The effect of annealing on the morphologies and conductivities of sub-micrometer sized nickel particles used for electrically conductive adhesive

The development of Electrically Conductive Adhesives (ECA) as an alternative to solder balls has received extensive attention in flip chip assembly as it offers an array of advantages like finer pitch interconnect, green process, lower cost and low temperature processing. Nickel with its lower cost than silver and better thermal stability than copper, appears to be the most suitable material used for making ECA particles. However, according to our previous research, a spiky surface morphology of the Ni particle synthesized by means of a hydrothermal reduction method was clearly observed. The spiky surface morphology may have a detrimental effect on both the thermal and electrical conductivity of the ECA flip chip interconnects due to its smaller contact surface. In this paper, we investigated the annealing effect on the surface morphologies of Ni particles. It was found that the surface structure of the nickel changes with the annealing conditions. A smooth surface has been observed after annealing the Ni particle for 4 h at a temperature of 360 °C. It was observed that the morphology changes brought about by heat treatment had contributed to the improved thermal and electrical conductivity of the Ni particles.