Polyimide-Over-UBM Process: The Challenges and Solutions on Plating Bump Process
Bibliographic record
Abstract
ABSTRACT Polyimide over under-bump metallization (UBM), also known as POU, is a new bump structure in which the polyimide sits on top of the UBM. Conventional structure has the UBM sitting on top of the polyimide layer. The difficulty with the conventional technique stems from the relative positions of the polyimide layer, the UBM layer, and the solder bumps. Because the polyimide layer is essentially separated from the solder bumps by the UBM, the stress-reducing abilities of the polyimide layer are not available to the solder bumps. Accordingly, high mechanical stresses may be inflicted on the solder bumps, particularly at the edges of the solder bumps near the interfaces with the UBM. If the stresses are acute enough, particularly on lead-free solder bumps -- which are relatively less ductile than eutectic solder -- mechanical failure of the solder bumps can occur and produce electrical device failure. The POU solution attempts to overcome or reduce the effects of one or more of the foregoing disadvantages by strategically moving the edge of the solder bump to a location where the stress-reducing ability of the polyimide is made available to the solder bump. With printing process, POU was done by sputtering, patterning, and etching the UBM first, and then dispensing and patterning the polyimide layer -- just the opposite of the conventional process. However, on a plated bump process, the use of the UBM as plating bar requires the UBM etching process to be done after the bump plating process, which turns out to have issues using the POU process. The use of the plated solder as etch resist also required a different method of masking in POU process. This paper will discuss the challenges in doing plated POU bump and solutions to address and resolve these challenges.
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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 | 0.001 | 0.001 |
| Meta-epidemiology (narrow) | 0.001 | 0.001 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.002 | 0.005 |
| Open science | 0.002 | 0.001 |
| Research integrity | 0.003 | 0.004 |
| Insufficient payload (model declined to judge) | 0.004 | 0.003 |
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".