Mechanical and electrical characterisation of individual ACA conductor particles

Anisotropic conductive adhesives (ACAs) consist of a polymer adhesive matrix containing fine conductive particles. The primary objective of this experimental research is to establish a clearer understanding of the effects of the bonding force on the deformation of individual ACA particles and their resulting conductivity when in contact with an appropriate metallic surface. This has been achieved through simultaneous measurements of the deformation and electrical resistance whilst applying force using a specially configured nano-indenter machine, where the "indenter", instead of being pointed, had a flat tip about 20-30 mum in diameter. The merit of using this machine is that very small forces, of the order of 100 mN, can be accurately applied to the particles to a resolution of 100 nN and the resulting deformations, of less than 6 mum, can then be recorded to a resolution of 0.1 nm. The results showed that the ACA particle deformation was nonlinear and that the force/deformation at which particle crushing occurs was affected by the load rate. The resistance was observed to decrease as the deformation increased up to the crush point at which stage it increased slightly. The voltage versus current behaviour of a deformed ACA particle was also found to be linear.