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Electric corrosion of resistors is a chemical reaction between a resistive film and moisture.
Resistors have protective coating on the surface, but in places with high humidity, moisture (water) or ionic impurities permeate the inside of resistors and adhere to the resistive film. When electricity flows there, water is decomposed by ionic impurities and electricity, and ionized into hydrogen ions and hydroxide ions. The hydroxide ions decompose the resistive film and it causes resistance value changes.
Generally, electric corrosion erodes the resistive film on the plus pole (anode) side.
Electric corrosion is especially frequent with carbon film resistors, and it may occur even with metal film resistors very rarely.
Electric corrosion is also called anodizing because the resistive film oxidizes. (Example: C + O2 → CO2)
In a film type resistor, the higher the resistance value, the thinner the resistive film and making it more susceptible to the above effects.
If resistors are used in an environment with high temperature and humidity or in the presence of harmful gas, or if resistors are encapsulated with resin or rubber tubes, the probability of electric corrosion increases.
Moisture and impurities may also adhere to products in the manufacturing process of electronic/electrical equipments.
Therefore, it is necessary to pay attention to places where resistors are used and to the manufacturing process of resistors.
Our efforts
The most effective countermeasure against electric corrosion is to use metal glazed thick film resistors.
Each resistors maker including us has a lineup of these products.
However, metal glazed thick film resistors are more expensive than general carbon film resistors and metal film resistors, so they are not actively used.
It seems that many companies first adopt carbon film resistors and metal film resistors, and then replace them with metal glazed thick film resistors only when problems occur.
Under these circumstances, we reviewed the materials and production processes of resistors from the ground up in collaboration with a certain customer of us. Furthermore, as a result of striving to improve the performance by repeating our original anti-corrosion performance acceleration evaluation tests, we succeeded in developing a moisture-resistant resistor (HDM series – High Reliability Humidity Proof Type Special Film Resistor).
The HDM series is based on carbon film resistors, which are generally considered to be prone to electric corrosion. The HDM series is highly versatile because it is based on carbon film resistors. Furthermore, the HDM series have been used by many customers who have had in trouble for a long time due to electric corrosion problems. Since its sales release in 2002, the HDM series has continued to have no failures in the market.
In addition, we also succeeded in developing a moisture-resistant resistor (RNV series– High Voltage Anti Moisture Metal Film Resistors) based on metal film resistors.
The RNV series achieves high resistance accuracy (1%) and small TCR (100ppm / ℃) peculiar to metal films.
Moreover, we utilize these experiences and know-how in the production of all our products. We are striving to improve quality by making our factory an “electric corrosion resistant factory”.
Lineup of Anti Corrosive Products
