1. Safety Preparations
Safety is always the top priority when performing any electronic measurements. For PCB resistor testing, you must:
- Complete Power Disconnection: Unplug all power sources, including batteries and power adapters
- Discharge Treatment: Discharge high-capacity capacitors (use a 10kΩ/5W resistor for discharge)
- ESD Protection: Wear an anti-static wristband and use an anti-static mat on the workbench
- Environment Check: Ensure the workspace is dry, well-ventilated, and maintains 30-70% relative humidity
Pro Tip: For high-voltage circuit boards (>60V), wait at least 5 minutes to ensure complete discharge before proceeding
2. Multimeter Selection
Choosing the right measurement instrument directly impacts the accuracy of test results:
Recommended Digital Multimeter Specifications
- Basic Requirements:
- Accuracy: At least ±0.5% + 3 digits
- Resistance Range: 200Ω – 20MΩ
- Test Current: <1mA (to avoid damaging sensitive components)
- Advanced Options:
- 4-wire Kelvin measurement (eliminates lead resistance effects)
- Auto-ranging capability
- Data logging function
Range Selection Guidelines
| Nominal Resistance | Recommended Range | Resolution |
|---|
| <200Ω | 200Ω range | 0.1Ω |
| 200Ω-2kΩ | 2kΩ range | 1Ω |
| 2kΩ-20kΩ | 20kΩ range | 10Ω |
| >20kΩ | Auto-range | – |
3. Key Measurement Techniques
Offline Measurement (Recommended Method)
- Use a desoldering pump or hot air gun to remove one end of the resistor
- For SMD resistors, gently lift one end with tweezers
- Through-hole resistors: Place probes perpendicular to the leads
- SMD resistors: Use fine-point probes (0.5mm diameter ideal)
- Miniature components: Recommended to use test hooks
- Normal value: Within ± tolerance of nominal value
- Abnormal conditions:
- “OL” display: Open circuit failure
- Near 0Ω: Short circuit failure
- Unstable fluctuation: Internal poor contact
Online Measurement (Emergency Method)
- Equivalent Circuit Analysis:
Draw a partial circuit diagram, calculate the parallel equivalent resistance
- Voltage Drop Method:
Measure voltage (V) across the resistor, use known current (I) to calculate R=V/I
- Comparison Method:
Measure identical resistors in the same circuit as a reference
4. Error Analysis and Quality Control
Common Error Sources
| Error Type | Impact Level | Solution |
|---|
| Contact Resistance | ±(1-10Ω) | Use a 4-wire measurement |
| Temperature Drift | ±0.4%/°C | Record the ambient temperature and compensate |
| EMI Interference | Random error | Use shielded test leads |
| Probe Oxidation | +5% error | Regularly clean probe tips |
Quality Assessment Standards
Per IPC-A-600G standard:
- Pass: Measured value within ±10% of nominal value (standard resistors)
- Fail:
- Resistance exceeds ±10%
- Unstable readings (>5% variation)
- Physical damage (cracks, burn marks, etc.)
5. Advanced Application Techniques
Precision Resistor Measurement
- Constant Current Method: Use a 1mA current source + a high-precision voltmeter
- Temperature Compensation: Record ambient temperature, convert using formula R25=Rt/[1+α(T-25)]
Special Resistor Testing
- Fusible Resistors: Requires overcurrent testing after measurement
- NTC/PTC: Measure the resistance curve at different temperatures
- High-Voltage Resistors: Use an insulation tester (500V DC)
Batch Testing Solutions
- Automated test fixture + multiplex scanner
- Statistical analysis of CPK values (requirement >1.33)