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Proven Solutions to Bolster Reliability and Longevity in ADAS Sensors

Posted on July 17th, 2021 by

Realizing the mass potential of advanced driver-assistance systems (ADAS) as early as the 1970s and commercializing the first ADAS feature in 1991, engineers have improved on these systems with numerous design iterations, prototyping, and engineering refinements. Thirty years after commercialization, ADAS has evolved and continues to make up for human shortcomings on the road, such as distractions, poor judgment, physical limitations, and even aggressive driving. 

ADAS Market Growth

Many factors serve as the impetus for the impressive growth of the global ADAS market. Research indicates that the rising awareness of ADAS capabilities to foster road and vehicle safety and increasing incidences of road accidents is one reason.  ADAS demand is also fueled by regulatory interest in safety applications that protect drivers and reduce accidents.  Countries like the United States, the United Kingdom, France, and Germany continue to implement regulations mandating the inclusion of ADAS within new vehicles.  Examples include the European Union and the United States’ requirements that all cars be equipped with autonomous emergency braking systems and forward-collision warning systems by 2020. 

Consumers are also becoming more interested in ADAS applications that promote comfort and economy, including parking assist and blind-spot monitoring.  Additionally,  the potential for lowered system costs, adaptability of system technology across vehicle types, and growing automation capabilities in automobiles fuel the market growth.

By 2030, over half of the vehicles sold globally will have some form of autonomous driving capability.  There have been significant investments in research and development from both OEMs and big tech players like Google.  The semiconductor industry is also expected to enter the market in the coming years.

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ADAS Functions and Features

ADAS are electronic systems in a vehicle that use advanced technologies to assist the driver.  These safety features are enabled by sensors that are part of the ADAS, such as radar and cameras that interpret the world around them, provide information to the driver, or take automatic actions.

ADAS features typically provide warning type information after receiving communication from the sensors.  For example,  sensors may detect objects in an area where the driver may have a blind spot when driving or parking.  Sensors also monitor lane departure activities and send data to the modules to warn the driver to recalibrate their lane position.

The importance of ADAS cannot be underestimated; active safety systems that engage control breaking or steering can save lives. The Insurance Institute for Highway Safety found that forward collision warning systems lower front-to-rear crashes by 27%; when the system includes the ability to brake automatically, the number nearly doubles.  Rearview cameras reduce backing crashes by 17%, but automatic rear braking lowers them by 78%. 

Sensor Technology – A Key Driver of ADAS Development

ADAS functions feed off a continuous stream of information about the vehicle’s environment as the sensors provide that information. Sensors can be divided into four main categories:  Radar, Lidar, Ultrasonic, and Cameras, detecting what the driver sees and, critically, what the driver cannot or does not see. Consequently, ADAS can provide reactions that are much faster than human reactions.  The required robustness and durability of these crucial sensors can vary based on where they are in the vehicle.  Some are located in the vehicle cabin, while others are in more vulnerable areas such as the corners of bumpers or behind the grille and can be subjected to more hostile environments.  In addition to harsh environments, these sensors may need replacement or recalibration in the case of car accidents.

As such, vehicle applications place high demands on the reliability and resiliency of the sensors used in ADAS.  They can be affected by vibration, direct moisture, or extreme heat and cold.  To handle the demands of these new technologies, along with increased miniaturization of electronic components, manufacturers face many challenges, including corrosion protection for these components.

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Fostering ADAS Sensor Reliability with Corrosion Resistance

ADAS electronics can be corrosion protected in various ways: mechanical seals, enclosures, or conventional liquid conformal coatings (acrylics, silicones, etc.). Mechanical seals and enclosures are designed to prevent moisture ingress but present a design challenge. If moisture gets in, it becomes trapped and can cause catastrophic failure of the device over time. Mechanical seals can also become dislodged if exposed to physical impact and may deform or crack over time and continuous vibration. Material selection can also be a challenge as not all materials can protect against water, humidity, and commonly used automotive fluids. The below chart shows an overview of how different materials perform in operating environments:

Protection Characteristics Unprotected PCB Mechanical Seal Silicone/Acrylic Coatings Parylene Coating
Protection Barrier None Good, but can be compromised with drops & temperature. Good, but can be thick & porous depending on the application. Excellent. Can peel if not properly applied.
Hydrophobic No No Yes Partial
Thickness N.A. Millimeters μm – Millimeters 2μm – 50μm
Protection Against Water Poor Good – Ingress Poor – Penetration Good Excellent
Salt/Chemical Protection Poor Poor Varies Excellent
Durability Low Varies Varies High
Submersion Test Time to Failure Seconds (IP Rating N.A.) Varies Varies Days to Weeks (IPX7 – IPX8)
Parylene Performance Characteristics Versus Competitor Solutions.

