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40 SMT007 MAGAZINE I OCTOBER 2026 Profile B were most pronounced when paired with Paste 2. Additionally, the performance gap between pastes widened under the 4-mil stencil condition, suggesting that material-process compatibility is critical when solder volume is limited. Taken together, these results establish a clear hierarchy of influence: Stencil Thickness » Reflow Profile > Solder Paste > Paste × Profile > Paste × Stencil Thickness Interactions between solder paste and stencil thickness, while statistically significant, were the smallest in magnitude. This analysis supports a key interpretation: Stencil thickness sets the baseline for void performance, while reflow profile and solder paste offer oppor- tunities for further optimization. Importantly, reflow adjustments alone cannot overcome limitations imposed by stencil design or suboptimal material choices. Finally, these results align with the reduced-factor design of experiment (DOE) approach used in this study. The decision to focus on OSP surface finish helped isolate and evaluate the primary process variables without introducing confounding effects. Future work will expand this analysis to include ImSn surface finishes to confirm whether these findings generalize to other production-relevant surface metallization. Figure 4 presents representative X-ray images of QFN components assembled using an OSP surface finish. The comparison includes two solder pastes (Paste 1 and Paste 2), two stencil thicknesses (4 mil and 5 mil), and two reflow profiles (Profile A and Profile B). Clear differences in voiding behavior were observed. Assemblies produced with the 4-mil stencil showed a higher percentage of voiding compared to those made with the 5-mil stencil. This is likely due to thinner solder deposits restricting the release of entrapped gases during reflow. Paste 2 generally exhibited smaller and more evenly distributed voids than SAC305, especially when used with the 5-mil stencil. These observa- tions suggest that reflow profiles influence not only Figure 4: Representative of X-ray images of OSP 4-mil and 5-mil stencil.