Introduction
This page helps define the basic characteristics of an E-Coated Heatsink when the treatment is applied to the surface of heatsinks used to assist in the cooling of heat-generating devices (typically electronic components). We will focus on thermal performance compared to an anodized coating.
What is E-Coating?
E-Coating is a method of immersion wet painting that utilizes electrical current to deposit paint onto a metal workpiece. E-Coating is a generic term and has many industry names, including:
- Electro Painting
- Electro Coating (E-Coating)
- Electro Coating Primer
- Electrophoretic Lacquering
- Cathodic Electrodeposition (CED Coating)
- Cationic Epoxy
Specifically, the process is described as Cathodic Epoxy Electrodeposition Primer.
The process is similar to electro-deposition of metals except E-Coating uses organic paint. The two main industry specifications are MIL-DTL-53084 and A-A-52474. After application, E-Coating provides a consistent, corrosion-resistant finish.
The most common paint color is black, although other colors may be specified for decorative purposes. Parts require an electrically conductive surface in order to be E-Coated.
The E-Coating process consists of four main steps:
- Pretreatment – Cleans and prepares the part surfaces.
- Electrocoat Bath – The bath typically consists of 80–90% deionized water with suspended acrylic or epoxy paint solids. Voltage controls coating thickness.
- Rinsing – Excess paint is rinsed off and recycled.
- Baking – Cures the paint to promote cross-linking; typically 20 minutes at 375°F (or 180°F for low-temperature paints).
Advantages of an E-Coated Heatsink
- Only one coat required for primer and color.
- Compatible with liquid and powder topcoats.
- Cost-effective across all production volumes.
- Complete coverage, including hard-to-reach areas.
- Thinner than powder coating (typically 0.5–1.5 mils).
- Threads and holes generally do not require masking.
- Excellent resistance to salt spray, humidity, corrosion, and chemicals.
- Hard, durable finish resistant to chipping, scratching, and peeling.
- Environmentally friendly with low VOCs and HAPs.
- RoHS, REACH, OSHA, and EPA compliant.
- Assemblies can be coated provided all surfaces are electrically conductive.
Disadvantages
- Parts must withstand the baking process.
- Low resistance to ultraviolet (UV) light, making it unsuitable for prolonged outdoor use.
- Production lines typically use only one color (most commonly black), making color changes difficult.
- As an epoxy paint, E-Coating slightly inhibits thermal transfer, although the impact is minimal due to its thin coating.
Anodizing vs. E-Coating
Aluminum is typically anodized for corrosion resistance and coloring. However, die-cast aluminum often produces a matte black finish due to its silicon content. Since silicon distribution is not homogeneous, the surface color may vary.
If appearance is an important requirement, E-Coating should be considered.
Thermal Performance Testing
Since E-Coating is a paint, it is important to compare its thermal performance with anodizing.
Radian performed convection testing using a 3U test bench with a die-cast aluminum 356.0 pin-fin heatsink mounted to a dummy heater block with thermocouples attached. The heater was set to 10 W, and fan speed varied from 200–800 LFM.
The results showed that E-Coating averaged approximately 1°C higher than anodizing, with an overall thermal impact of approximately 0.1°C/W.
Drawing Callout
The requirement for an E-Coated Heatsink should be specified on the engineering drawing using the following callout:
E-Coating, Black
When Should E-Coating Be Used?
E-Coating should be considered when:
- Material is die-cast aluminum (356.0).
- The operating environment is indoors.
- Cosmetic appearance is important.
- The slight thermal impact is acceptable.