I’m working on a small sensor board (STM32 + analog ICs) for an unsealed outdoor enclosure. I need clear potting for moisture and vibration protection while keeping LEDs visible for inspection. Given typical outdoor temperature swings, how do clear epoxy, polyurethane, and silicone compare in terms of long-term yellowing and thermal cracking?
1 Like
You should consider silicone, followed by aliphatic polyurethane. Epoxy is rigid and will crack due to CTE mismatch during outdoor temperature swings. Silicone remains flexible and is inherently UV-stable. If you go with polyurethane, it must be aliphatic, or it will yellow quickly in sunlight.
1 Like
I’d also compare the manufacturer’s UV/weathering data and thermal-cycling performance rather than choosing purely by material type. For a clear potting compound, the specific formulation can make a big difference in yellowing, flexibility, and long-term adhesion to the PCB and components.
One other thing I’d check is adhesion to the PCB solder mask and component surfaces. Even if the potting material survives the temperature and UV exposure, poor adhesion or moisture paths at the interfaces can undermine the protection. A manufacturer’s moisture-resistance and adhesion data would be useful to compare alongside UV and thermal-cycle ratings.
One point I’d add is that silicone’s flexibility doesn’t automatically make it the best moisture barrier. Silicone can have higher water-vapor permeability than some epoxy and polyurethane systems, so for an unsealed enclosure I’d also compare water absorption/permeability and corrosion-resistance data for the specific formulation.