Лако-красочные материалы — производство

Alan M. Lyons and D. W. Dahringer

AT&T Bell Laboratories, Murray Hill, New Jersey, U. S.A.

I. INTRODUCTION

Electrically conductive adhesives perform two primary functions. Like other types of adhesives, these materials provide a physical bond between two surfaces. In addition, an electrical interconnection between the two bonded surfaces is formed. This dual func­tionality is usually achieved by composite materials composed of metallic particles dis­persed in an adhesive matrix. The electrical resistivity of conductive adhesives is compared to values of pure metals and polymers in Table 1.

There are two types of conductive adhesives: conventional materials that conduct electricity equally in all directions (isotropic conductors) and those materials that conduct in only one direction (anisotropic conductors). Isotropically conductive materials are typically formulated by adding silver particles to an adhesive matrix such that the percola­tion threshold is exceeded. Electrical currents are conducted throughout the composite via an extensive network of particle-particle contacts. Anisotropically conductive adhesives are prepared by randomly dispersing electrically conductive particles in an adhesive matrix at a concentration far below the percolation threshold. A schematic illustration of an anisotropically conductive adhesive interconnection is shown in Fig. 1. The concentration of particles is controlled such that enough particles are present to assure reliable electrical contacts between the substrate and the device (Z direction), while too few particles are present to achieve conduction in the X-Y plane. The materials become conductive in one direction only after they have been processed under pressure; they do not inherently conduct in a preferred direction. Applications, electrical conduction mechanisms, and formulation of both isotropic and anisotropic conductive adhesives are discussed in detail in this chapter.