When conducting PCBA reliability testing, we must perform high-voltage testing and insulation resistance testing simultaneously, as they respectively correspond to dielectric withstand capability and leakage path blocking capability, and neither can be omitted. For example, a batch of industrial control motherboards did not undergo the 1500VAC 60-second high-voltage test before leaving the factory, and within three months after going online, batch relay misoperation occurred. During rework, it was found that local microcracks in the FR4 board caused arc breakdown, and this defect could not be detected at all in conventional AOI and ICT.

The parameter settings for high-voltage testing must be strictly based on the dual constraints of IPC-9592 and customer agreements. The Jia Jinyuan production line implements 1000VDC/60 seconds for consumer PCBA, 1500VAC/60 seconds for industrial PCBA, and 2100VAC/60 seconds for medical PCBA. Moreover, the leakage current threshold of the tester must be calibrated with a standard resistor before and after each test; otherwise, if the calibration deviation exceeds ±5%, the actual existing 0.8mA leakage may be misjudged as qualified, and this value has far exceeded the 0.25mA safety upper limit specified by IEC60950.

Insulation testing cannot only rely on the final reading; it is more important to observe the change in curve slope. When testing a certain power board, we found that the initial insulation resistance was 1200MΩ, but it dropped sharply to 85MΩ after 30 seconds of voltage application. Further disassembly confirmed that the Flux residue in the bottom BGA area carbonized, forming an ion migration path in a humid environment. This gradual failure is easily overlooked in static testing, and must be retested after temperature and humidity cycling to be exposed.

The contact reliability of the test fixture directly affects the authenticity of the results. We once had spring probe oxidation leading to increased contact resistance, which caused the voltage actually loaded on the PCB to attenuate by 12%, resulting in the entire batch of 500 boards being falsely judged as insulation qualified. Later, we switched to gold-plated probes and added a contact impedance self-check function, which reduced the misjudgment rate to below 0.3%. This detail has been mandatorily implemented on all aging lines of Jia Jinyuan.

There is a strong correlation between the cleaning process and insulation performance. After water-based cleaning, if the drying temperature is lower than 110℃ or the time is less than 15 minutes, the organic acid remaining on the board surface will continuously corrode the copper foil and generate conductive salts. We found in comparative experiments that the average insulation resistance of the same model PCBA after drying at 105℃ for 10 minutes was 320MΩ, while after extending to 18 minutes, it directly jumped to above 2100MΩ, indicating that there is a clear critical point for thermal stress release and complete moisture removal.

Failed PCBA must not be directly reworked. Flying probe testing must first be used to locate abnormal networks, and then X-ray is combined to check for physical defects such as solder joint bridging, interlayer drilling burrs, or copper skin lifting. Otherwise, blind cleaning or rework will instead expand the contamination area. The Jia Jinyuan SMT workshop stipulates that all NG boards must complete the FA analysis closed loop within 2 hours to ensure that problems do not flow into the next process.