Why do resistors need to undergo anti sulfurization treatment?

Analysis of the necessity of resistance sulfurization treatment
As a fundamental component in electronic circuits, the stability of resistance directly affects the reliability of the entire system. In specific environments, resistors are susceptible to sulfurization phenomena, leading to parameter drift and even failure. Therefore, anti sulfurization treatment has become a key technology to improve the environmental resistance performance of resistors. The necessity of resistance vulcanization treatment is systematically analyzed from four dimensions: vulcanization mechanism, failure mode, treatment technology, and application scenarios.
1、 The essence and source of sulfurization phenomenon
1. Mechanism of vulcanization reaction
Sulfurization refers to the process in which sulfur-containing substances (such as hydrogen sulfide H ₂ S, sulfur dioxide SO ₂) react chemically with metallic elements to form sulfides (such as Ag ₂ S, Cu ₂ S). In resistors, sulfurization mainly acts on:
Terminal electrode: usually made of metals such as silver (Ag) and copper (Cu), which are prone to react with sulfur.
Lead materials such as copper alloy and nickel chromium alloy are prone to corrosion in sulfur-containing environments.
2. Sources of sulfurized substances
Industrial environment: Sulfides are present in the exhaust gases emitted by industries such as chemical, petroleum, and natural gas.
Natural environment: Hydrogen sulfide gas released by volcanic eruptions and geological activities.
Biodegradation: Hydrogen sulfide produced by the decay of organic matter (such as biogas, sewage environment).
2、 Failure modes of sulfurization on resistors
1. Resistance drift
Mechanism: Sulfides (such as Ag ₂ S) have a much higher electrical resistivity than metallic silver, resulting in an increase in resistance value.
Impact: In precision circuits, resistance deviation may cause system errors (such as sensor signal distortion).
2. Poor contact
Mechanism: Thickening of the sulfide layer leads to an increase in contact resistance between the electrode and the solder pad.
Impact: Poor contact in switch circuits may cause intermittent faults (such as relay misoperation).
3. Mechanical fracture
Mechanism: The expansion coefficient of sulfides differs greatly from that of metals, and repeated thermal cycling leads to stress concentration.
Impact: In vibration environments, resistance leads may break (such as in automotive electronic control units).
4. Short circuit risk
Mechanism: The sulfide layer falls off to form tiny particles, which may bridge adjacent electrodes.
Impact: In high-voltage circuits, short circuits may cause fires (such as power modules).
3、 The core technology of anti sulfurization treatment
1. Material optimization
Sulfide resistant electrode: Using inert metals such as gold (Au) and palladium (Pd) instead of silver to reduce sulfurization reactions.
Alloyed leads, such as nickel chromium alloy (NiCr) and constantan (CuNi), enhance corrosion resistance.
2. Surface coating
Organic coating: Epoxy resin and polyimide (PI) form a physical barrier to prevent sulfide penetration.
Inorganic coatings: Glass glaze and ceramic coatings are resistant to high temperatures and corrosion, suitable for harsh environments.
3. Structural design improvement
End thickening: Increase electrode thickness to delay the penetration time of the sulfide layer.
Lead sealing: using glass packaging and metal tube shell to isolate the external environment.
4、 Application scenarios of sulfur resistant resistors
1. Industrial control
Scene: Chemical plant, oil and gas field, sewage treatment plant.
Requirement: The resistor needs to withstand an environment with an H ₂ S concentration of over 50ppm.
Typical products: Fenghua High tech CR series (sulfur resistant film resistors), KOA RK73B series (military grade sulfur resistant resistors).
2. Automotive Electronics
Scenario: Engine compartment, fuel system, emission control system.
Requirement: The resistor needs to pass AEC-Q200 certification and withstand high temperature and high humidity sulfurization environments.
Typical products: Vishay PR02 series (automotive grade power resistors), Yuyang Technology ML series (miniature sulfur resistant resistors).
3. Communication equipment
Scenario: Base station, switch, optical module.
Requirement: The resistor needs to withstand an environment with a SO ₂ concentration of up to 10ppm to ensure signal integrity.
Typical products: Yageo RC series (universal anti sulfurization resistor), thick sound CR series (high-power anti sulfurization resistor).
4. Medical equipment
Scene: Ventilator, hemodialysis machine, endoscope.
Requirement: The resistor needs to meet biocompatibility standards and withstand trace sulfide environments.
Typical products: Wald WR series (nano film sulfide resistance), KOA SG73S series (high-precision sulfide resistance).
5、 Economic Analysis of Anti sulfurization Treatment
1. Cost composition
Material cost: The cost of sulfide resistant metals and special coating materials is 20% -50% higher than that of ordinary resistors.
Process cost: The complexity of coating and packaging processes increases, resulting in a 10% -30% increase in production costs.
2. Long term returns
Extended lifespan: The lifespan of sulfur resistant resistors can reach 3-5 times that of ordinary resistors, reducing maintenance costs.
Reliability improvement: Reduce system failures caused by resistance failure and avoid associated losses.
Resistance sulfurization treatment is a key technology for improving the environmental resistance of electronic devices. Through material optimization, surface coating, and structural design improvement, anti sulfurization resistors can effectively resist failure modes such as resistance drift, poor contact, and mechanical fracture caused by sulfurization phenomena. They are widely used in industrial control, automotive electronics, communication equipment, medical equipment, and other fields. Although sulfurization treatment may increase certain costs, the extended lifespan and improved reliability it brings are of great significance for ensuring stable system operation and reducing full lifecycle costs.