing durability, design versatility, and weight reduction, commonly used in various applications, including consumer electronics, lighting, and instrumentation.

Material Selection for Device Assemblies

The selection of assembly materials for medical devices is of utmost importance due to the critical nature of these devices. Medical device assemblies face various challenges, including exposure to liquids, shock, and extreme temperatures. Considering that these devices often come into contact with the human body, any malfunction can pose severe risks and potential liability issues. Therefore, it is crucial to collaborate with a PCB manufacturer experienced in high-reliability electronics design, particularly Class 3 standards, which ensure the highest reliability. Several key factors influence the choice of materials and substrates best suited for specific medical applications:

Compliance with RoHS regulations.

Capability to handle RF signals and/or high frequency/transmission speed signals.

Maximum operating temperature.

Connectivity options, such as WiFi, Bluetooth, etc.

Size and shape of the case.

Material Selection for Cleanliness

Maintaining a safety-first approach also involves emphasizing cleanliness. Medical devices must be easy to clean and disinfect, influencing the choice of enclosure material. Stainless steel is a popular solution for medical needs due to its ease of cleaning and disinfection. Alternatively, conformal coating can protect against various contaminants like moisture, corrosion, dust, salt spray, etc. However, the disinfection process may involve ozone exposure, which can degrade certain electronics components. Therefore, careful component selection becomes paramount in such scenarios to ensure compatibility with the disinfection methods used in medical settings.

Designing for Miniaturization

Miniaturization has been enabling the development of smaller medical devices. There are several factors that contribute to the creation of these more efficient and compact devices through medical device PCB design, discussed below.

Miniaturize Your Board with HDI Technology

High density interconnects (HDI) and Via-in-Pad technology is instrumental in reducing the PCB’s size footprint. This approach involves creating high-density connection boards (HDI) that accommodate numerous and complex connections within a smaller area, resulting in closely packed traces. To achieve the high component density required, HDI technology frequently employs a significant number of interconnections and via holes, including blind and buried vias. The capability of HDI technology to create laser-made via holes, via-in-pad, and narrow tracks contributes to drastically reducing the PCB’s size. Via-in-pad technology is particularly useful for highly integrated components like BGAs or those with numerous pins and a narrow pitch. This technology allows holes to be directly created on the pads, establishing connections with internal layers. Producing HDI PCBs for medical use requires substantial investments in expensive equipment like direct laser imaging (LDI) and additive/semi-additive processes (mSAP). These processes contribute to a higher manufacturing cost of the PCB. Such investments are necessary to meet stringent requirements related to trace width and spacing, especially when aiming for IPC Class 3 standards (discussed further below), which mandate minimal line width reduction during processing.

SMT Technology

In general, in medical applications it is preferable to use SMT technology, as it allows the use of smaller components, reducing the size of the PCB and increasing the density of components on the board. Furthermore, for the assembly of SMD components it is not necessary to drill any holes, reducing both the costs and the time required for the fabrication and assembly of the printed circuit board. One of the smallest SMD packages currently available on the market is the 008004, which features a size of only 0.25mm x 0.125mm.

Standards for the Design of Medical Electronic Devices

Medical devices and equipment are held to stricter regulatory standards compared to many other electronics products. As a result, each stage of medical device development is subject to rigorous regulatory oversight to ensure optimal performance and safety. The development process follows a well-defined Quality Management System (QMS) that diligently monitors and analyzes potential risks. To create medical-grade PCBs, extensive knowledge of IPC Class 2 and IPC Class 3 specifications and HALT/HASS testing is essential. IPC Class 3 standards prioritize reliability and mandate no annular ring breakout, a minimum of 1 mil plating in through holes, and tighter tolerances on conductor spacing and widths.

