Polymer adhesives are commonly used in electronic applications, mostly to seal and protect components. Because of the sensitive nature of electronics, these adhesive products are almost always modified with specialized filler materials in order to make the polymer product more useful in the end application. Specialty adhesive formulators use fillers to increase or induce certain qualities in the polymer product. Below are five different polymer qualities that can be influenced by filler elements.
1: Exothermic Heat Control
Fillers reduce the amount of resin per unit volume, thus reducing the heat production per unit volume as the system reacts and exotherms. Thermally conductive fillers can further help exotherm control by effectively dissipating heat as it’s produced.
2: Flame Retardant
Certain applications require that all components exhibit fire retardant qualities, such as automotive and aerospace applications. Loading an adhesive with a flame-retardant material will induce the required qualities in the cured epoxy system. UL 94V is the official flame resistant standard and epoxies that pass this standard are considered UL 94V listed.
Fillers can be used to give pre-cured polymer resins specific viscosity, and thixotropy, qualities. Certain fillers are better for this than others. Fibrous fillers, for example, generally have a greater effect on viscosity than particulate fillers.
4: CTE - Coefficient of Thermal Expansion
As polymer adhesives are cycled through different temperatures, the molecular structure can expand and contract, potentially harming bonded substrates and components. Filling polymer adhesives with a material that has an extremely low CTE will severely influence the CTE of the final product. CTE reduction is important to applications that involve the bonding of sensitive electronics.
5: Electrical Conductivity
Loading polymer adhesives with electrically conductive materials can decrease the inherent electrical resistivity of the polymer products. Loaded epoxies can have resistivity as low as 1x10^-4 ohm⋅cm. Electrically conductive polymers make great solder alternatives for electronics applications.