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

摘要

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