The performance of surface mount resistors after failure is diverse, depending on the root cause of the failure. The following are common failure manifestations and their corresponding possible causes:
Completely open circuit (infinite resistance - ∞ Ω):
Performance: The two ends of the resistor are completely non-conductive, and the resistance value measured with a multimeter is infinite. This is the most common failure mode.
Reason:
Overcurrent/Overpower: When the current exceeds the rated value or the power exceeds the rated power, it causes the conductive materials inside the resistor (such as metal film, thick film paste) to overheat, melt, burn, or vaporize. This is the most common reason.
Mechanical stress/damage: PCB bending, impact, vibration, or excessive welding stress can cause internal breakage of resistors or cracking of solder joints (including the connection between the internal end electrodes of the resistor and the ceramic substrate).
Voltage breakdown: Excessive voltage causes the insulation layer or dielectric inside the resistor to be broken down, forming an open circuit (although short circuits may also occur, open circuits are more common).
Severe overload aging: After long-term operation near the limit state, the material gradually degrades and eventually opens up.
Corrosion/Pollution: Severe environments (moisture, salt spray, chemical pollution) can cause electrodes or internal connections to be corroded and disconnected.
Resistance drift (increasing or decreasing):
Performance: The resistance value deviates from the nominal value, may increase or decrease, but has not reached the level of open circuit or short circuit. The circuit function may be abnormal or unstable (such as inaccurate power output voltage, changes in amplification factor, signal distortion).
Reason:
Long term aging: Under normal use, the resistance value will undergo slight changes over time (usually within the specification range). Aging accelerates under extreme conditions (high temperature, high humidity).
Thermal stress/temperature cycling: Repeated temperature changes cause stress due to differences in thermal expansion coefficients between the internal materials of the resistor (conductive film, terminal electrode) and the ceramic substrate, resulting in microcracks or connection degradation.
Mild overload: Long term operation in a state close to rated power or current, causing slow degradation of conductive materials and usually increasing resistance.
Moisture/electrolysis: Moisture invades the resistor and may undergo electrochemical reactions (electrolysis) under high voltage direct current, resulting in a slow change in resistance (usually an increase).
Manufacturing defects: uneven raw materials, uneven film thickness, laser resistance micro crack propagation, etc.
Electrostatic discharge: ESD impact may cause local damage, resulting in resistance drift (often increased).
Short circuit (resistance close to 0 Ω):
Performance: The resistance at both ends of the resistor shows a very low resistance value (close to 0 Ω). This is relatively rare compared to an open circuit, but the harm may be greater as it can cause overcurrent in the circuit, burn out other components or power supplies.
Reason:
Severe overvoltage/arc: Extremely high voltage causes arc discharge inside the resistor, instantly melting conductive material to form a low resistance path.
Metal migration/tin whisker: Under specific conditions (high temperature and humidity, DC bias), electrode metal (such as silver) or solder will migrate and grow along the surface or interior, connecting the two end electrodes to form a short circuit.
External conductive pollutants: solder spatter, metal debris, conductive dust, etc. are connected across the two ends of the resistor.
Manufacturing defect: There are metal impurities bridging the conductive path inside (very rare).
Burning carbonization: When severely overloaded and burned, the carbonized conductive material may form a short-circuit path (less common than an open circuit).
Intermittent fault (unstable resistance):
Performance: Resistance value fluctuates or changes unstably between normal value, high resistance value, and open circuit. The circuit function fluctuates between good and bad, or only malfunctions under specific conditions such as vibration and temperature changes.
Reason:
Microcracks: There are tiny cracks in the conductive film, terminal electrode connections, or solder joints inside the resistor, which intermittently come into contact when subjected to stress (thermal, mechanical).
Virtual soldering/cold soldering: Poor soldering results in unreliable contact between the resistance pin and the solder pad.
Tin whiskers/migration: Growing tin whiskers or migrating metals form unstable connections under specific conditions.
Pollution: Moisture absorbing pollutants cause a decrease in insulation resistance, leading to unstable electrical leakage at specific humidity levels.
Physical damage (visible):
Performance: Cracking, crushing, burning, discoloration, bubbling, coating peeling, electrode detachment, etc. of the resistor body.
Reason:
Overload burning: usually accompanied by blackening, bulging, and cracking.
Mechanical stress: Fracture caused by impact and excessive bending.
Thermal stress: Local overheating or repeated thermal shock leading to material fracture and delamination.
Welding problem: The soldering iron temperature is too high or the time is too long, which burns the resistor; The hot air gun was damaged during repair.
External environment: chemical corrosion, high-voltage arc burns, etc.
Common methods for detecting failed resistors:
Visual inspection: Look for obvious physical damage, discoloration, and burnt marks.
Power off measurement: Use the resistance range (Ω range) of a digital multimeter to measure the resistance at both ends of the resistor (must be done after the circuit is powered off and the capacitor is discharged!). Compare with the nominal value to determine if there is an open circuit, short circuit, or severe drift.
On road measurement (with caution): Measurements are taken on the circuit board, but the results are affected by parallel components and can only be used as preliminary judgments (such as measuring near 0 Ω, which may be a short circuit or a parallel inductor/low resistance path; measuring near infinity, which may be an open circuit or a parallel capacitor/high resistance path).
Functional testing: Analyze abnormal circuit functions and determine whether the function at the location of the resistor is missing or abnormal based on the schematic diagram.
Thermal imaging: Observe the resistance temperature with a thermal imager while powered on. Failed resistors (especially those with overload or abnormal resistance) may generate abnormal heat (or not generate heat at all, such as an open circuit).
Curve tracker: Apply voltage and measure current to depict the V-I characteristic curve, which can more accurately detect anomalies such as nonlinearity and soft breakdown.
Summary:
The most common failure of surface mount resistors is open circuit (infinite resistance), followed by resistance drift (usually increasing). Short circuits are relatively rare but pose significant risks. Physical damage is usually related to overload or external forces. When analyzing circuit faults, measuring the actual resistance value of the resistor (in a power-off state) is the most direct method to determine whether it has failed. Understanding the manifestations and causes of different failure modes can help quickly locate the fault point.
Important reminder: When detecting or replacing faulty resistors, it is necessary to first disconnect the circuit power and discharge the large capacitor to ensure safety. At the same time, when replacing a new resistor, it is necessary to choose a resistor with the same specifications (resistance value, accuracy, power, size, temperature coefficient), and check whether the failure is caused by other circuit problems (such as short-circuit load) to avoid further damage to the new resistor.