Issue link: https://iconnect007.uberflip.com/i/1540984
70 SMT007 MAGAZINE I NOVEMBER 2025 • Flexibility vs. Stiffness and CTE Mismatch The modulus of elasticity (E), or Young's modulus, describes how a material deforms under stress. A higher modulus indicates a more rigid material, while a lower modulus indicates a more flexible one. This property is critical when selecting a conformal coating because flexibility generally allows a material to better accommodate coefficient of thermal expansion (CTE) mismatches, differences in rates of thermal expansion and contraction between the coating and the PCB. The CTE describes how much a material expands or contracts with temperature changes. If a coating is too rigid, it may crack fragile component leads during thermal cycling as the coating and PCB expand at different rates. Conversely, if the coat- ing is too flexible, it can tear, creating gaps in the protective barrier that allow moisture and contami- nants to penetrate the electronic assembly. To address this, material suppliers are formulat- ing conformal coatings with E values tailored for spe- cific temperature ranges, adjusting the glass transi- tion temperature (Tg) to balance toughness and flexibil- ity. At MacDermid Alpha, these design principles guide the development of advanced conformal coatings to ensure long-term reliability even under thermal cycling. • Component Coverage and Coating Thickness Most conformal coatings on the market are solvent-based. Their low viscosity allows for uniform application by brushing, dipping, or spraying, typically at thicknesses between 25–75 µm. However, surface tension and capillary effects create challenges in achiev- ing uniform coverage. As the coating flows, it thins out over the top surfaces and along sharp edges of components, leaving insuffi- cient protection in these areas. These weak points create entry points for condensa- tion, humidity, or other contaminants. At the same time, capillary forces drive the coating to accumulate at the base and lead termina- tions of components, forming thicker depos- its that are prone to cracking under thermal cycling stresses (CTE mismatch). By contrast, MacDermid Alpha's new solvent-free, thixotropic coating is engineered to enable con- trolled flow and improved component coverage. At rest, it remains thick and viscous, preventing drip- ping and unwanted flow. During spray application, the applied shear temporarily decreases the viscosity, enabling a smooth, controlled application. This rheo- logical profile makes the solvent-free coating highly compatible with automated selective-spray sys- tems, enabling controlled deposition and consistent component coverage at film thicknesses ranging from 150–350 µm and higher. Combined with programma- ble robotic arms and spray nozzles, this technology ensures the coating is applied only where needed, optimizing material usage and reducing waste. ▼ Ty p i c a l c o m m e rc i a l l y ava i l a b l e U V- c u re c o at i n g o n I P C - B24 S I R c o u p o n s : t h e r m a l cyc l i n g -4 0 ° C to +1 2 5 ° C ( 3 0 - m i n u te d we l l ) . U V F l ex c o at i n g o n I P C - B24 S I R c o u p o n s : t h e r m a l cyc l i n g -4 0 ° C to +1 2 5 ° C ( 3 0 - m i n u te d we l l ) . ▼ ▼ C o m p o n e nt c ove ra g e of s o l ve nt- b a s e d c o nfo r m a l c o at i n g .