Electronic engineers face many challenges when designing products for medical applications. Safety, reliability and regulatory compliance are primary considerations. Depending on the end use, other factors to review include environmental conditions, limited space (miniaturisation), battery life, biocompatibility and in-service life.
In this post, we cover the issues to consider when specifying a custom thick film resistor device for medical applications.
Resistors In Medical Devices
Medical applications require protection against overload and transient conditions. They often need signal conditioning, current sensing and amplification circuits to facilitate precision measurement. Resistors are key components in these circuits.
Thick film heater resistors find application in a wide variety of medical devices. These include incubation of cultures, fluid heating before injection, DNA analysis, diagnostic equipment and various sensors.
The Need For Customisation
The unique challenges of medical applications can make a standard resistor device impractical. In some applications, a custom thick film device is the only solution.
A thick film resistor can be custom-designed to meet specific resistance values, tolerances, and power ratings. As a result, resistance characteristics can be tailored precisely to the application’s requirements.
When specifying a resistor the key trade off is often size versus power rating. This is particularly important in many medical heater applications.
Often, heat must be delivered to a specific point of contact in a controlled manner. A custom-designed electronic component can fit into tight spaces and consume minimal power.
Medical devices are subject to strict regulatory standards to ensure patient safety. Customised resistors, specifically designed and tested to meet these regulations, deliver full compliance.
Why Thick Film?
There are many resistor technologies, each with advantages in a given application. A selection is usually made after considering cost vs performance.
Regulatory requirements are an additional consideration. Reliability is key, as in many applications, component failure cannot be tolerated.
In medical applications thick film resistors offer several advantages over other technologies. These include:
Mechanical – In medical devices, space constraints are often critical. Thick film resistors can fit into small and intricate spaces within the device’s layout.
The technology is robust and can withstand harsh environmental conditions, including humidity and mechanical stress. This is crucial for medical devices exposed to various operating conditions.
Thick film resistors are typically more resistant to contaminants and moisture ingress than other resistor types. This makes them suitable for medical devices that must be sterilised or operate in challenging environments.
Electrical – Thick film resistors can have lower temperature coefficients than other resistor types, making them more stable in varying temperature environments. Resistor stability is important in medical devices where accuracy and reliability are paramount.
Heater Applications – Thick film technology has excellent heat transfer properties, thermal efficiency and temperature uniformity across a surface. Substrates may be custom-designed to fit in small, difficult-to-access areas and apply heat exactly where required.
Design And Material Issues
Before starting the thick film resistor design process, it is important to define the basic specification. This includes:
- Resistance value.
- Power/Voltage rating.
- Maximum dimensions.
- Mounting method (including lead finish).
- Price expectations.
With the basics in place, it is then vital to consider application issues including:
Finally, regulatory requirements and relevant specifications must be clearly defined.
As discussed elsewhere on this blog, the above all impact on material selection and the manufacturing process. Failure to account for the above in the design process could cause the thick film resistor to degrade over time (or fail). Long-term resistor stability and the impact of ageing over time require careful consideration.
In conclusion, custom thick film resistors have proven applications in medical systems. Whether it’s in patient monitoring equipment, diagnostic devices, or therapeutic instruments. Their versatility, precision, and durability make them vital components in medical devices.
In many medical applications, resistor failure is not an option. It is, therefore, important to clearly define specifications and application-specific environmental conditions before starting the resistor design process.