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Figure 5: Examples of AE locations in the laminates.
Data analysis
Though the acoustic emission method has been proven to detect pad cratering of PCB laminates [2, 3], no study has reported which AE parameters are good indicators for comparing the susceptibility of PCB laminates to pad cratering. In this analysis, we considered the following parameters as response variables:
1. The mean applied load when the first AE event with amplitude greater than 40dB occurs
2. The mean applied load of the first four AE events with amplitude greater than 40dB
3. The mean number of AE events with amplitude greater than 40dB with applied load up to 30lbs
4. The mean number of AE events with amplitude greater than 40dB with applied load up to 50lbs
5. The cumulative energy of all AE events with amplitude greater than 40dB with applied load up to 30lbs
6. The cumulative energy of all AE events with amplitude greater than 40dB with applied load up to 50lbs
Of the measured data, the peak decibel level of the first sensor of locatable AE events was used. The AE energy, a parameter which usually represents acoustic magnitude better than amplitude when errors arise was correlated to the amplitudes measured after tests and found to be close to 1:1 correlation.
There are 12 boards for each laminate, a total of 72 boards. Four boards of each laminate were pre-conditioned through 3, 5, and 7 reflow cycles at 260°C peak temperature for 10 seconds. The boards subjected to 3 reflow cycles were used for AE test setup. No statistically significant difference between boards with 5 and 7 reflow cycles was found. Thus, eight boards for each laminate (consisting of 4 boards subjected to 5 reflow cycles and 4 boards subjected to 7 reflow cycles) were used for this analysis.
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