The Pros of Conformal Coatings

Choosing the right coating to preserve and protect electronics in harsh environments

Introduction

Many chemicals found in the oil, gas, and petrochemical industries can consign electronic components to a short life, creating high failure rates and low reliability. Corrosive agents such as H
2 S gas, hydrocarbons, chlorobenzene, and chemical by-products play havoc with components that control and manage processes, or transport vital data between control centers and remote sites. What is required is a protective coating that can isolate the components from the harsh reality of industrial settings. Conformal coatings, as the name suggests, do just that by conforming to the contours of elements that populate printed circuit boards (PCBs) and other components present in electronic assemblies and systems. Conformal coatings are thin layers of synthetic industrial resins or organic polymers applied to PCBs and electronic components for protection
against environmental, mechanical, electrical, and chemical problems including contaminants such as dust, dirt, fungus, moisture, chemicals, thermo mechanical stress, mechanical shock, and vibration. Conformal coating types include urethane, silicone, acrylics, epoxies, and parylene.This paper will focus on networking products components as they are now heavily migrating into industrial settings, and the protection of these devices is vital in the proper functioning of networks that manage and control various processes. A Harsh Environment Conformal Coating is engineered to resist H
2 S gas and other corrosive agents, including humidity. Adding harsh environment conformal coating improves and extends the working life of the industrial networking product and ensures security and reliability of performance. But not all conformal coatings are created equal.

The Environmental Attack

Studies have shown that hydrogen sulfide (H
2 S ) contaminants in concentrations as low as 10 ppm may attack surface mount (SMT) electronic components. Long filaments of silver sulfide known as "silver whiskers" can form on the surface of the silver electrical contacts of these electronic components, when exposed to environments containing low levels ofH
2 S . The presence of heat, chemicals and moisture can accelerated these formations. These deposits can potentially create short or open circuits that can cause a networking product such as an Ethernet switch or other electronic component to ultimately malfunction or fail. Hardened networking boxes are extremely robust, meeting and exceeding IPC/IEC/MIL standards for survivability in power utility and heavy industrial environments. However, specific environmental hazards such as the effects of H
2 S gas and other corrosive agents on surface mount electronic components are not specifically addressed by normally hardened networking products. The issue of excessive heat on components can be partially solvedwith the use of a thermally conductiveconformal coating applied between a heat-generating electrical device and a heat sink in order to improve heat dissipation. It forms a thermally conductive layer on thesubstrate, either between components or within a finished product. 1