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The failure modes and mechanisms that are likely to occur differ depending on the type of resistor, but the main factors are shown in Table 1.
Table 1 Failure modes and mechanisms/factors
Most of the failures that are likely to occur in the market are disconnection or increased resistance values.
Short circuits are extremely rare, and overload factors can sometimes cause a slight decrease in resistance value.
(1) Disconnection due to overload
If parts other than resistors on the board break down or fall into an unexpected state, the resistors may be overloaded.
Since resistors are heat-generating components, there is a risk of causing a serious accident if the rated power (voltage) is exceeded. Therefore, it is necessary to pay particular attention to overload.
The following are common symptoms depending on the load level.
Although there are differences in the level of change and the length of time, the resistance value of any type decreases once and then increases. The tendency of this change can be best seen in the Metal Oxide Film Resistor’s graph. (The graphs of other resistors do not clearly show the tendency of this change.)
The resistance value of a Metal Oxide Film Resistor shows a relatively large reduction rate because oxidized metal is reduced by the heat of overload and a chemical reaction, and becomes closer to pure metal. As a result, the conductivity temporarily increases. If the overload condition continues, the resistor will deteriorate and burn out, and the resistance value will increase.
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(2) Disconnection due to high-temperature/humidity or corrosive environment
High-temperature/humidity and corrosive environment are factors that deteriorate and damage electronic components.
The following are the most common cases.
In particular, electric corrosion of carbon resistors is caused not only by high-temperature/humidity environment but also by the presence of ionic impurities. In some cases, the true cause (source) cannot be identified in the usage environment. Electric corrosion of carbon resistors is a difficult phenomenon to deal with.
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