Neodymium magnets are susceptible to corrosion, oxidation, and degradation.
This happens when they are exposed to harsh environments.
That’s where Parylene coating comes in.
It is a thin, conformal polymer coating.
It can significantly enhance the performance and durability of magnets.
In this post, we’ll dive into Parylene coating for magnets.
Let’s get started.
What is Parylene?
Parylene is a family of polymers.
Parylene C and Parylene N are the most common variants for coating magnets.
We can apply through a vapor deposition process.
- Parylene forms a thin, pinhole-free, and conformal coating on the magnet’s surface.
- The typical coating thickness ranges from 300 nm to 500 nm (0.3 – 0.5 μm).
- It adds almost negligible distance to the magnets.
Why Parylene?
With Parylene coatings, you can protect your electronic devices from those risks.
Parylene for electronics in harsh environments has benefits such as:
Biocompatibility
The Food and Drug Administration (FDA) has approval for medical devices containing Parylene coatings.
- The coatings comply with USP Class VI Plastics requirements.
- And they are MIL-I-46058C / IPC-CC-830B listed.
Conformity
Properly applied parylene coating is pinhole-free with uniform controllable thickness greater than 0.5 micrometers to 1 millimeter on any surface or design.
Durability
The formation process ensures lightweight, protective performance over time.
Parylene has high-quality barrier, physical and electrical properties.
Stability
Parylene coatings can handle very hot and very cold temperatures without breaking down.
- The coating won’t peel, crack, or lose effectiveness between -200°C / -328°F and +200°C / 842°F.
Stress-free
Parylene coats at room temperature, avoiding thermal stresses that could compromise adhesion or accelerate cracking.
The stress-free formation preserves coating integrity and prolongs protective function.
Inert and stable
Parylene is totally chemically inactive.
- Harsh chemicals cannot react with or break down the coating.
- This inertness provides an impermeable shield against corrosion, even in acidic or caustic environments.
Parylene also resists molds, bacteria, and other biological growths that could degrade the coating.
- As an inert barrier, Parylene isolates and protects the magnet surface from external threats like moisture, chemicals, dirt, and microbes.
- Users benefit from Parylene’s unrivaled environmental stability and longevity across a broad range of conditions.
Protectablity
Parylene coats even 0.01mm cracks on neodymium magnets, fully encapsulating the porous surface. This seals vulnerable gaps thoroughly against corrosion, maximizing magnet longevity. The complete, void-free coating provides comprehensive protection.
Parameters & Specifications
Here are the key parameters and specifications for Parylene coating on magnets:
Coating Thickness
The typical thickness of Parylene coating on magnets ranges from 300 nm to 500 nm (0.3 – 0.5 μm).
This thin, conformal coating is applied through a vapor deposition process.
Coating Types
The most commonly used Parylene variants for coating magnets are Parylene C and Parylene N.
Parylene C is preferred for its better moisture barrier and chemical resistance properties.
Temperature Resistance
Parylene C coated magnets can withstand temperatures up to 150°C without degradation for short-term use (1,000 hours).
For continuous 10-year service life, the recommended maximum temperature is 80°C in oxygen environments and 230°C in inert environments.
Corrosion & Chemical Resistance
Parylene acts as an excellent moisture and chemical barrier, protecting magnets from corrosion, oxidation, and degradation from exposure to acids, alkalis, and solvents.
It exhibits minimal swelling when exposed to various chemicals like hydrochloric acid, sulfuric acid, nitric acid, etc.
Electrical Insulation
Parylene coating provides good electrical insulation properties with high dielectric strength (e.g., 220 V/micron for Parylene C).
It has high volume resistivity (e.g., 8.8 x 10^16 ohm-cm for Parylene C) and surface resistivity.
Biocompatibility
Parylene C is biocompatible, making it suitable for medical implants and devices in contact with the human body.
Lubricity and Wear Resistance
Parylene coatings have a low coefficient of friction, providing lubricity and reducing wear and abrasion on magnets.
