E-coated Heatsink

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.