Impact of Conformal Coating Induced Stress on Wafer Level Chip Scale Package Thermal Cycling Performance
Why this work is in the frame
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Bibliographic record
Abstract
ABSTRACT Conformal coating is commonly used for harsh environment to protect electronics from moisture and chemical contaminants. But the stresses imparted by the conformal coating can cause degradation to the package thermal cycle performance. Full coverage of the component with conformal coating material can prevent potential corrosion induced degradation but imply a local compression stress during thermal cycling, resulting a different thermal cycling performance compared to non-coated components. In this study, 8×8mm 2 wafer level chip scale packages (WLCSP) were subjected to 5% NaCl aqueous spray test with and without full conformal coating, then thermal cycled from −40°C to +125°C. Weibull reliability statistics indicated that fully conformal coated components experience characteristic life cycle number reduction from 404 cycles to 307 cycles, a 24% lifetime reduction, comparing to no conformal coated, no salt spray test applied components. The correlation between crack propagation and localized recrystallization were compared in a series of cross section analyses using polarized imaging and electro-backscattered diffraction (EBSD), which revealed that the conformal coating induced a z-axis tension and compression strain during thermal cycling, resulting in an accelerated degradation at the solder interconnect. Linear Laser profilometer measurements showed that fully conformal coated samples experienced a higher z-axis height displacement change relative to non-conformal coated samples when exposed to 125°C with 10 minutes dwell. To prevent this z-axis strain a reworkable edgebond adhesive was applied with full conformal coating configuration, which demonstrate an increase of characteristic lifecycle number to 2783 cycles, suggesting that the mitigation of the z-axis strain can vastly enhance the thermal cycling performance.
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Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from it