The interrelationships between electronically conductive adhesive formulations, substrate and filler surface properties, and joint performance. Part II: the effects of bonding pressure

Electronically conductive adhesives (ECAs) have received a great deal of attention in recent years for interconnection applications. Even though ECAs have excellent potential for being efficient and less costly alternative to solder joining in electronic components, they still suffer from a number of problems relative to durability and design to meet specific needs. These include issues with the formulations of the conductive adhesive and its interactions with the substrate surface. In order to study these problems, we prepared two different adherends varying in surface characteristics and bonded them with three different conductive adhesive formulations with varying particle loadings, shapes and sizes of conductive nickel fillers. Joints were also prepared with two different adhesive thicknesses, and the effects were discussed in Part I of this paper. This part discusses the effects of filler surface properties, volume fraction and bonding under different levels of pressure to gain insight into the influence of these parameters on the joint strength, deformation and joint conductivity. Our results showed that chemical etching of particles, which changes the shape of the particles, has a profound effect on the joint strength, deformation and electrical conduction behavior. We note that prolonged period of chemical etching of spherical Ni-110 particles with hydrochloric acid causes irregularities in the shape of the nickel particles, and an increase of 60% in the joint resistance. Higher bonding pressure generally resulted in lower failure load and ultimate displacement values, indicating the possibility of squeeze flow for the neat resin under high pressure. Incorporation of larger particles in the adhesive formulation yielded a more efficient resin squeeze mechanism.