Resins used for these applications can be of various chemical types. Epoxy resins have been widely used for many years ; they are generally hard and tough and exhibit low shrinkage on cure. They are characterised by an excellent level of mechanical properties, good high temperature performance and good adhesion to a wide variety of substrates chemical resistance is also good. The cross-linking or curing process generally takes place slowly especially where small volumes of resin are involved. Fast cure hardeners can be used but these generate much heat during cure, giving rise to a high exotherm which can damage electronic components and cause high mechanical stresses on both components and the circuit.
Epoxy and acrylate resin based sealing and molding compounds are often used in electronics to protect electronic components, semiconductors and subassemblies. The encapsulation protects components from moisture, dust, dirt and solvents. Used to fill cavities or encapsulate components, sealing compounds also provide effective protection from mechanical stress.
The Epoxy Resins generally offer a higher temperature range, with lower shrinkage than Polyurethanes. They may also be harder, stronger, have better adhesion to many substrates, and with superior chemical resistance. The Polyurethane resins can offer greater flexibility, elasticity and abrasion resistance. The possible rapid cure with low exotherm is found useful. Special polyurethane products are particularly interesting for their extreme low temperature flexibility, low di-electric constant or UV stable optical clarity.
Resin systems are designed to protect and insulate printed circuit boards (PCBs) and electronic components from the threats of harsh and challenging environments, including; moisture, vibration, thermal or physical shock and general contamination. By encapsulating the entire device, resins can form a complete barrier against such environments offering superior performance under extreme conditions.