Contact resistance of metal‐coated polymer particles used in anisotropically conductive adhesives

The increasing demand for fine pitch interconnections has led to a growth of interest in anisotropically conductive adhesives (ACAs) as an alternative to solder joints in high density applications. The understanding of the conduction mechanisms for ACAs is of vital importance when choosing the right adhesive for a specific application. In the conductivity model, a formula has been created that can be used to estimate how the degree of deformation of the particles effects the resistance, especially in the case of soft metal‐coated polymer particles. Using this model, it is possible to estimate the total contact resistance. Some comparisons are made with real measurements for gold and indium‐tin‐oxide (ITO) surfaces, using gold‐coated polymer particles and gold bumped chips. For gold surfaces, the measurements have shown reasonably good correlation with the model. In the case of the ITO surface, the interface resistances seem to be the major part of the total resistance.