Read the definitive paper on electronic protection methods

Meanwhile, conventional conformal coatings have been used extensively on automotive electronics, but they present challenges of their own; the weight and required thickness of these materials can be bulky and heavy. Choosing a suitable conformal coating material is crucial because selected chemistry can directly impact aspects of sensor functionality and reliability. Differing chemistries yield unique performance characteristics when considering variables like gas permeability, water vapor transmission rate, dielectric properties, or other performance standards.

Understanding these design challenges and their consequences, HZO offers industry-leading solutions for ADAS, with a special focus on printed circuit board protection. Our solution satisfies automotive business requirements by providing Parylene, “the gold standard of conformal coating protection,” with more cost-effectiveness, convenience, and scalability.

Download HZO’s Parylene datasheet

Parylene conformal coatings come in various types and have nearly 50 years of performance history with critical applications and industries, including sensors and other electronics in automobiles. The coating is superior in uniform coverage, barrier properties, and performance at comparably thinner films, with less stress on mechanical structures and virtually no added weight.

 

Class Type Speciman – Average Coating Thickness [μm]
    1 2 3 4
XY Parylene N 25 25 23 23
XY Parylene C 31 30 30 32
XY Parylene F 46 36 43 29
AR/UR Acrylic 73 73 69 72
SR Silicone 102 99 114 154
AR/UR Acrylated Polyurethane 91 91 107 107
HZO’s Parylene passed all IPC CC-830C at 50% of the Film Thickness of the Traditional Conformal Coatings. 

Unlike liquid conformal coating methods that may lead to coating defects, Parylene coatings are produced using a repeatable vapor deposition process unique in its ability to polymerize and deposit uniform coatings onto substrates maintained at room temperature. The result is extremely thin, pinhole-free, high purity coatings that fulfill the reliability requirements of automotive design. Parylene is highly conformal, offering the best protection on corners & edges of components, creating a thin 3D type film across the PCBA.  The high conformality at low thickness offers design flexibility & results in extremely low contact / interfacial resistance. These properties are due to the chemical vapor deposition (CVD) process specific to Parylene.

Parylene is also unique due to the ability to be deposited in several different chemical variants that demonstrate unique film performance characteristics.  Each Parylene composition offers exceptional salt, mist, moisture, dust, and environmental protection.  However, some Parylene types exhibit performance qualities that excel in specific circumstances or application environments.  Examples of these variants include Parylene C, which is the most effective conformal coating available for corrosion protection at its thickness. Meanwhile, Parylene F exhibits superior thermal resistance and is ideal for maintaining protective performance while exposed to high heat.

 

Polymer Gas Permeability at 25 °C, (cc·mm)/(m2·day·atm) WVTR,(g·mm)/(m2·day)

N2

O2

CO2

H2

H2S

SO2

Cl2

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 D 1.8 12.6 5.1 0.6 1.9 0.2 0.09
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 1,81 0.93
Silicone (SR) 19,685 118,110 17,717

HZO Coated Automotive Assemblies were exposed to HAST (Highly Accelerated Temperature and Humidity Stress Test) at 130 °C and 90% RH for 48 hours, while powered at 14 V and a sampling rate of 0.5 Hz. HZO coatings pass by preventing any current spikes over 0.5 Amps.

Parylene F is used for exposure to higher temperatures in the -55°C to 200°C range while Parylene C can be utilized from -55°C to 85°C. Exposed to the HAST conditions pictured above, Parylene F would best serve applications like ECMs found in the engine compartment and exposed to high-temperature environments. Parylene C is a better alternative for corrosion protection for ECUs in areas of the vehicle that do not have high-temperature considerations but need resistance to moisture, humidity, salt, or other chemical exposure.

With trusted, proven proprietary processes, HZO’s Parylene coatings can offer superior protection for automotive applications, including sensors, demonstrating aptitude through various test trials we have conducted to meet necessary performance requirements and specifications. In addition, HZO has experience with the PPAP process to ensure that production parts will be executed in a highly repeatable and quality-focused manufacturing environment. With a unique ability to handle large and complex parts due to proprietary coating and automation equipment with exceptionally high yield rates, our customer-focused solutions can be delivered with highly customizable end to end business models as our team of dedicated engineers and SMEs work with clients through every step of the coating process. To learn more, contact us today.

Read more about HZO coatings for ADAS applications

Lisa RizzoLisa Rizzo

Lisa Rizzo joined HZO 2019 as Director of Product Management, focusing on next-generation thin-film solutions to meet the industries' evolving needs. She has worked with internal and external customers to ensure that market trends are identified and translated into innovative solutions. In her new capacity as Business Director of Thin Film and Emerging Technology, Lisa continues to focus on executing innovative strategies for new HZO product technologies to service the broader conformal coating marketplace.

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