The application scope of conductive adhesives increasescontinuously, requiring new and improved properties. In general,isotropic conductivity is achieved by loading a resistive polymer(mainly epoxy resins) with 70-80 wt% metal filler particles. Duringcure, resin shrinkage lowers contact resistance between neighbouringparticles, giving a conductive 3D network. However, at high currents,local current density at neighbouring particle contact spots may be alimiting factor. Due to the filler content percolation effect, electronsflow through very small contact spot areas, so local current densitycannot be calculated from applied current and adhesive bond geometry.This may lead to electromigration, resulting in Ag atom transport withinthe filler particles and then by diffusion through the polymer. Thiseffect occurs even if self-heating is neglected. In this study,early-stage resistance degradation for bisphenol-A type andcycloaliphalic resins, loaded with Ag flakes and porous Ag powderrespectively, is examined using adhesive stripe samples on FR-4.Resistance is measured by a four-point technique. Samples are held atconstant temperature in an inert liquid, and a pulsed DC-current isapplied. Tests with temperatures from 80-130° C and 2-33 A/mm2 current densities are performed. A linear increase or decrease inresistance with time is observed for flake and porous Ag filledadhesives, respectively, due to current application, whereby a sinteringprocess for the porous Ag must be taken into account. Current densityand temperature dependences for various parameters are discussed; adegradation model is proposed
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