Conductive adhesives mainly consist of a resin matrix, conductive particles, dispersing additives, and auxiliaries. The matrix primarily includes epoxy resins, acrylate resins, and polyurethanes. Although highly conjugated polymers themselves possess conductivity, such as macromolecular pyridine structures, and can conduct electricity via electrons or ions, the conductivity of these conductive adhesives can only reach the level of semiconductors at best; they cannot have the low resistance of metals and are therefore insufficient for conductive bonding. Most conductive adhesives used in the market are filler-based.
In principle, the resin matrix of filler-based conductive adhesives can use various adhesive types. Commonly used ones include thermosetting adhesives such as epoxy resins, silicone resins, polyimide resins, phenolic resins, polyurethanes, and acrylic resins. After curing, these adhesives form the molecular framework structure of the conductive adhesive, providing mechanical and adhesive properties and creating channels for the conductive filler particles. Because epoxy resins can cure at room temperature or below 150°C and offer a wide range of customizable formulations, epoxy resin-based conductive adhesives dominate the market.
Conductive adhesives require conductive particles with good conductivity and a suitable particle size range to form conductive pathways within the adhesive matrix. Conductive fillers can be powders of gold, silver, copper, aluminum, zinc, iron, and nickel, as well as graphite and some conductive compounds.
Another important component of conductive adhesives is the solvent. Since the amount of conductive filler added is at least 50%, the viscosity of the resin matrix increases significantly, often affecting the adhesive's processing properties. To reduce viscosity and achieve good processability and rheological properties, in addition to selecting low-viscosity resins, solvents or reactive diluents are generally added. Reactive diluents can directly act as the resin matrix for curing. Although the amount of solvent or reactive diluent is small, it plays a crucial role in conductive adhesives, affecting not only conductivity but also the mechanical properties of the cured product. Commonly used solvents (or diluents) should generally have a large molecular weight, slow evaporation, and a polar structure, such as carbon-oxygen polar segments. The amount of solvent added must be controlled within a certain range to avoid affecting the overall bonding performance of the conductive adhesive.
Besides the resin matrix, conductive filler, and diluent, the other components of conductive adhesives are the same as those of adhesives, including crosslinking agents, coupling agents, preservatives, toughening agents, and thixotropic agents.
