Implementation of Increased CU Levels (1%) in SAC Alloys for PBGA Applications
Bibliographic record
Abstract
ABSTRACT With Pb-free solder implementation and the higher Sn composition of the solder and higher reflow temperatures, Cu pad consumption is a concern and is often closely monitored. Certain applications require relatively thin Cu pad structures. Therefore, Cu pad consumption during soldering and reflow may become critical. BGA applications may be of particular concern, since the ratio of the solder volume to the Cu pad surface area is large, and the Cu consumption effect cannot be neglected. In this context, work was undertaken to characterize the effect of using SAC alloy solders with higher levels of Cu to mitigate the Cu consumption effect. SAC alloy solder joints with 3.0 wt % Ag content and with Cu composition ranging from 0.5% to 1.5 weight % were characterized, as a function of reflow conditions. Important reductions in dissolution and consumption of the Cu pad structures were observed, as initial solder sphere Cu content was increased. In the compositional range of Cu initially present in the solder spheres, it was found that the Cu content of BGA solder joints on Cu pad structures reached identical Cu concentrations within approximately 2 reflow cycles. Saturation values of approximately 1.2 wt % Cu were found, at a 250 °C, peak reflow temperature. The resulting solder joints were evaluated, using ball pull testing, metallurgical cross sectioning, polarized light microscopy, SEM examination and hardness testing of the solder. Different PBGA module types were prepared with SAC310 solder alloys and were tested in thermal cycling and shock and vibration testing and thermal aging, to resolve any potentially important differences in behavior and these results were compared to general application requirements using the SAC305 as a control. It was found that increasing the initial levels of Cu in solder had little impact on basic solder joint properties, but had the significant benefit of diminishing the Cu pad dissolution during solder reflow, with no impact to reliability testing results normally required to qualify this type of change in solder composition for field applications. Implementation of the Cu rich SAC alloys enables more flexibility for the thermal treatment of the solder joints and dramatically improves solder joint reworkability in the context of thin Cu pad structures.
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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".