The Corrosion of Electronic Resistors

Abstract

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 60 C, 4 ppm H 2 S 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 H 2 S 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 (Ag 2 S) and nickel sulphur residue.Index Terms-Atmospheric corrosion, precision thick chip resistors, printed circuit board (PCB), silver sulphide (Ag 2 S).

Testing method for measuring corrosion resistance of surface mount chip resistors

“…The main failure point was observed at the interface between the surface finish and the overcoat, which is consistent with the literature and field data [12][13][14][15][16]. The locus of failure would indicate that the Ni/Sn layer overlap of the glass layer did not perform as a barrier/hermitic seal for the protection of the Ag layer.…”

“…The locus of failure would indicate that the Ni/Sn layer overlap of the glass layer did not perform as a barrier/hermitic seal for the protection of the Ag layer. The overlap is clearly crucial to the overall corrosion reliability of the resistor [12][13][14][15][16]. The resistor types that exhibited failures demonstrated the poorest overlap as shown in Table II.…”

“…However, resistor failures in some systems are often responsible for complete functional breakdown [11][12][13][14][15][16]. Typically, resistor failure modes include open circuits, resistive shorts or variations in resistance indicating intermittent failure [17].…”

Analysis of Ag Corrosion Products

“…This indicates that AgO and Ag 2 O are reduced at the same potential in Na 2 SO 4 . Therefore, in Figure 2 for the sample with preformed Ag 2 S that was then exposed to ozone, RH and UV, the plateau at −0.08 V MSE must be due to reduction of Ag 2 SO 4 . This indicates that the unknown plateau at this potential for Ag exposed at West Jefferson corresponds to the reduction of Ag 2 SO 4 .…”

“…However, it is possible that strong oxidizing species, such as O 3 , can oxidize SO 2 to SO 4 2− 12 which then reacts with Ag ions to form Ag 2 SO 4 . Another possible Ag 2 SO 4 formation pathway involves airborne sulfate aerosols.…”