Advanced Silicones for ADAS in Light Vehicles

Material solutions for thermal management, protection and assembly.

February 12, 2025

Joseph Sootsman

An ADAS radar sensor could be made with Si EMI sealants, thermally conductive silicones and Si Fast assembly adhesives, Dow claims. (Dow)

Today’s ADAS designers are adding more electronic components and redundant computing systems to printed circuit boards (PCBs). These heat-generating electronic assemblies are installed in enclosures that provide environmental protection, but the high heat generated by high-performance computing systems can degrade ADAS performance or cause device failure.

Silicone materials, including thermally conductive silicones, encapsulants and gels, and Si foams, could be used throughout an ADAS camera sensor assembly. (Dow)

Not all thermal management materials can withstand temperatures up to 200 C (392 F), and most do not retain their flexibility at elevated temperatures. This creates a problem when PCB components expand and contract at different rates due to mismatches in their coefficients of thermal expansion.

In addition to high-temperature resistance and thermal stability, automotive engineers need materials that resist shock and vibration. The enclosures that house ADAS electronics components can be sealed to exclude water, however additional PCB-level protection with a conformal coating can be used to prevent moisture or debris from impacting device performance. With the increasing number of electronic components and high-frequency devices like radar in light vehicles, shielding against electromagnetic interference (EMI) is also needed.

Furthermore, because the number of ADAS components continues to increase, the fast and efficient assembly of these modules presents challenges. Engineers need materials that support automated dispensing and rapid curing. Increased environmental sustainability initiatives are also driving the demand for a reduction in the amount of energy that heat curing requires. Automakers are pushing engineers to use materials that cure at room temperature or with ultraviolet (UV) light, but ADAS designers still need solutions for protection and assembly that are compatible with a variety of PCB materials, provide chemical resistance, and are cost-effective to apply.

Advanced silicones solve multiple challenges

Advanced silicones can meet these challenges and offer important advantages over organic materials. For example, advanced silicones can withstand temperatures up to 200 C. By contrast, epoxies are prone to cracking from thermal stresses. In addition, silicones retain their flexibility even when fillers that impart thermal or electrical conductivity are added. With their low modulus, silicones can relieve stresses that result when different PCB materials, such as metals and plastics, expand and contract at varying rates.

Advanced silicones also resist the shock and vibration that is common in automotive environments. They also absorb significantly less water for long-term moisture and water resistance, can be formulated to resist the spread of fire and can cure at room temperature or with UV instead of with ovens. When electrically conductive fillers are added, silicones can shield ADAS electronics from EMI. When thermally conductive fillers are added, these compounds can move heat away from sensitive electronics.

Thermal management

Thermally conductive silicones for ADAS include gap fillers, greases, adhesives and encapsulants. These materials work by filling voids between a heat sink and source that would otherwise be filled with air, which has a thermal conductivity of just W/m-K. Gap fillers can be used in applications with large gaps or where different component sizes need to be managed. Greases also create a path for heat to travel but are used in thinner gaps and are non-curing. Adhesives provide a mechanical bond between electronic components within a heat-generating assembly. Encapsulants dissipate heat while covering or encapsulating whole electronic components.

Silicone gap fillers are available in a range of thermal conductivities. For example, the higher power demands of ECUs may require products with high thermal conductivity. Materials with lower (2.0 W/m-K) and higher (9.5 W/m-K) thermal conductivities are available to provide the right level of performance. Because silicone gap fillers are stress-relieving, they resist vibrations and are not prone to cracking when PCB materials expand and contract at different rates. These advanced silicones support automated dispensing and room-temperature curing.

Thermally conductive silicone greases are one-part products that do not require curing and are easy to dispense or print with automated equipment. Because they do not cure, greases are easy to rework and can be wiped clean. They come in a range of thermal conductivities and can be used to dissipate heat from a wide variety of ADAS electronics components. Among their other benefits, thermal greases can support thin bond lines for improved device performance.

Like gap fillers, thermally conductive silicone adhesives are available in either one-part or two-part formulations. Both are designed to cure at room temperature but can use ovens for accelerated curing. These adhesives are easy to dispense and have thermal conductivities that can range from ~1 to 8 W/m-K. These silicone adhesives provide mechanical adhesion that can be used to fix the heat sink to the heat source, which is a benefit in applications where there may be limited space for mechanical fasteners.

