There is an increasing interest in the industry in attaching unpackaged IC chips directly onto circuits. Potential advantages are lower assembly costs, increased operating speeds and higher component density. Established interconnect techniques for these chip-on-board assemblies include wire bonding, tape automated bonding, and solder flip-chip. For the most part, these are well-developed technologies. In this paper, we will discuss feasibility study results on direct chip interconnect (DCI) using anisotropic conductive polymer material on both flexible and rigid substrates. The concept is to simultaneously attach and electrically interconnect IC chips to circuit traces. When conductors are joined under heat and pressure to form a bond, metallic spheres within the adhesive layer make contact with both surfaces but not each other, hence, the anisotropic conductivity. Since process parameters (such as temperature, pressure, and cure time) as well as chip/substrate registration are equally critical to the success of making electrical interconnections, we have developed a real-time interconnect process monitor and methods to identify the root causes of interconnection failures during, and after, the bonding process. The process monitor and the techniques used to verify the establishment of interconnections will be elaborated in this paper. Electrically anisotropic conductive adhesives offer numerous other advantages in the assembly of electronic circuits, including low temperature assembly, fluxless bonding which eliminates the need for cleaning, and low cost. In addition, the anisotropy inherent to these materials makes them excellent candidates for very fine pitch components.
