Low Temperature Formation of SAC-SnBi BGA Interconnections using Solid Liquid Inter-Diffusion (SLID)
Bibliographic record
Abstract
We propose a novel approach to adopt SLID to low temperature BGA interconnections that enables both ball attach and card attach at SnBi eutectic reflow temperatures and enables the formation of a homogeneous, stable hypoeutectic SnBi connection of considerably lower Bi content than its eutectic counterpart.The SLID mechanism and its diffusion kinetics were investigated by selecting appropriate sized SAC spheres and eutectic Sn58Bi solder paste volumes then evaluating the resultant ball attach connections. It was determined that hypoeutectic SnBi connections in the range of 18-26% Bi could be effectively formed as homogeneous or near-homogeneous compositions under temperature excursions representative of typical cumulative Sn58Bi reflow profiles.Microstructural observations after reflow (t0) and aging at 100 °C showed some differences between the hypoeutectic connections and the eutectic or near eutectic (Sn57BiAg) connections within the bulk solder regions. The most significant difference was observed at the solder-ENIG interface where a thick layer formed with aging of the eutectic and near eutectic connections whereas no such layer formed with the hypoeutectic connections.Shear testing appeared to correlate the interfacial differences to mechanical integrity. Hypoeutectic connections exhibited mostly ductile fracture within the bulk solder while eutectic and near-eutectic connections failed in a brittle fashion near the solder-Ni interface and at lower shear strengths.
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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 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.001 |
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".