Thermally conductive encapsulants are typically two-part products that cure as a soft elastomer at room temperature or with added heat for accelerated curing. They are readily flowable to fill into narrow cavities and have viscosities ranging from 3,000 to 25,000 mPa after mixing. Not all silicone encapsulants are thermally conductive, but they can be formulated to have thermal conductivities up to 4 W/m-K. Silicone encapsulants can be used for environmental protection and product assembly. They can also provide thermal management in certain applications.

Protection and assembly

Non-conductive silicone encapsulants and gels are used to protect a wide variety of electronics across automotive applications. These advanced materials are waterproof, flame-retardant, stress-relieving, electrically insulating and vibration-damping. Silicone gels are soft and typically have low or no filler content. This enables them to have significantly lower viscosities, but they are not as tough as encapsulants. Both gels and encapsulants can cure at a wide range of temperatures and some can support UV curing for accelerated assembly.

Conformal coatings are another type of advanced silicone for ADAS modules. These thin, protective coatings resist moisture, dust and debris. Depending on the specific product, they can provide either UL94 V-0 or UL94 V-1 flame resistance. Silicone conformal coatings can be formulated with a wide range of hardness to minimize internal stress generation. They are also available in different viscosities to fill small gaps and accelerate ADAS assembly. These products can be formulated to cure at room temperature, with heat, and in some cases can be cured with UV curing in seconds.

Dow has developed silicone materials like conformal coatings, EMI sealants and gels for lidar sensor assemblies. (Dow)

EMI shielding adhesives and gaskets that provide sealing and adhesion are also used in ADAS assembly. Silicone EMI shielding adhesives are designed to protect ADAS electronics across a broad range of frequencies up to the 77-79 GHz range used in radar and lidar. They adhere well to a variety of substrates, have durable mechanical properties, and are used in numerous ADAS applications. Among their many advantages, these products are easy to dispense and cure either with heat or at room temperature. ADAS designers can choose materials that meet a wide range of elongation and mechanical performance needs.

Formed-in-place gaskets (FIPGs), cured-in-place gaskets (CIPGs), and dispensed foam gaskets (DFGs) are used to seal and bond ADAS cameras and radar and lidar sensors. Formed-in-place gaskets are thixotropic, meaning that they become less viscous when shear is applied. They cure in place after assembly at room temperature and bond with a variety of substrates. Cured-in-place gaskets are dispensed, cured and then assembled. They may require heat to cure but provide a robust seal with moderate compressive force. Dispensed foam gaskets seal with lower clamping forces and cure with or without added heat. Both CIPGs and DFGs are repairable and meant to provide an accessible seal.

Finally, advanced silicones for ADAS assembly and protection include a wide variety of adhesives that are engineered to provide designers with controlled viscosity and thixotropy for application-specific requirements. There are multiple options for room-temperature curing products. These specialized adhesives are suitable for many PCB materials and are available in either electrically insulating or electrically conductive formulations.

The importance of supplier selection

Using decades of experience in automotive electronics, Dows world-class R&D scientists provide a broad portfolio of innovative, proven silicone materials developed for ADAS applications. (Dow)

Automotive engineers who partner with the right material supplier can accelerate product development and improve vehicle reliability. For example, Dow has a global team of application experts who work closely with ADAS designers to recommend the optimal material for each application need. This close collaboration adds value throughout the entire product life cycle, and Dow maintains research laboratories that use the latest technologies to test materials under real-world conditions.

Suppliers who take a collaborative approach like this work closely with partners to understand their specific challenges and goals. In turn, this ensures that the materials a supplier recommends are aligned with the customer’s requirements for thermal management, protection, and assembly. Delivering cutting-edge solutions to clients is important, but it takes a collaborative, data-driven approach to ensure that ADAS materials meet the highest standards for quality and reliability.

Joseph Sootsman is principal TS&D scientist, electronics application development at Dow. Lu Zou is senior TS&DsScientist, electronics application development at Dow.