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JUNE 2026 I SMT007 MAGAZINE 15 • Assembly optimization: Refine reflow profiles to minimize residue entrapment, optimize stencil design to control paste volume, and implement strict handling procedures to reduce contamination. • Cleaning validation: Where cleaning processes are employed, SIR testing pro- vides objective data on residue removal effectiveness, process consistency following changes, and electrical safety of any remaining residues. • Reliability implications: Highly dense assemblies operate with minimal tolerance for contamination. As a result, cleanliness has a direct and measurable impact on field failure rates, warranty costs, long-term prod- uct stability, high-speed signal performance, and safety-critical system reliability. In sectors such as aerospace, medical devices, automotive, and defense, these factors are not optional considerations; they are fundamental requirements. Figure 10: Insulation resistance as a function of time. Conclusion As electronic designs push the limits of density and performance, traditional assumptions about flux residues and cleanliness are no longer sufficient. What was once considered acceptable can now pose significant reliability risks. In highly dense assemblies, cleanliness must be treated as a critical design and process parameter. Through a combi- nation of advanced testing, disciplined process control, and a deeper understanding of contami- nation-driven failure mechanisms, manufacturers can better ensure the long-term reliability of their products. By mastering the principles outlined here, professionals can better design, build, and qualify assemblies that meet the demanding requirements of today's technology landscape. SMT007 Mike Bixenman is VP/CTO at Magnalytix. Elapsed Time (Hours) Surface Insulation Resistance (Ohms)