pixel

Parylene Coating for Diabetes Devices: How to Design Safer, More Reliable CGMs

A child with a continuous glucose monitor near water

Posted on May 20th, 2021 by

Responsible for 1.5 million deaths in 2019, diabetes is a global epidemic. An estimated 463 million people worldwide currently live with diabetes, and projections show that by 2045, this number will rise to around 700 million.

Medical manufacturers have developed sophisticated devices that provide more reliable and effective diabetes management to mitigate this developing crisis. For example, traditional blood glucose meters provide single glucose readings only, but continuous glucose meters (CGMs) can offer dynamic, real-time information. These monitoring systems automatically measure blood glucose levels 24 hours a day, providing readings at specific intervals.

CGMs comprises three main components: a sensor, inserted with the aid of a needle under the skin, a transmitter that sends wireless information to the receiver through radio waves, and the receiver itself, a component that receives and displays data from the sensor. This hardware must meet medical standards of excellence, and conformal coating protection is often chosen to help achieve requisite reliability and safety.

Conformal Coatings for Diabetes Devices

As continuous glucose meters (CGMs) are portable and powered by electronics, water-resistant or – ideally – waterproof diabetes products are a design priority. Consumers must wear them at all times, in all types of environments, even though water can easily cause sensitive circuitry to fail. The external electronics used in CGMs also need protection from humidity, biofluids, and cleaning fluids to avoid short-circuits or corrosion. Traditional waterproofing methods such as mechanical seals can be damaged or breached, allowing water into the device. This vulnerability makes more robust conformal coating protection, used together with seals or alone, appealing.

Parylene conformal coatings are unique in their ability to be polymerized and deposited by vapor deposition onto substrates maintained near room temperature. 

Conformal coating protection can also add benefits in the form of thin layers. Microns thick films will not interfere with miniaturized form factors or wireless communication. CGM components require protection with minimal bulk and weight that can conform to the product design. Components that transmit information need adequate protection without distorting signals to avoid failures in information delivery.

Parylene for Diabetes Devices

Despite the benefits of conformal coatings, selecting suitable material that can meet every application requirement for CGM protection is a challenge, as conventional coatings may satisfy one, or at most, two. Among the family of conformal coatings, product design teams should consider Parylene, as it meets every requirement at a fraction of the mass.

Parylene conformal coatings have exhibited exceptional performance in critical applications and industries for nearly 50 years. The coating is often superior in uniform coverage, barrier properties, and performance at comparably thinner films, with less stress on mechanical structures and virtually no added weight.

Download our Parylene datasheet

Unlike liquid conformal coating methods that may lead to coating voids and defects, Parylene conformal coatings are unique in their ability to be polymerized and deposited by vapor deposition onto substrates maintained near room temperature. The result is extremely thin, pinhole-free, high purity coatings that can protect external components on CGMs reliably and safely.

Protective Parylene films offer CGM protection by providing:

  • Biocompatibility and biostability
  • Excellent barrier properties
  • Ultra-thin coatings that offer waterproof protection with no signal loss or transfer

Biocompatibility and Biostability

Any medical device that comes into contact with the human body, including CGMs, must be biostable and biocompatible. Parylene is not only biostable and biocompatible but is considered environmentally friendly, addressing sustainability concerns. No initiators or catalysts are used in the polymerization process, and the coating is pure and free from trace ionic impurities. Parylene is REACH, RoHS, PFOA/PFOS-free, and CA Prop 65 compliant.

Learn more about Parylene’s biostability

Designing Diabetes Products that are Waterproof with Parylene – Barrier Properties

In general, Parylene performs exceptionally well as a barrier against corrosion caused by biofluids, moisture, and cleaning fluids because of the coating’s properties, including:

  • Oxygen permeability − low oxygen permeability for a polymer coating
  • Water vapor permeability − very low WVTR for a polymer coating
  • Liquid water uptake − Parylene absorbs very little water
  • Ionic permeability − salts have a difficult time passing through the coating
  • Coating porosity − at a minimum thickness of just 5 to 8 microns, Parylene can form a pinhole/pore-free coating

Table 1: Barrier Properties of Conformal Coatings

Polymer Gas Permeability at 25 °C, (cc·mm)/(m2·day·atm) WVTR,(g·mm)/(m2·day)
N2 O2 CO2 H2 H2S SO2 CI2
Parylene C 0.4 2.8 3.0 43.3 5.1 4.3 0.1 0.08
Parylene N 3.0 15.4 84.3 212.6 313 745 29.2 0.59
Parylene F (VT-4) 16.7 0.28
Epoxy (ER) 1.6 4 3.1 43.3 0.94
Polyurethane (UR) 31.5 78.7 1,181 0.93
Silicone (SR) 19,685 118,110 17,710
Ref.: Licari, James J. Coating Materials for Electronic Applications – Polymers, Processes, Reliability, Testing. William Andrew Publishing, 2003 and various companies’ literature.

Humidity

Humidity is perhaps one of the most apparent causes of corrosion-related failure for CGM components because metal components and connections can react with moisture in the atmosphere. Humidity testing is standard to ensure that the humidity resistance of a coating can be maintained long-term.

