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Automotive Conformal Coatings: Some Like it Hot

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Mallory McGuinness | October 21, 2020

By 2030, electronic components will account for 50% of a car’s total cost worldwide. These electronic workhorses are powering the electrification of hybrids, battery electric vehicles, and Fuel Cell EVs. New EV-only OEMs such as Tesla and Rivian have entered the market, competing against traditional OEMs, and over 1 million plug-in electric vehicles are operating on American roads.

But electric vehicles are just a start. Autonomous cars are expected to account for about 12% of car registrations by 2030. As the automotive landscape shifts towards automation, one thing is clear: for functions from convenience to criticality; each component must function consistently. For automotive OEMs, the severe temperatures of the automotive service environment make achieving this type of component reliability a formidable challenge.

 

Road Hazards Ahead

Location

On Engine / Trans
At Engine / Manifold
Under Hood / Near Engine
Under Hood / Remote Location
Exterior
Passenger Compartment

Max Operating Temperature

155°C
140°C
125°C
105°C
125°C or 105°C
105°C or 85°C

 

Under the hood, the heat is on. Thermal cycling is intense, as temperatures can quickly fluctuate from outdoor freezing to extreme heat. As electronics are concurrently exposed to corrosives and many contaminants on the road, they require protection. Still, many automotive conformal coating solutions cannot maintain adequate protection through temperature extremes.

Traditionally, thick conformal coatings such as silicones have been used to offer component protection that can stand up to heat, but the extra weight and bulk can impede “lightweighting” endeavors, affecting consumer decisions about which car to purchase, as heavier cars use more gasoline than lighter ones. Size and weight can also impede efforts to place more PCBs into vehicles, an issue for designers and manufacturers who need to include more components to increase functionality.

Parylene, a thin-film coating applied in layers as thin as 2 microns, can also maintain performance in extreme heat while offering strong chemical resistance and can perform more effectively in severely cold environments without physical damage.

Properties

Max Operating Temperature
Minimum Coating Thickness to Meet IPC Standards
Chemical Resistance

Parylene C

290°C
12.5–50μm
High

Parylene F

400°C
12.5–50μm
High

Silicone

305°C
50–200μm
Low

Heat Dissipation for Automotive Conformal Coating

Another beneficial thermal property that Parylene exhibits is for heat dissipation. Heat must be dissipated to prevent overheating in electronics, typically through a heat sink. Unfortunately, conformal coatings have low thermal conductivity, and when applied in thick layers, are good heat barriers.

Therefore, traditional conformal coatings can interfere with the heat transfer path, impeding heat dissipation. As thermal conduction is inversely proportional to thickness, it is critical to integrate the thinnest coating possible.

Coating

Desired
Parylene N
Parylene C
Acrylic
Epoxy
Silicone
Urethane

Thermal Conductivity (W/mK)

High
0.13
0.08
0.13-0.25
0.17-0.21
0.15-0.31
0.21

Film Thickness (μm)

Low
2-50
2-40
30-130
30-130
50-210
30-130

Size and weight can also impede efforts to place more PCBs into vehicles, an issue for designers and manufacturers who need to include more components to increase functionality.  

Objects May Be Closer Than They Appear

Electronic vehicles have already happened, and before long, autonomous will overtake EVs, using sensor data to transport passengers safely and avoid catastrophic accidents. The future of the automotive market is now. Are you taking action to ensure your critical electronic components are up to the challenges?

Mallory McGuinness

Mallory is an electronics protection evangelist who writes content for HZO. In her free time she is reading non-fiction, and hanging out with her beta fish, King Awesome.

Ryan MooreRyan Moore

Ryan is a 9-year veteran to the world of protecting electronics from harsh environments and a lover of all things technology.

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