A Study of the Influence of FIP Bead Shape on Compression Force in PCB/Shield Assemblies

Electrically conductive elastomers are used on electronic equipments to provide shielding against electromagnetic interference (EMI) as well as protect the enclosure against external environmental conditions. The gasket is rendered electrically conductive through the use of metal fillers embedded in a base polymer matrix. Typically, they are prepared either by compression molding or extrusion. One of the most economical and convenient ways of preparing EMI gaskets, however, is by dispensing the material directly on a shield assembly and allowing it to cure and form in place (FIP). The amount of force needed to compress an elastomer gasket is critical to its shielding effectiveness. A typical Form-in-Place (FIP) gasket should have low compression force to deflect the gasket sufficiently to ensure proper electrical continuity between two adjacent substrates. This study presents the evaluation of the effect of varying bead shapes on the compression force of FIP gaskets. The samples tested were heat- and moisture-cured silicone elastomers with Ag/ Cu and Ag/Al fillers, dispensed on shield assemblies. The gaskets were dispensed in different shapes: single- (S) and double-layered (D) D-shaped beads, as well as single-layered triangular (T) beads. Compression forces were measured under dynamic and static conditions.