Types of Parylene Coatings
There are four main types of Parylene coatings:
- Parylene N
- Parylene C
- Parylene D
- Parylene HT (also known as Parylene AF-4 or Parylene F)
Here are the key differences between them.
Parylene N
The basic, unsubstituted form of Parylene, consisting of a linear carbon-hydrogen polymer chain.
- Has a low dielectric constant and dissipation factor, making it suitable for high-frequency applications.
- Exhibits high vacuum stability and has a high melting point of 420°C.
- Provides excellent crevice and penetration ability, second only to Parylene HT.
Parylene C
Produced from the same raw material as Parylene N, but with one chlorine atom substituted for a hydrogen atom on the phenyl ring.
- The most widely used type due to its low permeability to moisture and corrosive gases, as well as ease of deposition.
- Offers a useful combination of electrical and physical properties, including high corrosion resistance.
- Can withstand continuous exposure at 100°C in oxygen environments for up to 10 years.
Parylene D
Similar to Parylene C, but with two chlorine atoms substituted for hydrogen atoms on the phenyl ring.
- Has a slightly higher temperature tolerance than Parylene C, withstanding up to 125°C.
- Lacks sufficient biocompatibility for widespread use in medical devices.
Parylene HT (AF-4 or F)
Fluorine atoms replace hydrogen atoms, either on the aliphatic chain (AF-4) or the aromatic ring (F).
- Exhibits high oxidative resistance, UV stability, and low coefficient of friction.
- Suitable for high-temperature applications up to 450°C (short-term) and UV exposure.
- Has the highest crevice penetration ability among Parylenes.
- More expensive and less commonly used due to complex synthesis and lower deposition rates.
When to use
Parylene coatings can be a suitable option for neodymium magnets in certain conditions.
Here are some situations where Parylene coatings may be appropriate:
Medical and dental applications
Parylene coatings are commonly used to protect neodymium magnets in medical and dental applications, particularly when the magnets will be used intra-orally.
Corrosion resistance
Parylene coatings provide excellent resistance to moisture and chemicals, making them suitable for use in harsh environments where corrosion is a concern.
Conformal coverage
Parylene coatings offer excellent conformal coverage, meaning they can coat complex shapes and surfaces uniformly.
Electrical insulation
Parylene coatings have excellent electrical insulation properties, making them useful for applications where electrical insulation is required.
It’s worth noting that the durability of Parylene coatings can be influenced by various factors, including the specific application, environmental conditions, and proper application techniques.
Advantages over PTFE
Parylene offers advantages in terms of durability, conformal coating capabilities, chemical resistance, and electrical insulation.
Application Flexibility
Parylene is often a better choice due to its application-specific considerations.
It offers more flexibility in terms of its suitability for various applications.
Crack and Wear Resistance
Parylene tends to have better resistance against cracking and wear compared to PTFE.
This makes it a more durable option, especially in environments where mechanical stress or friction is a concern.
Conformal Coating
Parylene is a conformal coating, meaning it can uniformly cover complex shapes and surfaces with a thin, pinhole-free film[6]. This makes it suitable for protecting delicate electronic components and ensuring proper performance.
Chemical Resistance
Parylene exhibits excellent chemical resistance, making it suitable for applications where exposure to harsh chemicals or solvents is expected.
It can provide a protective barrier against corrosive substances.
Electrical Insulation
Parylene is an exceptional electrical insulator[5]. It is commonly used in the manufacture of printed circuit boards (PCBs) and electrical cables, where it provides insulation and protection against electrical shorts.
According to our experience and simulated tests, the choice between Parylene and PTFE depends on the specific requirements of the application.
- PTFE may have a lower coefficient of friction.
Recommended Applications
Here are some specific applications where Parylene is good choice.
Medical Devices
Parylene is commonly used to coat medical devices such as coronary stents, probes, needles, catheters, and hearing aids.
It is a biocompatible material that can provide a protective barrier against bodily fluids and other contaminants.
