Reliability of Mixed Solder Interconnects – Case Studies
Bibliographic record
Abstract
ABSTRACT The effects of different degrees of solder alloys mixing on the reliability of lead-free (LF) Sn-3.0Ag-0.5Cu (wt.%) (SAC 305) ball grid array (BGA) devices assembled with a Sn-Pb eutectic paste were investigated. The first case involved eight memory modules in a back-to-back configuration reflowed on standard graphic cards. In the second case, one LF BGA ASIC component per board was assembled on the graphics cards of different design. Depending on the reflow conditions, the solder interconnects displayed varied degrees of Sn-Pb and LF solders intermixing. It was established that in order to receive a homogeneous solder alloy, the reflow peak temperature had to be in the 218°C-222°C range. The reliability of solder interconnects of memory and ASIC modules was assessed by subjecting the cards to up to 1500 cycles of accelerated thermal-cycling with a profile from 0°C to 100°C. In the first case, the control Sn-Pb/Sn-Pb assemblies were more reliable than the mixed assemblies. Regardless of a degree of homogeneity of the BGA balls, the predominant failure mode of the mixed solder joints was interfacial cracking through a Pb-rich phase near the intermetallic layer. In contrast, only partial cracks propagating diagonally through the bulk solder were present on the control boards. In the second case, despite only partial mixing, no fatal cracks were observed in the solder joints. It was concluded that a combination of state of stress and segregation of the Pb-rich phase at the interface was responsible for the shortened thermal-mechanical fatigue life of the mixed solder interconnects.
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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 | 0.003 | 0.008 |
| Meta-epidemiology (narrow) | 0.001 | 0.001 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.002 | 0.001 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 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".