STANDARDS AND REGULATIONS RELEVANT FOR MEDICAL DEVICES PCB DESIGN.
Standards and Regulations	Description
FCC Title 47 of Electronic Code of Federal Regulations	Regulates radio frequency (RF) devices and their compliance to electromagnetic interference (EMI) regulations.
US FDA 21 CFR Part 807	Regulates firms involved in manufacturing, repackaging, relabeling, and importing medical devices sold in the United States.
IEC 60601-1	Outlines general requirements for basic safety and essential performance of medical electrical equipment.
IEC 61010-1	Specifies safety requirements for electrical equipment used for measurement, control, and laboratory purposes.
IPC 6011	A generic performance specification for printed boards.
ISO 13485	Establishes Quality Management Systems requirements for medical devices with a focus on regulatory compliance.
ISO 14971	Guides the application of risk management to medical devices.
IPC Class 3 standards	Prioritizes reliability and mandates minimal line width reduction during processing. Crucial for medical-grade PCBs.
HALT/HASS testing	Essential for high-reliability electronics design.

Moreover, several additional regulations and standards govern the development and manufacturing of medical devices, including:

FCC Title 47 of Electronic Code of Federal Regulations
US FDA 21 CFR Part 807, which regulates firms involved in manufacturing, repackaging, relabeling, and importing medical devices sold in the United States
IEC 60601-1, which outlines general requirements for basic safety and essential performance of medical electrical equipment
IEC 61010-1, specifying safety requirements for electrical equipment used for measurement, control, and laboratory purposes
IPC 6011, a generic performance specification for printed boards
ISO 13485, which establishes Quality Management Systems requirements for medical devices with a focus on regulatory compliance
ISO 14971, guiding the application of risk management to medical devices.

Additional Medical Device PCB Design Workflow Tips

There’s a lot of various aspects that go into medical device PCB design. For this reason, it might be easy to overlook smaller board improvements. Consider the following additional workflow tips while designing your medical device PCB.

Medical Device PCB Design Guidelines

Prototype design should anticipate modifications and consider easy access to traces and vias for soldering and modifications.
Design PCBs with test points to facilitate testing and debugging, and keep them accessible on the exposed side of the board during assembly.
Consider reusing sub-circuits from previous designs, and pre-existing off-the-shelf sensors to save time and effort.
To improve signal integrity and reduce noise, utilize ground planes on all layers connected with vias, and use reliable instrumentation amplfiiers.
Thermal simulation is crucial for detecting possible hot spots in medical PCBs under various operating conditions, enabling engineers to make necessary changes early in the design phase to meet reliability and safety requirements without costly post-production thermal analyses.

Device interconnectivity is crucial for medical systems and data transfer, making IoT considerations important in PCB design for medical devices.
Predicting component obsolescence in medical PCB design is crucial to avoid premature project end-of-life and potential delays in obtaining required approvals from regulatory bodies.
Digital Twin simulation brings significant benefits to medical-grade PCB design, reducing development costs and time-to-market by identifying potential mistakes early on and creating a virtual model of the circuit for data analysis and system monitoring.
Design for ease of assembly and serviceability, considering component placement and connector accessibility.
Make sure your sensors and all other integrated components are rated for the operating conditions you expect for your medical devices (humidity, temperature, etc.).

Importance of Compliance and Regulation

Compliance with Class 3 electronic requirements is of paramount importance for companies seeking to manufacture invasive medical devices. Since many medical devices and equipment belong to Class 3, partnering with a PCB manufacturer experienced in producing Class 3 electronics is crucial to ensure PCBs meet the necessary compliance standards. Alongside Class 3 requirements, medical industry PCBs must adhere to installation qualification, operation qualification, and process qualification standards.

An essential aspect of compliance is meticulous record-keeping. In the medical industry, lot tracking of components is particularly critical, and detailed records of test and inspection processes may be necessary. Adhering to ISO standards and FDA regulations becomes an integral part of this record-keeping process, reinforcing the importance of precise documentation in the medical device manufacturing landscape. Before selecting an electronics contract manufacturer, conducting thorough research into their ability to meet Class 3 requirements and maintain comprehensive records is imperative.

If you’re looking for CAD models for common components, or reliable information to help ensure your medical device PCB design adheres to industry rules and standards, and follows best practices, Ultra Librarian helps by compiling all your sourcing and CAD information in one place.

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