The Corrosion of Electronic Resistors

Precision thick chip resistors are used in a variety of different industries, from telecommunications to automotive electronics, and as such can be exposed to mild and aggressive corrosive environments. This paper investigates the corrosion performance of two generic precision thick chip resistors in a controlled corrosive atmosphere consisting of 60degC, 4 ppm H₂S and water vapor in purified air. The resistors were exposed in an environmental chamber for periods of 5, 10, 15, 30, and 60 days. Following exposure, the samples were cross sectioned and subjected to surface analysis using microscopy and microanalysis. After the initial stages of exposure, corrosion was observed on only one of the two types of resistors. The corrosion developed because H₂S gas and water vapor diffuses through the thin protective organic layer on the resistor, and subsequently reacts with the silver conductor layer. Corrosion was facilitated by poor overlapping of the solder and nickel layer and, in particular the glass binder over the glass overcoat, which allowed silver and sulphur to diffuse along the interface. In addition, this poor overlapping allowed contact between the nickel layer and the silver layer resulting in the development of an electrochemical corrosion cell. The main corrosion products that developed were silver sulfide (Ag₂S) and nickel sulphur residue.