December 27, 2022
Anodizing For Electrical Insulation

by J. Cooney

Industries are constantly looking for cutting edge technology to improve their products or solve problems discovered during development. The drive to maximize available space while making devices smaller is a major catalyst to the production of better and more efficient systems. In regards to anodizing, coating improvements have created a larger market for its use as an electrical insulator.

        Courtesy: Jeff Spotts, NASA

Anodization is used heavily in space, military, and tech spheres for the various benefits it brings to aluminum components. Corrosion resistance, hardness, and durability are often the main attraction; however, significant jumps in electrical resistance have increased its value as an insulator. Technical specifications often require coatings to reach a minimum voltage, per the given coating thickness, before current breaks through the oxide. We use a HIPOT tester to apply a high voltage direct current to the coating and record the dielectric voltage breakdown (DBV), this allows us to standardize the electrical resistance. 

When aluminum is anodized it grows an inorganic insulative oxide (Al2O3)  with pores that penetrate the surface and also extend out of it.

Courtesy: Mahadev Metals

This oxide layer acts as an effective electrical insulator while generally adding under 25 microns of increased dimension – a huge benefit as the weight and dimensional changes are nearly negligible. At this micron scale it becomes a challenge to increase the DBV, but there are some key techniques we use to maximize the insulative strength. It is important to note that the choice of alloy has a large impact.

There are many different anodizing processes so choosing the right one is a critical step towards obtaining the desired coating properties. The choice generally comes down to the electrolyte bath solution and the processing conditions. Sulfuric acid anodizing has become the standard for a majority of applications, especially because it can form hard coat anodize – a much stronger and insulated coating.

Due to qualities such as increased thickness, Type III hard coat is considered the best for having high insulative strength. Sulfuric clear coats and other acid electrolytes are available but they are typically used for cosmetic purposes – having much worse insulative properties.

    Courtesy of Semano Inc: VBD vs. Thickness for 3 Different Processes on 6061 aluminum

Semano has 30 years experience testing anodized coatings and pushing the limits of what was thought possible. Precise control over the surface preparation, acid solution temperature, current density, and sealing conditions greatly impact the results. Our standard hard coat consistently exceeds 900 volts per mil of coating which is a very respectable number within the industry. It is also not unheard of to reach 1200 volts per mil, but it is not a common occurrence or benchmark that can be consistently reached by anodize shops. Semano is the only company in the world that currently produces coatings that exceed 1700 vb/mil and can reach a DBV of 4900 volts at 3 mils thickness. However, the high durability and electrical insulation that AX200 offers may only be necessary for some very select applications.

Anodizing provides an alternative to organic insulators like parylene or polyurethane which are thicker coatings that can unintentionally trap particles leading to contamination of their environment. There are other options like ceramic spray coatings, however these are one of the most expensive coatings available. The insulative properties of ceramic coatings are fantastic as it can reach extremely high DBV values, but they do not come close to anodizing on a per mil basis. For example, yttrium oxide is a ceramic that can exceed 5000 volts DBV but the coating is regularly 5-7+ mils thick which is less than 1000 volts per mil. The advantage of anodizing is that it provides a far cheaper, smoother, and thinner option.

Courtesy of SEMANO Inc.

The anodizing process is adaptable, allowing for precise locating of the oxide layer and ability to leave other areas free of anodize. This means the insulative barrier can be placed anywhere on the aluminum surface that electrical flow needs to be impeded. 

We continually research and experiment to improve coating properties and depending on what our customer wants we can adapt to fit their needs. If you’re looking for a supplier that specializes in anodizing for rapid prototyping then look no further. Submit a quote or contact our engineering team today to find out how we can achieve the best coating for your project.


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