" 3 Levels of Environmental Protection"
By Shirley Powers, VP of Quality (Comair Rotron)
Tim Shafer, Application Engineer (Comair Rotron)

Introduction

For years, a major problem in the electronic industry has been the deterioration of electrical components from the natural elements such as rain, sleet and snow. Other conditions such as salt from coastal areas or road salts cause accelerated corrosion on electrical components. Even sulfur dioxide produced from the burning of coal has a major impact on electrical component life. Cooling fans are no exception to this rule. To combat the effects of harsh environmental conditions, several chemical coatings have been developed to form a protective barrier between the electrical components and the environments that they must operate in. These coatings range from a 1 mil thick conformal coating to fully encapsulated assemblies. This application note is written to identify the problems with corrosion and the methods available to combat them. To understand the effects of corrosion on electrical components, a brief explanation is written that describes the chemical reactions that occur and the conditions that they occur in. An example will discuss the process of corrosion that attacks electrical components such as copper wire. After understanding how corrosion occurs and the environments that accelerate this process, we will discuss several methods of protection.

Corrosion Explained

Corrosion is best understood as an oxidation - reduction reaction between 2 or more elements. Oxidation-Reduction reactions, also known as redox reactions, occurs when one element loses an electron to another element. In the reaction between zinc (Zn) and copper (Cu), zinc is oxidized (gives up electrons) and the copper is reduced (accepts electrons).

Zn(s) + Cu⁺²(aq) ® Zn⁺²(aq) + Cu(s)

Because there is a transfer of electrons between the elements, a voltage potential is created between them. This voltage can be either positive or negative. A positive voltage would indicate a spontaneous reaction where a negative voltage would be a non-spontaneous reaction. This is demonstrated in the 2 half reactions of Zn(s) and Cu⁺²(aq).

Cu⁺²(aq) + 2e^- ® Cu(s)                          + 0.34 vdc
Zn(s) ® Zn⁺²(aq) + 2e^-                           + 0.76 vdc
Zn(s) + Cu⁺²(aq) ® Zn⁺²(aq) + Cu(s)      + 1.10 vdc

The redox reaction above occurs spontaneously because the reaction produces a positive 1.10 vdc potential. Other redox reactions occur spontaneously in nature such as the corrosion of iron. When iron (Fe) comes into contact with oxygen (O₂) and water (H₂O) a redox reaction occurs that oxidizes the iron into Fe₂O3 · H₂O, or more commonly known as "rust".

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