Лако-красочные материалы — производство

Several processing techniques have been developed to achieve anisotropic conductivity. One method aligns the conductive metal particles in a magnetic field [41-43]. Alternatively, anisotropy can be achieved in materials with random dispersions of metal particles. Using an adhesive composite where the concentration of metal particles is below but close to pc results in a material with a short-range percolation length X. If the separation distance between substrate and device is less than X, whereas the pitch is much greater than X, anisotropic conduction is achieved. This approach is difficult to implement, as shorts between adjacent conductors, as well as opens between the substrate and device, are statistically possible.

Most commercially available anisotropically conductive adhesives are formulated on the bridging concept, as illustrated in Fig. 1. A concentration of conductive particles far below the percolation threshold is dispersed in an adhesive. The composite is applied to the surface either by screen printing a paste or laminating a film. When a device is attached to a PWB, the placement force displaces the adhesive composite such that a layer the thickness of a single particle remains. Individual particles span the gap between device and PWB and form an electrical interconnection. For successful implementation of anisotro — pically conductive adhesives, the concentration of metal particles must be carefully con­trolled such that a sufficient number of particles is present to assure reliable electrical conductivity between the PWB and the device (Z direction) while electrical isolation is maintained between adjacent pads (X, Y directions).