Assembly Feasibility and Property Evaluation of Low Ag, Bi-Containing Solder Alloys
Bibliographic record
Abstract
ABSTRACT While SAC305 has become the current standard lead-free alloy for commercial use, it poses some significant disadvantages over the now banned tin-lead (SnPb) solder. SAC305 is much stiffer then SnPb and therefore exhibits poor mechanical properties. Additionally, the increased melting temperature requires higher glass transition temperature (T g ) boards, leading to failures by Pad Cratering. Finally, the high cost of silver makes this alloy unattractive for commercial use. Bismuth (Bi) containing alloys had been avoided during the initial transition away from Pb because of the possibility of forming a low melting temperature phase in a mixed Pb/Pb-free system. As the SnPb components have for the most part been removed from the supply chain, this is less of an issue and therefore it is now time to re-examine bismuth as a possible alloying element. Ball grid array (BGA) and leaded components were assembled using SAC305 conventional Pb-free solder and three low Ag Pb-free alloys containing Bi. The peak reflow temperatures were about 10°C below acceptable reflow temperature for SAC305 assembly. Normal T g (those commonly used for SnPb solder), and high T g board materials (those now required for SAC305 and other high melting temperature solders) were used. This paper will discuss the feasibility of assembly using these solder alloys when SAC305 ball BGA components as well as Pb-free compatible leaded and leadless components are used. Additionally, drop testing was used to evaluate the mechanical properties of these alloys as compared with SAC305. The alloy and board material combinations were examined. This paper describes the results of the manufacturing feasibility and drop testing. The results and failure modes are correlated to microstructural characteristics of each material.
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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 | 0.001 |
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".