Fine Powder Solder Paste with Novel Water Soluble Chemistry — An Enabler for Next Generation System-in-Package Assembly
Bibliographic record
Abstract
Water-soluble solder pastes containing fine powders (Type-6 and Type-7) are becoming progressively critical in semiconductor assembly applications due to their advantages in printing performance and cleanability. However, achieving optimal print quality while ensuring effective residue removal—particularly on small passive components and low stand-off geometries—remains a significant challenge. Common issues such as slump and bridging often compromise the quality of fine-feature and fine-pitch printing with water-soluble formulations. In this study, we introduce a novel water-soluble solder paste featuring an innovative flux chemistry designed to deliver superior printing performance. The new formulation effectively minimizes slump and bridging, enabling high-quality prints even for intricate designs. Post-reflow flux residues can be removed using deionized (DI) water alone, eliminating the need for chemical or organic cleaning agents. This advancement not only improves manufacturing efficiency but also supports environmental sustainability by reducing reliance on harsh cleaning substances. Interactions between solder powder and flux were investigated for both Type-6 and Type-7 pastes through comprehensive rheological experiments. The study compares printing performance of traditional solder pastes with those formulated using the novel flux chemistry across two particle sizes. As the semiconductor industry—particularly in surface mount technology (SMT)—demands higher efficiency in finefeature printing, there is a growing shift toward finer solder powders. This research explores whether a single flux chemistry can effectively accommodate varying particle sizes. Flux-powder network stability was assessed using shear rate ramp rheology, revealing improved structural integrity in pastes with the new flux. Thixotropy loop tests evaluated structural breakdown under shear stress and recovery during rest, while amplitude sweep measurements confirmed the compact and solid structure of the solder paste. Step shear rate recovery tests demonstrated the paste's ability to maintain performance during prolonged denaturation printing. Stencil printing trials were conducted to compare transfer efficiencies, which were then correlated with rheological data. This study provides valuable insights into the rheological behavior of solder pastes and highlights the differences in printing performance between formulations with distinct flux chemistries. In addition to excellent printability, the new chemistry also exhibited superior residue cleanability following standard Pb-free reflow in a nitrogen environment. The combination of fine-feature printing capability and effective residue removal positions this new solder paste chemistry as a potential benchmark for future industry standards.
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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 | 0.000 |
| 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 | 0.001 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.001 | 0.001 |
| 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".