Abstract
Conductive adhesives are widely used in electronic packaging applications such as die attachment and solderless interconnections, component repair, display interconnections, and heat dissipation. The effects of film thickness as functions of filler volume fraction, conductive filler size, shape, as well as uncured adhesive matrix viscosity on the electrical conduction behavior of epoxy-based adhesives are presented in this work. For this purpose, epoxy-based adhesives were prepared using conductive fillers of different size, shape, and types, including Ni powder, flakes, and filaments, Ag powder, and Cu powder. The filaments were 20 μm in diameter, and 160 or 260 μm in length. HCl and H3PO4 acid solutions were used to etch and remove the surface oxide layers from the fillers. The plane resistance of filled adhesive films was measured using the four-point method. In all cases of conductive filler addition, the planar resistivity levels for the composite adhesive films increased when the film thickness was reduced. The shape of resistivity-thickness curves was negative exponential decaying type and was modeled using a mathematical relation. The relationships between the conductive film resistivities and the filler volume fractions were also derived mathematically based on the experimental data. Thus, the effects of surface treatment of filler particles, the type, size, shape of fillers, and the uncured epoxy viscosity could be included empirically by using these mathematical relations based on the experimental data. By utilizing the relations we proposed to model thickness-dependent and volume fraction-dependent conduction behaviors separately, we were able to describe the combined and coupled volume fraction-film thickness relationship mathematically based on our experimental data.
Highlights
IntroductionThe use of electrically conductive adhesive (ECA’s) has expanded rapidly in the microelectronics industry
Over the past decades, the use of electrically conductive adhesive (ECA’s) has expanded rapidly in the microelectronics industry
By utilizing the relations we proposed to model thickness-dependent and volume fraction-dependent conduction behaviors separately, we were able to describe the combined and coupled volume fraction-film thickness relationship mathematically based on our experimental data
Summary
The use of electrically conductive adhesive (ECA’s) has expanded rapidly in the microelectronics industry. Conductive adhesives form joints with sufficient strength so that they can bond two surfaces, and second, an electrical interconnection is formed between the two bonded surfaces. This dual functionality is usually achieved in composite form by dispersion of particles in an insulating adhesive matrix [3,4]. The primary properties of these adhesives are high and stable electrical conductivity. These adhesives have an electrical resistivity of 104 -cm (Ohm-cm), which is about two orders of magnitude higher than the best metallic conductors. The metal fillers, which are added to the epoxy resin usually improve its other properties such as strength, thermal conductivity etc., and can be used to impart specific composite properties such as thermal expansion, thermal conductivity, shrinkage and heat resistance [5,6]
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