Table 2: IEC Testing Summary

Testing Spec. Reference Time Parylene N Parylene C Parylene F Acrylic Silicone Acrylated Urethane
96 hours temp humidity exposure IEC 60068-2-30 0 2.00E+06 2.00E+06 3.00E+06 8.00E+05 4.00E+06 1.00E+08
Day 1 1.29E+03 7.41E+03 3.63E+03 2.04E+02 6.17E+03 2.45E+04
Day 2 3.47E+03 1.23E+04 3.98E+03 5.13E+02 1.17E+04 2.69E+04
Day 3 3.55E+03 9.12E+03 3.80E+03 3.24E+02 8.71E+03 3.63E+05
Day 4 5.50E+03 1.23E+04 7.94E+03 7.08E+02 1.48E+04 2.82E+04
Ambient 2.45E+04 1.00E+06 1.00E+05 1.62E+05 3.63E+06 3.89E+06
MFG IC 60068-2-60 0 (Ambient) 1.37E+05 1.81E+05 1.71E+05 1.88E+01 6.77E+04 1.89E+05
Day 3 7.83E+04 8.46E+04 5.90E+04 1.14E+03 3.00E+04 1.31E+05
Day 5 8.46E+04 6.63E+04 1.84E+04 1.44E+03 2.22E+04 6.69E+04
Day 6 3.65E+04 2.35E+04 5.34E+04 1.66E+03 1.85E+04 6.63E+04
Day 7 4.87E+04 6.91E+04 4.72E+04 1.89E+03 1.40E+04 8.51E+04
Day 10 4.58E+04 7.92E+04 4.88E+04 2.43E+03 1.72E+04 9.20E+04
Day 11 9.02E+04 3.91E+04 5.93E+04 2.62E+03 1.64E+04 3.08E+04
Day 12 8.39E+04 8.52E+04 5.31E+04 2.71E+03 1.90E+04 1.23E+05
Day 13 6.28E+04 9.01E+04 5.65E+04 2.46E+03 1.63E+04 1.23E+05
Day 14 7.08E+04 5.13E+04 5.25E+04 2.47E+03 1.41E+04 6.10E+04
IEC 60068-2-30: 96 hours temperature humidity exposure
IEC 60068-2-60: Test ke, Method 4, 14 days, MFG

Results:

comparing the anomalies of parylene n, parylene c, and parylene f

As the chart and images indicate, Parylene passed all of the IEC testings at 50% of the film thickness of the traditional conformal coatings.

Communication Interference

Because of Parylene’s unique capabilities, no other conformal coating can be applied as thin and still provide the same protection level. Therefore, Parylene offers all of the necessary safeguarding against hazards without compromising the functional attributes of the device. Additionally, Paryene aids electrical communication, as its low dielectric constant ensures minimal energy loss in RF signals, and the thinness of the coating ensures signal transmission integrity.

Table 3: Parylene thickness levels and best applications

Thickness (μm) 0.1 to 5 5 to 12.5 12.5 to 18 12.5 to 25 12.5 to 50.8
Relevant Standards UT Type** in Upcoming IPC-CC-830C UT Type** in Upcoming IPC-CC-830C MIL-I-46058C IPC-CC-830B NASA-STD-8739.1B
Protection Level*** IPX3 / IPX4 IPX4 / IPX7 IPX7 / IPX8 IPX7 / IPX8 IPX7 / IPX8
Appropriate Products Consumer Electronic & MEMS Devices Consumer & Industrial Electronics Aerospace & Defense Aerospace, Automotive, Industrial, Medical Device, Telecom, & Other High-Reliability Markets Aerospace, Defense, & Very Harsh Industrial
* Relative to Parylene C and including the same pump down time for evacuating the deposition chamber with the same number and type of products to be coated.
** UT Type describes a general class of ultrathin coatings that range from 0.1 to 12.5 microns thick.
*** The protection level as related to IEC 60529 – Degrees of protection provided by enclosures (IP Code), but is also dependent on product design.

Other advantages of Parylene over Traditional Conformal Coatings include:

  • High levels of submersion protection – IPX8+, also depending on device design (learn more about IP ratings)
  • Excellent conformality. Can completely penetrate spaces as narrow as 0.01mm
  • Optically transparent and can be used to coat optical elements
  • Room temperature formation makes the coatings effectively stress-free
  • High tensile strength
  • No cure time
  • No pooling of coating in low areas

Parylene Conformal Coating Services With HZO

At HZO, we strive to provide tailored Parylene solutions that are convenient, easy to implement, and cost-effective. Our proprietary equipment decreases turnaround time and automates more labor-intensive processes, ensuring that you can easily save on Parylene protection and scale up to mass production. We offer various flexible business models, including outsourcing and “factory-in-factory,” and configure our processes so that they can easily be incorporated at many points in production. These benefits, coupled with a turnkey solution and dedicated engineers to walk through the coating process with you step by step, make us a perfect fit for your CGM project. To learn more, reach out to us today.

Mallory McGuinnessMallory McGuinness

Mallory is an electronics protection evangelist who writes content for HZO. In her free time she is reading non-fiction, and hanging out with her beta fish, King Awesome.

Discover how HZO can protect your product

Share This