Microstructures Resulting from the Use of Solder Balls of One Composition with Paste of a Different Composition on a Copper Substrate
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Bibliographic record
Abstract
ABSTRACT With the development and use of a variety of Pb-free solders, it is probable that some solder joints in electronic assemblies may be made with solders of two different compositions, one of which may be eutectic Pb-Sn. To investigate some possible resulting microstructures, small balls of four different SAC Pb-free solders were each melted with eutectic Pb-Sn solder paste, as well as with various SAC pastes, on a copper substrate. Two paste levels were used, 20 and 29 weight percent of the total sample weight. In all cases, the sample was held for 90 seconds at a temperature above the melting point of the solder paste. For samples made with PbSn paste, two different values of maximum temperature were used, 210°C and 220°C, while for samples made with SAC paste, the maximum temperatures used were 235°C and 245°C. The resulting microstructures were evaluated metallographically using both optical and scanning electron microscopes. It was observed that the use of Pb-Sn solder paste introduced some Pb-Sn eutectic microstructure and changed the ternary eutectic present from Ag 3 Sn-Cu 6 Sn 5 -Sn, normally observed in SAC alloys, to Ag 3 Sn-Pb-Sn. The high Sn content of the SAC alloys used led to rapid dissolution of the copper substrate, often resulting, on cooling, in formation of primary Cu 6 Sn 5 crystals and Cu 6 Sn 5 -Sn binary eutectic regions. Similar experiments were also carried out using balls of the Sn-Zn-Al solder alloy.
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Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.002 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.000 | 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 it