Strain Rate and Cyclic Dependencies of PCBA Pad Crater Susceptibility
Bibliographic record
Abstract
ABSTRACT Pad cratering has been widely recognized as a dominant mechanical failure mode in printed circuit board assemblies (PCBAs) that are subjected to SnAgCu solder alloy processing temperatures. This susceptibility is especially noted in cost competitive, phenolic-cured epoxy based composites, filled with ceramic particles or microclays. A Spherical Bend Test (SBT) program developed by the authors has identified a relationship between the principal rising strain rate associated with PCBA mechanical deformation and the maximum survivable strain for PBGA components. In this work, those results are compared to a similar new experiment using varied design parameters and multiple board materials with the intent of identifying a material independent descriptive equation. On one typical laminate material the experimentation is expanded beyond a single deformation excursion to failure in an attempt to define a surface of safe working strain over a range of cyclic exposures. The scope of this experiment covers a range of strain excursions bounded by strain rate on one axis and SBT cycle count on the other. The limits of this test parameter range are intended to represent strain rate excursions and cycle counts that might reasonably be expected to occur in normal manufacturing environments. This paper describes the theory and practice of material selection, test vehicle design, assembly, and test methods used to generate data. Selected test results, meaningful relationships and the particulars of the failure modes determined by physical failure analysis are discussed.
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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 | 0.003 |
| 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) | 0.003 | 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".