Effects of mixing procedures on the volume fraction of silver particles in conductive adhesives

This article reports the effects of several different mixing procedures on the apparent critical volume fraction of silver particles in conductive adhesives made of acrylic and epoxy resins, The mixing was conducted on either a two-roll or a three-roll mill. The mixture was then made into a film about 80 mum thick and its resistivity was measured. The results suggested that a three-roll mill provided better mixing than a two-roll mill. Additionally, by heating the conglomerate slightly during mixing, films were obtained with a smaller apparent critical volume fraction of silver particles. The results also indicated that a more uniform mixture was achieved through enhanced axial movement of the mixture on a roll mill. The effect of changing the silver particle size by grinding was also studied. The addition of a small amount of ethylene glycol was necessary to bring about the expected improvement in conductivity using smaller particles.