The conductive adhesive is mainly composed of resin matrix, conductive particles, dispersing additives and auxiliaries. The matrix mainly includes epoxy resin, acrylic resin, polychloride ester and so on. Although the highly conjugated type of polymer structure itself also has electrical conductivity, such as macromolecular pyridine structure, can conduct electricity through electrons or ions, but the conductivity of this kind of conductive adhesive can only reach the degree of semiconductor, can not have low resistance like metal, difficult to play the role of conductive connection. The conductive adhesive used on the market is mostly filler type.
The resin matrix of the filler conductive adhesive, in principle, can use a variety of adhesive types of resin matrix, commonly used thermosetting adhesives such as epoxy resin, organic silicone resin, polyimide resin, phenolic resin, polyurethane, acrylic resin and other adhesive systems. These adhesives formed the molecular skeleton structure of the conductive adhesive after curing, provided mechanical properties and bonding properties, and enabled the conductive filler particles to form channels. Because epoxy resins can be cured at room temperature or below 150℃ and have abundant formulation-designable properties, epoxy-based conductive adhesives are dominant.
Conductive adhesive requires conductive particles themselves to have good conductive property and the particle size should be added to the conductive adhesive matrix to form conductive path within a suitable range. Conductive fillers can be gold, silver, copper, aluminum, zinc, iron, nickel powder and graphite and some conductive compounds.
Another important component of conductive adhesive is solvent. Because the amount of conductive filler is at least more than 50%, the viscosity of the resin matrix of the conductive adhesive is greatly increased, which often affects the technological performance of the adhesive. In order to reduce viscosity and achieve good technology and rheology, in addition to the selection of low viscosity resin, generally need to add solvent or active diluent, which can be directly used as the resin matrix, reaction curing. Although the amount of solvent or active diluent is not large, it plays an important role in conductive adhesive, which not only affects the conductivity, but also affects the mechanical properties of the cured substance. Commonly used solvents (or diluents) should generally have a large molecular weight, volatilization is slow, and the molecular structure should contain polar structure such as carbon oxygen polar chain segments. The amount of solvent added should be controlled within a certain range, so as not to affect the overall bonding performance of conductive colloids.
In addition to resin matrix, conductive filler and diluent, other components of conductive adhesive and adhesive, also include crosslinking agent, coupling agent, preservative, toughening agent and thixotropic agent.