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38 SMT007 MAGAZINE I OCTOBER 2026 In contrast, the mixed-alloy system (Paste 2) consistently achieved lower voiding across both OSP and ImSn conditions, reinforcing alloy selec- tion as a secondary but important lever. Trial 3 (OSP, 5 mil) demonstrated the lowest voiding overall, with Paste 2 achieving values of 6.94% and 6.88%, well below the IPC-A-610 Class 3 threshold. This confirms the strong influence of stencil thickness in reducing voiding, while also highlighting that alloy performance interacts with surface finish. The mixed-alloy solder paste paired with OSP and a 5-mil stencil delivered the most robust voiding IPC compliance and lowest overall risk. Discussion The statistical analysis presented in Figure 3 confirms that stencil thickness is the most influential factor affecting solder joint voiding in QFN assem- blies. Assemblies printed with the 5-mil stencil consistently exhibited lower voiding compared to those printed with the 4-mil stencil. This trend held across all solder pastes and reflow profiles. The effect is attributed to increased solder volume, which creates a deeper molten pool during reflow. This facilitates more effective outgassing of vola- tiles, resulting in reduced void formation. Solder paste composition was the next most significant contributor. Paste 2, a mixed-alloy DFHR material, outperformed the SAC305 control (Paste 1) across all test conditions. Its enhanced wetting behavior and early coalescence likely allow for more efficient volatile release, leading to fewer and smaller voids. Reflow profile was the third key factor. Profile B, characterized by a slightly faster ramp rate between 180°C and 220°C, consistently reduced voiding rela- tive to Profile A. This profile likely promotes earlier flux activation and more efficient outgassing during the critical reflow phase. However, the impact of reflow profile, while measurable, was secondary to stencil thickness and solder paste selection. The highest single-void sizes occurred with the 4-mil stencil and Paste 1 under Profile A, while the smallest voids were observed using the 5-mil stencil, Paste 2, and Profile B. Interaction effects were also statistically significant, particu- larly between Paste × Profile and Paste × Stencil Thickness. These interactions demonstrate that the benefits of Profile B and thicker stencils are not uniform across all materials. For example, the advantages of Figure 3: Effect summary and prediction profiler of multiple factors.