Reliability Studies of Flip Chip Package with Reflowable Underfill
Bibliographic record
Abstract
ABSTRACT Reflowable underfill is originated to simplify the Flip-Chip assembly process. In this study, JEDEC level 3 moisture sensitivity preconditioning followed by thermal cycling (TCB, −55°C~125°C) was conducted. Two reflowable underfill mainly differentiated by curing kinetics and adhesion strength, namely Underfill A and Underfill C, were evaluated. Failure analysis was carried out via C-SAM and cross section. Unit failure that was electrically identified in present study was defined as occurrence of bridging and/or open circuit. The results showed that for packages assembled with Underfill A that has superior adhesion with silicon nitride passivation, all units can pass preconditioning but bridging commenced to appear at 750 cycles. Open circuitry was encountered between 1750 and 2000 cycles. While for Underfill C with fast cure characteristics and relatively weaker adhesion compared to Underfill A, bridging and open circuitry started to surface at 500 and 1250 cycles, respectively. Failure analysis indicated that bridging mainly resulted from solder bump extrusion through micro voids trapped between adjacent bumps during assembly process; meanwhile the gap between neighboring bumps is too close to prevent convergence of two extruded bumps. Open circuitry is originated by several factors such as insufficient wetting, underfill delamination, die crack, underfill crack etc. On the whole, no underfill delamination and die crack have been observed before 1000 cycles in present study. Most importantly, no solder crack that is the direct reflection of CTE mismatch has been observed throughout the whole reliability test. This fact suggests that assemblies with relatively-higher-CTE reflowable underfill still can meet general reliability standard.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.001 |
| 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 | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 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 itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".