Crack Paths and Fracture Loads of BGA Solder Joints under Bending as a Function of Strain Rate and Mode Ratio
Bibliographic record
Abstract
ABSTRACT Printed circuit boards (PCBs) populated with ball grid array (BGA) solder joints undergo various failure modes depending on the loading conditions. In this study, experiments were performed to characterize the fracture behavior of a package-on-board solder joint system without underfill as a function of the speed of loading. A piece of FR4 was bonded to the free side of the package to build a double cantilever beam (DCB) test specimen from a section of the PCB containing the package. Loading brackets were bonded to both PCB members and a servoelectric testing machine as used to apply an opening speed of either 0.002 mm/s or 4.23 mm/s. This increase in strain rate caused an obvious change in the crack path. Fracture through the PCB was observed in quasi-static loading, whereas predominantly solder joint fracture was detected at the higher strain rate. Depending on the type of PCB and the arrangement of the BGA, the crack front in quasistatic fracture was either continuous, across the entire width of the PCB including the gaps between the solder pads, or it was discontinuous, and only present as discrete sections of pad cratering. Two solder alloy compositions were examined (i.e. SAC305 and SAC0807), with SAC0807 yielding a slightly larger fracture load than SAC305 loaded at the intermediate strain rate. The results are discussed in terms of the fracture strengths of the crack paths and their sensitivity to strain rate.
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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 | 0.001 | 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) | 0.002 | 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".