Conductive powder includes silver powder, gold powder, copper powder, nickel powder, aluminum powder, zirconium powder, cobalt powder, graphite, carbon black, nickel carbide, silicon carbide, carbon fiber, silver-plated metal powder, silver-plated silica powder, silver-plated glass beads and so on.
Gold powder, which has excellent chemical stability and conductivity, is the best conducting particle in the conducting resin. But it is very expensive and only can be used in the products that require extremely high stability and reliability.
Silver powder, which has excellent conductivity and chemical stability, is a kind of ideal and most widely used conductive filler. Silver powders that made by different production methods will have different particle size and shapes. The dosage of silver powder is usually 2-4 times of resin, besides, by comprehensively considering the conductivity and adhesion, the most appropriate proportion between silver powder and resin should be 20:80. In order to ensure that silver powder can contact closely in the adhesive layer, the mixed filler of superfine silver powder and scaly shape silver powder that are made by electrolytic method should be used. Epoxy resin silver powder conducting resin can be used in the adhesion that requires good conductivity and mechanical property, for example, it can be used in printing circuit board, wave guide, high frequency shielding and so on. However, silver powder is expensive; it has large density and is easy to precipitate; besides, silver ions will migrate under damp condition. In spite of this, in the preparation of conducting resin, silver powder is still a kind of ideal and most widely used conducting particle.
Copper powder, aluminum powder and nickel powder also have good conductivity and low cost, but they are easy to oxidize in the air, which will reduce the conductivity. Conducting resins that made by copper powder, aluminum powder and nickel powder have lower stability and reliability than silver powder conducting resin, which can only be used in the products that require low stability and reliability. Relevant assistant should be added when copper powder and nickel powder are used as the conductive filler so as to remove the surface oxide layer and improve conductivity. For example, copper powder conductive adhesive often uses epoxy resin and phenolic resin as the sticky material; epoxy resin is produced by using amine as the curing agent and adding silane coupling agent. The dosage of copper powder is about 3 times of resin, besides, its specific resistance can reach up to (2-3)×10-3Ω•cm as well as the shear strength can reach 10-15MPa.
Carbon powder and graphite powder both have low cost, small relative density and good dispersion, but they have poor conductivity, which can only be used in shielding and anti-static products.
Inorganic conducting resin that can be resistant to more than 600 degrees Celsius can be made by phosphoric acid, aluminum hydroxide, special copper oxide powder and other conductive fillers, besides, the inorganic conducting resin that is made by silicate and conductive filler can be resistant to more than 1000 degrees Celsius. However, as inorganic conducting adhesive has low bonding strength and poor water resistance, its application is limited.
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