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One of the failure modes of resistors is “disconnection/open”. And one of the causes of the disconnection/open is “electric corrosion”. If the resistor is broken due to electric corrosion, a serious malfunction that sometimes leads to the stoppage of the electronic device occurs. Electric corrosion is a phenomenon that tends to occur in high humidity and corrosive environments. As a measure to prevent electric corrosion even in such environments, we recommend a resistor using a metal glazed film. The features of metal glazed film resistors are as described below.
In addition, the results of our electric corrosion acceleration experiments and the lifecycle of metal glazed film resistors considered from the results are also explained below.
Metal Glazed Film Resistors
Anti Electrical Corrosion Resistors AEC series
Special Power Type Anti Surge Resistors ASR/ASRM series
Thick Film Chip Resistors CR series
Anti Sulfurated Thick Film Chip Resistors CRA series
Surge Current Thick Film Chip Resistors CRS series
→ Application
Power supply, UPS, Semiconductor manufacturing equipment,
FA equipment, In-vehicle products, Lighting, and General home appliances
Structure of Metal Glazed Film Resistors
Structure of a metal glazed film resistor is the same as a general resistor, but as shown in Fig. 1 and Table 1, the structure of the conductive layer (film) part is different from a general resistor and is advantageous in withstanding electric corrosion and causticity.
Fig. 1 Structural diagram of the conductive layer in the resistor
Table 1 Comparison of conductive layer structure
Explanation of the principle that “failure due to electric corrosion does not occur”
The following two points are important.
Most of the malfunctions caused by electric corrosion of resistors on the market are due to the use of carbon resistors. The mechanism is that carbon (C), which is a conducting substance, and OH-ions generated by electrolysis of water chemically react and become CO2 (gas), resulting in loss of conductivity (increased resistance, disconnection).
On the other hand, as the conducting substance of the metal glazed film is ruthenium oxide (RuO2), the above electric corrosion mechanism does not apply.
(2) Conducting substance is protected by glass
If the conducting substance is not carbon and the conductive layer is only ruthenium oxide, a malfunction may occur due to a mechanism other than the above, such as electrochemical migration. （→Wikipedia）
However, the entire conductive layer of the metal glazed film is mainly made of glass (borosilicate glass). This is a structure in which the conducting substance is protected by glass, so to speak.
It is well known that glass is used in various fields because it has excellent corrosion resistance. Among them, borosilicate glass has higher heat resistance than general glass and corrosion resistance to halogen, water, neutral/acidic solutions, so it is used in optical components, physical/chemical appliance, medical equipment, and thermometers, etc. Examples of borosilicate glass that are easy to imagine are brown bottles, beakers, and flasks containing reagents used in chemical experiments. The metal glazed film, which has the same structure as those, is the strongest resistor in terms of corrosion resistance. Although the price is higher than general resistors, we promise cost performance (reliability and durability) higher than that price.
For Your Information
|
Glass is not all-purpose and corrodes with limited substances such as hydrogen fluoride (HF) and alkalis.
Hydrogen fluoride is often used in glass crafts, etc., taking advantage of the above properties.
Hydrogen fluoride is unlikely to be present in nature or in electrical equipment where resistors are used. Also, the rate at which hydrogen fluoride is corroded by alkali is very slow at room temperature, and such corrosion is not severe and only “the surface becomes matte glass”. Therefore, even if hydrogen fluoride is present to some extent, the effect on resistors is extremely small. |
Electric corrosion (causticity) acceleration experiments of metal glazed film resistors – “Lifecycle is 48,000 years!?”
◎ Experiment description
Resistors are energized while immersed in tap water and an aqueous solution of phosphoric acid, and the resistance to electric corrosion is evaluated by the change in resistance value.
◎ Samples and conditions
We conducted a comparative experiment with “Anti Electrical Corrosion Resistors (AEC series) and general-purpose carbon resistors (RDM series). The details are as follows.
We used resistors with the exposed conductive layer (without film protection/exterior coating).
N=10 each
Fig. 2 Picture of the experiment
◎ Result of experiment
Carbon Resistors:
Within 20 seconds after the start of the test, all of them got into the OPEN state. Especially the resistors under phosphoric acid solution, they got disconnected in a few seconds.
Metal glazed film resistors:
Even 300 seconds after the start of the experiment, the rate of change in resistance was less than 10%.
As the lead wires of resistors under the phosphoric acid solution got broken due to corrosion, the experiment was stopped. But the damage to the resistive film was slight.
Fig. 3 shows how the resistance values changed. (Plotted resistance value changes of each n = 10)
Fig. 3 Graph of time-resistance change rate (Note: “①② “and “③④ “have different time scales)
Pictures of sample resistors after the experiment
◎ Considerations: How many hours does the experiment result correspond to when applied to products on the market?
Normally, evaluation is performed using commercially available products (with film protection and exterior coating), so it is difficult to verify under the conditions of our experiment as the above. However, we referred to our database of results of the electric corrosion acceleration test we conducted in the past using carbon resistors (commercially available) and calculated simply the lifecycle using the data. The calculation result was amazing that “5 seconds under tap water conditions in the above experiment” is “equivalent to more than 100 years”. (Assuming “resistance value change rate + 20% = lifetime”)
Assuming that “5 seconds = 100 years”, the “300 seconds” obtained from the above experiment results of metal glazed film resistors is equivalent to “100 years x 300 seconds/5 seconds = 6,000 years”!!
Furthermore, comparing the degree of resistance change between the tap water condition and the phosphoric acid solution condition in the above experiment, the latter can be estimated to be about 10 times the change in the former, so the lifecycle of the metal glazed resistor under the phosphoric acid solution condition is equivalent to “6,000 years x 10x (240 seconds/300 seconds) = 48,000 years”!!!
It is an unreal number of years that is hard to understand, but it certainly takes a considerable amount of time for the lead wires of resistors inside electronics devices to corrode (to disappear?) and break. Therefore we guess that you could understand that “48,000 years” is not so unreal.
The last point we would like to emphasize is that 48,000 years is the lifetime of the lead wire, and it can be inferred from the above experiment results that the metal glazed film is much more durable.
Metal Glazed Film Resistors
Anti Electrical Corrosion Resistors AEC series
Special Power Type Anti Surge Resistors ASR/ASRM series
Thick Film Chip Resistors CR series
Anti Sulfurated Thick Film Chip Resistors CRA series
Surge Current Thick Film Chip Resistors CRS series
⇒ Application
Power supply, UPS, Semiconductor manufacturing equipment, FA equipment,
In-vehicle products, Lighting, and General home appliances
Related columns:
Electric corrosion mechanism & Design for countermeasures
What is electric corrosion? – Our efforts
