The indicator most likely to exceed limits in hot-state testing is hot-state insulation resistance below 200 MΩ. This problem accounts for over 60% of actual tests, mainly caused by incomplete sintering or sealing failure.
The three most common indicators that fail to meet standards and their common causes:
|
Indicator |
Acceptance Standard |
Exceeding Standard |
Main Cause |
|
Hot-state insulation resistance |
≥200 MΩ |
<200 MΩ, even close to 0 |
Insufficient sintering temperature, short holding time, poor sealing leading to moisture intrusion |
|
Power-off response time |
Measurement within 2 seconds |
Measurement delayed for more than 5 seconds |
Improper operation, lack of rapid testing equipment |
|
Temperature rise curve |
Stable rise without fluctuations |
Slow temperature rise or localized overheating |
Uneven filling density, magnesium oxide dampness, or interruption of the heat conduction path |
Failure to meet hot-state insulation resistance standards is the most typical example of exceeding limits, especially in rework parts that have not undergone moisture testing verification, with an incidence rate as high as 70%.
In-depth Analysis of Frequently Occurring Problems
Sudden Drop in Hot Insulation Resistance
Symptoms: Cold state ≥500 MΩ, hot state <200 MΩ after power-off measurement after 30 minutes of operation;
Root Cause: Inactive grain recrystallization during sintering, micropore structure enlarges at high temperature, forming leakage channels;
Risk: Equipment can operate for short periods, but the probability of breakdown exceeds 80% within 3 months.
Delayed Measurement After Power-Off
Symptoms: Insulation resistance reading not completed within 2 seconds after power-off;
Consequences: Component temperature drops, resulting in higher measured data, masking true defects;
Improvement: Use an insulation tester with automatic triggering function to improve consistency.
Abnormal Temperature Rise and Current Fluctuations
Symptoms: Stable power but slow temperature rise or localized reddening;
Cause: Low filler density (<2.8 g/cm³) or presence of voids, affecting heat conduction;
Investigation: Confirm internal structural integrity using X-ray inspection.