Electronics
Parylene is an excellent electrical insulator and is commonly used in the manufacture of printed circuit boards (PCBs) and electrical cables.
It can provide insulation and protection against electrical shorts.
Industrial Applications
Parylene is a conformal coating that can uniformly cover complex shapes and surfaces with a thin, pinhole-free film.
This makes it suitable for protecting industrial components such as bearings, pipe liners, valves, pumps, and sealing components.
Chemical Resistance
Parylene exhibits excellent chemical resistance, making it suitable for applications where exposure to harsh chemicals or solvents is expected.
It can provide a protective barrier against corrosive substances.
High Temperature Applications
Parylene can be used in high-temperature applications up to 450°C.
It is useful in applications where long-term UV stability is required.
Common quality issues
Some frequently occurring coating problems that can occur if Parylene is not properly applied are as below.
Bubbles
These are air pockets or voids that form within or under the Parylene coating, creating an uneven or rough surface. Bubbles can affect the smoothness, uniformity, and quality of the coated product. Bubbles can be caused by moisture, air, or solvents trapped in the coating during the curing process, or by overheating or overcuring the coating.
Moisture diffusion
This is when water molecules penetrate through the Parylene coating and reach the substrate, causing corrosion, oxidation, or degradation of the coated product. Moisture diffusion can affect the electrical insulation, chemical resistance, and mechanical strength of the Parylene coating. Moisture diffusion can be influenced by the environmental humidity, temperature, pressure, and exposure time.
Pinholes
These are small holes or gaps in the Parylene coating that expose the substrate to the environment. Pinholes can increase the risk of corrosion, oxidation, or contamination of the coated product. Pinholes can be caused by dust, dirt, or foreign particles on the coating surface, or by insufficient coating thickness or coverage.
Potential Drawbacks
There are several potential drawbacks and limitations to using Parylene coatings on magnets.
Durability & Wear Resistance
Limited Abrasion and Wear Resistance
Parylene coatings are relatively soft with low durometer values.
Therefore, they are susceptible to damage and wear during routine handling or applications involving friction or abrasion.
Coating Breach under Intra-oral Forces
A study found that single and double Parylene coatings on NdFeB magnets showed visible abrasion and breaches in the coating after simulated grinding and crushing forces mimicking intra-oral conditions.
The conclusion was that Parylene coatings are unlikely to withstand the forces encountered in the mouth.
Adhesion Challenges
Poor Adhesion to Metals
Without proper adhesion techniques, Parylene adheres poorly to metals.
Just like gold, silver, and stainless steel, which are commonly used in magnets and electronic components.
Additional adhesion promotion methods may be required, increasing complexity and cost.
Delamination Risk
Delamination, where the coating separates from the substrate, can occur if proper surface preparation, cleaning, and compatibility between Parylene and the substrate are not ensured.
Process Limitations
Batch Processing and Limited Throughput
The chemical vapor deposition (CVD) process for Parylene requires batch processing with a limited physical space in the deposition chamber. This limits the quantity of items that can be coated in a single run, potentially increasing cost and processing time.
Masking Requirements
Functional electrical components and areas need to be masked during the CVD process to prevent unwanted Parylene deposition, adding labor and preparation time.
Coating Removal Challenges
Parylene’s chemical inertness and heat resistance make it difficult to remove from substrates if rework or repairs are needed.
- Micro-abrasion is often the only reliable method for removal.
Parylene coatings offers advantages like corrosion resistance and biocompatibility for magnets.
But you still should consider these potential drawbacks.
Especially in applications involving wear, abrasion, or harsh environments.
Final Thoughts
Parylene coating, particularly Parylene C, is excellent for enhancing the performance and durability of magnets in various demanding applications.
It has features like corrosion resistance, high-temperature stability, electrical insulation, biocompatibility, and lubricity.
Does it look like an ideal choice for your application?
If you need Parylene coated magnets, make sure to send us an email!