In the PCBA manufacturing process, testing is a critical step in ensuring the functionality and reliability of circuit boards. However, the testing process is often affected by electromagnetic interference (EMI), leading to unstable signals, testing errors, and even an inability to accurately assess product performance. This issue is particularly pronounced when verifying the functionality of high-frequency signals and sensitive analogue circuits. Therefore, mastering practical techniques to effectively reduce electromagnetic interference during testing is of great significance for improving testing accuracy and overall manufacturing yield.
1、Optimise the layout and grounding methods of testing fixtures
If the fixtures used in PCBA testing have poor grounding, they can easily amplify electromagnetic interference. The cable routing, grounding design, and shielding structure within the testing fixtures all influence EMI levels.
Practical recommendations:
- Test fixtures should use a unified ground reference point to avoid ‘ground loops.’
- Add metal shielding layers in high-frequency test areas to prevent external electromagnetic leakage from affecting test points.
- Signal lines and power lines should be routed separately and kept as far as possible from high-noise components.
2、Proper wiring to control high-frequency interference paths
During the PCBA design phase, wiring methods directly affect EMI. However, during testing, attention should also be paid to the conduction paths of high-frequency signals and the quality of probe contact.
Practical recommendations:
- For RF or high-speed signals, use dedicated test fixtures and impedance-matched probes.
- Avoid testing with long suspended cables; instead, use coaxial cables or flat ribbon cables to reduce signal crosstalk.
- When performing multi-point testing, signals can be triggered in stages to reduce signal disturbances caused by simultaneous activation.
3、Use filtering and power stabilisation techniques
If the power supply system of the test equipment itself has fluctuations, it may introduce low-frequency interference or coupled noise during testing. Some power adapters or desktop power supplies that have not been isolated may indirectly affect test stability.
Practical recommendations:
- Install EMI filters or ferrite rings at the power input of the test platform.
- Introduce voltage regulation modules or linear power supplies on critical power channels to reduce high-frequency noise injection.
- For analogue signal inputs prone to interference, use RC filtering or isolation amplifiers for processing.
4、Control environmental noise sources to create a clean test environment
Electromagnetic interference from the test environment itself must also be controlled, including external interference sources such as lighting, motors, and wireless signals.
Practical Recommendations:
- Use anti-static mats with grounding and EMI-proof workbenches in the test area.
- Physically isolate the test area from production or aging areas.
- Prohibit the use of high-frequency wireless devices (such as Wi-Fi hotspots or Bluetooth headphones) around the test platform.
5、Test data acquisition methods and filtering processing
The data acquisition methods of the test system can also be affected by EMI, especially when using high-speed ADCs or complex sensor sampling, where interference signals may falsely trigger decision logic.
Practical recommendations:
- Implement software filtering mechanisms, such as moving average or median filtering, to reduce jitter effects.
- Set software decision delays to avoid misjudgments caused by transient peak signals.
- Incorporate redundant decision mechanisms in critical test logic to ensure consistency.
Test quality in PCBA manufacturing depends not only on the testing process itself but also on environmental interference control, electrical design optimisation, and testing tool standards, all of which directly determine the accuracy of the results. Reducing electromagnetic interference not only improves testing efficiency but also reduces rework rates and enhances customer satisfaction. For PCBA companies pursuing high-quality delivery, EMI control is a critical aspect that cannot be overlooked. By gradually implementing the above practical techniques, the stability and reliability of the testing process can be significantly enhanced.