Thermal Preconditioning, Microstructure Restoration and Property Improvement in Bi-Containing Solder Alloys
Bibliographic record
Abstract
ABSTRACT It has been well-established that the properties of lead-free solder alloys such as SAC 305 (Sn-3.0Ag-0.5Cu) degrade over time as the result of the coarsening of the intermetallic phases such as Ag 3 Sn and Cu 6 Sn 5 . In earlier studies, it was shown that the inclusion of bismuth (Bi) in Sn, Sn-Ag, Sn-Cu, and SAC-based alloys leads to a stabilization of the as solidified mechanical properties after aging at temperatures above the alloy's solvus (where all precipitates are allowed to dissolve into and diffuse through the β-Sn matrix, leading to a uniform, homogenous microstructure). Further, the β-Sn grain structure becomes more refined, transitioning from consisting of only a few large grains to having many smaller, randomly-oriented grains. However, most practical operating conditions lie below the solvus temperature. This results in Ostwald ripening of the Bi precipitates, which may become sufficiently brittle to be a reliability concern. This paper contains details from a recently patented process which allows for the improvement of the properties of the solder joint, either post-reflow, or after some amount of product lifetime. The treatment was analyzed by comparing the creep properties of Violet, an alloy containing 2.25% Ag, 0.5% Cu, and 6.0% Bi, with SAC 305. An above-solvus aging treatment was performed on each alloy, either after solidification, or after below-solvus aging. It was found that the creep resistance of both alloys is reduced after below-solvus aging, but the creep resistance of Violet is significantly improved after above-solvus aging (regardless of prior thermal history). These results show that this aforementioned thermal treatment is a viable method to improve the long-term reliability of solder joints in electronic assemblies.
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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 | 0.000 |
| 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 | 0.000 | 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".