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46 DESIGN007 MAGAZINE I SEPTEMBER 2025 • Mixing ratio: Precise ratio control is essential to achieve complete curing and optimal mechanical and thermal properties. • Dispense pattern: Spiral, bead, or dot pat- terns are chosen based on the surface area and the geometry of the gap being filled. • Cure time and temperature: Cure profiles can be adjusted for room-temperature curing or accelerated thermal curing, depending on production requirements. • Equipment design: The pumps and valves in the dispensing system must be designed to handle abrasive fillers to ensure stable and consistent flow. Automated dispensing systems enable consistent bondline thickness, minimize voids, and ensure reliable wet-out, delivering optimal thermal contact and long-term durability. fillers cure in place, they resist squeeze-out under clamping pressure (unlike greases). For applications that demand precise thickness control, spacer beads or mechanical stops are commonly used. For gap fillers, BLTs typically range from 200 µm to several millimeters. This wide range allows them to bridge both small and large gaps while accommodating varying assembly tolerances. Their versatility makes them suitable for diverse applications that require reliable thermal contact to be maintained across uneven surfaces, from high- performance computing and telecom infrastructure to EV battery modules and power converters. Outgassing, Ionic Contamination, and Electrical Safety Beyond thermal and mechanical performance, TIM2 gap fillers must meet stringent requirements for chemical stability, cleanliness, and safety, particularly in high-reliability or safety-critical applications. • Outgassing: Volatile compounds can con- dense on nearby components, risking elec- trical and optical failures. To assess this risk, TIMs are tested using total mass loss (TML) and collected volatile condensable materi- als (CVCM) in accordance with ASTM E595 standards. Low-outgassing formulations are critical for applications like satellite electron- ics, infrared (IR) targeting systems in missile guidance, and automotive cameras used in advanced driver-assistance systems (ADAS). • Ionic contamination: Mobile ions such as sodium (Na + ), potassium (K + ), and chloride (Cl - ) can cause corrosion and leakage currents in high-voltage systems. To minimize this, high- purity raw materials and tight process con- trols are used to keep ionic content below accepted industry thresholds, typically below 10 ppm. • Electrical insulation: Many TIM2 materials must also insulate electrically. Silicone-based formulations with ceramic fillers offer both high thermal conductivity and electrical resis- tance. Dielectric breakdown strength and vol- ume resistivity are key metrics for validating electrical insulation performance across operational voltage ranges. " " Au to m ate d d i s p e n s i n g syste m s e n a b l e c o n s i ste nt b o n d l i n e t h i c k n e s s , m i n i m i ze vo i d s , a n d e n s u re re l i a b l e wet- o u t , d e l i ve r i n g o pt i m a l t h e r m a l c o nt a ct a n d l o n g - te r m d u ra b i l i t y. Addressing Surface Roughness Through Material Design MacDermid Alpha gap fillers are specifically formu- lated to maximize both conformability and surface wetting. By engineering them with low hardness and viscoelastic properties, they can conform to surface roughness, compensate for variations in planarity, and fill voids without the need for high assembly pressure. Surface wetting is optimized to improve contact with mating surfaces, reducing contact resistance (Rcontact). This, in turn, lowers overall thermal impedance, particularly when combined with a well-tuned dispensing pressure and pattern. Bondline Thickness and Assembly Pressure Bondline thickness (BLT) is determined by the size of the gap, assembly tolerances, and specific application requirements. Because 2K silicone gap