How to Select the Right Silicone Oil for Electronic Coating and Lubrication?

Dielectric strength of a material indicates how much of an electric field it can withstand before it loses its insulating properties and becomes electrically conductive, and it is an important attribute for voltage printed circuit boards, precision instruments, and power electronic components, as it reduces the risk of the system breaking down due to arcing, short circuiting, and system failure. Therefore when dealing with equipment that is rated above 1 kilovolt, the insulation's ability to resist current flow via its surface area becomes extremely important for safety. Volume Resistivity also measures how well insulation resists current flow. In a system, the higher the insulation, the less current will leak, and the better balanced the cells will be. In precision sensing equipment, the silicone oil helps to provide the correct insulation to ensure the precision of the adjustable output, and also prolongs the life of the equipment due to its better than average dielectric properties. In the 2023 report by ElectroInsight, it states that  materials that have a dielectric strength of less than 15 kV/mm, have 34% higher failure in transformers and switchgear. These materials should be avoided for electric vehicle battery management systems. Massage oil is another example.

It still works well under repeated heating and cooling cycles, and it still works under climate conditions that would usually speed up deterioration and jeopardize the operation of the power grid.

BreaKdown Voltage: Methyl vs. Phenyl Modified Silicone Oil

Methyl Modified Silicone Oil has a breakdown voltage of 15 to 18 kV/mm and a thermal stability index of 0.85 while Phenyl Modified Silicone Oil has a breakdown voltage of 22 to 28 kV/mm and a thermal stability index of 1.12. Standard testing of these materials has shown Phenyl Modified Silicone Oil to have higher breakdown voltage and thermal stability index than Methyl Modified Silicone Oil. This difference can be explained by phenyl groups. Phenyl groups, being an aromatic structure, are able to hold and pack molecules closer together. This process makes the materials less susceptible to ionization when the materials are subject to an extreme electric field. These phenyl modified oils are able to retain approximately 92% of their dielectric properties while the temperature is ranging from 0 to 200 degrees celsius. This is in contrast to the regular methyl modified oils that only retain about 78% of their dielectric properties. This is the reason that engineers often choose phenyl modified oils for electrically insulated transformers and electrical systems in aircraft. While methyl modified oils are able to retain approximately 78% of their original dielectric properties, phenyl modified oils are able to retain about 92% of their original dielectric properties, thus making them more desirable for use in electrically insulated transformers and aircraft electrical systems.  These materials, when modified to meet the other applicable industry standards, have been shown to provide a reductin in the frequency of mechanical failure and to assist in the overall longevity of the mechanical systems. This is especially true in electrically insulated transformers and in other applications where a high degree of reliability is required.

Optimization of viscosity for direct lubrication and coating adhesion

 Silicone oil viscosity (50–1,000 cSt) in relation to the dynamics of motion of: MEMS actuators, EV contractors, and relay mechanisms

With varying configurations for mechanical and electrical applications, it is essential to select the appropriate viscosity for the intended use. For example, MEMS actuators operating above 100 Hz require low viscosity 50-100 cSt oils to facilitate rapid microsecond responses by minimizing inertia-related resistance. For EV contactors expected to handle more than 500 amps, a medium viscosity oil of 200-500 cSt is ideal to manage electrical arc welding while enabling rapid disengagement of the contacts. Additionally, a relay mechanism subjected to multiple shock impacts of 10 G's or more will require a high viscosity oil in the range of 500-1000 cSt to ensure consistent lubrication is provided despite the occurrence of sudden shocks. In all of the above examples, engineers have to determine the localized shear and pressure behavior at those points. Design specifications must account for rapid changes in temperature, as unmitigated, will compromise the oil film.

Viscosity's influence on film retention, migration control, and long-term lubrication in sealed enclosures

Silicone oils between 350 and 1,000 cSt are great for maintaining film across sealed electronics. These oils are less likely to be affected by gravitational set displacement, thus forming stable boundary layers around 3 to 5 microns thick on contacts and bearings. This is extremely important for automotive control units that are subject to continuous shaking. They exhibit an extremely wide temperature operating range (−40 to 200 °C) and throughout this entire temperature range, these oil grades maintain a viscosity index of >200. This viscosity helps eliminate capillary creep issues, which result in frustrating dry spots. These formulations remain shear stable, and thus, they will not separate from thickening agents over time. This is why many aerospace components and industrial sensors using these oils can be maintenance-free for >10 years, which satisfies the MIL-PRF-27617 certification requirements.

Material Compatibility and Thermal Reliability Across Electronic Substrates
Chemical compatibility with silicone oil with EPDM seals, polyimide coatings, FR-4 laminates, and solder masks 
For silicone oil to serve its purpose, it must remain chemically neutral to its surroundings, close to the same materials used in the manufacture of electronic devices. Considering the EPDM seal in the connectors and housing assembly, it should not result in swelling, brittleness, or compression set with the silicone oil after multiple mating cycles. With polyimide coatings on flexible circuits, silicone oil may cause plasticization that may weaken the adhesive and disrupt its dimensional stability. For silicone oil to be satisfactorily compatible with FR-4 boards, it should not cause resin migration or delamination and should not cause insulation failure. For solder masks, silicone oils should not cause conductive anodic filament formation or blisters in the protective coating. Compatibility issues are not trivial. For incompatible materials, recent industry data from the 2023 Failure Analysis Consortium reports about 23% of automobile sensor seal failures and 17% of industrial relay failure issues.

Thermal stability limits and oxidative resistance: Ensuring performance across -40°C to 200°C operating ranges

Because of their structure and built-in antioxidants, oils can operate at extreme temperatures. They can operate down to -50°C, which is very important for use in the polar regions, because this is where lubrication failure can lead to extreme equipment damage. They have also been proven to maintain their insulating and electrical insulating properties in high-performance phenyl-modified oils that operate above 180°C. They have also been tested using ASTM D943 which showed a low rate of oxidation, and a lot of low rate of sludge build-up, preventing corrosion on the mechanical components. For the best formulas, the stability to temperature variations meets the UL 2580 safety standards for electric vehicle battery applications and the DO-160 Section 25 for thermal failures in electronic aviation.

FAQ

What is dielectric strength? 

The dielectric strength is determined by the maximum amount of stress a dielectric material can handle before it suffers an electrical breakdown. This is extremely important when considering applications that are high voltages since it can help prevent arc tracking and shorts with dielectric failures.

Why is viscosity significant for silicone oils?

The viscosity of silicone oils determines their ability to withstand and flow during mechanical or electrical operations. This makes it significant for precision work.

What differentiates phenyl-modified silicone oils from methyl ones?

Compared to methyl-modified silicone oils, phenyl-modified silicone oils are more reliable when it comes to high thermal and electrical breakdown voltages. Thus, they are ideal for use in high performing electrical applications.

What determines the compatibility of silicone oil with an electronic component?

The silicone oil gets compatibility with electronic components by remaining chemically neutral to the EPDM seals, polyimide coatings, FR-4 laminates, and solder masks. This makes it important to avoid breakdown and failures.