Preventing resistor failure is a crucial step in ensuring the reliable operation of electronic devices. Here are some systematic methods and strategies, starting from design selection, production process, to usage and maintenance:
1、 Design selection stage (source control)
Power derating design:
Core principle: Never use the resistor at full rated power.
Method: Choose a resistor with a rated power much higher than the actual power consumption (P_actual) in the circuit. The magnitude of the derating depends on the ambient temperature, heat dissipation conditions, and reliability requirements.
Rule of thumb:
General occasions: Actual power ≤ 50% -60% nominal power.
High temperature environment: The higher the ambient temperature, the greater the derating amplitude needs to be (refer to the power temperature derating curve of the resistor). When approaching the maximum operating temperature, the allowable power may be less than 50%.
High reliability requirement: The derating amplitude needs to be larger (such as ≤ 30% -40%).
Consider pulse power: For pulse working scenarios, ensure that the pulse power and energy do not exceed the limits allowed by the resistance specification. Surface mount resistors are highly sensitive to instantaneous pulse overload.
Voltage derating design:
Core principle: The working voltage (including peak voltage) is lower than the maximum working voltage of the resistor.
Method: Choose a resistor with a maximum operating voltage (or maximum overload voltage) much higher than the maximum possible voltage in the circuit (including switch transients, surges).
Attention: Thin film resistors (especially high resistance values) are extremely sensitive to overvoltage and are prone to open circuit failure. If necessary, parallel TVS tubes at both ends of the resistor or use RC absorption circuits to suppress voltage spikes.
Choose the appropriate type and material of resistor:
Application matching:
Precision, low noise, low temperature drift: metal film resistors, precision thin film resistors, metal foil resistors.
High power: wound resistance, metal oxide resistance, thick film power resistance (note pulse capability).
High frequency: thin film resistors, non inductive wound resistors.
High pulse/surge tolerance: winding resistance, certain specially designed thick/thin film resistors, oxide film resistors (pay attention to voltage).
High voltage: a specialized high voltage resistor.
Environment matching:
High temperature environment: Choose a resistor with a high temperature rating (such as 175 ° C).
High humidity/corrosive environment: Choose packaging with good moisture resistance (such as molding, sealing), or use glass glaze resistors. Consider applying three proof paint.
Sulfur containing environment: Avoid using surface mount resistors with silver electrodes (which are prone to sulfurization and blackening failure), and choose sulfur resistant resistors (usually palladium silver or gold electrodes).
High mechanical stress/vibration: wound resistors or resistors with sturdy packaging may be more suitable; SMT resistors require attention to PCB design and reinforcement.
Resistance selection:
Avoid using resistors with extremely high resistance (>10M Ω) or extremely low resistance (<1 Ω) unless necessary, as they may be more fragile or sensitive to the process. High resistance resistors are more sensitive to pollution and moisture.
Heat dissipation design:
PCB layout: Provide sufficient heat dissipation copper foil area (floor) for power resistors, away from heat sources. Use thermal vias to conduct heat to the inner or back copper layer for heat dissipation.
Heat sink: For high-power resistors, install a heat sink if necessary.
Spacing: Ensure sufficient space between resistors to facilitate air circulation and heat dissipation.
Consider environmental stress:
Estimate the environment that the equipment will face in the design (temperature range, humidity, vibration, impact, chemical pollution, etc.), and select resistors and protective measures that meet the specifications based on this (such as potting, sealing the chassis).
2、 Production process and assembly stage
Welding process control:
Temperature curve: Strictly follow the temperature time curve of welding (especially reflow soldering, wave soldering) to avoid overheating or thermal shock.
Manual soldering: Control the temperature and soldering time of the soldering iron (generally not exceeding 3-5 seconds) to avoid local overheating and damage to the internal structure or solder pads of the resistor.
Electrostatic protection: Implement ESD protection measures for electrostatic sensitive resistors (such as certain thin film resistors).
Avoid mechanical stress:
Surface mount resistor: PCB design should avoid excessive bending at the resistor position (such as near connectors or screw holes). Splitting process (such as V-cut, milling cutter) should avoid generating excessive stress near the resistance. Avoid applying mechanical force to welded resistors.
Plug in resistor: Avoid bending at the root during pin formation to prevent stress concentration. Avoid excessive pulling of pins during installation.
Cleaning and protection:
Thoroughly clean the flux residue after welding, especially for high resistance resistors, as residue may cause leakage or corrosion.
Coating three proof paint on PCBA used in harsh environments is an effective means of protecting resistors (especially surface mount resistors) from moisture, pollutants, chemical corrosion, and minor mechanical damage. Choose the appropriate type of three proof paint and coating process.
3、 Usage and maintenance phase
Working within the specification range:
Ensure that the equipment operates within the designed electrical and environmental parameters, avoiding resistance from being subjected to excessive power, voltage, and temperature.
Environmental control:
Keep the operating environment of the equipment clean, dry, and well ventilated, avoiding overheating, excessive humidity, dust accumulation, and chemical pollution.
Regular maintenance and testing:
Visual inspection: Check for obvious physical damage such as burning, cracking, discoloration, and bulging of the resistor.
Functional testing: Monitor whether the relevant circuit functions are normal during system level testing.
Parameter detection (if necessary): For critical or high reliability applications, a multimeter can be used during maintenance to measure resistance values (with power off and possible disconnection from the circuit), and observe whether there is significant drift in resistance values (beyond specifications or historical baselines).
Infrared thermography: Regular inspections are conducted to detect abnormal heating of resistors (which may be a sign of overload or poor contact).
Failure analysis:
Once a resistance failure occurs, a root cause analysis should be conducted to determine whether it is caused by design defects, improper selection, production issues, improper use, or environmental factors, in order to take targeted improvement measures and prevent similar failures from happening again.
Summary:
Preventing resistor failure is a systematic project that needs to be implemented throughout the entire lifecycle of the product
Design selection is the cornerstone: strict derating design and the selection of resistor types that match the environment and application are crucial.
The production process is to ensure: control welding temperature/time, avoid mechanical stress, and do a good job of cleaning and protection (such as three proof paint).
Proper use and maintenance are key to extending lifespan: ensuring that work is within specifications, controlling the environment, and conducting regular inspections and maintenance.
By taking these comprehensive measures, the probability of resistance failure can be significantly reduced, and the overall reliability and lifespan of electronic devices can be improved.