Conductive adhesives have been used in the electronics industry for several years to attach chips to package lead frames in the semiconductor industry and for general interconnection of components to flexible circuits for various consumer products. Generally, these materials conduct equally in all directions. TO obtain pad isolation, the adhesives are screen printed to the pattem of the circuit pads. In the last few years, a new class of adhesives that are conductive in a single direction have been developed. These are referred to as Anisotropic Conductive Adhesive Films (ACAF). These anisotropically conductive adhesives provide electrical as well as mechanical interconnections for fine pitch Lipplications. The conductivity of ACAF materials is only in the Z-direction (perpendicular to the plane of the board) while electrical isolation is maintained in the X-Y plane.Currently, at least 15 ACAF materials are commercially available. We have developed a methodology for evaluating these materials for their mechanical and electrical properties and interconnection use in the 8 to 15 mil pitch range. In addition, we characterized the materials as to their physical properties and cure characteristics. This paper details our findings with a comparison of physical form to assembly/cure and final elecmcal properties. We include in this w d y data from scanning electron microscopy, thermal analysis of the ACAFs, and cure and assembly studies on mixed substrate test vehicles . Information on initial electrical testing and long term reliability testing is also given.
There is a n 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, w e 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 conductor surfaces but not each other, hence the anisotropic conductivity.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.
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