There are various reasons for resistor failure, which can be summarized into the following main categories:
Overpower (overheating): This is the most common cause.
Reason: The current flowing through the resistor is too high (or the applied voltage is too high), causing its actual power consumption (P=I ² R or P=V ²/R) to exceed its rated power.
Consequences:
Burning open circuit: Resistance materials (such as thin films, thick films, and winding wires) melt, vaporize, or oxidize severely due to overheating, causing the circuit to disconnect.
Permanent drift of resistance: Material properties undergo irreversible changes due to high temperatures, resulting in a significant increase or decrease in resistance.
Appearance changes: The surface of the resistor turns black, burnt, blistered, the coating peels off, and the leads change color.
Causes: Circuit design errors (insufficient power margin), load short circuits, component failures leading to abnormal increase in current, poor heat dissipation (high ambient temperature, poor ventilation, unreasonable PCB layout), surge currents (at the moment of startup, lightning strikes, switch operations).
Overvoltage (voltage breakdown):
Reason: The voltage applied across the resistor exceeds its maximum operating voltage or pulse withstand voltage limit.
Consequences:
Arc/flashover: In high resistance resistors (especially thin film resistors in high-voltage applications), excessive voltage may cause arc discharge between adjacent conductors on the surface or inside the resistor.
Internal breakdown: The insulation medium (for certain structures) or material itself inside the resistor is electrically broken through.
Resistance drift or open circuit: Arc or breakdown can burn local materials, causing permanent changes in resistance or open circuit.
Causes: Insufficient design voltage margin, high voltage surges (ESD, lightning strikes, switch transients), poor insulation design (insufficient creepage distance, electrical clearance).
Environmental stress:
Temperature:
High temperature: Long term exposure to high temperatures can accelerate the aging, oxidation, and internal stress release of resistance materials, leading to a gradual drift (usually increase) in resistance value. Extreme high temperatures can directly lead to burning.
Low temperature: Some materials may become brittle or undergo significant changes in resistance characteristics at extremely low temperatures. Temperature cycling (thermal shock) can cause inconsistent expansion and contraction of materials, resulting in mechanical stress that may cause cracking, solder joint failure, or unstable resistance.
Humidity/Chemical Corrosion:
Electrolytic corrosion: In the presence of voltage and humid environments (especially in the presence of ion pollution), the electrodes of the resistor (especially the silver electrode) may undergo electrochemical migration or corrosion, resulting in an increase in resistance, open circuit or short circuit (dendrite growth).
Sulfurization/oxidation: Sulfur containing environments (such as rubber, release of certain sealing materials) can cause silver electrodes to sulfide and turn black, resulting in increased contact resistance or even open circuits. Exposure to corrosive gases can also corrode electrodes and resistors.
Mechanical stress:
Vibration/Shock: Severe vibration or shock may cause the resistor to rupture, internal connections to break (film cracking, thick film peeling), lead breakage, or solder joint cracking (failure).
Mechanical overload: Applying excessive external force during installation or maintenance (such as excessively bending leads) may cause internal damage.
Radiation: High energy radiation (such as space and nuclear environments) can alter the properties of semiconductor materials (affecting the silicon substrate or certain thin films in SMD resistors), leading to resistance drift.
Manufacturing defects/material degradation:
Internal defects: uneven resistance film layer, presence of pinholes, impurities, internal microcracks, etc.
Poor soldering: Poor soldering between pins and resistors (virtual soldering, cold soldering), or poor PCB solder joints.
Electrode/termination issues: Poor contact between electrode material and resistor, defects or aging of the electrode itself.
Packaging issue: Poor sealing of packaging materials leads to moisture infiltration and packaging cracking.
Material aging: Over long-term use, the physical and chemical properties of the material itself slowly change (such as adhesive aging, metal diffusion), leading to a slow drift in resistance (usually allowed within the specified lifespan in the specification, but exceeding or inferior components will significantly fail).
Electrostatic discharge:
Reason: High voltage, short duration ESD pulses are applied to resistors (especially resistors in high impedance circuits).
Consequence: It may lead to the breakdown and burning of a small pit in the thin film layer of the thin film resistor, resulting in a local increase in resistance or an open circuit. The impact is particularly significant for precision or high resistance resistors.
Overcurrent (not dominated by overheating):
Reason: Although it is related to excessive power, it particularly emphasizes the instantaneous and extremely large current (such as short circuit).
Consequences:
Insurance resistor: designed to quickly open and fuse during overcurrent, serving as a fuse.
Lead/solder joint melting: Excessive current causes the lead or solder joint to melt before the resistor.
Metal film/foil resistance: may withstand high pulse currents well, but can still be damaged in extreme situations.
Winding resistance: The wire may melt.
Thick film/thin film resistor: The conductive path may be burned out.
Pulse stress (exceeding rated value):
Reason: The resistor is subjected to transient signals exceeding its rated pulse power or pulse voltage.
Consequences: Similar to excessive power and voltage, causing local overheating or breakdown, resistance drift or open circuit. Metal oxide resistors have relatively poor ability to withstand pulses.
Summary of Failure Modes:
Open circuit: The most common modes are burning, corrosion, fracture, and melting.
Resistance drift: significantly exceeding the tolerance range (increasing or decreasing).
Short circuit: relatively rare, but may be caused by internal breakdown, severe pollution (electrochemical migration), or external conductor overlap.
Parameter degradation: such as decreased temperature coefficient, increased noise, decreased voltage coefficient, etc.
Preventive measures:
Reasonable selection: power margin (usually reduced by 50%), voltage margin, resistance tolerance, temperature coefficient, pulse withstand capacity, environmental adaptability (waterproof, moisture-proof, and sulfur resistant).
Good design: heat dissipation design (heat sink, PCB copper foil), surge suppression (TVS, RC absorption), ensuring electrical clearance and creepage distance.
Optimize manufacturing process: ensure welding quality.
Control environment: Avoid high temperature, high humidity, corrosive environment, and severe vibration; If necessary, use protective coating or potting.
ESD protection: Pay attention to anti-static measures during design and use.
Understanding the root cause of resistor failure is crucial for circuit design, fault analysis, reliability improvement, and selecting appropriate resistor types.